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Distributed revision control with Mercurial

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1. 125 10 9 12 cag alter tagging a changeset cios ss ee eed We Bae Se e ds 125 10 9 13 update after updating or merging working directory 4 125 11 Customising the output of Mercurial 127 11 1 Using precanned ontput styles oa se ee e e ee ee we N 127 ILII Setting a deranltstvl s cs poke a wai amp aha Rh Bae E E eas Bee a 128 11 2 Commands that support styles and templates o o e 00000004 128 11 3 The basics of template 1 20 02 ke LRA ra SSR a Se ES ale hc i 128 11 4 Common template keywords oo eee eee eS 129 Lio scape SE QUEDCES 00 0 cake ea teks PUE A IA A e 130 11 6 Filtering keywords to change their results 2 2220 12 4 131 NE cal AAA Be ew eS eA ESAS BASS 132 11 7 Bromitemplates IO styles ss ce e WES De ee RR ee E EEA ee Ew 132 Liv The smmplestol SNIE MES ose a Bee eee de Bot ge eee e eS 134 TL2 Style mle SA fod bee eR ER ORE A Se RS REE E 134 11 8 Style files by example 2 644 cs ee ea ee eR we ee 134 11 8 1 Identifying mistakes in style files o o e 134 11 8 2 Uniquely identifying a repository ooo somo rosana e a a G 135 11 8 3 Mimicking Subversion s output lt esso ccoo terest tueta tre 135 12 Managing change with Mercurial Queues 137 121 The pateh management probleth ocni s e cas BA A A dis BAS es 137 12 2 The prehistory of Mercurial Queues lt lt lt lt RR ee EME SRE 137 a e UNE
2. A tag is nothing more than a symbolic name for a revision Tags exist purely for your convenience so that you have a handy permanent way to refer to a revision Mercurial doesn t interpret the tag names you use in any way Neither does Mercurial place any restrictions on the name of a tag beyond a few that are necessary to ensure that a tag can be parsed unambiguously A tag name cannot contain any of the following characters e Colon ASCII 58 e Carriage return ASCII 13 r 79 e Newline ASCII 10 An You can use the hg tags command to display the tags present in your repository In the output each tagged revision is identified first by its name then by revision number and finally by the unique hash of the revision hg tags tip 1 d8bf5b36ec51 v1 0 0 37cc3lacedcl Notice that tip is listed in the output of hg tags The tip tag is a special floating tag which always identifies the newest revision in the repository In the output of the hg tags command tags are listed in reverse order by revision number This usually means that recent tags are listed before older tags It also means that tip is always going to be the first tag listed in the output of hg tags When you run hg log if it displays a revision that has tags associated with it it will print those tags hg log changeset 1 d8bf5b36ec51 tag tip user Bryan O Sullivan lt bos
3. D 5 Good practice recommendations In addition to the requirements of this license it is requested from and strongly recommended of redistributors that 1 If you are distributing Open Publication works on hardcopy or CD ROM you provide email notification to the authors of your intent to redistribute at least thirty days before your manuscript or media freeze to give the authors time to provide updated documents This notification should describe modifications if any made to the document All substantive modifications including deletions be either clearly marked up in the document or else described in an attachment to the document Finally while it is not mandatory under this license it is considered good form to offer a free copy of any hardcopy and CD ROM expression of an Open Publication licensed work to its author s D 6 License options The author s and or publisher of an Open Publication licensed document may elect certain options by appending language to the reference to or copy of the license These options are considered part of the license instance and must be included with the license or its incorporation by reference in derived works A To prohibit distribution of substantively modified versions without the explicit permission of the author s Sub stantive modification is defined as a change to the semantic content of the document and excludes mere changes in format or typographical corrections
4. When neither of these techniques works patch prints a message saying that the hunk in question was rejected It saves rejected hunks also simply called rejects to a file with the same name and an added rej extension It also saves an unmodified copy of the file with a orig extension the copy of the file without any extensions will contain any changes made by hunks that did apply cleanly If you have a patch that modifies foo with six hunks and one of them fails to apply you will have an unmodified foo orig a foo rej containing one hunk and foo containing the changes made by the five successful five hunks 12 6 3 Some quirks of patch representation There are a few useful things to know about how patch works with files 145 hg qapplied first patch second patch 5 hg qpop Now at first patch hg qseries first patch econd patch hg qapplied irst patch ine 1 ine 2 s f cat filel 1 1 1 ine 3 Figure 12 11 Modifying the stack of applied patches hg qpush a applying second patch Now at second patch cat filel line 1 line 2 line 3 line 4 Figure 12 12 Pushing all unapplied patches This should already be obvious but patch cannot handle binary files Neither does it care about the executable bit it creates new files as readable but not executable patch treats the removal of a file as a diff between the file to be removed and the empty file So y
5. Figure 10 5 A simple hook that checks for trailing whitespace As a final aside note in figure 10 6 the use of per1 s in place editing feature to get rid of trailing whitespace from a file This is concise and useful enough that I will reproduce it here perl pi e s s filename 10 7 Bundled hooks Mercurial ships with several bundled hooks You can find them in the hgext directory of a Mercurial source tree If you are using a Mercurial binary package the hooks will be located in the hgext directory of wherever your package installer put Mercurial 10 7 1 acl access control for parts of a repository The acl extension lets you control which remote users are allowed to push changesets to a networked server You can protect any portion of a repository including the entire repo so that a specific remote user can push changes that do not affect the protected portion This extension implements access control based on the identity of the user performing a push not on who commit ted the changesets they re pushing It makes sense to use this hook only if you have a locked down server environment that authenticates remote users and you want to be sure that only specific users are allowed to push changes to that server Configuring the acl hook In order to manage incoming changesets the acl hook must be used as a pretxnchangegroup hook This lets it see which files are modified by each incoming changeset and rol
6. In a sprint a number of people get together in a single location a company s conference room a hotel meeting room that kind of place and spend several days more or less locked in there hacking intensely on a handful of projects A sprint is the perfect place to use the hg serve command since hg serve does not requires any fancy server infrastructure You can get started with hg serve in moments by reading section 6 4 below Then simply tell the person next to you that you re running a server send the URL to them in an instant message and you immediately have a quick turnaround way to work together They can type your URL into their web browser and quickly review your changes or they can pull a bugfix from you and verify it or they can clone a branch containing a new feature and try it out The charm and the problem with doing things in an ad hoc fashion like this is that only people who know about your changes and where they are can see them Such an informal approach simply doesn t scale beyond a handful people because each individual needs to know about n different repositories to pull from 6 2 3 A single central repository For smaller projects migrating from a centralised revision control tool perhaps the easiest way to get started is to have changes flow through a single shared central repository This is also the most common building block for more ambitious workflow schemes Contributors start by cl
7. You can pull and push changes securely over a network connection using the Secure Shell ssh protocol To use this successfully you may have to do a little bit of configuration on the client or server sides If you re not familiar with ssh it s a network protocol that lets you securely communicate with another computer To use it with Mercurial you ll be setting up one or more user accounts on a server so that remote users can log in and execute commands If you are familiar with ssh you ll probably find some of the material that follows to be elementary in nature 6 5 1 How to read and write ssh URLs An ssh URL tends to look like this ssh bosthg serpentine com 22 hg hgbook 1 The ssh part tells Mercurial to use the ssh protocol 2 The bos component indicates what username to log into the server as You can leave this out if the remote username is the same as your local username 3 The hg serpentine com gives the hostname of the server to log into 4 The 22 identifies the port number to connect to the server on The default port is 22 so you only need to specify this part if you re not using port 22 5 The remainder of the URL is the local path to the repository on the server 63 There s plenty of scope for confusion with the path component of ssh URLs as there is no standard way for tools to interpret it Some programs behave differently than others when dealing with th
8. bob searching for changes adding changesets adding manifests 54 adding file changes added 1 changesets with 1 changes to 1 files 1 heads run hg heads to see heads hg merge to merge hg merge 1 files updated 0 files merged 0 files removed 0 files unresolved branch merge don t forget to commit ls bar quux I personally find this behaviour quite surprising which is why I wanted to explicitly mention it here I would have expected Mercurial to prompt me with a three way choice instead do I want to keep only bar only quux or both In practice when you rename a source file it is likely that you will also modify another file such as a makefile that knows how to build the source file So what will happen if Anne renames a file and edits Makefile to build it under its new name while Bob does the same but chooses a different name for the file is that after the merge there will be two copies of the source file in the working directory under different names and a conflict in the section of the Makefile that both Bob and Anne edited This behaviour is considered surprising by other people too see Mercurial bug no 455 for details 5 4 3 Convergent renames and merging Another kind of rename conflict occurs when two people choose to rename different source files to the same destina tion In this case Mercurial runs its normal merge machinery and lets you guide it to a suitable resolut
9. gt myfile hg commit m Fix a bug hg push pushing to tmp branchingx8gzam stable searching for changes adding changesets adding manifests adding file changes added 1 changesets with 1 changes to 1 files MA 0 UY GF e Y Because Mercurial repositories are independent and Mercurial doesn t move changes around automatically the stable and main branches are isolated from each other The changes that you made on the main branch don t leak to the stable branch and vice versa You 1l often want all of your bugfixes on the stable branch to show up on the main branch too Rather than rewrite a bugfix on the main branch you can simply pull and merge changes from the stable to the main branch and Mercurial will bring those bugfixes in for you cd main hg pull stable pulling from stable searching for changes adding changesets adding manifests adding file changes added 1 changesets with 1 changes to 1 files 1 heads run hg heads to see heads hg merge to merge hg merge merging myfile files updated 1 files merged 0 files removed 0 files unresolved branch merge don t forget to commit hg commit m Bring in bugfix from stable branch cat myfile This is a fix to a boring feature This is exciting and new NY I O 3 The main branch will still contain changes that are not on the stable branch but it will also contain all of the bugfixes fr
10. gt spaan e be bok we ee A GS Gee 2e MPMOUN AAA E EA 2 8 1 Pulling changes from another repository lt s eso 2 be ee eR Re 28 2 Updating the working directory its ec snub Abe Ged Le Bie a OSE Bee es 2 8 3 Pushing changes to another repository 2 oce a ck eR eke a ee a 2 8 4 Sharing changes overanetwork eee eee eee A tour of Mercurial merging work Sell MESE steams GF WORK rae lt 2 4 SG Yee Eee ae BAS Bee aS Bae amp Sede BA leg Sulol Head CNANSESHS s c pcg p e s whe ee RE RRR OR A l2 Peroni he m s zanio tor one ee Ghd owe Sha POSS ee eee eh S102 Committing the Tesults Of the Mere oe es O E A ERA 32 Merging conc une Gnanses ori eh we hee Sie eRe REDS ORS R EE he oh SS 32 1 Usinpapraphical merce tool 2 ek ee ee RO RR ee ee R A 42 2 A worked example 253 b e842 oe bee bea ee Ba eee eee ea 3 3 Simplifying the pull merge commit sequence 2 0 0000 eee eee eee Behind the scenes 4 1 Mercunal s histoncal record os bk ee ee ew ee ee be Se eee HS 4 1 1 Tracking the history of asinglefile maue a e eee ee ee eee eee es 441 25 Managing tracked MES e oca Ee ee 6 ERAS Slee 8 Res 4 1 3 Recording changesetinformation 0 000000000000 4 1 4 Relationships between TEVISIONS sos ee a Pe ee ee ee 42 Safe EMICIENDSTOTALE oc osooso aaee ee Bee ea een Ped eee Sd 4 2 1 Etfcient storage ss ibaa rr Kae Sw A Rk we SS Reds oe 47 2 SAC OPSAHON es coe Bae OLA R LRA RE ERR ew eee REE
11. printf hello again n It might seem a bit strange that hg pull doesn t update the working directory automatically There s actually a good reason for this you can use hg update to update the working directory to the state it was in at any revision in the history of the repository If you had the working directory updated to an old revision to hunt down the origin of a bug say and ran a hg pull which automatically updated the working directory to a new revision you might not be terribly happy However since pull then update is such a common thing to do Mercurial lets you combine the two by passing the u option to hg pull hg pull u If you look back at the output of hg pull in section 2 8 1 when we ran it without u you can see that it printed a helpful reminder that we d have to take an explicit step to update the working directory run hg update to get a working copy To find out what revision the working directory is at use the hg parents command hg parents changeset 5 fal321bf0c80 tag tip user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 05 50 2007 0000 summary Added an extra line of output If you look back at figure 2 1 you Il see arrows connecting each changeset The node that the arrow leads from in each case is a parent and the node that the arrow leads fo is its child The working dire
12. command and telling it which repository to pull from hg tip changeset 4 b57 9a090b62 tag tip user Bryan O Sullivan lt bos serpentine com gt date Tue Sep 06 15 43 07 2005 0700 summary Trim comments hg pull my hello pulling from my hello searching for changes adding changesets adding manifests adding file changes added 1 changesets with 1 changes to 1 files run hg update to get a working copy hg tip changeset 5 fal321bf0c80 tag tip user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 05 50 2007 0000 summary Added an extra line of output As you can see from the before and after output of hg tip we have successfully pulled changes into our repository There remains one step before we can see these changes in the working directory 2 8 2 Updating the working directory We have so far glossed over the relationship between a repository and its working directory The hg pull command that we ran in section 2 8 1 brought changes into the repository but if we check there s no sign of those changes in the working directory This is because hg pull does not by default touch the working directory Instead we use the hg update command to do this 21 grep printf hello c printf hello world hg update tip 1 files updated 0 files merged 0 files removed 0 files unresolved grep printf hello c printf hello world
13. print applied patches The hg qapplied command prints the current stack of applied patches Patches are printed in oldest to newest order so the last patch in the list is the top patch B 1 2 hg qcommit commit changes in the queue repository The hg qcommit command commits any outstanding changes in the hg patches repository This command only works if the hg patches directory is a repository i e you created the directory using hg qinit c or ran hg init in the directory after running hg qinit This command is shorthand for hg commit cwd hg patches B 1 3 hg qdelete delete a patch from the series file The hg adelete command removes the entry for a patch from the series file in the hg patches directory It does not pop the patch if the patch is already applied By default it does not delete the patch file use the option to do that Options f Delete the patch file B 1 4 hg qdiff print a diff of the topmost applied patch The hg qdiff command prints a diff of the topmost applied patch It is equivalent to hg diff r 2 1 B 1 5 hg qfold merge fold several patches into one The hg qfold command merges multiple patches into the topmost applied patch so that the topmost applied patch makes the union of all of the changes in the patches in question The patches to fold must not be applied hg qfold will ex
14. 39 66 output of hg log hg tip and other commands that display the same kind of output echo hello again gt gt myfile hg commit m Second commit hg tip changeset 1 3af68d4362fb branch foo tag tip user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 42 2007 0000 summary Second commit The hg log like commands will print the branch name of every changeset that s not on the default branch As a result if you never use named branches you ll never see this information Once you ve named a branch and committed a change with that name every subsequent commit that descends from that change will inherit the same branch name You can change the name of a branch at any time using the hg branch command hg branch foo hg branch bar echo new file gt newfile hg commit A m Third commit adding newfile hg tip changeset 2 4 00549a48el branch bar 85 tag tip user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 43 2007 0000 summary Third commit In practice this is something you won t do very often as branch names tend to have fairly long lifetimes This isn t a tule just an observation 8 6 Dealing with multiple named branches in a repository If you have more than one named branch in a repository Mercurial will remember the branch that your working directory on when yo
15. All files modified added or removed by this changeset 129 1 hg log r1 template author author n 2 author Bryan O Sullivan lt bos serpentine com gt 3 hg log r1 template desc n desc n 4 desc 5 added line to end of lt lt hello gt gt file 7 in addition added a file with the helpful name at least i hope that some might consider it so of goodby s hg log r1 template files files n 9 files goodbye hello w hg log r1 template file adds file_adds n 1 file_adds 2 hg log r1 template file dels file_dels n 13 file_dels u hg log r1 template node node n is node ee709a2e8cd1224c94823aa7f402437b28a2bf2c is hg log r1 template parents parents n 17 parents w hg log r1 template rev rev n 19 rev 1 2 hg log r1 template tags tags n 21 tags mytag Figure 11 1 Template keywords in use file_adds List of strings Files added by this changeset file_dels List of strings Files removed by this changeset node String The changeset identification hash as a 40 character hexadecimal string parents List of strings The parents of the changeset rev Integer The repository local changeset revision number tags List of strings Any tags associated with the changeset A few simple experiments will show us what to expect when we use these keywords you can see the results in figure 11 1 As we n
16. It can prune entire branches of history with a single probe which is how it operates so efficiently 9 5 1 Using the bisect extension Here s an example of bisect in action To keep the core of Mercurial simple bisect is packaged as an extension this means that it won t be present unless you explicitly enable it To do this edit your hgrc and add the following section header if it s not already present extensions Then add a line to this section to enable the extension hbisect Note That s right there s a h at the front of the name of the bisect exten sion The reason is that Mercurial is written in Python and uses a standard Python package called bisect If you omit the h from the name hbisect Mercurial will erroneously find the standard Python bisect package and try to use it as a Mercurial extension This won t work and Mercurial will crash repeatedly until you fix the spelling in your hgrc Ugh Now let s create a repository so that we can try out the bisect extension in isolation 101 20 21 22 23 24 25 26 27 28 29 hg i cd mybug nit mybug We ll simulate a project that has a bug in it in a simple minded way create trivial changes in a loop and nominate one specific c hange that will have the bug This loop creates 35 changesets each adding a single file to the repository We ll represent
17. The in progress group Patches that are actively being developed and should not be submitted anywhere yet The backport group Patches that adapt the source tree to older versions of the kernel tree The do not ship group Patches that for some reason should never be submitted upstream For example one such patch might change embedded driver identification strings to make it easier to distinguish in the field between an out of tree version of the driver and a version shipped by a distribution vendor Now to return to the reasons for ordering groups of patches in this way We would like the lowest patches in the stack to be as stable as possible so that we will not need to rework higher patches due to changes in context Putting patches that will never be changed first in the series file serves this purpose We would also like the patches that we know we ll need to modify to be applied on top of a source tree that resembles the upstream tree as closely as possible This is why we keep accepted patches around for a while The backport and do not ship patches float at the end of the series file The backport patches must be applied on top of all other patches and the do not ship patches might as well stay out of harm s way 13 8 Maintaining the patch series In my work I use a number of guards to control which patches are to be applied Accepted patches are guarded with accepted I enable this guard
18. Use qcommit to commit changes to this queue repository Figure 12 3 How to verify that MQ is enabled You can use MQ with any Mercurial repository and its commands only operate within that repository To get started simply prepare the repository using the hg qinit command see figure 12 4 This command creates an empty directory called hg patches where MQ will keep its metadata As with many Mercurial commands the hg qinit command prints nothing if it succeeds UY Ur US Ur UU U 7 hg init mq sandbox cd mq sandbox echo line 1 gt filel echo another line 1 gt file2 hg add filel file2 hg commit m first change hg qinit Figure 12 4 Preparing a repository for use with MQ 12 5 1 Creating a new patch To begin work on a new patch use the hg qnew command This command takes one argument the name of the patch to create MQ will use this as the name of an actual file in the hg patches directory as you can see in figure 12 5 Also newly present in the hg patches directory are two other files series and status The series file lists all of the patches that MQ knows about for this repository with one patch per line Mercurial uses the status file for internal book keeping it tracks all of the patches that MQ has applied in this repository 140 hg tip changeset 0 93d314596e46 tag tip user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18
19. and there s plenty more scope for head scratching Most of these potential problems occur on the server side not the client side The good news is that once you ve gotten a configuration working it will usually continue to work indefinitely Before you try using Mercurial to talk to an ssh server it s best to make sure that you can use the normal ssh or putty command to talk to the server first If you run into problems with using these commands directly Mercurial surely won t work Worse it will obscure the underlying problem Any time you want to debug ssh related Mercurial problems you should drop back to making sure that plain ssh client commands work first before you worry about whether there s a problem with Mercurial The first thing to be sure of on the server side is that you can actually log in from another machine at all If you can t use ssh or putty to log in the error message you get may give you a few hints as to what s wrong The most common problems are as follows e If you get a connection refused error either there isn t an SSH daemon running on the server at all or it s inaccessible due to firewall configuration e If you get a no route to host error you either have an incorrect address for the server or a seriously locked down firewall that won t admit its existence at all e If you get a permission denied error you may have mistyped the username on the server or you could have m
20. and transaction visibility has nothing to do with the problem As the size of a project and the time it takes to build and test grows you rapidly run into a wall with this try before you buy approach where you have more changesets to test than time in which to deal with them The inevitable result is frustration on the part of all involved An approach that scales better is to get people to build and test before they push then run automated builds and tests centrally after a push to be sure all is well The advantage of this approach is that it does not impose a limit on the rate at which the repository can accept changes 109 10 4 A short tutorial on using hooks It is easy to write a Mercurial hook Let s start with a hook that runs when you finish a hg commit and simply prints the hash of the changeset you just created The hook is called commit hg init hook test ed hook test echo hooks gt gt hg hgre echo commit echo committed HG_NODE gt gt hg hgre cat hg hgre hooks commit echo committed SHG_NODE echoa gt a hg add a hg commit m testing commit hook committed dcf0754a0aa69832b527f6e4094f8ebc314c2f95 Figure 10 1 A simple hook that runs when a changeset is committed All hooks follow the pattern in example 10 1 You add an entry to the hooks section of your hgrcOn the left is the name of the event to trigger on on the right is the action to take As
21. as a template body If the rest of the line does not start with a quote character it is treated as the name of a file the contents of this file will be read and used as a template body 11 8 Style files by example To illustrate how to write a style file we will construct a few by example Rather than provide a complete style file and walk through it we ll mirror the usual process of developing a style file by starting with something very simple and walking through a series of successively more complete examples 11 8 1 Identifying mistakes in style files If Mercurial encounters a problem in a style file you are working on it prints a terse error message that once you figure out what it means is actually quite useful cat broken style changeset Notice that broken style attempts to define a changeset keyword but forgets to give any content for it When instructed to use this style file Mercurial promptly complains hg log r1 style broken style abort broken style 1 parse error 134 This error message looks intimidating but it is not too hard to follow e The first component is simply Mercurial s way of saying I am giving up 1 abort broken style 1 parse error e Next comes the name of the style file that contains the error 1 abort broken style 1 parse error e Following the file name is the line number where the error was encountered
22. but it falls off rapidly as the number of users grows beyond a few dozen Modestly large Perforce installations require the deployment of proxies to cope with the load their users generate Chapter 2 A tour of Mercurial the basics 2 1 Installing Mercurial on your system Prebuilt binary packages of Mercurial are available for every popular operating system These make it easy to start using Mercurial on your computer immediately 2 1 1 Linux Because each Linux distribution has its own packaging tools policies and rate of development it s difficult to give a comprehensive set of instructions on how to install Mercurial binaries The version of Mercurial that you will end up with can vary depending on how active the person is who maintains the package for your distribution To keep things simple I will focus on installing Mercurial from the command line under the most popular Linux distributions Most of these distributions provide graphical package managers that will let you install Mercurial with a single click the package name to look for is mercurial Debian apt get install mercurial Fedora Core yum install mercurial Gentoo emerge mercurial OpenSUSE yum install mercurial Ubuntu Ubuntu s Mercurial package is based on Debian s To install it run the following command 1 apt get install mercurial The Ubuntu package for Mercurial tends to lag behind the Debian version
23. eae S 130 Template Tiere wWACHON as acs eee So ee ee be ok Gwe ae ee ek bab bee amp 4 133 Simple us s of the diff and paten commands 2 20 4446 bs ewes e eS Eee ee ee eS 139 Contents to add to hgrc to enable the MQ extension 2 0202 0022 oe 140 How to verily that MQisenabled o o e eos ako Ree ae he eR RRS RES eS 140 Preparing a repository for use with MQ ee 140 Creating anew Paleo ck ok be se ee RE Ee pS ew aE ee SO ee ee eee 141 1X 120 RETMESHIOS A Pare carnosas ao ar A a aes BR Bee G 142 12 7 Refresh a patch many times to accumulate changes o e 00 ee eee 143 12 8 Stacking a second patch on top of the first oaoa ee 144 12 9 Understanding the patch stack with hg qseries and hg gapplied 145 12 10 Applied and unapplied patches in the MQ patch stack o ooo 145 12 1 1 Modifying the stack of applied patches gt s saos bb ee Ee eR ee Ee RS 146 12 V Pushing all unapplied patches cc ee ha BR EER Se ER eS EGA Awe 146 12 180 Foscibly creating apalei s bn cose a YE RS Sc ae ER ee eRe a 147 12 14Using MQ s tag features to work with patches 2 2 0 0 0 0 000000004 150 12 15Thediffstat filterdiff and lsdiff commands s sacs smara ba a pa ee 152 Preface Distributed revision control is a relatively new territory and has thus far grown due to people s willingness to strike out into ill charted territory Iam writing a
24. extdiff This introduces a command named hg extdiff which by default uses your system s diff command to generate a unified diff in the same form as the built in hg diff command hg extdiff making snapshot of 1 files from rev 271c4b32e6fb making snapshot of 1 files from working dir diff Npru a 271c4b32e6fb myfile a myfile a 271c4b32e6fb myfile 2007 06 17 18 03 49 000000000 0000 a myfile 2007 06 17 18 03 49 000000000 0000 ee 1 1 2 ee The first line The second line The result won t be exactly the same as with the built in hg diff variations because the output of diff varies from one system to another even when passed the same options As the making snapshot lines of output above imply the hg extdiff command works by creating two snapshots of your source tree The first snapshot is of the source revision the second of the target revision or working directory The hg extdiff command generates these snapshots in a temporary directory passes the name of each directory to an external diff viewer then deletes the temporary directory For efficiency it only snapshots the directories and files that have changed between the two revisions Snapshot directory names have the same base name as your repository If your repository path is quux bar foo then foo will be the name of each snapshot directory Each snapshot directory name has its changeset ID appended if app
25. hg qnew second patch hg log style compact limit 2 2 qtip second patch tip 554fbb07 820 2007 06 17 18 03 0000 bos New patch second patch 1 first patch qbase 403df3ef5ecd 2007 06 17 18 03 0000 bos patch queue first patch echo line 4 gt gt filel hg qrefresh hg tip style compact patch 2 qtip second patch tip 86100a6142b9 2007 06 17 18 03 0000 bos patch queue second patch diff r 403df3ef5ecd r 86100a6142b9 filel a filel Sun Jun 17 18 03 57 2007 0000 b filel Sun Jun 17 18 03 57 2007 0000 1 3 1 4 line 1 line 1 line 2 line 3 line 4 hg annotate filel 0 line 1 1 line 2 1 line 3 2 line 4 Figure 12 8 Stacking a second patch on top of the first people still do this but it s somewhat rare with modern revision control tools Alice would unpack a tarball edit her files then decide that she wanted to create a patch So she d rename her working directory unpack the tarball again hence the need for the rename and use the r and N options to diff to recursively generate a patch between the unmodified directory and the modified one The result would be that the name of the unmodified directory would be at the front of the left hand path in every file header and the name of the modified directory would be at the front of the right hand path Since someone receiving a patch from the Alices of the net would be unlikely to have unmodified and modifie
26. it can respond with a result instantaneously avoiding the need to scan every directory and file in the repository Recall the ten seconds that I measured plain Mercurial as taking to run hg status on a 150 000 file repository With the inotify extension enabled the time dropped to 0 1 seconds a factor of one hundred faster Before we continue please pay attention to some caveats e The inotify extension is Linux specific Because it interfaces directly to the Linux kernel s inot ify subsys tem it does not work on other operating systems e It should work on any Linux distribution that was released after early 2005 Older distributions are likely to have a kernel that lacks inotify or a version of glibc that does not have the necessary interfacing support e Not all filesystems are suitable for use with the inot ify extension Network filesystems such as NFS are a non starter for example particularly if you re running Mercurial on several systems all mounting the same network filesystem The kernel s inotify system has no way of knowing about changes made on another system Most local filesystems e g ext3 XFS ReiserFS should work fine The inotify extension is not yet shipped with Mercurial as of May 2007 so it s a little more involved to set up than other extensions But the performance improvement is worth it The extension currently comes in two parts a set of patches to the Mercurial source code and a library of P
27. project s main branch and possibly other maintenance branches too It s a rare developer who wants to fix the same bug multiple times so let s look at a few ways that Mercurial can help you to manage these bugfixes without duplicating your work In the simplest instance all you need to do is pull changes from your maintenance branch into your local clone of the target branch cd hg clone myproject myproject merge 3 files updated 0 files merged 0 files removed 0 files unresolved cd myproject merge hg pull myproject 1 0 1 pulling from myproject 1 0 1 searching for changes adding changesets adding manifests adding file changes 83 added 1 changesets with 1 changes to 1 files 1 heads run hg heads to see heads hg merge to merge Yov ll then need to merge the heads of the two branches and push back to the main branch hg merge 1 files updated 0 files merged 0 files removed 0 files unresolved branch merge don t forget to commit hg commit m Merge bugfix from 1 0 1 branch hg push pushing to tmp branch repo8JmRu myproject searching for changes adding changesets adding manifests adding file changes added 2 changesets with 1 changes to 1 files 8 5 Naming branches within one repository In most instances isolating branches in repositories is the right approach Its simplicity makes it easy to understand and so it s hard to make mistake
28. s nothing to prevent you from using hg serve to serve up a repository on your own computer then use commands like hg clone hg incoming and so on to talk to that server as if the repository was hosted remotely This can help you to quickly get acquainted with using commands on network hosted repositories 6 4 1 A few things to keep in mind Because it provides unauthenticated read access to all clients you should only use hg serve in an environment where you either don t care or have complete control over who can access your network and pull data from your repository The hg serve command knows nothing about any firewall software you might have installed on your system or network It cannot detect or control your firewall software If other people are unable to talk to a running hg serve instance the second thing you should do after you make sure that they re using the correct URL is check your firewall configuration By default hg serve listens for incoming connections on port 8000 If another process is already listening on the port you want to use you can specify a different port to listen on using the p option Normally when hg serve starts it prints no output which can be a bit unnerving If you d like to confirm that it is indeed running correctly and find out what URL you should send to your collaborators start it with the v option 6 5 Using the Secure Shell ssh protocol
29. usually the tip already exhibits the problem introduced by the buggy change so we ll mark it as bad hg bisect bad Our next task is to nominate a changeset that we know doesn t have the bug the bisect extension will bracket its search between the first pair of good and bad changesets In our case we know that revision 10 didn t have the bug TIl have more words about choosing the first good changeset later hg bisect good 10 Testing changeset 22 8ef86493d946 24 changesets remaining 4 tests 0 files updated 0 files merged 12 files removed 0 files unresolved Notice that this command printed some output e It told us how many changesets it must consider before it can identify the one that introduced the bug and how many tests that will require e It updated the working directory to the next changeset to test and told us which changeset it s testing We now run our test in the working directory We use the grep command to see if our bad file is present in the working directory If it is this revision is bad if not this revision is good if grep q i have a gub x then result bad else result good fi echo this revision is result this revision is bad hg bisect result Testing changeset 16 5bal4030bbee 12 changesets remaining 3 tests 0 files updated 0 files merged 6 files removed 0 files unresolved WV VV V V XD 103 This test looks
30. 03 56 2007 0000 summary first change hg qnew first patch hg tip changeset 1 42507102e3aa tag qtip tag first patch tag tip tag qbase user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 56 2007 0000 summary New patch first patch ls hg patches first patch series status Figure 12 5 Creating a new patch Note You may sometimes want to edit the series file by hand for example to change the sequence in which some patches are applied However manually editing the status file is almost always a bad idea as it s easy to corrupt MQ s idea of what is happening Once you have created your new patch you can edit files in the working directory as you usually would All of the normal Mercurial commands such as hg diff and hg annotate work exactly as they did before 12 5 2 Refreshing a patch When you reach a point where you want to save your work use the hg grefresh command figure 12 5 to update the patch you are working on This command folds the changes you have made in the working directory into your patch and updates its corresponding changeset to contain those changes You can run hg grefresh as often as you like so it s a good way to checkpoint your work Refresh your patch at an opportune time try an experiment and if the experiment doesn t work out hg revert your modifications back to the last time you refreshed
31. 1 abort broken style 1 parse error e Finally a description of what went wrong 1 abort broken style 1 parse error The description of the problem is not always clear as in this case but even when it is cryptic it is almost always trivial to visually inspect the offending line in the style file and see what is wrong 11 8 2 Uniquely identifying a repository If you would like to be able to identify a Mercurial repository fairly uniquely using a short string as an identifier you can use the first revision in the repository hg log r0 template node 63a3051ad6a521005e78e10cC863876935cad219b This is not guaranteed to be unique but it is nevertheless useful in many cases e It will not work in a completely empty repository because such a repository does not have a revision zero e Neither will it work in the extremely rare case where a repository is a merge of two or more formerly indepen dent repositories and you still have those repositories around Here are some uses to which you could put this identifier e As a key into a table for a database that manages repositories on a server e As half of a repository ID revision ID tuple Save this information away when you run an automated build or other activity so that you can replay the build later if necessary 11 8 3 Mimicking Subversion s output Let s try to emulate the default output format used by another revision
32. 1 cd mercurial version 2 python setup py install force home SHOME Once the install finishes Mercurial will be in the bin subdirectory of your home directory Don t forget to make sure that this directory is present in your shell s search path You will probably need to set the PYTHONPATH environment variable so that the Mercurial executable can find the rest of the Mercurial packages For example on my laptop I have set it to home bos lib python The exact path that you will need to use depends on how Python was built for your system but should be easy to figure out If you re uncertain look through the output of the installer script above and see where the contents of the mercurial directory were installed to C 2 On Windows Building and installing Mercurial on Windows requires a variety of tools a fair amount of technical knowledge and considerable patience I very much do not recommend this route if you are a casual user Unless you intend to hack on Mercurial I strongly suggest that you use a binary package instead If you are intent on building Mercurial from source on Windows follow the hard way directions on the Mercu rial wiki at http www selenic com mercurial wiki index cgi WindowsInstall and expect the process to involve a lot of fiddly work 179 Appendix D Open Publication License Version 1 0 8 June 1999 D 1 Requirements on both unmodified and modified versions The Open Publi
33. 12 5 3 Stacking and tracking patches Once you have finished working on a patch or need to work on another you can use the hg qnew command again to create a new patch Mercurial will apply this patch on top of your existing patch See figure 12 8 for an example Notice that the patch contains the changes in our prior patch as part of its context you can see this more clearly in the output of hg annotate So far with the exception of hg qnew and hg qrefresh we ve been careful to only use regular Mercurial commands However MQ provides many commands that are easier to use when you are thinking about patches as illustrated in figure 12 9 141 echo line 2 gt gt filel hg diff diff r 42507102e3aa filel a filel Sun Jun 17 18 03 56 2007 0000 b filel Sun Jun 17 18 03 56 2007 0000 ee 1 1 1 2 line 1 line 1 line 2 hg qrefresh hg diff hg tip style compact patch l qtip first patch tip qbase 78bfae8e7765 2007 06 17 18 03 0000 bos patch queue first patch diff r 93d314596e46 r 78bfae8e7765 filel a filel Sun Jun 17 18 03 56 2007 0000 b filel Sun Jun 17 18 03 57 2007 0000 1 1 1 2 line 1 line 1 line 2 Figure 12 6 Refreshing a patch e The hg qseries command lists every patch that MQ knows about in this repository from oldest to newest most recently created e The hg qapplied command lists every patch that MQ has app
34. 122 124 update command 21 22 27 28 33 39 59 78 86 87 99 148 151 C option 86 87 148 update hook 107 125 urlescape template filter 132 user template filter 132 version command 11 66 172 vim system command 168 wiggle system command 147 tags zip system command 71 configuration file Mercurial ini Windows 64 hgre Linux Unix 66 70 72 88 101 108 110 112 115 119 128 161 162 166 168 environment variables EMAIL 18 HGMERGE 29 31 HGUSER 18 HG_NODE 110 121 HG_PARENT1 121 HG_PARENT2 121 HG_SOURCE 121 HG_URL 121 122 PATH 66 187 PYTHONPATH 66 69 112 179 global options debug option 66 115 exclude option 77 include option 76 quiet option 17 verbose option 12 16 17 I option 76 77 X option 77 q option 17 75 v option 12 16 17 63 75 111 hooks acl 114 bugzilla 116 117 changegroup 107 109 122 124 commit 107 110 111 122 123 125 incoming 107 116 122 124 outgoing 107 108 123 124 prechangegroup 107 122 124 precommit 107 113 122 125 preoutgoing 107 109 123 124 pretag 107 124 125 pretxnchangegroup 88 107 109 114 122 124 pretxncommit 107 109 111 113 116 122 125 preupdate 107 125 126 tag 107 124 125 update 107 125 Mercurial bug database bug 29 55 bug 311 144 145 bug 455 55 tip 122 124 special tag names qbase 149 atip 149 template filters addbre
35. 212 6 212 15 static __inline__ void test_headers void h snip Testing and troubleshooting Do not forget that by default the notify extension will not send any mail until you explicitly configure it to do so by setting test to false Until you do that it simply prints the message it would send 10 8 Information for writers of hooks 10 An 8 1 In process hook execution in process hook is called with arguments of the following form 120 def myhook ui repo kwargs pass The ui parameter is amercurial ui ui object The repo parameter isa mercurial localrepo localrepository object The names and values of the kwargs parameters depend on the hook being invoked with the following common features e Ifa parameter is named node or parent N it will contain a hexadecimal changeset ID The empty string is used to represent null changeset ID instead of a string of zeroes e Ifa parameter is named url it will contain the URL of a remote repository if that can be determined e Boolean valued parameters are represented as Python bool objects An in process hook is called without a change to the process s working directory unlike external hooks which are run in the root of the repository It must not change the process s working directory or it will cause any calls it makes into the Mercurial API to fail If a hook returns a boolean false value it is considered to have
36. 4 outgoing after changesets are propagated This hook is run after a group of changesets has been propagated out of this repository for example by a hg push or hg bundle command One possible use for this hook is to notify administrators that changes have been pulled Parameters to this hook node A changeset ID The changeset ID of the first changeset of the group that was sent source A string The source of the of the operation see section 10 8 3 If a remote client pulled changes from this repository source will be serve If the client that obtained changes from this repository was local source will be bundle pull or push depending on the operation the client performed url A URL The location of the remote repository if known See section 10 8 3 for more information See also preoutgoing section 10 9 7 10 9 5 prechangegroup hefore starting to add remote changesets This controlling hook is run before Mercurial begins to add a group of changesets from another repository This hook does not have any information about the changesets to be added because it is run before transmission of those changesets is allowed to begin If this hook fails the changesets will not be transmitted One use for this hook is to prevent external changes from being added to a repository For example you could use this to freeze a server hosted branch temporarily or permanently so that users cannot push to it while still allowi
37. 90 108 122 124 148 151 u option 22 push command 23 78 122 124 puttygen system command 64 putty system command 65 gapplied command mq extension 142 145 151 174 qcommit command mq extension 151 174 adelete command mq extension 174 adel command mq extension f option 174 adiff command mq extension 174 afold command 174 afold command mq extension 154 174 e option 174 175 1 option 175 m option 175 aguard command 158 qguard command mq extension 157 158 qheader command mq extension 175 qimport command mq extension 144 175 ginit command 151 174 qinit command mq extension 139 140 150 174 175 178 c option 150 151 174 175 178 qnew command 143 qnew command mq extension 140 141 143 144 175 f option 143 175 m option 175 qnext command mq extension 175 apop command 143 147 148 151 apop command mq extension 142 143 148 149 176 a option 142 147 148 151 176 f option 143 176 n option 148 176 aprev command mq extension 176 apush command 147 148 151 qpush command mq extension 142 143 146 149 154 158 165 166 175 178 a option 142 147 148 151 165 176 1 option 176 m option 148 176 n option 177 qrefresh command mq extension 141 143 145 147 149 151 154 175 177 e option 177 1 option 177 m option 177 grename command mq extension 177 grestore command mq extension 177 asave command 148 as
38. Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 42 2007 0000 summary Initial commit hg branches default 0 7070a49b08e8 Since you haven t created any named branches yet the only one that exists is default To find out what the current branch is run the hg branch command giving it no arguments This tells you what branch the parent of the current changeset is on hg branch default 84 To create a new branch run the hg branch command again This time give it one argument the name of the branch you want to create hg branch foo hg branch foo After you ve created a branch you might wonder what effect the hg branch command has had What do the hg status and hg tip commands report hg status hg tip changeset 0 7070a49b08e8 tag tip user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 42 2007 0000 summary Initial commit Nothing has changed in the working directory and there s been no new history created As this suggests running the hg branch command has no permanent effect it only tells Mercurial what branch name to use the next time you commit a changeset When you commit a change Mercurial records the name of the branch on which you committed Once you ve switched from the default branch to another and committed you ll see the name of the new branch show up in the
39. Just remember to eliminate contenders that can t possibly exhibit the bug perhaps because the feature with the bug isn t present yet and those where another problem masks the bug as I discussed above Even if you end up early by thousands of changesets or months of history you will only add a handful of tests to the total number that bisect must perform thanks to its logarithmic behaviour 106 Chapter 10 Handling repository events with hooks Mercurial offers a powerful mechanism to let you perform automated actions in response to events that occur in a repository In some cases you can even control Mercurial s response to those events The name Mercurial uses for one of these actions is a hook Hooks are called triggers in some revision control systems but the two names refer to the same idea 10 1 An overview of hooks in Mercurial Here is a brief list of the hooks that Mercurial supports We will revisit each of these hooks in more detail later in section 10 8 changegroup commit incoming outgoing prechangegroup precommit preoutgoing pretag pretxnchangegroup pretxncommit preupdate tag update This is run after a group of changesets has been brought into the repository from elsewhere This is run after a new changeset has been created in the local repository This is run once for each new changeset that is brought into the repository from elsewhere Notice the difference from changegroup
40. Manually merging a backout change It remembers the current parent of the working directory Let s call this changeset orig It does the equivalent of a hg update to sync the working directory to the changeset you want to back out Let s call this changeset backout It finds the parent of that changeset Let s call that changeset parent For each file that the backout changeset affected it does the equivalent of a hg revert r parent on that file to restore it to the contents it had before that changeset was committed It commits the result as a new changeset This changeset has backout as its parent If you specify merge on the command line it merges with orig and commits the result of the merge An alternative way to implement the hg backout command would be to hg export the to be backed out changeset as a diff then use the reverse option to the patch command to reverse the effect of the change without fiddling with the working directory This sounds much simpler but it would not work nearly as well The reason that hg backout does an update a commit a merge and another commit is to give the merge machinery the best chance to do a good job when dealing with all the changes between the change you re backing out and the current tip If you re backing out a changeset that s 100 revisions back in your project s history the chances that the patch command will be able to apply a reverse diff cleanly
41. Mercurial installation If you can t quickly find a local copy on your system simply download one from the master Mercurial repository at http www selenic com repo hg raw file tip hgweb cgi You ll need to copy this script into your public_html directory and ensure that it s executable cp hgweb cgi public_html chmod 755 public_html hgweb cgi 67 N The 755 argument to chmod is a little more general than just making the script executable it ensures that the script is executable by anyone and that group and other write permissions are not set If you were to leave those write permissions enabled Apache s suexec subsystem would likely refuse to execute the script In fact suexec also insists that the directory in which the script resides must not be writable by others chmod 755 public_html What could possibly go wrong Once you ve copied the CGI script into place go into a web browser and try to open the URL http myhostname myuser hgweb cgi but brace yourself for instant failure There s a high probability that trying to visit this URL will fail and there are many possible reasons for this In fact you re likely to stumble over almost every one of the possible errors below so please read carefully The following are all of the problems I ran into on a system running Fedora 7 with a fresh installation of Apache and a user account that I created specially to perform this
42. Ss 52 5 3 3 How to make changes not follow a copy o o ee ee eee 52 5 3 4 Behaviour of the hg copy command 0 0 0 ee eee eee ee 52 SA Renaming MES 2 844 kek eas BA Se KE A ee we EG A os 53 54 1 Renaming tiles and merging changes c eos ta 24 Gee Ve BN e ea PUSS Bee we a 54 34 2 Diverpent renames and METeIDE cocos aace E a siones a a E G 54 5 4 3 Convergent renames and Mega 55 SAA Other name related comercases ccoo ke rms e e a i i a 55 5 9 Recoverme from mistakes cs lt e recrei 444040 Rew eee e ee ee Ee ees 55 Collaborating with other people 57 GI Mercunal s web mierach 545 255 42258 See a tnd Sheed eh ee eee A 57 6 2 Collaboration model ess cn E RK AAA A RR 57 621 Factors to keep IDO as e A a AI CEs EHS S 57 62 2 Informal anarchy ico a a A RA eR a ee eS 58 6 2 3 Asmimele central repository lt occocoso cerrs we ee 58 6 2 4 Working with multiple branches e 58 623 PRATS branch s o e 264546044 a A Y 61 626 Thereleasetain coec oraino e a a SESS A SS SS 61 627 The Linux kernelmadel 2 4 4 5540n Ea ap bean este es ae AR 61 6 2 8 Pull only versus shared push collaboration o o e 62 6 2 9 Where collaboration meets branch management 62 Oa Tostechirsal Sus Ol SOME gt ei a e ts 62 64 Informal sharing with hg Serve os rodri ra A eee eS 62 6 4 1 Afew things to keepin Mid 63 6 5 Using the Secure Shell ssh proto
43. a descriptive extension could give you an immediate hint as to why the hook failed see section 10 4 2 for an example 110 10 4 2 Controlling whether an activity can proceed In our earlier examples we used the commit hook which is run after a commit has completed This is one of several Mercurial hooks that run after an activity finishes Such hooks have no way of influencing the activity itself Mercurial defines a number of events that occur before an activity starts or after it starts but before it finishes Hooks that trigger on these events have the added ability to choose whether the activity can continue or will abort The pret xncommit hook runs after a commit has all but completed In other words the metadata representing the changeset has been written out to disk but the transaction has not yet been allowed to complete The pret xncommit hook has the ability to decide whether the transaction can complete or must be rolled back If the pretxncommit hook exits with a status code of zero the transaction is allowed to complete the commit finishes and the commit hook is run If the pretxncommit hook exits with a non zero status code the transaction is rolled back the metadata representing the changeset is erased and the commit hook is not run cat check_bug_id bin sh check that a commit comment mentions a numeric bug id hg log r 1 template desc grep q lt bug 0 9 echo pretxncommit bug_id_requ
44. across copies your source file would now contain the bug and unless you remembered to propagate the bug fix by hand the bug would remain in your copy of the file By automatically propagating the change that fixed the bug from the original file to the copy Mercurial prevents this class of problem To my knowledge Mercurial is the only revision control system that propagates changes across copies like this Once your change history has a record that the copy and subsequent merge occurred there s usually no further need to propagate changes from the original file to the copied file and that s why Mercurial only propagates changes across copies until this point and no further 5 3 3 How to make changes not follow a copy If for some reason you decide that this business of automatically propagating changes across copies is not for you simply use your system s normal file copy command on Unix like systems that s cp to make a copy of a file then hg add the new copy by hand Before you do so though please do reread section 5 3 2 and make an informed decision that this behaviour is not appropriate to your specific case 5 3 4 Behaviour of the hg copy command When you use the hg copy command Mercurial makes a copy of each source file as it currently stands in the working directory This means that if you make some modifications to a file then hg copy it without first having committed those changes the new
45. address john q publictexample com is not a valid Bugzilla user name nor does it have an entry in your usermap that maps it to a valid Bugzilla user name 10 7 3 notify send email notifications Although Mercurial s built in web server provides RSS feeds of changes in every repository many people prefer to receive change notifications via email The notify hook lets you send out notifications to a set of email addresses whenever changesets arrive that those subscribers are interested in As with the bugzilla hook the notify hook is template driven so you can customise the contents of the notifi cation messages that it sends By default the notify hook includes a diff of every changeset that it sends out you can limit the size of the diff or turn this feature off entirely It is useful for letting subscribers review changes immediately rather than clicking to follow a URL Configuring the notify hook You can set up the notify hook to send one email message per incoming changeset or one per incoming group of changesets all those that arrived in a single pull or push 1 hooks 2 send one email per group of changes 3 changegroup notify python hgext notify hook 4 send one email per change s incoming notify python hgext notify hook Configuration information for this hook lives in the notify section of a hgrc file test By default this hook does not send out email at all instead it prints the mess
46. among revision control systems so don t take it for granted Most require readers to be able to lock a repository to access it safely and this requires write permission on at least one directory which of course makes for all kinds of nasty and annoying security and administrative problems Mercurial uses locks to ensure that only one process can write to a repository at a time the locking mechanism is safe even over filesystems that are notoriously hostile to locking such as NFS If a repository is locked a writer will wait for a while to retry if the repository becomes unlocked but if the repository remains locked for too long the process attempting to write will time out after a while This means that your daily automated scripts won t get stuck forever and pile up if a system crashes unnoticed for example Yes the timeout is configurable from zero to infinity Safe dirstate access As with revision data Mercurial doesn t take a lock to read the dirstate file it does acquire a lock to write it To avoid the possibility of reading a partially written copy of the dirstate file Mercurial writes to a file with a unique name in the same directory as the dirstate file then renames the temporary file atomically to dirstate The file named dirstate is thus guaranteed to be complete not partially written 4 5 4 Avoiding seeks Critical to Mercurial s performance is the avoidance of seeks of the disk head since any seek is far more e
47. any time you try to update your client s view of the repository The forking non problem It has been suggested that distributed revision control tools pose some sort of risk to open source projects because they make it easy to fork the development of a project A fork happens when there are differences in opinion or attitude between groups of developers that cause them to decide that they can t work together any longer Each side takes a more or less complete copy of the project s source code and goes off in its own direction Sometimes the camps in a fork decide to reconcile their differences With a centralised revision control system the technical process of reconciliation is painful and has to be performed largely by hand You have to decide whose revision history is going to win and graft the other team s changes into the tree somehow This usually loses some or all of one side s revision history What distributed tools do with respect to forking is they make forking the only way to develop a project Every single change that you make is potentially a fork point The great strength of this approach is that a distributed revision control tool has to be really good at merging forks because forks are absolutely fundamental they happen all the time If every piece of work that everybody does all the time is framed in terms of forking and merging then what the open source world refers to as a fork becomes purely a social
48. are not good because intervening changes are likely to have broken the context that patch uses to determine whether it can apply a patch if this sounds like gibberish see 12 4 99 for a discussion of the patch command Also Mercurial s merge machinery will handle files and directories being renamed permission changes and modifications to binary files none of which patch can deal with 9 4 Changes that should never have been Most of the time the hg backout command is exactly what you need if you want to undo the effects of a change It leaves a permanent record of exactly what you did both when committing the original changeset and when you cleaned up after it On rare occasions though you may find that you ve committed a change that really should not be present in the repository at all For example it would be very unusual and usually considered a mistake to commit a software project s object files as well as its source files Object files have almost no intrinsic value and they re big so they increase the size of the repository and the amount of time it takes to clone or pull changes Before I discuss the options that you have if you commit a brown paper bag change the kind that s so bad that you want to pull a brown paper bag over your head let me first discuss some approaches that probably won t work Since Mercurial treats history as accumulative every change builds on top of all changes that preced
49. arriving from another repository via a bundle The acl allow section controls the users that are allowed to add changesets to the repository If this section is not present all users that are not explicitly denied are allowed If this section is present all users that are not explicitly allowed are denied so an empty section means that all users are denied The acl deny section determines which users are denied from adding changesets to the repository If this section is not present or is empty no users are denied The syntaxes for the acl allow and acl deny sections are identical On the left of each entry is a glob pattern that matches files or directories relative to the root of the repository on the right a user name In the following example the user docwriter can only push changes to the docs subtree of the repository while intern can push changes to any file or directory except source sensitive lacl allow docs docwriter acl deny source sensitive intern Testing and troubleshooting If you want to test the acl hook run it with Mercurial s debugging output enabled Since you ll probably be running it on a server where it s not convenient or sometimes possible to pass in the debug option don t forget that you can enable debugging output in your hgrc ui debug true 115 With this enabled the acl hook will print enough information to let you figure out why it is al
50. book about distributed revision control because I believe that it is an important subject that deserves a field guide I chose to write about Mercurial because it is the easiest tool to learn the terrain with and yet it scales to the demands of real challenging environments where many other revision control tools fail 0 1 This book is a work in progress I am releasing this book while I am still writing it in the hope that it will prove useful to others I also hope that readers will contribute as they see fit 0 2 About the examples in this book This book takes an unusual approach to code samples Every example is live ceach one is actually the result of a shell script that executes the Mercurial commands you see Every time an image of the book is built from its sources all the example scripts are automatically run and their current results compared against their expected results The advantage of this approach is that the examples are always accurate they describe exactly the behaviour of the version of Mercurial that s mentioned at the front of the book If I update the version of Mercurial that P m documenting and the output of some command changes the build fails There is a small disadvantage to this approach which is that the dates and times you ll see in examples tend to be squashed together in a way that they wouldn t be if the same commands were being typed by a human Where a human can issue no more than one com
51. both a number and a hexadecimal string e The revision number is only valid in that repository e while the hex string is the permanent unchanging identifier that will always identify that exact changeset in every copy of the repository This distinction is important If you send someone an email talking about revision 33 there s a high likelihood that their revision 33 will not be the same as yours The reason for this is that a revision number depends on the order in which changes arrived in a repository and there is no guarantee that the same changes will happen in the same order in different repositories Three changes a b c can easily appear in one repository as 0 1 2 while in another as 1 0 2 Mercurial uses revision numbers purely as a convenient shorthand If you need to discuss a changeset with some one or make a record of a changeset for some other reason for example in a bug report use the hexadecimal identifier 2 4 2 Viewing specific revisions To narrow the output of hg log down to a single revision use the r or rev option You can use either a revision number or a long form changeset identifier and you can provide as many revisions as you want 14 20 21 22 23 24 hg log r 3 changeset 3 5d7b70a2a9 user Bryan O Sullivan lt bos serpentine com gt date Tue Sep 06 13 15 58 2005 0700 summary Get make to generate the final binary from a o file hg log r 5d7b70a
52. by a considerable time margin at the time of writing seven months which in some cases will mean that on Ubuntu you may run into problems that have since been fixed in the Debian package 2 1 2 Solaris XXX 10 2 13 MacOSX Lee Cantey publishes an installer of Mercurial for Mac OS X at http mercurial berkwood com This package works on both Intel and Power based Macs Before you can use it you must install a compatible version of Universal MacPython BI This is easy to do simply follow the instructions on Lee s site 2 1 4 Windows Lee Cantey also publishes an installer of Mercurial for Windows at http mercurial berkwood com This package has no external dependencies it just works Note The Windows version of Mercurial does not automatically convert line endings between Windows and Unix styles If you want to share work with Unix users you must do a little additional configuration work XXX Flesh this out 2 2 Getting started To begin we ll use the hg version command to find out whether Mercurial is actually installed properly The actual version information that it prints isn t so important it s whether it prints anything at all that we care about hg version Mercurial Distributed SCM version 2937d0dbfab0 Copyright C 2005 2006 Matt Mackall lt mpm selenic com gt This is free software see the source for copying conditions There is NO warranty not even for MERCHANTABILI
53. can be determined If a hook exits with a status of zero it is considered to have succeeded If it exits with a non zero status it is considered to have failed 10 8 3 Finding out where changesets come from A hook that involves the transfer of changesets between a local repository and another may be able to find out infor mation about the far side Mercurial knows how changes are being transferred and in many cases where they are being transferred to or from Sources of changesets Mercurial will tell a hook what means are or were used to transfer changesets between repositories This is provided by Mercurial in a Python parameter named source or an environment variable named HG_SOURCE serve Changesets are transferred to or from a remote repository over http or ssh pull Changesets are being transferred via a pull from one repository into another push Changesets are being transferred via a push from one repository into another bundle Changesets are being transferred to or from a bundle 121 Where changes are going remote repository URLs When possible Mercurial will tell a hook the location of the far side of an activity that transfers changeset data between repositories This is provided by Mercurial in a Python parameter named url or an environment variable named HG_URL This information is not always known If a hook is invoked in a repository that is being served via http or ssh Mercurial cannot tell whe
54. change css 54 4 sanan YS eee e EES See oe Bes 921 Filemanagcement enS oeg ee oop ae id HG A Ae Ged ee ee ag PHS E Nee 9 3 Dealing withcommitted changes c s cess saos d A a a a eS ER ae ae Sow a 9 3 1 Backing outa changeset o coa esye skaner E kE ee e e E a behead 9 3 2 Backing out the tip changeset s c co s senaid osa sr Re e a a a ae 9 3 3 Backing outianon lpchange oeri ecsedi eya ew ee ee ee eee E 9 3 4 Gaining more control of the backout process o e 93 Why hg Dackoul Works asit does ke ee A em a eee eee amp 9 4 Changes that should never have been 2 maiki ee 94 1 Protect yourself from escaped changes os ss stoe lt lt s 29 BIOS SOMES OL a bee ale dk g eR ELS A Bee dee he dg eee e eS 931 Using he bisect Extensiom os ese a Re RE ee ee Re RRA 95 2 Cleaning up after your search 2 44 bea aba ee wee ee eee ee 96 Tipsfor finding bugseitectively ooo opa ee AK eR ee OR ey ee a 9 6 1 lt GIVECONSIStENT MPU s sse eeri irked i ON a 962 Antomateas touch as possible oo pias Be ake ES BES RSS os 9 6 3 Check yourresulig se 6 544 6544288 ba DBA ee a ea ee ee eae 9 6 4 Beware interference between bugs eee eee eee 06 5 Bracket your search lazily css cc eR eM Ae eee a oC eee ea Rs oO Handling repository events with hooks 10 1 An overview of hooks in Mercurial ee 10 2 Hooks and seCunty iiss a ce a A Ae ha ARE ae SB ae aia Se 102 1
55. changeset somewhere then roll it back then pull from the repository you pushed to is that the changeset will reappear in your repository If you absolutely know for sure that the change you want to roll back is the most recent change in the repository that you pushed to and you know that nobody else could have pulled it from that repository you can roll back the changeset there too but you really should really not rely on this working reliably If you do this sooner or later a change really will make it into a repository that you don t directly control or have forgotten about and come back to bite you 9 1 5 You can only roll back once Mercurial stores exactly one transaction in its transaction log that transaction is the most recent one that occurred in the repository This means that you can only roll back one transaction If you expect to be able to roll back one transaction then its predecessor this is not the behaviour you will get hg rollback rolling back last transaction hg rollback no rollback information available Once you ve rolled back one transaction in a repository you can t roll back again in that repository until you perform another commit or pull 9 2 Reverting the mistaken change If you make a modification to a file and decide that you really didn t want to change the file at all and you haven t yet committed your changes the hg revert command is the one you ll need It
56. control tool Subversion svn log r9653 r9653 sean hefty 2006 09 27 14 39 55 0700 Wed 27 Sep 2006 5 lines On reporting a route error also include the status for the error rather than indicating a status of 0 when an error has occurred 135 Signed off by Sean Hefty lt sean hefty intel com gt Since Subversion s output style is fairly simple it is easy to copy and paste a hunk of its output into a file and replace the text produced above by Subversion with the template values we d like to see expanded cat svn template r rev author user date isodate date rfc822date desc strip fi1176 There are a few small ways in which this template deviates from the output produced by Subversion e Subversion prints a readable date the Wed 27 Sep 2006 in the example output above in parentheses Mercurial s templating engine does not provide a way to display a date in this format without also printing the time and time zone e We emulate Subversion s printing of separator lines full of characters by ending the template with such a line We use the templating engine s header keyword to print a separator line as the first line of output see below thus achieving similar output to Subversion e Subversion s output includes a count in the header of the number of lines in the commit message We cannot replicate this in Mercurial the templating engine does
57. exercise Your web server may have per user directories disabled If you re using Apache search your config file for a UserDir directive If there s none present per user directories will be disabled If one exists but its value is disabled then per user directories will be disabled Otherwise the string after UserDir gives the name of the subdirectory that Apache will look in under your home directory for example public_html Your file access permissions may be too restrictive The web server must be able to traverse your home directory and directories under your public_html directory and read files under the latter too Here s a quick recipe to help you to make your permissions more appropriate chmod 755 find public_html type d print0 xargs 0r chmod 755 find public_html type f print0 xargs 0r chmod 644 The other possibility with permissions is that you might get a completely empty window when you try to load the script In this case it s likely that your access permissions are too permissive Apache s suexec subsystem won t execute a script that s group or world writable for example Your web server may be configured to disallow execution of CGI programs in your per user web directory Here s Apache s default per user configuration from my Fedora system lt Directory home public_html gt AllowOverride FileInfo AuthConfig Limit Options MultiViews Indexes SymLinksIfOwnerMatch IncludesN
58. files There s nothing particularly magical about a repository it is simply a directory tree in your filesystem that Mercu rial treats as special You can rename or delete a repository any time you like using either the command line or your file browser 2 3 1 Making a local copy of a repository Copying a repository is just a little bit special While you could use a normal file copying command to make a copy of a repository it s best to use a built in command that Mercurial provides This command is called hg clone because 1t creates an identical copy of an existing repository hg clone http hg serpentine com tutorial hello destination directory hello requesting all changes adding changesets adding manifests adding file changes added 5 changesets with 5 changes to 2 files 2 files updated 0 files merged 0 files removed 0 files unresolved If our clone succeeded we should now have a local directory called hello This directory will contain some files ls 1 total 4 drwxrwxr x 3 bos bos 4096 Jun 17 18 05 hello ls hello Makefile hello c These files have the same contents and history in our repository as they do in the repository we cloned Every Mercurial repository is complete self contained and independent It contains its own private copy of a project s files and history A cloned repository remembers the location of the repository it was cloned from but it does not communicate
59. have already committed see chapter 9 56 Chapter 6 Collaborating with other people As a completely decentralised tool Mercurial doesn t impose any policy on how people ought to work with each other However if you re new to distributed revision control it helps to have some tools and examples in mind when you re thinking about possible workflow models 6 1 Mercurial s web interface Mercurial has a powerful web interface that provides several useful capabilities For interactive use the web interface lets you browse a single repository or a collection of repositories You can view the history of a repository examine each change comments and diffs and view the contents of each directory and file Also for human consumption the web interface provides an RSS feed of the changes in a repository This lets you subscribe to a repository using your favourite feed reader and be automatically notified of activity in that repository as soon as it happens I find this capability much more convenient than the model of subscribing to a mailing list to which notifications are sent as it requires no additional configuration on the part of whoever is serving the repository The web interface also lets remote users clone a repository pull changes from it and when the server is configured to permit it push changes back to it Mercurial s HTTP tunneling protocol aggressively compresses data so that it works efficiently even over low ban
60. head is a change that has no descendants or children as they re also known The tip revision is thus a head because the newest revision in a repository doesn t have any children but a repository can contain more than one head dp end bead Figure 3 2 Repository contents after pulling from my hello into my new hello In figure 3 2 you can see the effect of the pull from my hello into my new hello The history that was already present in my new hello is untouched but a new revision has been added By referring to figure 3 1 we can see that the changeset ID remains the same in the new repository but the revision number has changed This incidentally is a fine example of why it s not safe to use revision numbers when discussing changesets We can view the heads in a repository using the hg heads command hg heads changeset 6 fa1321bf0c80 tag tip parent 4 b57 9a090b62 user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 05 50 2007 0000 summary Added an extra line of output changeset 5 06795fee8236 user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 05 52 2007 0000 summary A new hello for a new day 3 1 2 Performing the merge What happens if we try to use the normal hg update command to update to the new tip 27 N hg update abort update spans branches use hg merge or hg update C to lose changes Mercurial is tel
61. issue If anything distributed tools lower the likelihood of a fork e They eliminate the social distinction that centralised tools impose that between insiders people with commit access and outsiders people without e They make it easier to reconcile after a social fork because all that s involved from the perspective of the revision control software is just another merge Some people resist distributed tools because they want to retain tight control over their projects and they believe that centralised tools give them this control However if you re of this belief and you publish your CVS or Subversion repositories publically there are plenty of tools available that can pull out your entire project s history albeit slowly and recreate it somewhere that you don t control So while your control in this case is illusory you are forgoing the ability to fluidly collaborate with whatever people feel compelled to mirror and fork your history 1 4 2 Advantages for commercial projects Many commercial projects are undertaken by teams that are scattered across the globe Contributors who are far from a central server will see slower command execution and perhaps less reliability Commercial revision control systems attempt to ameliorate these problems with remote site replication add ons that are typically expensive to buy and cantankerous to administer A distributed system doesn t suffer from these problems in the first place Better
62. it you ll need to add an allow_archive item to the web section of your hgrc 6 6 5 Web configuration options Mercurial s web interfaces the hg serve command and the hgweb cgi and hgwebdir cgi scripts have a number of configuration options that you can set These belong in a section named web allow_archive Determines which if any archive download mechanisms Mercurial supports If you enable this feature users of the web interface will be able to download an archive of whatever revision of a repository they are viewing To enable the archive feature this item must take the form of a sequence of words drawn from the list below 70 allowpull contact maxchanges maxfiles stripes style N templates bz2 A tar archive compressed using bzip2 compression This has the best compression ratio but uses the most CPU time on the server gz A tar archive compressed using gzip compression zip A zip archive compressed using LZW compression This format has the worst compression ratio but is widely used in the Windows world If you provide an empty list or don t have an allow_archive entry at all this feature will be disabled Here is an example of how to enable all three supported formats web allow_archive bz2 gz zip Boolean Determines whether the web interface allows remote users to hg pull and hg clone this repos itory over HTTP If set to no or false only the human o
63. its first publication maintenance releases tend to contain only bug fixes not new features In 58 parallel with these maintenance releases one or more future releases may be under development People normally use the word branch to refer to one of these many slightly different directions in which development is proceeding Mercurial is particularly well suited to managing a number of simultaneous but not identical branches Each development direction can live in its own central repository and you can merge changes from one to another as the need arises Because repositories are independent of each other unstable changes in a development branch will never affect a stable branch unless someone explicitly merges those changes in Here s an example of how this can work in practice Let s say you have one main branch on a central server hg init main cd main echo This is a boring feature gt myfile hg commit A m We have reached an important milestone adding myfile People clone it make changes locally test them and push them back Once the main branch reaches a release milestone you can use the hg tag command to give a permanent name to the milestone revision hg tag v1 0 hg tip changeset 1 bde8d458e45b tag tip user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 41 2007 0000 summary Added tag v1 0 for changeset al0bfd31f1c2 hg tags t
64. key to a file of your choosing or paste it from the window it s displayed in straight into the authorized keys file 64 6 5 4 Using an authentication agent An authentication agent is a daemon that stores passphrases in memory so it will forget passphrases if you log out and log back in again An ssh client will notice if it s running and query it for a passphrase If there s no authentication agent running or the agent doesn t store the necessary passphrase you ll have to type your passphrase every time Mercurial tries to communicate with a server on your behalf e g whenever you pull or push changes The downside of storing passphrases in an agent is that it s possible for a well prepared attacker to recover the plain text of your passphrases in some cases even if your system has been power cycled You should make your own judgment as to whether this is an acceptable risk It certainly saves a lot of repeated typing On Unix like systems the agent is called ssh agent and it s often run automatically for you when you log in You ll need to use the ssh add command to add passphrases to the agent s store On Windows if you re using PuTTY the pageant command acts as the agent It adds an icon to your system tray that will let you manage stored passphrases 6 5 5 Configuring the server side properly Because ssh can be fiddly to set up if you re new to it there s a variety of things that can go wrong Add Mercurial on top
65. know what those files were CVS has a muddled notion of tags and branches that I will not attempt to even describe It does not support renaming of files or directories well making it easy to corrupt a repository It has almost no internal consistency checking capabilities so it is usually not even possible to tell whether or how a repository is corrupt I would not recommend CVS for any project existing or new Mercurial can import CVS revision history However there are a few caveats that apply these are true of every other revision control tool s CVS importer too Due to CVS s lack of atomic changes and unversioned filesystem hierarchy it is not possible to reconstruct CVS history completely accurately some guesswork is involved and re names will usually not show up Because a lot of advanced CVS administration has to be done by hand and is hence error prone it s common for CVS importers to run into multiple problems with corrupted repositories completely bogus revision timestamps and files that have remained locked for over a decade are just two of the less interesting problems I can recall from personal experience 1 6 4 Commercial tools Perforce has a centralised client server architecture with no client side caching of any data Unlike modern revision control tools Perforce requires that a user run a command to inform the server about every file they intend to edit The performance of Perforce is quite good for small teams
66. log r1 template date hgdate n 1182103440 0 hg log r1 template date isodate n 2007 06 17 18 04 0000 hg log r1 template date rfc822date n Sun 17 Jun 2007 18 04 00 0000 hg log r1 template date shortdate n 2007 06 17 hg log r1 template desc n cut c 76 added line to end of lt lt hello gt gt file in addition added a file with the helpful name at least i hope that some m hg log r1 template desc addbreaks n cut c 76 added line to end of lt lt hello gt gt file lt br gt lt br gt in addition added a file with the helpful name at least i hope that some m hg log r1 template desc escape n cut c 76 added line to end of amp 1t amp lt hello amp gt gt file in addition added a file with the helpful name at least i hope that some m hg log r1 template desc 1i1168 n added line to end of lt lt hello gt gt file in addition added a file with the helpful name at least i hope that some might consider it so of goodbye hg log r1 template desc 1i1176 n added line to end of lt lt hello gt gt file in addition added a file with the helpful name at least i hope that some might consider it so of goodbye hg log r1 template desc firstline n added line to end of lt lt hello gt gt file hg log r1 template desc strip n cut c 76 added line to end of lt lt hel
67. looks at the changeset that s the parent of the working directory and restores the contents of the file to their state as of that changeset That s a long winded way of saying that in the normal case it undoes your modifications Let s illustrate how the hg revert command works with yet another small example We ll begin by modifying a file that Mercurial is already tracking cat file original content echo unwanted change gt gt file hg diff file diff r ddc4e8b595f2 file a file Sun Jun 17 18 03 48 2007 0000 b file Sun Jun 17 18 03 48 2007 0000 1 1 1 2 original content original content tunwanted change If we don t want that change we can simply hg revert the file hg status M file hg revert file cat file original content The hg revert command provides us with an extra degree of safety by saving our modified file with a orig extension 91 hg status file orig cat file orig original content unwanted change Here is a summary of the cases that the hg revert command can deal with We will describe each of these in more detail in the section that follows e If you modify a file it will restore the file to its unmodified state e If you hg add a file it will undo the added state of the file but leave the file itself untouched e If you delete a file without telling Mercurial it will restore th
68. of the source code repository that accompanies this book usr bin env python Adapter for using interdiff with mercurial s extdiff extension Copyright 2006 Bryan O Sullivan lt bos serpentine com gt 161 20 21 22 23 24 25 27 28 29 30 31 32 33 34 35 37 38 39 This software may be used and distributed according to the terms of the GNU General Public License incorporated herein by reference import os sys def walk base yield all non directories below the base path for root dirs files in os walk base for f in files path os path join root f yield path len base 1 path create list of unique file names under both directories files dict walk sys argv 1 files update walk sys argv 2 files files keys files sort def name base f interdiff requires two files use dev null if one is missing path os path join base f if os path exists path return path return dev null ret 0 for f in files if os system interdiff Ss Ss name sys argv 1 f name sys argv 2 f ret 1 sys exit ret With the hg interdiff program in your shell s search path you can run it as follows from inside an MQ patch directory hg extdiff p hg interdiff r A B my change patch Mercurial command again by editing your hgrc Since you ll probably want to use this long wind
69. often need to edit the series file by hand hence the support for comments and empty lines noted above For example you can comment out a patch temporarily and hg qpush will skip over that patch when applying patches You can also change the order in which patches are applied by reordering their entries in the series file Placing the series file under revision control is also supported it is a good idea to place all of the patches that it refers to under revision control as well If you create a patch directory using the c option to hg qinit this will be done for you automatically B 2 2 The status file The status file contains the names and changeset hashes of all patches that MQ currently has applied Unlike the series file this file is not intended for editing You should not place this file under revision control or modify it in any way It is used by MQ strictly for internal book keeping 178 Appendix C Installing Mercurial from source C 1 Ona Unix like system If you are using a Unix like system that has a sufficiently recent version of Python 2 3 or newer available it is easy to install Mercurial from source 1 Download a recent source tarball from http www selenic com mercurial download 2 Unpack the tarball 1 gzip dc mercurial version tar gz tar xf 3 Go into the source directory and run the installer script This will build Mercurial and install it in your home directory
70. only sending out email about changes that remote users pushed into this repository via a server for example See section 10 8 3 for the sources you can specify here 119 If you set the baseurl item in the web section you can use it in a template it will be available as webroot Here is an example set of notify configuration information notify really send email test false subscriber data lives in the notify repo config home hg repos notify notify conf repos live in home hg repos on server so strip 4 chars strip 4 template X Hg Repo webroot n Subject webroot desc firstline strip n From author n n changeset node short in root n details baseurl webroot cmd changeset node node short description n t desc tabindent strip web baseurl http hg example com This will produce a message that looks like the following X Da de di di ee Hg Repo tests slave Subject tests slave Handle error case when slave has no buffers te Wed 2 Aug 2006 15 25 46 0700 PDT changeset 3cba9bfe74b5 in home hg repos tests slave tails http hg example com tests slave cmd changeset node 3cba9bfe74b5 description Handle error case when slave has no buffers ffs 54 lines ff r 9d95df 7cf2ad r 3cbha9bfe74b5 include tests h a include tests h Wed Aug 02 15 19 52 2006 0700 b include tests h Wed Aug 02 15 25 26 2006 0700
71. opts followed by the name of the command to which the options apply This example defines a hg vimdiff command that runs the vim editor s DirDiff extension extdiff cmd vimdiff vim opts vimdiff f next execute DirDiff argv 0 argv 1 14 3 Cherrypicking changes with the transplant extension Need to have a long chat with Brendan about this 14 4 Send changes via email with the patchbomb extension Many projects have a culture of change review in which people send their modifications to a mailing list for others to read and comment on before they commit the final version to a shared repository Some projects have people who act as gatekeepers they apply changes from other people to a repository to which those others don t have access Mercurial makes it easy to send changes over email for review or application via its patchbomb extension The extension is so namd because changes are formatted as patches and it s usual to send one changeset per email message Sending a long series of changes by email is thus much like bombing the recipient s inbox hence patchbomb As usual the basic configuration of the pat chbomb extension takes just one or two lines in your hgrc extensions patchbomb 168 Once you ve enabled the extension you will have a new command available named hg email The safest and best way to invoke the hg email command is to always r
72. patches not yet applied The hg qunapplied command prints the names of patches from the series file that are not yet applied It prints them in order from the next patch that will be pushed to the last 177 B 1 21 hg qversion The hg qversion command prints the version of MQ that is in use B 1 22 hg strip remove a revision and descendants The hg strip command removes a revision and all of its descendants from the repository It undoes the effects of the removed revisions from the repository and updates the working directory to the first parent of the removed revision The hg strip command saves a backup of the removed changesets in a bundle so that they can be reapplied if removed in error Options b Save unrelated changesets that are intermixed with the stripped changesets in the backup bundle f Ifa branch has multiple heads remove all heads XXX This should be renamed and use f to strip revs when there are pending changes n Do not save a backup bundle B 2 MQ file reference B 2 1 The series file The series file contains a list of the names of all patches that MQ can apply It is represented as a list of names with one name saved per line Leading and trailing white space in each line are ignored Lines may contain comments A comment begins with the character and extends to the end of the line Empty lines and lines that contain only comments are ignored You will
73. processmail script and mapping committer names to user names Recall from section 10 7 2 above that the user that runs the Mercurial process on the server is also the one that will run the processmail script The processmail script sometimes causes Bugzilla to write to files in its configuration directory and Bugzilla s configuration files are usually owned by the user that your web server runs under You can cause processmail to be run with the suitable user s identity using the sudo command Here is an example entry for a sudoers file hg_user httpd_user NOPASSWD var www html bugzilla processmail wrapper s This allows the hg_user user to run a processmail wrapper program under the identity of httpd_user This indirection through a wrapper script is necessary because processmail expects to be run with its current directory set to wherever you installed Bugzilla you can t specify that kind of constraint in a sudoers file The contents of the wrapper script are simple bin sh cd dirname 0 amp amp processmail 1 nobody example com It doesn t seem to matter what email address you pass to processmail If your usermap is not set up correctly users will see an error message from the bugzilla hook when they push changes to the server The error message will look like this 118 1 cannot find bugzilla user id for john g public example com What this means is that the committer s
74. recommend that you upgrade 78 Chapter 8 Managing releases and branchy development Mercurial provides several mechanisms for you to manage a project that is making progress on multiple fronts at once To understand these mechanisms let s first take a brief look at a fairly normal software project structure Many software projects issue periodic major releases that contain substantial new features In parallel they may issue minor releases These are usually identical to the major releases off which they re based but with a few bugs fixed In this chapter we ll start by talking about how to keep records of project milestones such as releases We ll then continue on to talk about the flow of work between different phases of a project and how Mercurial can help you to isolate and manage this work 8 1 Giving a persistent name to a revision Once you decide that you d like to call a particular revision a release it s a good idea to record the identity of that revision This will let you reproduce that release at a later date for whatever purpose you might need at the time reproducing a bug porting to a new platform etc hg init mytag cd mytag echo hello gt myfile hg commit A m Initial commit adding myfile Mercurial lets you give a permanent name to any revision using the hg tag command Not surprisingly these names are called tags hg tag v1 0
75. s easy to make mistakes This is a simple case of the patch management problem You have an upstream source tree that you can t change you need to make some local changes on top of the upstream tree and you d like to be able to keep those changes separate so that you can apply them to newer versions of the upstream source The patch management problem arises in many situations Probably the most visible is that a user of an open source software project will contribute a bug fix or new feature to the project s maintainers in the form of a patch Distributors of operating systems that include open source software often need to make changes to the packages they distribute so that they will build properly in their environments When you have few changes to maintain it is easy to manage a single patch using the standard diff and patch programs see section 12 4 for a discussion of these tools Once the number of changes grows it starts to makes sense to maintain patches as discrete chunks of work so that for example a single patch will contain only one bug fix the patch might modify several files but it s doing only one thing and you may have a number of such patches for different bugs you need fixed and local changes you require In this situation if you submit a bug fix patch to the upstream maintainers of a package and they include your fix in a subsequent release you can simply drop that single patch when you re updat
76. sgi agp c 24 Hunk 1 static int __devinit agp_sgi_init void 37 File 2 a drivers char hvcs c 39 Hunk 1 static struct tty_operations hvcs_ops 53 Hunk 2 static int hvcs_alloc_index_list int n 69 File 3 a drivers message fusion mptfc c 71 Hunk 1 mptfc_GetFcDevPage0 MPT_ADAPTER ioc in 85 File 4 a drivers message fusion mptsas c 87 Hunk 1 mptsas_probe_hba_phys MPT_ADAPTER ioc 98 File 5 a drivers net fs_enet fs_enet mii c 100 Hunk 1 static struct fs_enet_mii_bus create_bu 111 File 6 a drivers net wireless ipw2200 c 113 Hunk static struct ipw_fw_error ipw_alloc_er 126 Hunk 2 static ssize_t clear_error struct device 140 Hunk static void ipw_irq _tasklet struct ipw_p 150 Hunk 4 static void ipw_pci_remove struct pci_de 164 File 7 a drivers scsi libata scsi c 166 Hunk 1 int ata_cmd_ioctl struct scsi_device sc 178 File 8 a drivers video aul100fb c 180 Hunk 1 void _ exit aul100fb_cleanup void This command prints three different kinds of number e in the first column a file number to identify each file modified in the patch e on the next line indented the line number within a modified file where a hunk starts and 154 e on the same line a hunk number to identify that hunk You ll have to use some visual inspection and reading of the patch to identify the file and hunk numbers you ll want but you can then pass them to to filterdiff s files and hunks options to select exactl
77. system command 61 171 172 grep system command 103 105 guards file 158 header template keyword 136 heads command 27 help command 11 12 139 174 hg interdiff file 161 162 hgdate template filter 131 hgext extension 162 hgmerge system command 29 31 125 hgrc configuration file 66 70 72 88 101 108 110 112 115 119 128 161 162 166 168 hgrc file acl allow section 115 acl deny section 115 acl section 114 bundle entry 115 pull entry 115 push entry 115 serve entry 114 sources entry 114 bugzilla section 116 117 db entry 117 host entry 116 notify entry 117 password entry 117 usermap entry 117 user entry 117 version entry 116 diff section showfunc entry 171 extdiff section 168 extensions section 33 161 166 hooks section 110 notify section 119 config entry 119 naxdiff entry 119 sources entry 119 strip entry 119 template entry 119 test entry 119 120 ui section username entry 18 verbose entry 111 usermap section 117 119 184 web section 70 72 118 120 accesslog entry 72 address entry 72 allow_archive entry 70 71 allowpull entry 71 baseurl entry 118 120 contact entry 71 description entry 71 errorlog entry 72 ipv6 entry 72 maxchanges entry 71 maxfiles entry 71 motd entry 71 name entry 71 port entry 72 stripes entry 71 style entry 71 templates entry 71 hgweb cgi file 67 69 70 72 hgweb config file 69 71 hgwebdir cgi file 69 71 hg s
78. the revisions to compare 1 Display the differences between the parent revision of the working directory and the working directory 2 Display the differences between the specified changeset and the working directory 3 Display the differences between the two specified changesets You can specify two revisions using either two r options or revision range notation For example the two revision specifications below are equivalent 171 hg diff r 10 r 20 hg diff r10 20 When you provide two revisions Mercurial treats the order of those revisions as significant Thus hg diff 110 20 will produce a diff that will transform files from their contents as of revision 10 to their contents as of revision 20 while hg diff r20 10 means the opposite the diff that will transform files from their revision 20 contents to their revision 10 contents You cannot reverse the ordering in this way if you are diffing against the working directory ignore all space also w A 3 hg version print version and copyright information This command displays the version of Mercurial you are running and its copyright license There are four kinds of version string that you may see e The string unknown This version of Mercurial was not built in a Mercurial repository and cannot determine its own version e A short numeric string such as 1 1 This is a build of a revision of Mercurial that was identified
79. to another candidate are looking for the point at which a problem was fixed then make mark revision as bad and update to the next revision to test mark revision as good and update to the next revision to test show help for a given bisect subcommand or all subcommands start a new bisection find and update to the next revision to test finish a bisection 102 The bisect extension works in steps Each step proceeds as follows 1 You run your binary test e If the test succeeded you tell bisect by running the hg bisect good command e If it failed use the hg bisect bad command to let the bisect extension know 2 The extension uses your information to decide which changeset to test next 3 It updates the working directory to that changeset and the process begins again The process ends when bisect identifies a unique changeset that marks the point where your test transitioned from succeeding to failing To start the search we must run the hg bisect init command hg bisect init In our case the binary test we use is simple we check to see if any file in the repository contains the string i have a gub If it does this changeset contains the change that caused the bug By convention a changeset that has the property we re searching for is bad while one that doesn t is good Most of the time the revision to which the working directory is synced
80. to how your team collaborates it s dense enough to merit treatment of its own in chapter 8 6 3 The technical side of sharing The remainder of this chapter is devoted to the question of serving data to your collaborators 6 4 Informal sharing with hg serve Mercurial s hg serve command is wonderfully suited to small tight knit and fast paced group environments It also provides a great way to get a feel for using Mercurial commands over a network Run hg serve inside a repository and in under a second it will bring up a specialised HTTP server this will accept connections from any client and serve up data for that repository until you terminate it Anyone who knows the URL of the server you just started and can talk to your computer over the network can then use a web browser or Mercurial to read data from that repository A URL for a hg serve instance running on a laptop is likely to look something like http my laptop local 8000 The hg serve command is not a general purpose web server It can do only two things 62 e Allow people to browse the history of the repository it s serving from their normal web browsers e Speak Mercurial s wire protocol so that people can hg clone or hg pull changes from that repository In particular hg serve won t allow remote users to modify your repository It s intended for read only use If you re getting started with Mercurial there
81. update section 10 9 13 10 9 12 tag after tagging a changeset This hook is run after a tag has been created Parameters to this hook local A boolean Whether the new tag is local to this repository instance i e stored in hg localtags or managed by Mercurial stored in hgtags node A changeset ID The ID of the changeset that was tagged tag A string The name of the tag that was created If the created tag is revision controlled the commit hook section 10 9 2 is run before this hook See also pretag section 10 9 8 10 9 13 update after updating or merging working directory This hook is run after an update or merge of the working directory completes Since a merge can fail if the external hgmerge command fails to resolve conflicts in a file this hook communicates whether the update or merge completed cleanly error A boolean Indicates whether the update or merge completed successfully 125 parentl A changeset ID The ID of the parent that the working directory was updated to If the working directory was merged it will not have changed this parent parent2 A changeset ID Only set if the working directory was merged The ID of the revision that the working directory was merged with See also preupdate section 10 9 11 126 Chapter 11 Customising the output of Mercurial Mercurial provides a powerful mechanism to let you control how it displays information The mechanism is based on templates You can u
82. updating since new heads added 13 run hg heads to see heads hg merge to merge w UA ALO E In this example I won t use Mercurial s normal hgmerge program to do the merge because it would drop my nice automated example running tool into a graphical user interface Instead I ll set HGMERGE to tell Mercurial to use the non interactive merge command This is bundled with many Unix like systems If you re following this example on your computer don t bother setting HGMERGE 31 export HGMERGE merge hg merge merging letter txt merge warning conflicts during merge merging letter txt failed 0 files updated 0 files merged 0 files removed 1 files unresolved There are unresolved merges you can redo the full merge using hg update C 1 hg merge 2 cat letter txt Greetings lt lt lt lt lt lt lt tmp tour merge conflictuwdiGK scam merge letter txt I am Shehu Musa Abacha cousin to the former I am Alhaji Abba Abacha son of the former gt gt gt gt gt gt gt tmp letter txt other p0KQru Nigerian dictator Sani Abacha Because merge can t resolve the conflicting changes it leaves merge markers inside the file that has conflicts indicat ing which lines have conflicts and whether they came from our version of the file or theirs Mercurial can tell from the way merge exits that it wasn t able to merge successfully so it tells us what commands we ll need to run
83. with MQ 2 2 2 0 0 2 ee 161 139 1 Organising patches im directories 2 RR ee he ee eee 161 vi 139 2 Viewing the history of a patch ss oos soss a ea E aa a R a eS da 14 Adding functionality with extensions 14 1 Improve performance with the inotify extension e 14 2 Flexible diff support with the extdiff extension assau e 14 2 1 Defining command aliases lt lt cos pe a Panni a A 14 3 Cherrypicking changes with the transplant extension e 14 4 Send changes via email with the patchbomb extension e 14 4 1 Changing the behaviour of patchbombs o saoao e A l hg add add files at the next commit e ee ee A 2 hg diff print changes in history or working directory oaoa OPUORS 23 05 ek a a eH a di A AA A A 3 hg version print version and copyright information ic A A A Command reference AZI A 3 1 B Mercurial Queues reference B 1 MOcommand TEierenc acs eni poe a a e e aaa la em OE B 1 1 B 1 2 B 1 3 B 1 4 B 1 5 B 1 6 B 1 7 B 1 8 B 1 9 B 1 10 B 1 11 B 1 12 B 1 13 B 1 14 B 1 15 B 1 16 B 1 17 B 1 18 B 1 19 B 1 20 B 1 21 B 1 22 hg hg hg hg hg hg hg hg hg hg hg hg hg hg hg hg hg hg gapplied print applied patches e qcommit commit changes in the queue repository s sooo qdelete del
84. with the contents that we modified e On the right is their version of the file the one that from the changeset that we re trying to merge with In the pane below these is the current result of the merge Our task is to replace all of the red text which indicates unresolved conflicts with some sensible merger of the ours and theirs versions of the file All four of these panes are locked together if we scroll vertically or horizontally in any of them the others are updated to display the corresponding sections of their respective files For each conflicting portion of the file we can choose to resolve the conflict using some combination of text from the base version ours or theirs We can also manually edit the merged file at any time in case we need to make further modifications There are many file merging tools available too many to cover here They vary in which platforms they are available for and in their particular strengths and weaknesses Most are tuned for merging files containing plain text while a few are aimed at specialised file formats generally XML 3 2 2 A worked example In this example we will reproduce the file modification history of figure 3 4 above Let s begin by creating a repository with a base version of our document cat gt letter txt lt lt EOF gt Greetings gt I am Mariam Abacha the wife of former gt Nigerian dictator Sani Abacha 30 5 gt EOF 6 hg add let
85. work on a project 1 1 2 The many names of revision control Revision control is a diverse field so much so that it doesn t actually have a single name or acronym Here are a few of the more common names and acronyms you 1l encounter e Revision control RCS e Software configuration management SCM or configuration management e Source code management e Source code control or source control e Version control VCS Some people claim that these terms actually have different meanings but in practice they overlap so much that there s no agreed or even useful way to tease them apart 1 2 A short history of revision control The best known of the old time revision control tools is SCCS Source Code Control System which Marc Rochkind wrote at Bell Labs in the early 1970s SCCS operated on individual files and required every person working on a project to have access to a shared workspace on a single system Only one person could modify a file at any time arbitration for access to files was via locks It was common for people to lock files and later forget to unlock them preventing anyone else from modifying those files without the help of an administrator Walter Tichy developed a free alternative to SCCS in the early 1980s he called his program RCS Revison Control System Like SCCS RCS required developers to work in a single shared workspace and to lock files to prevent multiple people from modifying them simultaneously La
86. yet you can easily set up multiple authoritative servers say one per site so that there s no redundant communication between repositories over expensive long haul network links Centralised revision control systems tend to have relatively low scalability It s not unusual for an expensive centralised system to fall over under the combined load of just a few dozen concurrent users Once again the typical response tends to be an expensive and clunky replication facility Since the load on a central server if you have one at all is orders of magnitude lower with a distributed tool because all of the data is replicated everywhere a single cheap server can handle the needs of a much larger team and replication to balance load becomes a simple matter of scripting If you have an employee in the field troubleshooting a problem at a customer s site they ll benefit from distributed revision control The tool will let them generate custom builds try different fixes in isolation from each other and search efficiently through history for the sources of bugs and regressions in the customer s environment all without needing to connect to your company s network 1 5 Why choose Mercurial Mercurial has a unique set of properties that make it a particularly good choice as a revision control system e Itis easy to learn and use e Itis lightweight e It scales excellently e It is easy to customise If you are at all familiar with revis
87. you 11 have to re enter the commit message after you fix the trailing whitespace and run hg commit again Figure 10 5 introduces a simple pret xncommit hook that checks for trailing whitespace This hook is short but not very helpful It exits with an error status if a change adds a line with trailing whitespace to any file but does not print any information that might help us to identify the offending file or line It also has the nice property of not paying attention to unmodified lines only lines that introduce new trailing whitespace cause problems The example of figure 10 6 is much more complex but also more useful It parses a unified diff to see if any lines add trailing whitespace and prints the name of the file and the line number of each such occurrence Even better if the change adds trailing whitespace this hook saves the commit comment and prints the name of the save file before exiting and telling Mercurial to roll the transaction back so you can use hg commit 1 filename to reuse the saved commit message once you ve corrected the problem 113 cat hg hgre hooks pretxncommit whitespace hg export tip egrep q t echo a gt a hg commit A m test with trailing whitespace adding a abort pretxncommit whitespace hook exited with status 1 transaction abort rollback completed echo a gt a hg commit A m drop trailing whitespace and try again
88. you could tag failed builds on the assumption that they re rare or simply not use tags to track buildability If you want to remove a tag that you no longer want use hg tag remove 80 hg tag remove v1 0 hg tags tip 3 05aa92698428 You can also modify a tag at any time so that it identifies a different revision by simply issuing a new hg tag command You ll have to use the f option to tell Mercurial that you really want to update the tag hg tag r 1 v1 1 hg tags tip 4 f0c034b7f9b2 v1 1 1 d8bf5b36ec51 hg tag r 2 v1 1 abort a tag named v1 1 already exists use f to force hg tag f r 2 v1 1 hg tags tip 5 b1b0057 92c9 v1 1 2 a78de6396931 There will still be a permanent record of the previous identity of the tag but Mercurial will no longer use it There s thus no penalty to tagging the wrong revision all you have to do is turn around and tag the correct revision once you discover your error Mercurial stores tags in a normal revision controlled file in your repository If you ve created any tags you ll find them in a file named hgtags When you run the hg tag command Mercurial modifies this file then automatically commits the change to it This means that every time you run hg tag you ll see a corresponding changeset in the output of hg log hg tip changeset 5 b1b0057 92c9 tag tip user Bryan O Sullivan lt bos serpe
89. your server s error logs 6 6 1 Web server configuration checklist Before you continue do take a few moments to check a few aspects of your system s setup 1 Do you have a web server installed at all Mac OS X ships with Apache but many other systems may not have a web server installed 2 If you have a web server installed is it actually running On most systems even if one is present it will be disabled by default 3 Is your server configured to allow you to run CGI programs in the directory where you plan to do so Most servers default to explicitly disabling the ability to run CGI programs If you don t have a web server installed and don t have substantial experience configuring Apache you should consider using the lighttpd web server instead of Apache Apache has a well deserved reputation for baroque and confusing configuration While lighttpd is less capable in some ways than Apache most of these capabilities are not relevant to serving Mercurial repositories And lighttpd is undeniably much easier to get started with than Apache 6 6 2 Basic CGI configuration On Unix like systems it s common for users to have a subdirectory named something like public_html in their home directory from which they can serve up web pages A file named foo in this directory will be accessible at a URL of the form http www example com sername foo To get started find the hgweb cgi script that should be present in your
90. 06 17 18 03 54 000000000 0000 ee 1 1 ee this is my first line my first line is here patch lt tiny patch patching file oldfile cat oldfile my first line is here Figure 12 1 Simple uses of the diff and patch commands The type of file that diff generates and patch takes as input is called a patch or a diff there is no difference between a patch and a diff We ll use the term patch since it s more commonly used A patch file can start with arbitrary text the patch command ignores this text but MQ uses it as the commit message when creating changesets To find the beginning of the patch content patch searches for the first line that starts with the string diff MQ works with unified diffs patch can accept several other diff formats but MQ doesn t A unified diff contains two kinds of header The file header describes the file being modified it contains the name of the file to modify When patch sees a new file header it looks for a file with that name to start modifying After the file header comes a series of hunks Each hunk starts with a header this identifies the range of line numbers within the file that the hunk should modify Following the header a hunk starts and ends with a few usually three lines of text from the unmodified file these are called the context for the hunk If there s only a small amount of context between successive hunks diff doesn t print a new hun
91. 146 149 154 158 165 166 175 178 a option 142 147 148 151 165 176 1 option 176 m option 148 176 n option 177 grefresh command 141 143 145 147 149 151 154 175 177 e option 177 1 option 177 m option 177 qrename command 177 qrestore command 177 qsave command 148 177 c option 148 e option 148 qselect command 158 qseries command 142 145 149 177 atop command 151 177 qunapplied command 177 qversion command 178 node template keyword 130 short filter 132 notify extension 119 120 164 obfuscate template filter 132 outgoing command 23 128 outgoing hook 107 108 123 124 pageant system command 65 185 parents command 22 28 29 39 172 parents template keyword 130 patchbomb extension 161 168 169 email command 169 plain option 169 a option 169 b option 169 d option 169 f option 169 m option 169 n option 169 s option 169 patchutils package 151 161 patch command 144 reverse option 99 p option 144 patch system command 99 100 137 139 143 147 173 perl system command 114 person template filter 132 plink system command 64 66 prechangegroup hook 107 122 124 precommit hook 107 113 122 125 preoutgoing hook 107 109 123 124 pretag hook 107 124 125 pretxnchangegroup hook 88 107 109 114 122 124 pretxncommit hook 107 109 111 113 116 122 125 preupdate hook 107 125 126 pull command 21 23 26 33 39 63 71 78 86
92. 20 141 144 161 164 166 167 170 174 exclude option 170 183 git option 170 172 ignore all space option 172 ignore blank lines option 170 ignore space change option 171 include option 170 nodates option 170 rev option 171 show function option 171 text option 170 B option 170 C option 167 I option 170 N option 144 X option 170 a option 170 173 b option 171 c option 167 g option 171 p option 171 r option 144 171 172 w option 172 diff system command 137 139 144 167 domain template filter 131 email command patchbomb extension 169 plain option 169 a option 169 b option 169 d option 169 f option 169 m option 169 n option 169 s option 169 email template filter 131 escape template filter 131 export command 99 extdiff command extdiff extension 162 167 168 o option 167 p option 167 extdiff extension 161 163 166 168 extdiff command 162 167 168 o option 167 p option 167 fetch command 33 fetch command fet ch extension 164 fet ch extension 33 164 fetch command 164 file_adds template keyword 130 file_dels template keyword 130 files template keyword 129 131 f11168 template filter 131 11176 template filter 131 filterdiff command files option 155 hunks option 155 i option 154 x option 154 filterdiff system command 151 152 154 155 firstline template filter 131 foo command 86 git
93. 23 Mercurial records 17 as the first parent of the merge and 23 as the second Whereas if I hg update to 23 and then hg merge with 17 it records 23 as the first parent and 17 as the second This affects Mercurial s choice of branch name when you merge After a merge Mercurial will retain the branch name of the first parent when you commit the result of the merge If your first parent s branch name is foo and you merge with bar the branch name will still be foo after you merge It s not unusual for a repository to contain multiple heads each with the same branch name Let s say I m working on the foo branch and so are you We commit different changes I pull your changes I now have two heads each claiming to be on the foo branch The result of a merge will be a single head on the foo branch as you might hope 87 But if Pm working on the bar branch and I merge work from the foo branch the result will remain on the bar branch hg branch bar hg merge 1 files updated 0 files merged 0 files removed 0 files unresolved branch merge don t forget to commit hg commit m Merge hg tip changeset 4 0423b2 2398c branch bar tag tip parent 2 4 00549a48el parent 3 5b570081d902 user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 44 2007 0000 summary Merge To give a more concrete example if I m working on the bleeding edge branch and I want to br
94. 2a9 changeset 3 5d7b70a2a9 user Bryan O Sullivan lt bos serpentine com gt date Tue Sep 06 13 15 58 2005 0700 summary Get make to generate the final binary from a o file hg log r 1 r 4 changeset 1 82e55d328c8c user mpm selenic com date Fri Aug 26 01 21 28 2005 0700 summary Create a makefile changeset 4 b57 9a090b62 tag tip user Bryan O Sullivan lt bos serpentine com gt date Tue Sep 06 15 43 07 2005 0700 summary Trim comments If you want to see the history of several revisions without having to list each one you can use range notation this lets you express the idea I want all revisions between a and b inclusive hg log r 2 4 changeset 2 057d3c2d823c user Bryan O Sullivan lt bos serpentine com gt date Tue Sep 06 13 15 43 2005 0700 summary Introduce a typo into hello c changeset 3 5d7b70a2a9 user Bryan O Sullivan lt bos serpentine com gt date Tue Sep 06 13 15 58 2005 0700 summary Get make to generate the final binary from a o file changeset 4 b57 9a090b62 tag tip user Bryan O Sullivan lt bos serpentine com gt date Tue Sep 06 15 43 07 2005 0700 summary Trim comments Mercurial also honours the order in which you specify revisions so hg log r 2 4 prints 2 3 4 while hg log r 4 2 prints 4 3 2 15 2 4 3 More detailed information While the summary information printed by hg log is us
95. 44e38d2f2 backs out changeset 1 92480a09996c the backout changeset is a new head do not forget to merge use backout merge if you want to auto merge Our new changeset is again a descendant of the changeset we backout out it s thus a new head not a descendant of the changeset that was the tip The hg backout command was quite explicit in telling us this 2 b5b85d3d30ee third change 1 92480a09996c second change 0 d185b5a7 54c first change hg log style compact 3 tip 1 93c44e38d2f2 2007 06 06 15 10 0000 bos back out second change 2007 06 06 15 10 0000 bos 2007 06 06 15 10 0000 bos 2007 06 06 15 10 0000 bos Again it s easier to see what has happened by looking at a graph of the revision history in figure 9 3 This makes it clear that when we use hg backout to back out a change other than the tip Mercurial adds a new head to the repository the change it committed is box shaped back out second change Figure 9 3 Backing out a change using the hg backout command 97 N After the hg backout command has completed it leaves the new backout changeset as the parent of the working directory hg parents changeset 3 93c44e38d2f2 tag tip parent 1 92480a09996c user Bryan O Sullivan lt bos serpentine com gt date Wed Jun 06 15 10 43 2007 0000 summary back out second change Now we have two iso
96. Creating a Mercurial configuration file To set a user name use your favourite editor to create a file called hgrc in your home directory Mercurial will use this file to look up your personalised configuration settings The initial contents of your hgrc should look like this 18 This is a Mercurial configuration file ui username Firstname Lastname lt email address domain net gt The ui line begins a section of the config file so you can read the username line as meaning set the value of the username item in the ui section A section continues until a new section begins or the end of the file Mercurial ignores empty lines and treats any text from to the end of a line as a comment Choosing a user name You can use any text you like as the value of the username config item since this information is for reading by other people but for interpreting by Mercurial The convention that most people follow is to use their name and email address as in the example above Note Mercurial s built in web server obfuscates email addresses to make it more difficult for the email harvesting tools that spammers use This reduces the likeli hood that you ll start receiving more junk email if you publish a Mercurial reposi tory on the web 2 7 2 Writing a commit message When we commit a change Mercurial drops us into a text editor to enter a message that will describe the modifi
97. Distributed revision control with Mercurial Bryan O Sullivan Copyright 2006 2007 Bryan O Sullivan This material may be distributed only subject to the terms and conditions set forth in version 1 0 of the Open Publication License Please refer to Appendix D for the license text This book was prepared from rev 8627f718517a dated 2007 09 10 19 38 0200 using rev 0d5d03844927 20070820 of Mercurial Contents Contents i Preface 2 0 1 This book 18 a work I progress nc Re o BRN OE A oe SE ERS ee 2 Q2 About the examples in this book c ccoa 264 Ae ha REEDS EO OE SOS ee a 2 0 3 Celophon this book is Free a a a ee a aE ee a e 2 1 Introduction 3 LA ADOUEFEVISIONCOOMOL o a ri A ee A ES 3 LLI Why use revision contol s e ed a E ee A a eS 3 Li2 Thematy names of tevision contol oc 544 4 6 eee Pe BS ee OE BR eS 4 1 2 Aushort history of revision control ee ee RE eee RR EEE eS 4 Ta Trends TA revigion contol anidar de he PRS SEE EES Bee eee See 5 1 4 A few of the advantages of distributed revision control o ooo o 000 4 5 1 4 1 Advantages for open source projects ee 6 14 2 Advantages for commercial projects soo s coe soe a e a a a ee a 6 13 Why choose Mercurial cocos cams daa ee ad a A 7 1 6 Mercurial compared with other tools lt s e oops cssooro conser 7 LOL SUBVERSION eee a e a a e a A E a ee ol a a 7 WG A A ARAN 8 O68 AE eS ER eR PO Gee ee EEE RSE PS 8 LGA Commercial i
98. ER EERE aS 42 9 WasttTerieval o ose Sade eka Bake SEAR Ee RRS ERED ESR SERED HO 4 2 4 Identification and strong integrity 0 20 0000 2 200 0 4 3 Revision history branching and merging s ms o escam er a ee 0022 eee eee 44 The working directory lt o seee fo A EB ee 6 EE Slee E Eee 4 4 1 What happens When you commit 0 200000000000 44 2 Creating anew Bead nico RRA LAS Merpinp Deads occiso coca 8b ba eA wee eee 45 Other interesting design features c copa eR A ee a 45 1 Clever compressione ss cae ROSA OMA we eee RAE ERR ERE Sas 45 2 Read write ordering and atomicity s s soose eee PR RE 45 5 CONCRITENLACCESS civic ERA ee A eae ASA Avoiding seeks io oa Bee BS eS Be e eR a BS amp a ww 4 5 5 Othercontents ofthe distat ee kw eee a ee ew Mercurial in daily use 5 1 Telling Mercurial which files to track o lt s er cocas ee ee 5 1 1 Explicit versus implicit Ale naming e nope kk Re rra 5 1 2 Asides Mercurial tracks files not directos oda a we a a e 32 How tostop tracking a file cisco A a Ra E a E a 5 2 1 Removing a file does not affect its history o e 322 MISSIDB files ojo 5s ey bed ek be ed Ae ee eb RR ee el s d a 5 2 4 Useful shorthand adding and removing files in one step o 50 33 Copyn DES compis a A a Bee Oe nly a 50 3 3 1 The results of copying during Amere coso E ea 50 35 2 Why should changes follow copies cyt pin Boke RN EHS
99. Hooks are run with your privileges o o cesa 2 08 bay ee a ee eS 102 2 Hooks donot Propagate sc kee a AS Bae ee a a Se A 102 3 Hooks can be overridden lt ea e PR ew ee eee Ade ee 10 2 4 Ensuring that critical hooks are run e 89 89 89 89 90 90 91 91 92 93 94 94 96 98 100 100 100 101 104 105 105 105 105 105 106 10 3 Care with pretxn hooks in a shared access repository 2 2 2 ee e 109 14 3 1 Theproblemillastrated o os c 6 GA ss we A a ee 109 10 4 A short tutorial on using hooks 2 2 ee 110 10 4 1 Performing multiple actions per event 2 2 2 2 eee 110 10 4 2 Controlling whether an activity can proceed s sac coea a ne ea a EEE a a a 111 10 5 Wao ng YOU GAR DOGKS cec aesa eaa ak 28 6 ea e a a e e ae e a Eee E S 111 10 5 1 Choosing how your hook shopld run lt s ci sieas 5064 4 eee E EA A G 111 1S2 Hok parine a a a E ee ER ee A Ee os 112 10 5 3 Hook return values and activity control lt lt s c cs s awena sa saa een e es 112 10 34 Writing anvextemal Book oe eii Ba a E ga T BR ae ae Soe a 112 10 5 5 Telling Mercurial to use an in process hook ooa e 112 103 6 Writing an in process DOOK s c pe eek a ss e k a AOS la Bw i 112 10 6 Some hook examples occiso agu hea a e e eS 113 10 6 1 Writing meaningful commit messages so oos RE e a 113 10 6 2 Checking for trailing whitespace 225 bee ep bea ee Peas eee at 113 107 ICU A 114 10 7 1 acl acces
100. Maybe your shell s search path usually set via the PATH environment variable is simply misconfigured e Perhaps your PATH environment variable is only being set to point to the location of the hg executable if the login session is interactive This can happen if you re setting the path in the wrong shell login script See your shell s documentation for details e The PYTHONPATH environment variable may need to contain the path to the Mercurial Python modules It might not be set at all it could be incorrect or it may be set only if the login is interactive If you can run hg version over an ssh connection well done You ve got the server and client sorted out You should now be able to use Mercurial to access repositories hosted by that username on that server If you run into problems with Mercurial and ssh at this point try using the debug option to get a clearer picture of what s going on 6 5 6 Using compression with ssh Mercurial does not compress data when it uses the ssh protocol because the ssh protocol can transparently compress data However the default behaviour of ssh clients is not to request compression Over any network other than a fast LAN even a wireless network using compression is likely to significantly speed up Mercurial s network operations For example over a WAN someone measured compression as reducing the amount of time required to clone a particularly large repository from 51 minutes to 17 minu
101. Mercurial from source C1 Ome Unix like System ecos wa ORAS EEA Eee a PEA C 2 On Windows Vil 164 164 166 168 168 168 169 170 170 170 170 172 172 174 174 174 174 174 174 174 175 175 175 175 175 176 176 176 177 177 177 177 177 177 177 178 178 178 178 178 D Open Publication License D 1 Requirements on both unmodified and modified versions o o D 2 Copyright D 3 Scope of license D4 Requirements onmodined WORKS o oe e 00 28 dese ences oye eh Bees ba As DS Good prachce recommendations ccce gab bb kke ee BG em ee Se we RE Boe eS D 6 License options Bibliography Index viii 180 180 180 180 181 181 181 182 182 List of Figures 2 1 Sel 3 2 3 3 3 4 3 5 4 1 4 2 4 3 4 4 4 5 4 6 4 7 4 8 4 9 Sil 6 1 9 1 9 2 9 4 10 1 10 2 10 3 10 4 10 5 10 6 11 1 11 2 12 1 122 123 12 4 12 3 Graphical history of the hello repository ses oo coso eee 14 Divergent recent histories of the my hello and my new hello repositories 26 Repository contents after pulling from my hellointomy new hello o 27 Working directory and repository during merge and following commit 28 Conflicting changes toa document e lt s sgor das me GR Se Se ee EE ee 30 Usmo kadiri to merge versions Ol AMS sc ee we BA See ee BR eS ESSE e a ee S 34 Relationships between files in working directory and
102. PATH right it should just work The following hgrc example snippet illustrates the syntax and meaning of the notions we just described hooks commit example python mymodule submodule myhook When Mercurial runs the commit example hook it imports mymodule submodule looks for the callable object named myhook and calls it 10 5 6 Writing an in process hook The simplest in process hook does nothing but illustrates the basic shape of the hook API def myhook ui repo kwargs pass 112 The first argument to a Python hook is always a mercurial ui ui object The second is a repository object at the moment it is always an instance of mercurial localrepo localrepository Following these two arguments are other keyword arguments Which ones are passed in depends on the hook being called but a hook can ignore arguments it doesn t care about by dropping them into a keyword argument dict as with kwargs above 10 6 Some hook examples 10 6 1 Writing meaningful commit messages It s hard to imagine a useful commit message being very short The simple pretxncommit hook of figure 10 4 will prevent you from committing a changeset with a message that is less than ten bytes long cat hg hgre hooks pretxncommit msglen test hg tip template desc wc c ge 10 echo a gt a hg add a hg commit A m too short abort pretxncommit msglen hook exited with status 1 transactio
103. TY or FITNESS FOR A PARTICULAR PURPOSE 2 2 1 Built in help Mercurial provides a built in help system This is invaluable for those times when you find yourself stuck trying to remember how to run a command If you are completely stuck simply run hg help 1t will print a brief list of commands along with a description of what each does If you ask for help on a specific command as below 1t prints more detailed information hg help init hg init e CMD remotecmd CMD DEST create a new repository in the given directory Initialize a new repository in the given directory If the given directory does not exist it is created If no directory is given the current directory is used It is possible to specify an ssh URL as the destination Look at the help text for the pull command for important details about ssh URLs options e ssh specify ssh command to use remotecmd specify hg command to run on the remote side 11 20 use hg v help init to show global options For a more impressive level of detail which you won t usually need run hg help v The v option is short for verbose and tells Mercurial to print more information than it usually would 2 3 Working with a repository In Mercurial everything happens inside a repository The repository for a project contains all of the files that belong to that project along with a historical record of the project s
104. To accomplish this add the phrase Distribution of substantively modified versions of this document is prohibited without the explicit permission of the copyright holder to the license reference or copy B To prohibit any publication of this work or derivative works in whole or in part in standard paper book form for commercial purposes is prohibited unless prior permission is obtained from the copyright holder To accomplish this add the phrase Distribution of the work or derivative of the work in any standard paper book form is prohibited unless prior permission is obtained from the copyright holder to the license reference or copy 181 Bibliography BI Bro Dic Dus Gru05 Mas 0 S06 Pyt RS Tat Wau Jean Delvare Andreas Gruenbacher Martin Quinson Patchwork quilt http savannah nongnu org projects quilt Ronald Oussoren Bob Ippolito Universal macpython http bob pythonmac org archives 2006 04 10 python and universal binaries on mac os x Neil Brown wiggle apply conflicting patches http cgi cse unsw edu au neilb source wiggle Thomas Dickey diffstat make a histogram of diff output http dickey his com diffstat diffstat html Andy Dustman Mysql for python http sourceforge net projects mysql python Andreas Gruenbacher How to survive with many patches introduction to quilt http www suse de agruen quilt pdf June 2005 Chris Mason mpat
105. a tion The second possible reason that hg diff might be printing diffs for a subset of the files displayed by hg status is that if you invoke it without any arguments hg diff prints diffs against the first parent of the working directory If you have run hg merge to merge two changesets but you haven t yet committed the results of the merge your working directory has two parents use hg parents to see them While hg status prints modifi cations relative to both parents after an uncommitted merge hg diff still operates relative only to the first parent You can get it to print diffs relative to the second parent by specifying that parent with the r option There is no way to print diffs relative to both parents 172 Generating safe binary diffs If you use the a option to force Mercurial to print diffs of files that are either mostly text or contain lots of binary data those diffs cannot subsequently be applied by either Mercurial s hg import command or the system s patch command If you want to generate a diff of a binary file that is safe to use as input for hg import use the hg diff git option when you generate the patch The system patch command cannot handle binary patches at all 173 Appendix B Mercurial Queues reference B 1 MQ command reference For an overview of the commands provided by MQ use the command hg help mg B 1 1 hg qapplied
106. a USB thumb drive formatted with a FAT32 filesystem on a Linux system Linux will handle names on that filesystem in a case preserving but insensitive way 7 7 1 Safe portable repository storage Mercurial s repository storage mechanism is case safe It translates file names so that they can be safely stored on both case sensitive and case insensitive filesystems This means that you can use normal file copying tools to transfer a Mercurial repository onto for example a USB thumb drive and safely move that drive and repository back and forth between a Mac a PC running Windows and a Linux box 77 7 7 2 Detecting case conflicts When operating in the working directory Mercurial honours the naming policy of the filesystem where the working directory is located If the filesystem is case preserving but insensitive Mercurial will treat names that differ only in case as the same An important aspect of this approach is that it is possible to commit a changeset on a case sensitive typically Linux or Unix filesystem that will cause trouble for users on case insensitive usually Windows and MacOS users If a Linux user commits changes to two files one named myfile c and the other named MyFile C they will be stored correctly in the repository And in the working directories of other Linux users they will be correctly represented as separate files If a Windows or Mac user pulls this change they will not initially have a problem because Me
107. a new day We should now have two copies of hello c with different contents The histories of the two repositories have also diverged as illustrated in figure 3 1 cat hello c Placed in the public domain by Bryan O Sullivan This program is not covered by patents in the United States or other countries include lt stdio h gt int main int argc char argv printf once more hello n 25 20 21 22 23 24 25 26 27 28 printf hello world return 0 cat my hello hello c Placed in the public domain by Bryan O Sullivan This program is not covered by patents in the United States or other countries include lt stdio h gt int main int argc char argv printf hello world printf hello again n return 0 hag no children dl a e e e e e Figure 3 1 Divergent recent histories of the my hello and my new hel lo repositories We already know that pulling changes from our my he1lo repository will have no effect on the working directory hg pull my hello pulling from my hello searching for changes adding changesets adding manifests adding file changes added 1 changesets with 1 changes to 1 files 1 heads run hg heads to see heads hg merge to merge However the hg pull command says something about heads 26 3 1 1 Head changesets A
108. ace the series with an introductory message in which you should describe the purpose of the series of changes you re sending 14 4 1 Changing the behaviour of patchbombs Not every project has exactly the same conventions for sending changes in email the patchbomb extension tries to accommodate a number of variations through command line options e You can write a subject for the introductory message on the command line using the s option This takes one argument the text of the subject to use e To change the email address from which the messages originate use the f option This takes one argument the email address to use e The default behaviour is to send unified diffs see section 12 4 for a description of the format one per message You can send a binary bundle instead with the b option e Unified diffs are normally prefaced with a metadata header You can omit this and send unadorned diffs with the plain option e Diffs are normally sent inline in the same body part as the description of a patch This makes it easiest for the largest number of readers to quote and respond to parts of a diff as some mail clients will only quote the first MIME body part in a message If you d prefer to send the description and the diff in separate body parts use the a option e Instead of sending mail messages you can write them to an mbox format mail folder using the m option That option takes one argument the name of the fil
109. address of a changeset s committer as the Bugzilla user name with which to update a bug If this does not suit your needs you can map committer email addresses to Bugzilla user names using a usermap section Each item in the usermap section contains an email address on the left and a Bugzilla user name on the right 1 usermap 2 jane user example com jane You can either keep the usermap data in a normal hgrc or tell the bugzilla hook to read the information from an external usermap file In the latter case you can store usermap data by itself in for example a user modifiable repository This makes it possible to let your users maintain their own usermap entries The main hgrc file might look like this 1 regular hgrc file refers to external usermap file 2 bugzilla 3 Jusermap home hg repos userdata bugzilla usermap conf While the usermap file that it refers to might look like this 1 bugzilla usermap conf inside a hg repository 2 usermap 3 stephanie example com steph Configuring the text that gets added to a bug You can configure the text that this hook adds as a comment you specify it in the form of a Mercurial template Several hgrc entries still in the bugzilla section control this behaviour 117 strip The number of leading path elements to strip from a repository s path name to construct a partial path for a URL For example if the repositories on your serv
110. age from hg qpush you should not continue Instead ask for help 5 Build and install the patched version of Mercurial python setup py build force 2 sudo python setup py install skip build Once you ve build a suitably patched version of Mercurial all you need to do to enable the inotify extension is add an entry to your hgrc extensions inotify When the inotify extension is enabled Mercurial will automatically and transparently start the status daemon the first time you run a command that needs status in a repository It runs one status daemon per repository The status daemon is started silently and runs in the background If you look at a list of running processes after you ve enabled the inotify extension and run a few commands in different repositories you ll thus see a few hg processes sitting around waiting for updates from the kernel and queries from Mercurial The first time you run a Mercurial command in a repository when you have the inot ify extension enabled it will run with about the same performance as a normal Mercurial command This is because the status daemon needs to perform a normal status scan so that it has a baseline against which to apply later updates from the kernel However every subsequent command that does any kind of status check should be noticeably faster on repositories of even fairly modest size Better yet the bigger your repository is the greater a perf
111. age that it would send Set this item to false to allow email to be sent The reason that sending of email is turned off by default is that it takes several tries to configure this extension exactly as you would like and it would be bad form to spam subscribers with a number of broken notifications while you debug your configuration config The path to a configuration file that contains subscription information This is kept separate from the main hgrc so that you can maintain it in a repository of its own People can then clone that repository update their subscriptions and push the changes back to your server strip The number of leading path separator characters to strip from a repository s path when deciding whether a repository has subscribers For example if the repositories on your server live in home hg repos and notify is considering a repository named home hg repos shared test setting strip to 4 will cause notify to trim the path it considers down to shared test and it will match subscribers against that template The template text to use when sending messages This specifies both the contents of the message header and its body maxdiff The maximum number of lines of diff data to append to the end of a message If a diff is longer than this it is truncated By default this is set to 300 Set this to 0 to omit diffs from notification emails sources A list of sources of changesets to consider This lets you limit notify to
112. agine that the consequences could be messy if you had a local 0 9 repository and acciden tally pulled changes from the shared 1 0 repository into it At worst you could be paying insufficient attention and push those changes into the shared 0 9 tree confusing your entire team but don t worry we ll return to this horror scenario later However it s more likely that you ll notice immediately because Mercurial will display the URL it s pulling from or you will see it pull a suspiciously large number of changes into the repository The hg rollback command will work nicely to expunge all of the changesets that you just pulled Mercurial groups all changes from one hg pull into a single transaction so one hg rollback is all you need to undo this mistake 9 1 4 Rolling back is useless once you ve pushed The value of the hg rollback command drops to zero once you ve pushed your changes to another repository Rolling back a change makes it disappear entirely but only in the repository in which you perform the hg rollback Because a rollback eliminates history there s no way for the disappearance of a change to propagate between reposi tories If you ve pushed a change to another repository particularly if it s a shared repository it has essentially escaped into the wild and you ll have to recover from your mistake in a different way What will happen if you push a 90
113. ain py src watcher _watcher c src watcher watcher py src xyzzy txt doy VY ey MN 7 2 Running commands without any file names Mercurial s commands that work with file names have useful default behaviours when you invoke them without pro viding any file names or patterns What kind of behaviour you should expect depends on what the command does Here are a few rules of thumb you can use to predict what a command is likely to do if you don t give it any names to work with e Most commands will operate on the entire working directory This is what the hg add command does for example e If the command has effects that are difficult or impossible to reverse it will force you to explicitly provide at least one name or pattern see below This protects you from accidentally deleting files by running hg remove with no arguments for example It s easy to work around these default behaviours if they don t suit you If a command normally operates on the whole working directory you can invoke it on just the current directory and its subdirectories by giving it the name 0 73 ng ng ng ng ng ng ng ng ng ng ng ed sre hg add n addi addi addi addi addi addi addi hg add n addi addi addi addi MANIFEST in examples performant py setup py main py watcher _watcher c watcher watcher py xyzzy txt main py watcher _watcher c watcher watcher py xyzzy txt Al
114. aks 131 age 131 basename 131 date 131 domain 131 email 131 escape 131 f11168 131 11176 131 firstline 131 hgdate 131 isodate 131 132 obfuscate 132 person 132 rfc822date 132 shortdate 132 short 132 strip 132 tabindent 131 132 urlescape 132 user 132 template keywords author 129 131 132 branches 129 date 129 131 132 desc 129 132 file_adds 130 file dels 130 files 129 131 header 136 node 130 parents 130 rev 130 tabindent 132 tags 130 188
115. al looks up the appropriate revision of the manifest to find out which files it was tracking at the time that changeset was committed and which revision of each file was then current It then recreates a copy of each of those files with the same contents it had when the changeset was committed The dirstate contains Mercurial s knowledge of the working directory This details which changeset the working directory is updated to and all of the files that Mercurial is tracking in the working directory 38 Just as a revision of a revlog has room for two parents so that it can represent either a normal revision with one parent or a merge of two earlier revisions the dirstate has slots for two parents When you use the hg update command the changeset that you update to is stored in the first parent slot and the null ID in the second When you hg merge with another changeset the first parent remains unchanged and the second parent is filled in with the changeset you re merging with The hg parents command tells you what the parents of the dirstate are 4 4 1 What happens when you commit The dirstate stores parent information for more than just book keeping purposes Mercurial uses the parents of the dirstate as the parents of a new changeset when you perform a commit Figure 4 5 shows the normal state of the working directory where it has a single changeset as parent That changeset is the tip the newest changeset in th
116. al that write to the repository pay attention to locks Write locks are necessary to prevent multiple simultaneous writers from scribbling on each other s work corrupting the repository Because Mercurial is careful with the order in which it reads and writes data it does not need to acquire a lock when it wants to read data from the repository The parts of Mercurial that read from the repository never pay attention to locks This lockless reading scheme greatly increases performance and concurrency With great performance comes a trade off though one which has the potential to cause you trouble unless you re aware of it To describe this requires a little detail about how Mercurial adds changesets to a repository and reads those changes When Mercurial writes metadata it writes it straight into the destination file It writes file data first then manifest data which contains pointers to the new file data then changelog data which contains pointers to the new manifest data Before the first write to each file it stores a record of where the end of the file was in its transaction log If the transaction must be rolled back Mercurial simply truncates each file back to the size it was before the transaction began When Mercurial reads metadata it reads the changelog first then everything else Since a reader will only access parts of the manifest or file metadata that it can see in the changelog it can never see partially written data Som
117. ame of the next patch in the series file after the topmost applied patch This patch will become the topmost applied patch if you run hg qpush 175 B 1 11 hg qpop pop patches off the stack The hg qpop command removes applied patches from the top of the stack of applied patches By default it removes only one patch This command removes the changesets that represent the popped patches from the repository and updates the working directory to undo the effects of the patches This command takes an optional argument which it uses as the name or index of the patch to pop to If given a name it will pop patches until the named patch is the topmost applied patch If given a number hg qpop treats the number as an index into the entries in the series file counting from zero empty lines and lines containing only comments do not count It pops patches until the patch identified by the given index is the topmost applied patch The hg qpop command does not read or write patches or the series file It is thus safe to hg apop a patch that you have removed from the series file or a patch that you have renamed or deleted entirely In the latter two cases use the name of the patch as it was when you applied it By default the hg gpop command will not pop any patches if the working directory has been modified You can override this behaviour using the f option which reverts all modifications in the working directo
118. and 50 145 add command 42 47 49 52 55 73 74 89 90 92 143 151 155 170 175 177 dry run option 170 exclude option 170 include option 170 I option 170 X option 170 n option 170 age template filter 131 annotate command 138 141 authorized_keys file 64 66 author template keyword 129 131 132 domain filter 131 email filter 131 person filter 132 user filter 132 backout command 93 100 merge option 94 96 99 m option 94 basename template filter 131 bisect command 103 105 bisect extension 2 100 106 138 164 branches command 84 branches template keyword 129 branch command 84 85 bugzilla extension 116 119 164 bugzilla hook 116 117 bundle command 123 changegroup hook 107 109 122 124 chmod system command 68 clone command 12 17 63 71 81 82 r option 81 commit command 18 20 29 39 47 50 84 110 113 149 151 153 174 176 addremove option 153 A option 50 1 option 113 u option 18 commit hook 107 110 111 122 123 125 config command 108 copy command 42 50 53 93 177 after option 53 cp command 52 cp system command 52 date template filter 131 date template keyword 129 131 132 age filter 131 date filter 131 hgdate filter 131 isodate filter 131 132 rfc822date filter 132 shortdate filter 132 desc template keyword 129 132 diffstat command p option 151 diffstat system command 151 152 169 diff command 17 18
119. anner You only need to set up the CGI script and configuration file one time Afterwards you can publish or unpublish a repository at any time by simply moving it into or out of the directory hierarchy in which you ve configured hgwebdir cgi to look Explicitly specifying which repositories to publish In addition to the collections mechanism the hgwebdir cgi script allows you to publish a specific list of reposi tories To do so create a paths section with contents of the following form 1 paths 2 repol my path to some repo 3 repo2 some path to another In this case the virtual path the component that will appear in a URL is on the left hand side of each definition while the path to the repository is on the right Notice that there does not need to be any relationship between the virtual path you choose and the location of a repository in your filesystem If you wish you can use both the collections and paths mechanisms simultaneously in a single configuration file Note If multiple repositories have the same virtual path hgwebdir cgi will not report an error Instead it will behave unpredictably 6 6 4 Downloading source archives Mercurial s web interface lets users download an archive of any revision This archive will contain a snapshot of the working directory as of that revision but it will not contain a copy of the repository data By default this feature is not enabled To enable
120. are influenced by Monotone Mercurial focuses on ease of use high performance and scalability to very large projects 1 3 Trends in revision control There has been an unmistakable trend in the development and use of revision control tools over the past four decades as people have become familiar with the capabilities of their tools and constrained by their limitations The first generation began by managing single files on individual computers Although these tools represented a huge advance over ad hoc manual revision control their locking model and reliance on a single computer limited them to small tightly knit teams The second generation loosened these constraints by moving to network centered architectures and managing entire projects at a time As projects grew larger they ran into new problems With clients needing to talk to servers very frequently server scaling became an issue for large projects An unreliable network connection could prevent remote users from being able to talk to the server at all As open source projects started making read only access available anonymously to anyone people without commit privileges found that they could not use the tools to interact with a project in a natural way as they could not record their changes The current generation of revision control tools is peer to peer in nature All of these systems have dropped the dependency on a single central server and allow people to distribute their revisi
121. ated merge Figure 9 2 Automated backout of a non tip change using the hg backout command Always use the merge option In fact since the merge option will do the right thing whether or not the changeset you re backing out is the tip i e it won t try to merge if it s backing out the tip since there s no need you should always use this option when you run the hg backout command 9 3 4 Gaining more control of the backout process While Pve recommended that you always use the merge option when backing out a change the hg backout command lets you decide how to merge a backout changeset Taking control of the backout process by hand is something you will rarely need to do but it can be useful to understand what the hg backout command is doing for you automatically To illustrate this let s clone our first repository but omit the backout change that it contains cd hg clone r1 myrepo newrepo requesting all changes adding changesets adding manifests adding file changes added 2 changesets with 2 changes to 1 files 1 files updated 0 files merged 0 files removed 0 files unresolved cd newrepo 96 As with our earlier example We ll commit a third changeset then back out its parent and see what happens reverting myfile echo third change gt gt myfile hg commit m third change hg backout m back out second change 1 changeset 3 93c
122. atus and displaying modifications against the current revision diff A Subversion working copy is as a result often approximately the same size as or larger than a Mercurial repository and working directory even though the Mercurial repository contains a complete history of the project Subversion is currently more widely supported by revision control aware third party tools than is Mercurial al though this gap is closing Like Mercurial Subversion has an excellent user manual Several tools exist to accurately and completely import revision history from a Subversion repository into a Mer curial repository making the transition from the older tool relatively painless 1 6 2 Git Git is a distributed revision control tool that was developed for managing the Linux kernel source tree Like Mercurial 1ts early design was somewhat influenced by Monotone Git has an overwhelming command set with version 1 5 0 providing 139 individual commands It has a reputation for being difficult to learn It does not have a user manual only documentation for individual commands In terms of performance git is extremely fast There are several common cases in which it is faster than Mercurial at least on Linux However its performance on and general support for Windows is at the time of writing far behind that of Mercurial While a Mercurial repository needs no maintenance a Git repository requires frequent manual repacks of its metadata W
123. aused the bug Here are a few scenarios to help you understand how you might apply this extension 100 e The most recent version of your software has a bug that you remember wasn t present a few weeks ago but you don t know when it was introduced Here your binary test checks for the presence of that bug e You fixed a bug in a rush and now it s time to close the entry in your team s bug database The bug database requires a changeset ID when you close an entry but you don t remember which changeset you fixed the bug in Once again your binary test checks for the presence of the bug e Your software works correctly but runs 15 slower than the last time you measured it You want to know which changeset introduced the performance regression In this case your binary test measures the performance of your software to see whether it s fast or slow e The sizes of the components of your project that you ship exploded recently and you suspect that something changed in the way you build your project From these examples it should be clear that the bisect extension is not useful only for finding the sources of bugs You can use it to find any emergent property of a repository anything that you can t find from a simple text search of the files in the tree for which you can write a binary test We ll introduce a little bit of terminology here just to make it clear which parts of the search process are your responsibi
124. ave command mq extension 148 177 c option 148 e option 148 qselect command mq extension 158 aseries command mq extension 142 145 149 177 atop command mq extension 151 177 qunapplied command mq extension 177 aversion command mq extension 178 remove command 42 48 49 53 73 92 155 177 after option 49 rename command 42 53 78 93 177 after option 53 revert command 50 55 56 91 93 99 141 rev template keyword 130 rfc822date template filter 132 rollback command 89 90 100 root command 74 sed system command 17 series file 140 141 148 151 158 160 174 178 serve command 57 58 62 63 70 72 p option 63 shortdate template filter 132 short template filter 132 ssh add system command 65 ssh agent system command 65 ssh keygen system command 64 186 ssh command C option 66 ssh system command 41 58 64 67 status command 17 18 20 4749 51 53 74 85 89 93 98 164 165 172 177 C option 51 53 status file 140 141 148 151 175 176 178 strip command 148 178 b option 178 f option 178 n option 178 strip template filter 132 sudo system command 118 tabindent template filter 131 132 tabindent template keyword 132 tags command 80 81 tags template keyword 130 tag command 59 79 82 f option 81 1 option 82 tag hook 107 124 125 tar system command 71 tip command 20 21 85 128 151 p option 151 transplant extension 168 unbundle command
125. ay yes that might be useful it should be clear that having them follow a rename is definitely important Without this facility it would simply be too easy for changes to become orphaned when files are renamed 5 4 2 Divergent renames and merging The case of diverging names occurs when two developers start with a file let s call it foo in their respective repos itories hg clone orig anne 1 files updated 0 files merged 0 files removed 0 files unresolved hg clone orig bob 1 files updated 0 files merged 0 files removed 0 files unresolved Anne renames the file to bar cd anne hg mv foo bar hg ci m Rename foo to bar Meanwhile Bob renames it to quux cd bob hg mv foo quux hg ci m Rename foo to quux I like to think of this as a conflict because each developer has expressed different intentions about what the file ought to be named What do you think should happen when they merge their work Mercurial s actual behaviour is that it always preserves both names when it merges changesets that contain divergent renames See http www selenic com mercurial bts issue455 ed orig hg pull u anne pulling from anne searching for changes adding changesets adding manifests adding file changes added 1 changesets with 1 changes to 1 files 1 files updated 0 files merged 1 files removed 0 files unresolved hg pull bob pulling from
126. bo 149 12 10Usetul things to knowabout neto ge ra rro ee bee hee oe bh bee eee eS 149 12 1 Managing patches in a repository lt o eb ee eA ee ee a etre es 149 12 11 1 MQ support for patch repositories o oo aoa ee 150 2 1124 few things to watch out for o o os e ea e e ee al a 151 12 12 Third party tools lor working with patches 2 ss s s s s soes acoso a a 151 12 13Good ways to work with patches o ae hw a 151 T2 HMO GCOGEBOOKE II 152 12 14 0 Manace trivial pathes o e es ye ae AA 4 e 152 12142 Combining enfre patches lt ps sira SSS A AAA he ia de 154 12 14 3 Merging part of one patch into another aoao e 154 17 15 Ditterences between guiltand MQ scos ee oma BER e ire a 155 13 Advanced uses of Mercurial Queues 156 13 1 The problem of Many targets o c ro ca a e a RSE E OS aa 156 13 1 1 Tempting approaches that don t work well o e 156 13 2 Conditionally applying patches with guards ee 157 13 3 Controlling the guards ona patei e e a a o eee A a T O 157 134 Selecione the guards QUES 20 00 ee bee RES A A es 158 13 5 MO s tules Tof appiyine patches lt lt oros ee ERM en SEEMS TREE PS 159 13 6 Tromins the workenymonment sci 24205864554 2446 04 8 2h 5 eee eed eho 159 13 7 Dividing p the Eres Te sc Re eR HE A Se wa E Ce SE Oe E 159 13 8 Maintaining the patch seres coccion AA 160 13 8 1 Theartof writing backpott patches oo 65 44 eaa SR ER a 161 13 9 Useful tips for developing
127. by a specific tag in the repository where it was built This doesn t necessarily mean that you re running an official release someone else could have added that tag to any revision in the repository where they built Mercurial e A hexadecimal string such as 875489e31abe This is a build of the given revision of Mercurial e A hexadecimal string followed by a date such as 875489e3labe 20070205 This is a build of the given revision of Mercurial where the build repository contained some local changes that had not been committed A 3 1 Tips and tricks Why do the results of hg diff and hg status differ When you run the hg status command you ll see a list of files that Mercurial will record changes for the next time you perform a commit If you run the hg diff command you may notice that it prints diffs for only a subset of the files that hg status listed There are two possible reasons for this The first is that hg status prints some kinds of modifications that hg diff doesn t normally display The hg diff command normally outputs unified diffs which don t have the ability to represent some changes that Mercurial can track Most notably traditional diffs can t represent a change in whether or not a file is executable but Mercurial records this information If you use the git option to hg diff it will display git compatible diffs that can display this extra inform
128. cation works may be reproduced and distributed in whole or in part in any medium physical or electronic provided that the terms of this license are adhered to and that this license or an incorporation of it by reference with any options elected by the author s and or publisher is displayed in the reproduction Proper form for an incorporation by reference is as follows Copyright c year by author s name or designee This material may be distributed only subject to the terms and conditions set forth in the Open Publication License vx y or later the latest version is presently available at http www opencontent org openpub The reference must be immediately followed with any options elected by the author s and or publisher of the document see section D 6 Commercial redistribution of Open Publication licensed material is permitted Any publication in standard paper book form shall require the citation of the original publisher and author The publisher and author s names shall appear on all outer surfaces of the book On all outer surfaces of the book the original publisher s name shall be as large as the title of the work and cited as possessive with respect to the title D 2 Copyright The copyright to each Open Publication is owned by its author s or designee D 3 Scope of license The following license terms apply to all Open Publication works unless otherwise explicitly stated in the document Mere aggregation of O
129. cations we ve made in this changeset This is called the commit message It will be a record for readers of what we did and why and it will be printed by hg log after we ve finished committing hg commit The editor that the hg commit command drops us into will contain an empty line followed by a number of lines starting with HG empty line HG changed hello c Mercurial ignores the lines that start with HG it uses them only to tell us which files it s recording changes to Modifying or deleting these lines has no effect 2 7 3 Writing a good commit message Since hg log only prints the first line of a commit message by default it s best to write a commit message whose first line stands alone Here s a real example of a commit message that doesn t follow this guideline and hence has a summary that is not readable changeset 73 584af0e231be user Censored Person lt censored person example org gt date Tue Sep 26 21 37 07 2006 0700 summary include buildmeister commondefs Add an exports and install As far as the remainder of the contents of the commit message are concerned there are no hard and fast rules Mercurial itself doesn t interpret or care about the contents of the commit message though your project may have policies that dictate a certain kind of formatting My personal preference is for short but informative commit messages that tell
130. ccurred even with simple searches on small repositories if the problem you re looking for is more subtle or the number of tests that bisect must perform increases the likelihood of operator error ruining the search is much higher Once I started automating my tests I had much better results The key to automated testing is twofold e always test for the same symptom and e always feed consistent input to the hg bisect command In my tutorial example above the grep command tests for the symptom and the if statement takes the result of this check and ensures that we always feed the same input to the hg bisect command The mytest function marries these together in a reproducible way so that every test is uniform and consistent 9 6 3 Check your results Because the output of a bisect search is only as good as the input you give it don t take the changeset it reports as the absolute truth A simple way to cross check its report is to manually run your test at each of the following changesets e The changeset that it reports as the first bad revision Your test should still report this as bad e The parent of that changeset either parent if it s a merge Your test should report this changeset as good e A child of that changeset Your test should report this changeset as bad 9 6 4 Beware interference between bugs It s possible that your search for one bug could be disrupted by the presence of another For example le
131. ch help solve patch rejects http oss oracle com mason mpatch Bryan O Sullivan Achieving high performance in mercurial In EuroPython Conference July 2006 XXX Python org ConfigParser configuration file parser http docs python org lib module ConfigParser html GNU Project volunteers Richard Stallman Gnu coding standards change logs http www gnu org prep standards html_node Change Logs html Simon Tatham Putty open source ssh client for windows http www chiark greenend org uk sgtatham putty Tim Waugh patchutils programs that operate on patch files http cyberelk net tim patchutils 182 Index hg hgrc file 71 108 hg localtags file 82 124 125 hg patches N directory 148 hg patches directory 140 149 151 174 175 hg store data directory 35 hgignore file 151 175 hgrc file 18 33 hgtags file 81 82 124 125 orig file 145 rej file 145 147 ssh config file 66 ssh directory 64 65 EMAIL environment variable 18 HGMERGE environment variable 29 31 HGUSER environment variable 18 HG_NODE environment variable 110 121 HG PARENT1 environment variable 121 HG_PARENT2 environment variable 121 HG_SOURCE environment variable 121 HG_URL environment variable 121 122 ercurial ini configuration file 64 PATH environment variable 66 PYTHONPATH environment variable 66 69 112 179 acl extension 114 116 164 acl hook 114 addbreaks template filter 131 addremove comm
132. changeset ba526719a3b3 saw a changeset Added tag mytag for changeset ee709a2e8cd1 saw a changeset added line to end of lt lt hello gt gt file H H H ou 6 in addition added a file with the helpful name at least i hope that some might consider it so of goodby 7 i saw a changeset added hello As you can see the string desc in the template has been replaced in the output with the description of each changeset Every time Mercurial finds text enclosed in curly braces and Y it will try to replace the braces and text with the expansion of whatever is inside To print a literal curly brace you must escape it as described in section 11 5 11 4 Common template keywords You can start writing simple templates immediately using the keywords below author String The unmodified author of the changeset branches String The name of the branch on which the changeset was committed Will be empty if the branch name was default date Date information The date when the changeset was committed This is not human readable you must pass it through a filter that will render it appropriately See section 11 6 for more information on filters The date is expressed as a pair of numbers The first number is a Unix UTC timestamp seconds since January 1 1970 the second is the offset of the committer s timezone from UTC in seconds desc String The text of the changeset description files List of strings
133. cic AS ok ek ee ee Pw See hee eS Phe Ss 138 12 2 2 From patchwork quilt to Mercurial Queues o 2 2 00 00000004 138 12 3 The huge advantage ol MO oo scoe eiaa eee AE ERA we Ee ae a ee RE ee a 138 124 Undetstandimg patches coca ee OA GREER Dae EES RS RSS S 139 12 5 Getting started with Mercurial Queues e 139 123 1 Creating a new patel cuina eR AE ee ee ee be es a ae a 140 123 2 Remeis a pah os sak a ks Se ae o oe AS Se See ee he ee 141 12 5 3 Stacking and tackine patches ed ce e Gee a ee Ate a e es 141 1254 Manipulating the patch stack lt opec neres akedt Se eee SEEKER o 142 12 5 5 Pushing and popping many patches 2 ioie 285 obi aw bb ed we Ped eh aw S 142 125 6 Safety checks and overriding hem coesa e e fe eae eH A SOS EE ee 143 12 5 7 Working on Several patches at ones 4 524544 248600 o a ote eee eda vhs 143 12 6 More about patches nb ie ee SR RR ee Oe A ae ee SSS 143 12 6 Thestepeount 2 4 0 8 4 bee eS eee bbe he Pe bea eee ea 143 12 6 2 Strategies for applying a pateh p o secs a eee eS ee ee 145 12 6 3 Some quirks of patch representation ese coase cederet iv este eee ee 145 1264 Beware the IZZ bse on a aa a A E eo G A 146 12 63 Handling TEJECHON lt caci a eo sde A a be e ey Eee eS 147 12 7 Getting the best performance out of MQ e seak di e ro Ad E i S 147 12 8 Updating your patches when the underlying code changes ooo oo 148 129 Ident yne paredes e cada E eee E AS e e de oh
134. ck out second change Figure 9 1 Backing out a change using the hg backout command This makes backing out any changeset a one shot operation that s usually simple and fast echo third change gt gt myfile hg commit m third change hg backout merge m back out second change 1 reverting myfile changeset 3 93c44e38d2f2 backs out changeset 1 92480a09996c merging with changeset 2 b5b85d3d30ee merging myfile 0 files updated 1 files merged 0 files removed 0 files unresolved branch merge don t forget to commit If you take a look at the contents of myf ile after the backout finishes you ll see that the first and third changes are present but not the second cat myfile first change third change As the graphical history in figure 9 2 illustrates Mercurial actually commits two changes in this kind of situation the box shaped nodes are the ones that Mercurial commits automatically Before Mercurial begins the backout process it first remembers what the current parent of the working directory is It then backs out the target changeset and commits that as a changeset Finally it merges back to the previous parent of the working directory and commits the result of the merge The result is that you end up back where you were only with some extra history that undoes the effect of the changeset you wanted to back out 95 back out econd change autom
135. ckup media are reliable and that your last backup was recent and actually worked With a distributed tool you have many backups available on every contributor s computer The reliability of your network will affect distributed tools far less than it will centralised tools You can t even use a centralised tool without a network connection except for a few highly constrained commands With a distributed tool if your network connection goes down while you re working you may not even notice The only thing you won t be able to do is talk to repositories on other computers something that is relatively rare compared with local operations If you have a far flung team of collaborators this may be significant 1 4 1 Advantages for open source projects If you take a shine to an open source project and decide that you would like to start hacking on it and that project uses a distributed revision control tool you are at once a peer with the people who consider themselves the core of that project If they publish their repositories you can immediately copy their project history start making changes and record your work using the same tools in the same ways as insiders By contrast with a centralised tool you must use the software in a read only mode unless someone grants you permission to commit changes to their central server Until then you won t be able to record changes and your local modifications will be at risk of corruption
136. col lt o o seoda ee AeA RR a a 63 6 5 1 Howto r ad and write sshURLs ooo nocte sedea Ee ea ewes 63 6 5 2 Finding an ssh client for your SYSTEM soos saca a ee ee 64 65 3 Generating akey pal ccs e s oe A heehee be ee a BAe ee ee 64 6 5 4 Using an authentication Agent 2 2 2 0 220 ee ee 65 65 5 lt Contigunmg the server side properly e os a ae 6 RO ea Re 65 630 Using compression withissh caras ea dr E he EHS S 66 66 Servine over UTP sme CG sis ok bea be ee AG ARE See a EE eS be 67 6 6 1 Webserver configuration checklist ooo 525 4 4 80S os Ee EEN SC RAS 67 662 Basic COL conmguraion oons os sk ee eS Re ee ee ER Re ER e 67 6 6 3 Sharing multiple repositories with one CGI script o oo a 69 66 4 Downloading source archives 2 2 2 2 ke eS sones a a ee 70 6 6 5 Web configuration options es soea eao Ae wee a ee ee 70 File names and pattern matching 73 ek BUITRE s 2D aed Bee AS DA ee GE beans Be g 73 7 2 Running commands without any file names o 0 0 0 2 00 eee eee 73 Ta LEIS YOu Whats SONG ON pira ha ES bh we ee ee eh 74 T Using patterns to identify Tiles s ooe e y ve eK A wa ES Ce eS Ee eS 75 74 1 Shellestyle glob pattems s r io ee Ee a 75 74 2 Regular expression matching with re patterns 2 2 ee ee eee ee 76 Ls Pilterme niles ooe ce ee ee RE ERA eae ea ee Me ee eee ee E 76 7 6 Ignoring unwanted files and directories 2 2 e 77 111 10 Dal Case SEDSILVIRO e sa cd Ste
137. considered to have failed For a hook that controls whether an activity can proceed zero false means allow while non zero true exception means deny 10 5 4 Writing an external hook When you define an external hook in your hgrc and the hook is run its value is passed to your shell which interprets 1t This means that you can use normal shell constructs in the body of the hook An executable hook is always run with its current directory set to a repository s root directory Each hook parameter is passed in as an environment variable the name is upper cased and prefixed with the string HG With the exception of hook parameters Mercurial does not set or modify any environment variables when running a hook This is useful to remember if you are writing a site wide hook that may be run by a number of different users with differing environment variables set In multi user situations you should not rely on environment variables being set to the values you have in your environment when testing the hook 10 5 5 Telling Mercurial to use an in process hook The hgrc syntax for defining an in process hook is slightly different than for an executable hook The value of the hook must start with the text python and continue with the fully qualified name of a callable object to use as the hook s value The module in which a hook lives is automatically imported when a hook is run So long as you have the module name and PYTHON
138. copy will also contain the modifications you have made up until that point I find this behaviour a little counterintuitive which is why I mention it here The hg copy command acts similarly to the Unix cp command you can use the hg cp alias if you prefer The last argument is the destination and all prior arguments are sources If you pass it a single file as the source and the destination does not exist it creates a new file with that name mkdir k hg copy a k ls k a Tf the destination is a directory Mercurial copies its sources into that directory 52 mkdir d 5 hg copy abd ls d a b Copying a directory is recursive and preserves the directory structure of the source hg copy ce copying c a c to e a c If the source and destination are both directories the source tree is recreated in the destination directory hg copy cd copying c a c to d c a c As with the hg rename command if you copy a file manually and then want Mercurial to know that you ve copied the file simply use the after option to hg copy 5cpa z hg copy after a z 5 4 Renaming files It s rather more common to need to rename a file than to make a copy of it The reason I discussed the hg copy command before talking about renaming files is that Mercurial treats a rename in essentially the same way as a copy Therefore knowing what Mercur
139. cords your name and address with each change that you commit so that you and others will later be able to tell who made each change Mercurial tries to automatically figure out a sensible username to commit the change with It will attempt each of the following methods in order 1 If you specify a u option to the hg commit command on the command line followed by a username this is always given the highest precedence 2 If you have set the HGUSER environment variable this is checked next 3 If you create a file in your home directory called hgrc with a username entry that will be used next To see what the contents of this file should look like refer to section 2 7 1 below 4 If you have set the EMAIL environment variable this will be used next 5 Mercurial will query your system to find out your local user name and host name and construct a username from these components Since this often results in a username that is not very useful it will print a warning if it has to do this If all of these mechanisms fail Mercurial will fail printing an error message In this case it will not let you commit until you set up a username You should think of the HGUSER environment variable and the u option to the hg commit command as ways to override Mercurial s default selection of username For normal use the simplest and most robust way to set a username for yourself is by creating a hgrc file see below for details
140. ctory has a parent in just the same way this is the changeset that the working directory currently contains To update the working directory to a particular revision give a revision number or changeset ID to the hg update command hg update 2 2 files updated 0 files merged 0 files removed 0 files unresolved hg parents changeset 2 057d3c2d823c user Bryan O Sullivan lt bos serpentine com gt date Tue Sep 06 13 15 43 2005 0700 summary Introduce a typo into hello c hg update 2 files updated 0 files merged 0 files removed 0 files unresolved If you omit an explicit revision hg update will update to the tip revision as shown by the second call to hg update in the example above 22 2 8 3 Pushing changes to another repository Mercurial lets us push changes to another repository from the repository we re currently visiting As with the example of hg pull above we ll create a temporary repository to push our changes into cd hg clone hello hello push 2 files updated 0 files merged 0 files removed 0 files unresolved The hg outgoing command tells us what changes would be pushed into another repository ed my hello hg outgoing hello push comparing with hello push searching for changes changeset 5 fal321bf0c80 tag tip user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 05 50 2007 0000 summary Added an extra li
141. d directories with exactly the same names the patch command has a p option that indicates the number of leading path name components to strip when trying to apply a patch This number is called the strip count An option of p1 means use a strip count of one If patch sees a file name foo bar baz in a file header it will strip oo and try to patch a file named bar baz Strictly speaking the strip count refers to the number of path separators and the components that go with them to strip A strip count of one will turn foo bar into bar but foo bar notice the extra leading slash into foo bar The standard strip count for patches is one almost all patches contain one leading path name component that needs to be stripped Mercurial s hg diff command generates path names in this form and the hg import command and MQ expect patches to have a strip count of one If you receive a patch from someone that you want to add to your patch queue and the patch needs a strip count other than one you cannot just hg qimport the patch because hg qimport does not yet have a p op tion see Mercurial bug no 311 Your best bet is to hg qnew a patch of your own then use patch pN to 144 hg qseries first patch second patch hg qapplied first patch second patch Figure 12 9 Understanding the patch stack with hg qseries and hg qapplied present In series forbid ille
142. d wrote an extension that he called Mercurial Queues which added quilt like behaviour to Mercurial The key difference between quilt and MQ is that quilt knows nothing about revision control systems while MQ is integrated into Mercurial Each patch that you push is represented as a Mercurial changeset Pop a patch and the changeset goes away Because quilt does not care about revision control tools it is still a tremendously useful piece of software to know about for situations where you cannot use Mercurial and MQ 12 3 The huge advantage of MQ I cannot overstate the value that MQ offers through the unification of patches and revision control A major reason that patches have persisted in the free software and open source world in spite of the availability of increasingly capable revision control tools over the years is the agility they offer Traditional revision control tools make a permanent irreversible record of everything that you do While this has great value it s also somewhat stifling If you want to perform a wild eyed experiment you have to be careful in how you go about it or you risk leaving unneeded or worse misleading or destabilising traces of your missteps and errors in the permanent revision record By contrast MQ s marriage of distributed revision control with patches makes it much easier to isolate your work Your patches live on top of normal revision history and you can make them disappear or reappear at
143. data for the changesets is erased This hook can access the metadata associated with the almost added changesets but it should not do anything permanent with this data It must also not modify the working directory While this hook is running if other Mercurial processes access this repository they will be able to see the almost added changesets as if they are permanent This may lead to race conditions if you do not take steps to avoid them This hook can be used to automatically vet a group of changesets If the hook fails all of the changesets are rejected when the transaction rolls back Parameters to this hook node A changeset ID The changeset ID of the first changeset in the group that was added All changesets between 39 66 this and tip inclusive were added by a single hg pull hg push or hg unbundle source A string The source of these changes See section 10 8 3 for details url A URL The location of the remote repository if known See section 10 8 3 for more information See also changegroup section 10 9 1 incoming section 10 9 3 prechangegroup section 10 9 5 124 10 9 10 pretxncommit before completing commit of new changeset This controlling hook is run before a transaction that manages a new commit completes If the hook succeeds the transaction completes and the changeset becomes permanent within this repository If the hook fails the transaction is rolled back and the commi
144. des a set of small utilities that follow the Unix philosophy each does one useful thing with a patch The pat chut ils command I use most is filterdiff which extracts subsets from a patch file For example given a patch that modifies hundreds of files across dozens of directories a single invocation of filterdiff can generate a smaller patch that only touches files whose names match a particular glob pattern See section 13 9 2 for another example 12 13 Good ways to work with patches Whether you are working on a patch series to submit to a free software or open source project or a series that you intend to treat as a sequence of regular changesets when you re done you can use some simple techniques to keep your work well organised Give your patches descriptive names A good name for a patch might be rework device alloc patch because it will immediately give you a hint what the purpose of the patch is Long names shouldn t be a problem you won t be typing the names often but you will be running commands like hg gapplied and hg qtop over and over Good naming becomes especially important when you have a number of patches to work with or if you are juggling a number of different tasks and your patches only get a fraction of your attention Be aware of what patch you re working on Use the hg qtop command and skim over the text of your patches frequently for example using hg tip p to be sure of where you
145. dr socklen_t addr_len sizeof addr if getsockname fd struct sockaddr gaddr amp addr_len 1 do_log LOG_ERR Could not get socket details m Let s say a few weeks or months pass and your package author releases a new version First bring their changes into the repository hg qpop a Patch queue now empty cd download netplug 1 2 8 tar bz2 hg clone netplug 1 2 5 netplug 1 2 8 18 files updated 0 files merged 0 files removed 0 files unresolved ed netplug 1 2 8 hg locate 0 xargs 0 rm cd tar jxf netplug 1 2 8 tar bz2 cd netplug 1 2 8 hg commit addremove message netplug 1 2 8 UF UL UY 999 The pipeline starting with hg locate above deletes all files in the working directory so that hg commit s addremove option can actually tell which files have really been removed in the newer version of the source Finally you can apply your patches on top of the new tree ed netplug hg pull netplug 1 2 8 pulling from netplug 1 2 8 searching for changes adding changesets adding manifests adding file changes added 1 changesets with 12 changes to 12 files run hg update to get a working copy 153 10 11 12 hg qpush a applying build fix patch Now at build fix patch 12 14 2 Combining entire patches MQ provides a command hg qfold that lets you combine entire patches This folds the pa
146. dwidth network connections The easiest way to get started with the web interface is to use your web browser to visit an existing repository such as the master Mercurial repository at http www selenic com repo hg style gitweb If you re interested in providing a web interface to your own repositories Mercurial provides two ways to do this The first is using the hg serve command which is best suited to short term lightweight serving See section 6 4 below for details of how to use this command If you have a long lived repository that you d like to make permanently available Mercurial has built in support for the CGI Common Gateway Interface standard which all common web servers support See section 6 6 for details of CGI configuration 6 2 Collaboration models With a suitably flexible tool making decisions about workflow is much more of a social engineering challenge than a technical one Mercurial imposes few limitations on how you can structure the flow of work in a project so it s up to you and your group to set up and live with a model that matches your own particular needs 6 2 1 Factors to keep in mind The most important aspect of any model that you must keep in mind is how well it matches the needs and capabilities of the people who will be using it This might seem self evident even so you still can t afford to forget it for a moment 57 I once put together a workflow model that seemed to make perfect sen
147. e BS Bases ows Ay ss A RE AR A eS Bee Thl Sate portable repository storage a e e e a E e Tia Detecting case COMICS cpi s oe opo eek ai ye Se nS Sy Bee died e AA ee Ae wee 6 ye eee EA ee Managing releases and branchy development 8 1 Giving a persistent name toa revision s coss 64 bb eae eA da 8 1 1 Handling tag conflicts during a merge 2 2 2 2 e 8 1 2 TABS and cloning o c 5 c 4c 4445244 AERA Doe eee ae eR EE 8 1 3 When permanent tags are too much ocioso he RR RS SS 8 2 The flow of changes big picture vs little o o 8 3 Managing big picture branches in repositories e 8 4 Don t repeat yourself merging across branches e 5 Naming branches within onerepository lt s es oi sas e a Bh SO 8 6 Dealing with multiple named branches in a repository o o 7 Branch mames atid merging s cotan aei i ee ewe SEERA A A 8 8 Branch naming is generally useful sp ss na cee ERE ERE ER N E Finding and fixing your mistakes 9 1 Erasnglocal history lt sr cc ccecce bee eae OE E E a a A 91 1 Theaccidental commit si o s 6 opa me a e a oe E ae d a a da ae 9 12 Rolling backs transaction ss e sypreis a ae a eS ee eS eR Se e y Ti Tiesnmonsous PIL e 20 AAA IAEA AI IA 9 1 4 Rolling back is useless once you ve pushed o o e So You camo ly roll back Once oie a FR EVR EEE ES SPAS O72 Reverting tie mistaken
148. e are local to that timezone they display what time and date it was for the person who created the changeset summary The first line of the text message that the creator of the changeset entered to describe the changeset The default output printed by hg log is purely a summary it is missing a lot of detail Figure 2 1 provides a graphical representation of the history of the hello repository to make it a little easier to see which direction history is flowing in We ll be returning to this figure several times in this chapter and the chapter that follows 4 b57 4 b57f Figure 2 1 Graphical history of the hello repository 2 4 1 Changesets revisions and talking to other people As English is a notoriously sloppy language and computer science has a hallowed history of terminological confusion why use one term when four will do revision control has a variety of words and phrases that mean the same thing If you are talking about Mercurial history with other people you will find that the word changeset is often compressed to change or when written cset and sometimes a changeset is referred to as a revision or a rev While it doesn t matter what word you use to refer to the concept of a changeset the identifier that you use to refer to a specific changeset is of great importance Recall that the changeset field in the output from hg log identifies a changeset using
149. e com gt hgtags Added tag v0 1 for changeset ba526719a3b3 921354c5e6bb tip hgtags Added tag mytag for changeset ee709a2e8cdl1 ba526719a3b3 v0 1 goodbye hello added line to end of lt lt hello gt gt file in addition added a file with the helpful name at least i hope that some might consider it so of goodbye ee709a2e8cd1 mytag hello added hello c4 58d082b6 You will not be shocked to learn that Mercurial s default output style is named default 11 1 1 Setting a default style You can modify the output style that Mercurial will use for every command by editing your hgrc file naming the style you would prefer to use ui style compact If you write a style of your own you can use it by either providing the path to your style file or copying your style file into a location where Mercurial can find it typically the templates subdirectory of your Mercurial install directory 11 2 Commands that support styles and templates 39 66 39 66 All of Mercurial s 1og like commands let you use styles and templates hg incoming hg log and hg tip As I write this manual these are so far the only commands that support styles and templates Since these are the most important commands that need customisable output there has been little pressure from the Mercurial user community to add style and template support to other commands hg out
150. e controlling hooks pretxncommit and pretxnchangegroup run when a transaction is almost complete All of the metadata has been written but Mercurial can still roll the transaction back and cause the newly written data to disappear If one of these hooks runs for long it opens a window of time during which a reader can see the metadata for changesets that are not yet permanent and should not be thought of as really there The longer the hook runs the longer that window is open 10 3 1 The problem illustrated In principle a good use for the pretxnchangegroup hook would be to automatically build and test incoming changes before they are accepted into a central repository This could let you guarantee that nobody can push changes to this repository that break the build But if a client can pull changes while they re being tested the usefulness of the test 1s zero an unsuspecting someone can pull untested changes potentially breaking their build The safest technological answer to this challenge is to set up such a gatekeeper repository as unidirectional Let 1t take changes pushed in from the outside but do not allow anyone to pull changes from it use the preoutgoing hook to lock it down Configure a changegroup hook so that if a build or test succeeds the hook will push the new changes out to another repository that people can pull from In practice putting a centralised bottleneck like this in place is not often a good idea
151. e file to its unmodified contents e If you use the hg remove command to remove a file it will undo the removed state of the file and restore the file to its unmodified contents 9 2 1 File management errors The hg revert command is useful for more than just modified files It lets you reverse the results of all of Mercu rial s file management commands hg add hg remove and so on If you hg ada a file then decide that in fact you don t want Mercurial to track it use hg revert to undo the add Don t worry Mercurial will not modify the file in any way It will just unmark the file echo oops gt oops hg add oops hg status oops oops hg revert oops hg status oops Y UY 4 gt 7 4 Ur Similarly if you ask Mercurial to hg remove a file you can use hg revert to restore it to the contents it had as of the parent of the working directory hg remove file hg status R file hg revert file hg status ls file file This works just as well for a file that you deleted by hand without telling Mercurial recall that in Mercurial terminol ogy this kind of file is called missing rm file hg status file hg revert file ls file file 92 N N N If you revert a hg copy the copied to file remains in your working directory afterwards untracked Since a copy doesn t affect the copi
152. e mpatch command can help with four common reasons that a hunk may be rejected e The context in the middle of a hunk has changed e A hunk is missing some context at the beginning or end e A large hunk might apply better either entirely or in part if it was broken up into smaller hunks e A hunk removes lines with slightly different content than those currently present in the file If you use wiggle or mpat ch you should be doubly careful to check your results when you re done In fact mpat ch enforces this method of double checking the tool s output by automatically dropping you into a merge program when it has done its job so that you can verify its work and finish off any remaining merges 12 7 Getting the best performance out of MQ MQ is very efficient at handling a large number of patches I ran some performance experiments in mid 2006 for a talk that I gave at the 2006 EuroPython conference O S06 I used as my data set the Linux 2 6 17 mm1 patch series which consists of 1 738 patches I applied these on top of a Linux kernel repository containing all 27 472 revisions between Linux 2 6 12 rc2 and Linux 2 6 17 On my old slow laptop I was able to hg qpush a all 1 738 patches in 3 5 minutes and hg apop a them all in 30 seconds On a newer laptop the time to push all patches dropped to two minutes I could hg qrefresh one of the biggest patches which made 22 779 lines of changes to 287 files in 6 6 sec
153. e repository that has no children It s useful to think of the working directory as the changeset I m about to commit Any files that you tell Mercurial that you ve added removed renamed or copied will be reflected in that changeset as will modifications to any files that Mercurial is already tracking the new changeset will have the parents of the working directory as its parents After a commit Mercurial will update the parents of the working directory so that the first parent is the ID of the new changeset and the second is the null ID This is shown in figure 4 6 Mercurial doesn t touch any of the files in the working directory when you commit it just modifies the dirstate to note its new parents 4 4 2 Creating a new head It s perfectly normal to update the working directory to a changeset other than the current tip For example you might want to know what your project looked like last Tuesday or you could be looking through changesets to see which one introduced a bug In cases like this the natural thing to do is update the working directory to the changeset you re interested in and then examine the files in the working directory directly to see their contents as they werea when you committed that changeset The effect of this is shown in figure 4 7 Having updated the working directory to an older changeset what happens 1f you make some changes and then commit Mercurial behaves in the same way as I outlined above The pa
154. e to Lighttpd 6 6 3 Sharing multiple repositories with one CGI script The hgweb cgi script only lets you publish a single repository which is an annoying restriction If you want to publish more than one without wracking yourself with multiple copies of the same script each with different names a better choice is to use the hgwebdir cgi script The procedure to configure hgwebdir cgi is only a little more involved than for hgweb cgi First you must obtain a copy of the script If you don t have one handy you can download a copy from the master Mercurial repository at http www selenic com repo hg raw file tip hgwebdir cgi You ll need to copy this script into your public_html directory and ensure that it s executable cp hgwebdir cgi public_html chmod 755 public_html public_html hgwebdir cgi With basic configuration out of the way try to visit http myhostname myuser hgwebdir cgi in your browser It should display an empty list of repositories If you get a blank window or error message try walking through the list of potential problems in section 6 6 2 The hgwebdir cgi script relies on an external configuration file By default it searches for a file named hgweb config in the same directory as itself You ll need to create this file and make it world readable The format of the file is similar to a Windows ini file as understood by Python s ConfigParser Pyt module The easiest way to config
155. e to write to e If you would like to add a diff stat format summary to each patch and one to the introductory message use the d option The diffstat command displays a table containing the name of each file patched the number of lines affected and a histogram showing how much each file is modified This gives readers a qualitative glance at how complex a patch is 169 Appendix A Command reference A l hg add add files at the next commit include also I exclude also X dry run also n A 2 hg diff print changes in history or working directory Show differences between revisions for the specified files or directories using the unified diff format For a description of the unified diff format see section 12 4 By default this command does not print diffs for files that Mercurial considers to contain binary data To control this behaviour see the a and git options A 2 1 Options nodates option Omit date and time information when printing diff headers ignore blank lines also B Do not print changes that only insert or delete blank lines A line that contains only whitespace is not considered blank include also I Exclude files and directories whose names match the given patterns exclude also X Include files and directories whose names match the given patterns text also a If this option is not specified hg diff will refuse to print diffs for f
156. east in theory whether you re working on a project by yourself or with a hundred other people A key question about the practicality of revision control at these two different scales lone hacker and huge team is how its benefits compare to its costs A revision control tool that s difficult to understand or use is going to impose a high cost A five hundred person project is likely to collapse under its own weight almost immediately without a revision control tool and process In this case the cost of using revision control might hardly seem worth considering since without it failure is almost guaranteed On the other hand a one person quick hack might seem like a poor place to use a revision control tool because surely the cost of using one must be close to the overall cost of the project Right 3 Mercurial uniquely supports both of these scales of development You can learn the basics in just a few minutes and due to its low overhead you can apply revision control to the smallest of projects with ease Its simplicity means you won t have a lot of abstruse concepts or command sequences competing for mental space with whatever you re really trying to do At the same time Mercurial s high performance and peer to peer nature let you scale painlessly to handle large projects No revision control tool can rescue a poorly run project but a good choice of tools can make a huge difference to the fluidity with which you can
157. ed 1t you generally can t just make disastrous changes disappear The one exception is when you ve just committed a change and it hasn t been pushed or pulled into another repository That s when you can safely use the hg rollback command as I detailed in section 9 1 2 After you ve pushed a bad change to another repository you could still use hg rollback to make your local copy of the change disappear but it won t have the consequences you want The change will still be present in the remote repository so it will reappear in your local repository the next time you pull If a situation like this arises and you know which repositories your bad change has propagated into you can try to get rid of the changeefrom every one of those repositories This is of course not a satisfactory solution if you miss even a single repository while you re expunging the change is still in the wild and could propagate further If you ve committed one or more changes after the change that you d like to see disappear your options are further reduced Mercurial doesn t provide a way to punch a hole in history leaving changesets intact XXX This needs filling out The hg replay script in the examples directory works but doesn t handle merge changesets Kind of an important omission 9 4 1 Protect yourself from escaped changes If you ve committed some changes to your local repository and they ve been pushed or pulled som
158. ed command a lot you can get hgext to make it available as a normal extdiff cmd interdiff hg interdiff This directs hgext to make an interdiff command available so you can now shorten the previous invocation of hg extdiff to something a little more wieldy hg interdiff r A B my change patch 162 Note The interdiff command works well only if the underlying files against which versions of a patch are generated remain the same If you create a patch modify the underlying files and then regenerate the patch interdiff may not produce useful output The extdiff extension is useful for more than merely improving the presentation of MQ patches To read more about it go to section 14 2 163 Chapter 14 Adding functionality with extensions While the core of Mercurial is quite complete from a functionality standpoint it s deliberately shorn of fancy features This approach of preserving simplicity keeps the software easy to deal with for both maintainers and users However Mercurial doesn t box you in with an inflexible command set you can add features to it as extensions sometimes known as plugins We ve already discussed a few of these extensions in earlier chapters e Section 3 3 covers the fetch extension this combines pulling new changes and merging them with local changes into a single command hg fetch e The bisect extension adds an efficient pruning search for c
159. ed from file in any way Mercurial doesn t do anything with the copied from file hg copy file new file hg revert new file hg status new file A slightly special case reverting a rename If you hg rename a file there is one small detail that you should remember When you hg revert a rename it s not enough to provide the name of the renamed to file as you can see here hg rename file new file hg revert new file hg status R file new file As you can see from the output of hg status the renamed to file is no longer identified as added but the renamed from file is still removed This is counter intuitive at least to me but at least it s easy to deal with hg revert file hg status new file So remember to revert a hg rename you must provide both the source and destination names By the way if you rename a file then modify the renamed to file then revert both components of the rename when Mercurial restores the file that was removed as part of the rename it will be unmodified If you need the modifications in the renamed to file to show up in the renamed from file don t forget to copy them over These fiddly aspects of reverting a rename arguably constitute a small bug in Mercurial 9 3 Dealing with committed changes Consider a case where you have committed a change a and another change b on top of it you then realise that chan
160. ee a E The first line The second line Launching a visual diff tool is just as easy Here s how to launch the kdiff3 viewer 167 N N hg extdiff p kdiff3 o If your diff viewing command can t deal with directories you can easily work around this with a little scripting For an example of such scripting in action with the mq extension and the interdiff command see section 13 9 2 14 2 1 Defining command aliases It can be cumbersome to remember the options to both the hg extdiff command and the diff viewer you want to use so the extdiff extension lets you define new commands that will invoke your diff viewer with exactly the right options All you need to do is edit your hgrc and add a section named extdiff Inside this section you can define multiple commands Here s how to add a kdiff3 command Once you ve defined this you can type hg kdiff3 and the extdiff extension will run kdiff3 for you extdiff cmd kdiff3 If you leave the right hand side of the definition empty as above the extdiff extension uses the name of the command you defined as the name of the external program to run But these names don t have to be the same Here we define a command named hg wibble which runs kdiff3 extdiff cmd wibble kdiff3 You can also specify the default options that you want to invoke your diff viewing program with The prefix to use is
161. eful if you already know what you re looking for you may need to see a complete description of the change or a list of the files changed if you re trying to decide whether a changeset is the one you re looking for The hg log command s v or verbose option gives you this extra detail hg log v r 3 changeset 3 5d7b70a2a9 user Bryan O Sullivan lt bos serpentine com gt date Tue Sep 06 13 15 58 2005 0700 files Makefile description Get make to generate the final binary from a o file If you want to see both the description and content of a change add the p or patch option This displays the content of a change as a unified diff if you ve never seen a unified diff before see section 12 4 for an overview hg log v p r 2 changeset 2 057d3c2d823c user Bryan O Sullivan lt bos serpentine com gt date Tue Sep 06 13 15 43 2005 0700 files hello c description Introduce a typo into hello c diff r 82e55d328c8c r 057d3c2d823c hello c a hello c Fri Aug 26 01 21 28 2005 0700 b hello c Tue Sep 06 13 15 43 2005 0700 ee 11 6 11 6 ee int main int argc char argv printf hello world n printf hello world return 0 2 5 All about command options Let s take a brief break from exploring Mercurial commands to discuss a pattern in the way that they work you may find this useful to keep in mind as we continue our tour Mercuria
162. en share different versions of the same patch stack among multiple underlying repositories I use this when I am developing a Linux kernel feature I have a pristine copy of my kernel sources for each of several CPU architectures and a cloned repository under each that contains the patches I am working on When I want to test a change on a different architecture I push my current patches to the patch repository associated with that kernel tree Figure 12 14 Using MQ s tag features to work with patches pop and push all of my patches and build and test that kernel Managing patches in a repository makes it possible for multiple developers to work on the same patch series without colliding with each other all on top of an underlying source base that they may or may not control 12 11 1 MQ support for patch repositories MQ helps you to work with the hg patches directory as a repository when you prepare a repository for working with patches using hg qinit you can pass the c option to create the hg patches directory as a Mercurial repository 150 Note If you forget to use the c option you can simply go into the hg patches directory at any time and run hg init Don t forget to add an entry for the status file to the hgignore file though hg ginit c does this for you automatically you really don t want to manage the status file As a convenience if MQ notices that the hg patches directory is a reposit
163. epository to work with MQ The hg qinit command prepares a repository to work with MQ It creates a directory called hg patches Options c Create hg patches as a repository in its own right Also creates a hgignore file that will ignore the status file When the hg patches directory is a repository the hg gimport and hg qnew commands automatically hg add new patches B 1 9 hg qnew create a new patch The hg qnew command creates a new patch It takes one mandatory argument the name to use for the patch file The newly created patch is created empty by default It is added to the series file after the current topmost applied patch and is immediately pushed on top of that patch If hg qnew finds modified files in the working directory it will refuse to create a new patch unless the f option is used see below This behaviour allows you to hg qrefresh your topmost applied patch before you apply a new patch on top of it Options f Create a new patch if the contents of the working directory are modified Any outstanding modifications are added to the newly created patch so after this command completes the working directory will no longer be modified m Use the given text as the commit message This text will be stored at the beginning of the patch file before the patch data B 1 10 hg qnext print the name of the next patch The hg qnext command prints the name n
164. er live under home hg repos and you have a repository whose path is home hg repos app tests then setting strip to 4 will give a partial path of app tests The hook will make this partial path available when expanding a template as webroot template The text of the template to use In addition to the usual changeset related variables this template can use hgweb the value of the hgweb configuration item above and webroot the path constructed using strip above In addition you can add a baseurl item to the web section of your hgrc The bugzilla hook will make this available when expanding a template as the base string to use when constructing a URL that will let users browse from a Bugzilla comment to view a changeset Example web baseurl http hg domain com Here is an example set of bugzilla hook config information bugzilla host bugzilla example com password mypassword version 2 16 server side repos live in home hg repos so strip 4 leading separators strip 4 hgweb http hg example com usermap home hg repos notify bugzilla conf template Changeset node short made by author in the webroot repo refers to this bug nFor complete details see hgweb webroot cmd changeset node node short nChangeset description n t desc tabindent Testing and troubleshooting The most common problems with configuring the bugzilla hook relate to running Bugzilla s
165. er than the once compressed form and so Mercurial will store the plain zip or JPEG Deltas between revisions of a compressed file are usually larger than snapshots of the file and Mercurial again does the right thing in these cases It finds that such a delta exceeds the threshold at which it should store a complete snapshot of the file so it stores the snapshot again saving space compared to a naive delta only approach Network recompression When storing revisions on disk Mercurial uses the deflate compression algorithm the same one used by the popular zip archive format which balances good speed with a respectable compression ratio However when transmitting revision data over a network connection Mercurial uncompresses the compressed revision data If the connection is over HTTP Mercurial recompresses the entire stream of data using a compression algorithm that gives a better compression ratio the Burrows Wheeler algorithm from the widely used bzip2 compression pack age This combination of algorithm and compression of the entire stream instead of a revision at a time substantiall y reduces the number of bytes to be transferred yielding better network performance over almost all kinds of network 40 If the connection is over ssh Mercurial doesn t recompress the stream because ssh can already do this itself 4 5 2 Read write ordering and atomicity Appending to files isn t the whole story when it comes to guaran
166. ern see below it s safest to tell you what it s doing For commands that behave this way you can silence them using the q option You can also get them to print the name of every file even those you ve named explicitly using the v option 7 4 Using patterns to identify files In addition to working with file and directory names Mercurial lets you use patterns to identify files Mercurial s pattern handling is expressive On Unix like systems Linux MacOS etc the job of matching file names to patterns normally falls to the shell On these systems you must explicitly tell Mercurial that a name is a pattern On Windows the shell does not expand patterns so Mercurial will automatically identify names that are patterns and expand them for you To provide a pattern in place of a regular name on the command line the mechanism is simple syntax patternbody That is a pattern is identified by a short text string that says what kind of pattern this is followed by a colon followed by the actual pattern Mercurial supports two kinds of pattern syntax The most frequently used is called glob this is the same kind of pattern matching used by the Unix shell and should be familiar to Windows command prompt users too When Mercurial does automatic pattern matching on Windows it uses glob syntax You can thus omit the glob prefix on Windows but it s safe to use it too The re syntax is more powerful it lets yo
167. ern in the group matches The e 99 character separates subpatterns and ends the group it negates the class making it match any single character hg status glob in py MANIFEST in setup py Watch out Don t forget that if you want to match a pattern in any directory you should not be using the match any token as this will only match within one directory Instead use the token This small example illustrates the difference between the two hg status glob py setup py hg status glob py examples simple py src main py examples performant py setup py src watcher watcher py VV Vv PP mv mM 7 4 2 Regular expression matching with re patterns Mercurial accepts the same regular expression syntax as the Python programming language it uses Python s regexp engine internally This is based on the Perl language s regexp syntax which is the most popular dialect in use it s also used in Java for example I won t discuss Mercurial s regexp dialect in any detail here as regexps are not often used Perl style regexps are in any case already exhaustively documented on a multitude of web sites and in many books Instead I will focus here on a few things you should know if you find yourself needing to use regexps with Mercurial A regexp is matched against an entire file name relative to the root of the repository In other words even if you
168. ese paths This isn t an ideal situation but it s unlikely to change Please read the following paragraphs carefully Mercurial treats the path to a repository on the server as relative to the remote user s home directory For example if user foo on the server has a home directory of home foo then an ssh URL that contains a path component of bar really refers to the directory home foo bar If you want to specify a path relative to another user s home directory you can use a path that starts with a tilde character followed by the user s name let s call them otheruser like this ssh server otheruser hg repo And if you really want to specify an absolute path on the server begin the path component with two slashes as in this example ssh server absolute path 6 5 2 Finding an ssh client for your system Almost every Unix like system comes with OpenSSH preinstalled If you re using such a system run which ssh to find out if the ssh command is installed it s usually in usr bin In the unlikely event that it isn t present take a look at your system documentation to figure out how to install it On Windows you ll first need to choose download a suitable ssh client There are two alternatives e Simon Tatham s excellent PuTTY package Tat provides a complete suite of ssh client commands e If you have a high tolerance for pain you can use the Cygwin port of OpenSSH In either case
169. ete a patch from the series file o qdiff print a diff of the topmost applied patch o afold merge fold several patches into one o o o qheader display the header description of a patch o qimport import a third party patch into the queue qinit prepare a repository to work with MQ o anew Creale anew patch ak eG eR A a A qnext print the name of the next patch apop pop patches off the stack 2 ee qprev print the name of the previous patch apush push patches onto the stack o o o qrefresh update the topmost applied patch o arename tename a patel 2 54 45 hb oA eS bE bee eS EES eA aS qrestore restore saved queue state gt s s oreca astan Ee ER qsave savye current queue state e qseries print the entire patch series oaoa e atop print the name of the current patch noonoo o qunapplied print patches not yet applied e JUBERA a A A A al ee a a a strip remove a revision and descendants o o B2 MU tile Teference n eseas paa pea ee Ah eee Pe a ee a A AA The series Te cocinan A HAs B22 The statue MO cora A AE A A ee eS B 2 1 C Installing
170. ewhere else this isn t necessarily a disaster You can protect yourself ahead of time against some classes of bad changeset This is particularly easy if your team usually pulls changes from a central repository By configuring some hooks on that repository to validate incoming changesets see chapter 10 you can automati cally prevent some kinds of bad changeset from being pushed to the central repository at all With such a configuration in place some kinds of bad changeset will naturally tend to die out because they can t propagate into the central repository Better yet this happens without any need for explicit intervention For instance an incoming change hook that verifies that a changeset will actually compile can prevent people from inadvertantly breaking the build 9 5 Finding the source of a bug While it s all very well to be able to back out a changeset that introduced a bug this requires that you know which changeset to back out Mercurial provides an invaluable extension called bisect that helps you to automate this process and accomplish it very efficiently The idea behind the bisect extension is that a changeset has introduced some change of behaviour that you can identify with a simple binary test You don t know which piece of code introduced the change but you know how to test for the presence of the bug The bisect extension uses your test to direct its search for the changeset that introduced the code that c
171. f the code beneath you will often need to sync up with the underlying code and fix up any hunks in your patches that no longer apply This is called rebasing your patch series The simplest way to do this is to hg qpop a your patches then hg pull changes into the underlying repos itory and finally hg qpush a your patches again MQ will stop pushing any time it runs across a patch that fails to apply during conflicts allowing you to fix your conflicts hg qrefresh the affected patch and continue pushing until you have fixed your entire stack This approach is easy to use and works well if you don t expect changes to the underlying code to affect how well your patches apply If your patch stack touches code that is modified frequently or invasively in the underlying repository however fixing up rejected hunks by hand quickly becomes tiresome It s possible to partially automate the rebasing process If your patches apply cleanly against some revision of the underlying repo MQ can use this information to help you to resolve conflicts between your patches and a different revision The process is a little involved 1 To begin hg qpush a all of your patches on top of the revision where you know that they apply cleanly 2 Save a backup copy of your patch directory using hg qsave e c This prints the name of the directory that it has saved the patches in It will save the patches to a directory called
172. ffect in particular it doesn t do anything to patches that are already applied With no arguments the hg qselect command lists the guards currently in effect one per line of output Each argument is treated as the name of a guard to apply hg qpop a Patch queue now empty hg qselect no active guards hg qselect foo number of unguarded unapplied patches has changed from 1 to 2 hg qselect foo In case you re interested the currently selected guards are stored in the guards file cat hg patches guards foo We can see the effect the selected guards have when we run hg qpush hg qpush a applying hello patch applying goodbye patch Now at goodbye patch 6699 A guard cannot start with a or character The name of a guard must not contain white space but most othter characters are acceptable If you try to use a guard with an invalid name MQ will complain hg qselect foo abort guard foo starts with invalid character 158 Changing the selected guards changes the patches that are applied hg qselect quux number of guarded applied patches has changed from 0 to 2 hg qpop a Patch queue now empty hg qpush a patch series already fully applied You can see in the example below that negative guards take precedence over positive guards hg qselect foo bar number of unguarded unapplied patches has c
173. filelogs in repository 36 Metadata relationship 5 ee be ke he ee ee ke ee 36 Snapshot of a revlog with incremental deltas o e e 37 URS RI A a a E e PDA A 43 The working directory can have two parents ee ee 44 The working directory gains new parents after a commit e 44 The working directory updated to an older changeset o o e 45 After a commit made while synced to an older changeset o o 45 IMEI WO REAUS co cia a a ar a 46 Simulating an empty directory using a hidden file o o 48 SAME DENSA ES A E AAA oe ees 61 Backing out a change using the hg backout command a soaa 95 Automated backout of a non tip change using the hg backout command 96 Backing out a change using the hg backout command 00 97 Manually merging a backout change ee 99 A simple hook that runs when a changeset is committed l o ea 110 Defining a second comti NOOK oe s s sacana e E RS OR ee eee Be 110 Using the pretxncommit hook to control commits s sd eee ee ee ee ee 111 A hook that forbids overly short commit messages 2 2 2 02 2 0 00000000000 113 A simple hook that checks for trailing whitespace ee ee 114 A better trailing whitespace hook o so Re RRR Re ee ee 115 Template keywords IIS 2 68 3d Pe a Eee oe A Bed
174. foo 20bar user Any text but most useful for the author keyword Return the user portion of an email address For example Bryan O Sullivan lt bos serpentine com gt becomes bos Note If you try to apply a filter to a piece of data that it cannot process Mercurial will fail and print a Python exception For example trying to run the output of the desc keyword into the isodate filter is not a good idea 11 6 1 Combining filters It is easy to combine filters to yield output in the form you would like The following chain of filters tidies up a description then makes sure that it fits cleanly into 68 columns then indents it by a further 8 characters at least on Unix like systems where a tab is conventionally 8 characters wide hg log r1 template description n t desc strip i1168 tabindent n description added line to end of lt lt hello gt gt file in addition added a file with the helpful name at least i hope that some might consider it so of goodbye Note the use of t a tab character in the template to force the first line to be indented this is necessary since tabindent indents all lines except the first Keep in mind that the order of filters in a chain is significant The first filter is applied to the result of the keyword the second to the result of the first filter and so on For example using i11168 tabindent gives very different results from tabinden
175. g its name or by a number By name is obvious enough pass the name foo patch to hg qpush for example and it will push patches until foo patch is applied As a shortcut you can refer to a patch using both a name and a numeric offset foo patch 2 means two patches before foo patch while bar patch 4 means four patches after bar patch Referring to a patch by index isn t much different The first patch printed in the output of hg qseries is patch zero yes it s one of those start at zero counting systems the second is patch one and so on MQ also makes it easy to work with patches when you are using normal Mercurial commands Every command that accepts a changeset ID will also accept the name of an applied patch MQ augments the tags normally in the repository with an eponymous one for each applied patch In addition the special tags qbase and qtip identify the bottom most and topmost applied patches respectively These additions to Mercurial s normal tagging capabilities make dealing with patches even more of a breeze e Want to patchbomb a mailing list with your latest series of changes 1 hg email qbase qtip Don t know what patchbombing is See section 14 4 e Need to see all of the patches since foo patch that have touched files in a subdirectory of your tree 1 hg log r foo patch gtip subdir Because MQ makes the names of patches available to the rest of Merc
176. g remove or hg rename Added files and copy and rename destinations are added to the patch while removed files and rename sources are removed Even if hg qrefresh detects no changes it still recreates the changeset that represents the patch This causes the identity of the changeset to differ from the previous changeset that identified the patch Options e Modify the commit and patch description using the preferred text editor m Modify the commit message and patch description using the given text 1 Modify the commit message and patch description using text from the given file B 1 15 hg qrename rename a patch The hg qrename command renames a patch and changes the entry for the patch in the series file With a single argument hg qrename renames the topmost applied patch With two arguments it renames its first argument to its second B 1 16 hg qrestore restore saved queue state XXX No idea what this does B 1 17 hg qsave save current queue state XXX Likewise B 1 18 hg qseries print the entire patch series The hg qseries command prints the entire patch series from the series file It prints only patch names not empty lines or comments It prints in order from first to be applied to last B 1 19 hg qtop print the name of the current patch The hg qtop prints the name of the topmost currently applied patch B 1 20 hg qunapplied print
177. gal params patch but not applied fix memory leak patch topmost ot EM 2030020300 a E changesets present a655daf15409 Figure 12 10 Applied and unapplied patches in the MQ patch stack apply their patch followed by hg addremove to pick up any files added or removed by the patch followed by hg grefresh This complexity may become unnecessary see Mercurial bug no 311 for details 12 6 2 Strategies for applying a patch When patch applies a hunk it tries a handful of successively less accurate strategies to try to make the hunk apply This falling back technique often makes it possible to take a patch that was generated against an old version of a file and apply it against a newer version of that file First patch tries an exact match where the line numbers the context and the text to be modified must apply exactly If 1t cannot make an exact match it tries to find an exact match for the context without honouring the line numbering information If this succeeds it prints a line of output saying that the hunk was applied but at some offset from the original line number If a context only match fails patch removes the first and last lines of the context and tries a reduced context only match If the hunk with reduced context succeeds it prints a message saying that it applied the hunk with a fuzz factor the number after the fuzz factor indicates how many lines of context patch had to trim before the patch applied
178. ge a was incorrect Mercurial lets you back out an entire changeset automatically and building blocks that let you reverse part of a changeset by hand Before you read this section here s something to keep in mind the hg backout command undoes changes by adding history not by modifying or erasing it It s the right tool to use if you re fixing bugs but not if you re trying to undo some change that has catastrophic consequences To deal with those see section 9 4 9 3 1 Backing out a changeset The hg backout command lets you undo the effects of an entire changeset in an automated fashion Because Mercurial s history is immutable this command does not get rid of the changeset you want to undo Instead it creates a new changeset that reverses the effect of the to be undone changeset The operation of the hg backout command is a little intricate so let s illustrate it with some examples First we ll create a repository with some simple changes hg init myrepo ed myrepo 93 echo first change gt gt myfile hg add myfile hg commit m first change echo second change gt gt myfile hg commit m second change Sie Ae G U Us The hg backout command takes a single changeset ID as its argument this is the changeset to back out Normally hg backout will drop you into a text editor to write a commit message so you can record why you re backing the change out In t
179. going 11 3 The basics of templating At its simplest a Mercurial template is a piece of text Some of the text never changes while other parts are expanded or replaced with new text when necessary Before we continue let s look again at a simple example of Mercurial s normal output 128 1 hg log r1 2 changeset 1 ee70 2e8cdl 3 tag mytag 4 user Bryan O Sullivan lt bos serpentine com gt s date Sun Jun 17 18 04 00 2007 0000 6 summary added line to end of lt lt hello gt gt file Now let s run the same command but using a template to change its output 1 hg log r1 template i saw a changeset n i saw a changeset N The example above illustrates the simplest possible template it s just a piece of static text printed once for each changeset The template option to the hg log command tells Mercurial to use the given text as the template when printing each changeset Notice that the template string above ends with the text An This is an escape sequence telling Mercurial to print a newline at the end of each template item If you omit this newline Mercurial will run each piece of output together See section 11 5 for more details of escape sequences A template that prints a fixed string of text all the time isn t very useful let s try something a bit more complex hg log template i saw a changeset desc n saw a changeset Added tag v0 1 for
180. hanged from 0 to 2 hg qpop a no patches applied hg qpush a applying hello patch applying goodbye patch Now at goodbye patch 13 5 MQ s rules for applying patches The rules that MQ uses when deciding whether to apply a patch are as follows e A patch that has no guards is always applied e If the patch has any negative guard that matches any currently selected guard the patch is skipped e If the patch has any positive guard that matches any currently selected guard the patch is applied e If the patch has positive or negative guards but none matches any currently selected guard the patch is skipped 13 6 Trimming the work environment In working on the device driver I mentioned earlier I don t apply the patches to a normal Linux kernel tree In stead I use a repository that contains only a snapshot of the source files and headers that are relevant to Infiniband development This repository is 1 the size of a kernel repository so it s easier to work with I then choose a base version on top of which the patches are applied This is a snapshot of the Linux kernel tree as of a revision of my choosing When I take the snapshot I record the changeset ID from the kernel repository in the commit message Since the snapshot preserves the shape and content of the relevant parts of the kernel tree I can apply my patches on top of either my tiny repository or a normal kernel tree Normally the base tree at
181. hanges that introduced bugs and we documented it in chapter 9 5 e In chapter 10 we covered several extensions that are useful for hook related functionality acl adds access control lists bugzilla adds integration with the Bugzilla bug tracking system and notify sends notification emails on new changes e The Mercurial Queues patch management extension is so invaluable that it merits two chapters and an appendix all to itself Chapter 12 covers the basics chapter 13 discusses advanced topics and appendix B goes into detail on each command In this chapter we ll cover some of the other extensions that are available for Mercurial and briefly touch on some of the machinery you ll need to know about if you want to write an extension of your own e In section 14 1 we ll discuss the possibility of huge performance improvements using the inotify extension 14 1 Improve performance with the inotify extension Are you interested in having some of the most common Mercurial operations run as much as a hundred times faster Read on Mercurial has great performance under normal circumstances For example when you run the hg status command Mercurial has to scan almost every directory and file in your repository so that it can display file status Many other Mercurial commands need to do the same work behind the scenes for example the hg diff command uses the status machinery to avoid doing an expensive comparison operation on fi
182. hanges that they are about to feed upstream and so on Others just publish a single tree 61 This model has two notable features The first is that it s pull only You have to ask convince or beg another developer to take a change from you because there are almost no trees to which more than one person can push and there s no way to push changes into a tree that someone else controls The second is that it s based on reputation and acclaim If you re an unknown Linus will probably ignore changes from you without even responding But a subsystem maintainer will probably review them and will likely take them 1f they pass their criteria for suitability The more good changes you contribute to a maintainer the more likely they are to trust your judgment and accept your changes If you re well known and maintain a long lived branch for something Linus hasn t yet accepted people with similar interests may pull your changes regularly to keep up with your work Reputation and acclaim don t necessarily cross subsystem or people boundaries If you re a respected but spe cialised storage hacker and you try to fix a networking bug that change will receive a level of scrutiny from a network maintainer comparable to a change from a complete stranger To people who come from more orderly project backgrounds the comparatively chaotic Linux kernel development process often seems completely insane It s subject to the whims of indiv
183. he extra step of printing the name of each file that it does something with This makes it more clear what is happening and reduces the likelihood of a silent and nasty surprise This behaviour is common to most Mercurial commands 5 1 2 Aside Mercurial tracks files not directories Mercurial does not track directory information Instead it tracks the path to a file Before creating a file it first creates any missing directory components of the path After it deletes a file it then deletes any empty directories that were in the deleted file s path This sounds like a trivial distinction but it has one minor practical consequence it is not possible to represent a completely empty directory in Mercurial Empty directories are rarely useful and there are unintrusive workarounds that you can use to achieve an ap propriate effect The developers of Mercurial thus felt that the complexity that would be required to manage empty directories was not worth the limited benefit this feature would bring If you need an empty directory in your repository there are a few ways to achieve this One is to create a directory then hg add a hidden file to that directory On Unix like systems any file name that begins with a period is treated as hidden by most commands and GUI tools This approach is illustrated in figure 5 1 hg init hidden example cd hidden example mkdir empty touch empty hidden hg add empty hidden hg comm
184. he file a but not the new file b If I were to push this changeset to a repository that I shared with a colleague the chances are high that something in a would refer to b which would not be present in their repository when they pulled my changes I would thus become the object of some indignation However luck is with me I ve caught my error before I pushed the changeset I use the hg rollback com mand and Mercurial makes that last changeset vanish hg rollback rolling back last transaction hg tip changeset 0 549de21446de tag tip user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 59 2007 0000 summary First commit hg status Ma b Notice that the changeset is no longer present in the repository s history and the working directory once again thinks that the file a is modified The commit and rollback have left the working directory exactly as it was prior to the commit the changeset has been completely erased I can now safely hg ada the file b and rerun my commit hg add b hg commit m Add file b this time for real 9 1 3 The erroneous pull It s common practice with Mercurial to maintain separate development branches of a project in different repositories Your development team might have one shared repository for your project s 0 9 release and another containing different changes for the 1 0 release Given this you can im
185. hg patches N where N is a small integer It also commits a save changeset on top of your applied patches this is for internal book keeping and records the states of the series and status files 3 Use hg pull to bring new changes into the underlying repository Don t run hg pull u see below for why 4 Update to the new tip revision using hg update C to override the patches you have pushed 5 Merge all patches using hg qpush m a The m option to hg qpush tells MQ to perform a three way merge if the patch fails to apply During the hg qpush m each patch in the series file is applied normally If a patch applies with fuzz or rejects MQ looks at the queue you hg qsave d and performs a three way merge with the corresponding changeset This merge uses Mercurial s normal merge machinery so it may pop up a GUI merge tool to help you to resolve problems When you finish resolving the effects of a patch MQ refreshes your patch based on the result of the merge At the end of this process your repository will have one extra head from the old patch queue and a copy of the old patch queue will be in hg patches N You can remove the extra head using hg qpop a n patches N or hg strip You can delete hg patches N once you are sure that you no longer need it as a backup 148 12 9 Identifying patches MQ commands that work with patches let you refer to a patch either by usin
186. his example we provide a commit message on the command line using the m option 9 3 2 Backing out the tip changeset We re going to start by backing out the last changeset we committed hg backout m back out second change tip reverting myfile changeset 2 93c44e38d2f2 backs out changeset 1 92480a09996c cat myfile first change You can see that the second line from myfile is no longer present Taking a look at the output of hg log gives us an idea of what the hg backout command has done hg log style compact 2 tip 93c44e38d2f2 2007 06 06 15 10 0000 bos back out second change 1 92480a09996c 2007 06 06 15 10 0000 bos second change 0 d185b5a7f54c 2007 06 06 15 10 0000 bos first change Notice that the new changeset that hg backout has created is a child of the changeset we backed out It s easier to see this in figure 9 1 which presents a graphical view of the change history As you can see the history is nice and linear 9 3 3 Backing out a non tip change If you want to back out a change other than the last one you committed pass the merge option to the hg backout command ed hg clone r1 myrepo non tip repo requesting all changes adding changesets adding manifests adding file changes added 2 changesets with 2 changes to 1 files 1 files updated 0 files merged 0 files removed 0 files unresolved ed non tip repo 94 N ba
187. ial does when you copy a file tells you what to expect when you rename a file When you use the hg rename command Mercurial makes a copy of each source file then deletes it and marks the file as removed hg rename a b The hg status command shows the newly copied file as added and the copied from file as removed hg status Ab Ra As with the results of a hg copy we must use the C option to hg status to see that the added file is really being tracked by Mercurial as a copy of the original now removed file hg status C Ab a Ra As with hg remove and hg copy you can tell Mercurial about a rename after the fact using the after option In most other respects the behaviour of the hg rename command and the options it accepts are similar to the hg copy command 53 5 4 1 Renaming files and merging changes Since Mercurial s rename is implemented as copy and remove the same propagation of changes happens when you merge after a rename as after a copy If I modify a file and you rename it to a new name and then we merge our respective changes my modifications to the file under its original name will be propagated into the file under its new name This is something you might expect to simply work but not all revision control systems actually do this Whereas having changes follow a copy is a feature where you can perhaps nod and s
188. iduals people make sweeping changes whenever they deem it appropriate and the pace of development is astounding And yet Linux is a highly successful well regarded piece of software 6 2 8 Pull only versus shared push collaboration A perpetual source of heat in the open source community is whether a development model in which people only ever pull changes from others is better than one in which multiple people can push changes to a shared repository Typically the backers of the shared push model use tools that actively enforce this approach If you re using a centralised revision control tool such as Subversion there s no way to make a choice over which model you ll use the tool gives you shared push and if you want to do anything else you ll have to roll your own approach on top such as applying a patch by hand A good distributed revision control tool such as Mercurial will support both models You and your collaborators can then structure how you work together based on your own needs and preferences not on what contortions your tools force you into 6 2 9 Where collaboration meets branch management Once you and your team set up some shared repositories and start propagating changes back and forth between local and shared repos you begin to face a related but slightly different challenge that of managing the multiple direc tions in which your team may be moving at once Even though this subject is intimately related
189. ies in Mercurial are self contained This means that the changeset we just cre ated exists only in our my hello repository Let s look at a few ways that we can propagate this change into other repositories 2 8 1 Pulling changes from another repository To get started let s clone our original hello repository which does not contain the change we just committed We ll call our temporary repository hello pull cd hg clone hello hello pull 2 files updated 0 files merged 0 files removed 0 files unresolved 20 We ll use the hg pull command to bring changes from my hello into hello pull However blindly pulling unknown changes into a repository is a somewhat scary prospect Mercurial provides the hg incoming command to tell us what changes the hg pull command would pull into the repository without actually pulling the changes in cd hello pull hg incoming my hello comparing with my hello searching for changes changeset 5 fal321bf0c80 tag tip user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 05 50 2007 0000 summary Added an extra line of output Of course someone could cause more changesets to appear in the repository that we ran hg incoming in before we get a chance to hg pull the changes so that we could end up pulling changes that we didn t expect Bringing changes into a repository is a simple matter of running the hg pull
190. if we want to redo the merging operation This could be useful if for example we were running a graphical merge tool and quit because we were confused or realised we had made a mistake If automatic or manual merges fail there s nothing to prevent us from fixing up the affected files ourselves and committing the results of our merge cat gt letter txt lt lt EOF gt Greetings gt I am Bryan O Sullivan no relation of the former gt Nigerian dictator Sani Abacha gt EOF hg commit m Send me your money hg tip changeset 3 ecc34a7fd0f9 tag tip parent 1 f1b10cfbf9f4 parent 2 b893b763b58b user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 05 59 2007 0000 summary Send me your money 3 3 Simplifying the pull merge commit sequence The process of merging changes as outlined above is straightforward but requires running three commands in se quence hg pull hg merge hg commit m Merged remote changes 32 In the case of the final commit you also need to enter a commit message which is almost always going to be a piece of uninteresting boilerplate text It would be nice to reduce the number of steps needed if this were possible Indeed Mercurial is distributed with an extension called fet ch that does just this Mercurial provides a flexible extension mechanism that lets people extend its functionality while keeping the core of Mercurial
191. ific to an individual repository A few web configuration items ought to be placed in a repository s local hg hgrc rather than a user s or global hgrc description name String A free form but preferably brief string that describes the contents or purpose of the repository String The name to use for the repository in the web interface This overrides the default name which is the last component of the repository s path 71 Options specific to the hg serve command Some of the items in the web section of a hgrc file are only for use with the hg serve command accesslog Path The name of a file into which to write an access log By default the hg serve command writes this information to standard output not to a file Log entries are written in the standard combined file format used by almost all web servers address String The local address on which the server should listen for incoming connections By default the server listens on all addresses errorlog Path The name of a file into which to write an error log By default the hg serve command writes this information to standard error not to a file ipv6 Boolean Whether to use the IPv6 protocol By default IPv6 is not used port Integer The TCP port number on which the server should listen The default port number used is 8000 Choosing the right hgrc file to add web items to It is important to remember that a web server
192. iles that it detects as binary Specifying a forces hg diff to treat all files as text and generate diffs for all of them 170 This option is useful for files that are mostly text but have a few embedded NUL characters If you use it on files that contain a lot of binary data its output will be incomprehensible ignore space change also b Do not print a line if the only change to that line is in the amount of white space it contains git also g Print git compatible diffs XXX reference a format description show function also p Display the name of the enclosing function in a hunk header using a simple heuristic This functionality is enabled by default so the p option has no effect unless you change the value of the showfunc config item as in the following example echo diff gt gt SHGRC echo showfunc False gt gt SHGRC hg diff diff r 425c85dc3df7 myfile c a myfile c Sun Jun 17 18 03 45 2007 0000 b myfile c Sun Jun 17 18 03 45 2007 0000 QQ 1 4 1 4 Qe int myfunc zj return 1 return 10 hg diff p diff r 425c85dc3df7 myfile c a myfile c Sun Jun 17 18 03 45 2007 0000 b myfile c Sun Jun 17 18 03 45 2007 0000 1 4 1 4 int myfunc int myfunc return 1 return 10 rev also r Specify one or more revisions to compare The hg diff command accepts up to two r options to specify
193. ing in the latest fixes from the stable branch Mercurial will choose the right bleeding edge branch name when I pull and merge from stable 8 8 Branch naming is generally useful You shouldn t think of named branches as applicable only to situations where you have multiple long lived branches cohabiting in a single repository They re very useful even in the one branch per repository case In the simplest case giving a name to each branch gives you a permanent record of which branch a changeset originated on This gives you more context when you re trying to follow the history of a long lived branchy project If you re working with shared repositories you can set up a pret xnchangegroup hook on each that will block incoming changes that have the wrong branch name This provides a simple but effective defence against people accidentally pushing changes from a bleeding edge branch to a stable branch Such a hook might look like this inside the shared repo s hgrc hooks pretxnchangegroup branch hg heads template branches grep mybranch 88 Chapter 9 Finding and fixing your mistakes To err might be human but to really handle the consequences well takes a top notch revision control system In this chapter we ll discuss some of the techniques you can use when you find that a problem has crept into your project Mercurial has some highly capable features that will help you to isolate the
194. ing to the newer release Maintaining a single patch against an upstream tree is a little tedious and error prone but not difficult However the complexity of the problem grows rapidly as the number of patches you have to maintain increases With more than a tiny number of patches in hand understanding which ones you have applied and maintaining them moves from messy to overwhelming Fortunately Mercurial includes a powerful extension Mercurial Queues or simply MQ that massively simpli fies the patch management problem 12 2 The prehistory of Mercurial Queues During the late 1990s several Linux kernel developers started to maintain patch series that modified the behaviour of the Linux kernel Some of these series were focused on stability some on feature coverage and others were more speculative The sizes of these patch series grew rapidly In 2002 Andrew Morton published some shell scripts he had been using to automate the task of managing his patch queues Andrew was successfully using these scripts to manage hundreds sometimes thousands of patches on top of the Linux kernel 137 12 2 1 A patchwork quilt In early 2003 Andreas Gruenbacher and Martin Quinson borrowed the approach of Andrew s scripts and published a tool called patchwork quilt AG or simply quilt see Gru05 for a paper describing it Because quilt substan tially automated patch management it rapidly gained a large following amo
195. ion 5 4 4 Other name related corner cases Mercurial has a longstanding bug in which it fails to handle a merge where one side has a file with a given name while another has a directory with the same name This is documented as Mercurial bug no 29 hg init issue29 ed issue29 echoa gt a hg ci Ama adding a echo b gt b hg ci Amb adding b hg up O 0 files updated 0 files merged 1 files removed 0 files unresolved mkdir b echo b gt b b hg ci Amc adding b b hg merge abort Is a directory tmp issue29f2wKNV issue29 b 5 5 Recovering from mistakes Mercurial has some useful commands that will help you to recover from some common mistakes The hg revert command lets you undo changes that you have made to your working directory For example if you hg ada a file by accident just run hg revert with the name of the file you added and while the file won t 55 be touched in any way it won t be tracked for adding by Mercurial any longer either You can also use hg revert to get rid of erroneous changes to a file It s useful to remember that the hg revert command is useful for changes that you have not yet committed Once you ve committed a change if you decide it was a mistake you can still do something about it though your options may be more limited For more information about the hg revert command and details about how to deal with changes you
196. ion control systems you should be able to get up and running with Mercurial in less than five minutes Even if not it will take no more than a few minutes longer Mercurial s command and feature sets are generally uniform and consistent so you can keep track of a few general rules instead of a host of exceptions On a small project you can start working with Mercurial in moments Creating new changes and branches trans ferring changes around whether locally or over a network and history and status operations are all fast Mercurial attempts to stay nimble and largely out of your way by combining low cognitive overhead with blazingly fast opera tions The usefulness of Mercurial is not limited to small projects it is used by projects with hundreds to thousands of contributors each containing tens of thousands of files and hundreds of megabytes of source code If the core functionality of Mercurial is not enough for you it s easy to build on Mercurial is well suited to scripting tasks and its clean internals and implementation in Python make it easy to add features in the form of extensions There are a number of popular and useful extensions already available ranging from helping to identify bugs to improving performance 1 6 Mercurial compared with other tools Before you read on please understand that this section necessarily reflects my own experiences interests and dare I say it biases I have used every one of the revision con
197. ip 1 bde8d458e45b v1 0 0 al0bfa31f1c2 Let s say some ongoing development occurs on the main branch cd main echo This is exciting and new gt gt myfile hg commit m Add a new feature cat myfile This is a boring feature This is exciting and new a sing the tag that was recorded at the milestone people who clone that repository at any time in the future can use hg update to get a copy of the working directory exactly as it was when that tagged revision was committed G cd hg clone U main main old cd main old hg update v1 0 files updated 0 files merged 0 files removed 0 files unresolved cat myfile This is a boring feature UE ee US A UA In addition immediately after the main branch is tagged someone can then clone the main branch on the server to a new stable branch also on the server 59 cd hg clone rv1 0 main stable requesting all changes adding changesets adding manifests adding file changes added 1 changesets with 1 changes to 1 files 1 files updated 0 files merged 0 files removed 0 files unresolved Someone who needs to make a change to the stable branch can then clone that repository make their changes commit and push their changes back there hg clone stable stable fix files updated 0 files merged 0 files removed 0 files unresolved cd stable fix echo This is a fix to a boring feature
198. ired check_bug_id HG_NODE gt gt hg hgrc echo a gt gt a hg commit m i am not mentioning a bug id abort pretxncommit bug_id_required hook exited with status 1 transaction abort rollback completed hg commit m i refer you to bug 666 committed cad7828eb18313e391ed072ec23016c0fc6d6fla date of commit Sun Jun 17 18 03 51 GMT 2007 Figure 10 3 Using the pretxncommit hook to control commits The hook in example 10 3 checks that a commit comment contains a bug ID If it does the commit can complete Tf not the commit is rolled back 10 5 Writing your own hooks When you are writing a hook you might find it useful to run Mercurial either with the v option or the verbose config item set to true When you do so Mercurial will print a message before it calls each hook 10 5 1 Choosing how your hook should run You can write a hook either as a normal program typically a shell script or as a Python function that is executed within the Mercurial process Writing a hook as an external program has the advantage that it requires no knowledge of Mercurial s internals You can call normal Mercurial commands to get any added information you need The trade off is that external hooks are slower than in process hooks An in process Python hook has complete access to the Mercurial API and does not shell out to another process so it is inherently faster than an external hook It is also easier t
199. ironment that contains both Linux or other Unix systems and Macs or Windows systems you should keep in the back of your mind the knowledge that they treat the case N versus n of file names in incompatible ways This is not very likely to affect you and it s easy to deal with if it does but it could surprise you if you don t know about it Operating systems and filesystems differ in the way they handle the case of characters in file and directory names There are three common ways to handle case in names e Completely case insensitive Uppercase and lowercase versions of a letter are treated as identical both when creating a file and during subsequent accesses This is common on older DOS based systems e Case preserving but insensitive When a file or directory is created the case of its name is stored and can be retrieved and displayed by the operating system When an existing file is being looked up its case is ignored This is the standard arrangement on Windows and MacOS The names foo and Fo0 identify the same file This treatment of uppercase and lowercase letters as interchangeable is also referred to as case folding e Case sensitive The case of a name is significant at all times The names foo and FoO identify different files This is the way Linux and Unix systems normally work On Unix like systems it is possible to have any or all of the above ways of handling case in action at once For example if you use
200. irstate to store some extra information so it can determine efficiently whether you have modified a file For each file in the working directory it stores the time that it last modified the file itself and the size of the file at that time When you explicitly hg add hg remove hg rename or hg copy files Mercurial updates the dirstate so that it knows what to do with those files when you commit When Mercurial is checking the states of files in the working directory it first checks a file s modification time If that has not changed the file must not have been modified If the file s size has changed the file must have been modified If the modification time has changed but the size has not only then does Mercurial need to read the actual contents of the file to see if they ve changed Storing these few extra pieces of information dramatically reduces the amount of data that Mercurial needs to read which yields large performance improvements compared to other revision control systems 42 Figure 4 4 43 Parents of working directory History in tepositary e7639888bb2f z x e7639888bb2f 000000000000 VUUUUUUUUUUY Figure 4 5 The working directory can have two parents History in repository Patents of watking ditectoty dfbbb33f3fa3 e7639888bb2f Tb064d8bacSe hath hh Figure 4 6 The working directory gains new parents after a commit History in tepositary Parents of watking ditecto
201. is has an interaction with tags that can surprise the unwary 81 Recall that a tag is stored as a revision to the hgtags file so that when you create a tag the changeset in which it s recorded necessarily refers to an older changeset When you run hg clone r foo to clone a repository as of tag foo the new clone will not contain the history that created the tag that you used to clone the repository The result is that you ll get exactly the right subset of the project s history in the new repository but not the tag you might have expected 8 1 3 When permanent tags are too much Since Mercurial s tags are revision controlled and carried around with a project s history everyone you work with will see the tags you create But giving names to revisions has uses beyond simply noting that revision 4237e45506ee is really v2 0 2 If you re trying to track down a subtle bug you might want a tag to remind you of something like Anne saw the symptoms with this revision For cases like this what you might want to use are local tags You can create a local tag with the 1 option to the hg tag command This will store the tag in a file called hg localtags Unlike hgtags hg localtags is not revision controlled Any tags you create using 1 remain strictly local to the repository you re currently working in 8 2 The flow of changes big picture vs little To return to the outline I sketched at the beginning of a chapter
202. is to decide what the file should look like Mercurial doesn t have a built in facility for handling conflicts Instead it runs an external program called hgmerge This is a shell script that is bundled with Mercurial you can change it to behave however you please What it does by default is try to find one of several different merging tools that are likely to be installed on your sys tem It first tries a few fully automatic merging tools if these don t succeed because the resolution process requires human guidance or aren t present the script tries a few different graphical merging tools It s also possible to get Mercurial to run another program or script instead of hgmerge by setting the HGMERGE environment variable to the name of your preferred program 29 Figure 3 4 Conflicting changes to a document 3 2 1 Using a graphical merge tool My preferred graphical merge tool is kdiff 3 which I ll use to describe the features that are common to graphical file merging tools You can see a screenshot of kdiff3 in action in figure 3 5 The kind of merge it is performing is called a three way merge because there are three different versions of the file of interest to us The tool thus splits the upper portion of the window into three panes e At the left is the base version of the file i e the most recent version from which the two versions we re trying to merge are descended e In the middle is our version of the file
203. is used that identifies the name of the patch If a patch contains a Mercurial patch header XXX add link the information in the patch header overrides these defaults Options a Push all unapplied patches from the series file until there are none left to push 1 Add the name of the patch to the end of the commit message m If a patch fails to apply cleanly use the entry for the patch in another saved queue to compute the parameters for a three way merge and perform a three way merge using the normal Mercurial merge machinery Use the resolution of the merge as the new patch content 176 n Use the named queue if merging while pushing The hg qpush command reads but does not modify the series file It appends one line to the hg status file for each patch that it pushes B 1 14 hg qrefresh update the topmost applied patch The hg qrefresh command updates the topmost applied patch It modifies the patch removes the old changeset that represented the patch and creates a new changeset to represent the modified patch The hg qrefresh command looks for the following modifications e Changes to the commit message i e the text before the first diff header in the patch file are reflected in the new changeset that represents the patch e Modifications to tracked files in the working directory are added to the patch 39 66 99 e Changes to the files tracked using hg add hg copy h
204. ision The more history that a file accumulates the more revisions you must read hence the longer it takes to reconstruct a particular revision Reviog index i file Revkog data 41 file E Figure 4 3 Snapshot of a revlog with incremental deltas The innovation that Mercurial applies to this problem is simple but effective Once the cumulative amount of delta information stored since the last snapshot exceeds a fixed threshold it stores a new snapshot compressed of course instead of another delta This makes it possible to reconstruct any revision of a file quickly This approach works so well that it has since been copied by several other revision control systems 37 Figure 4 3 illustrates the idea In an entry in a revlog s index file Mercurial stores the range of entries from the data file that it must read to reconstruct a particular revision Aside the influence of video compression If you re familiar with video compression or have ever watched a TV feed through a digital cable or satellite service you may know that most video compression schemes store each frame of video as a delta against its predecessor frame In addition these schemes use lossy compression techniques to increase the compression ratio so visual errors accumulate over the course of a number of inter frame deltas Because it s possible for a video stream to drop out occasionally due to signal glitches and to limit the accumu
205. istyped your key s passphrase or the remote user s password In summary if you re having trouble talking to the server s ssh daemon first make sure that one is running at all On many systems it will be installed but disabled by default Once you re done with this step you should then check that the server s firewall is configured to allow incoming connections on the port the ssh daemon is listening on usually 22 Don t worry about more exotic possibilities for misconfiguration until you ve checked these two first If you re using an authentication agent on the client side to store passphrases for your keys you ought to be able to log into the server without being prompted for a passphrase or a password If you re prompted for a passphrase there are a few possible culprits e You might have forgotten to use ssh add or pageant to store the passphrase e You might have stored the passphrase for the wrong key If you re being prompted for the remote user s password there are another few possible problems to check e Either the user s home directory or their ssh directory might have excessively liberal permissions As a result the ssh daemon will not trust or read their authorized_keys file For example a group writable home or ssh directory will often cause this symptom 65 e The user s authorized_keys file may have a problem If anyone other than the user owns or can write to that file the ssh daemon will not t
206. it m Manage an empty looking directory ls empty cd hg clone hidden example tmp files updated 0 files merged 0 files removed 0 files unresolved ls tmp empty ls tmp empty UE H 4h 4 XA 4 4h U 4 U U Figure 5 1 Simulating an empty directory using a hidden file Another way to tackle a need for an empty directory is to simply create one in your automated build scripts before they will need it 5 2 How to stop tracking a file Once you decide that a file no longer belongs in your repository use the hg remove command this deletes the file and tells Mercurial to stop tracking it A removed file is represented in the output of hg status with a R 48 hg init remove example cd remove example echo a gt a mkdir b echo b gt b b hg add a b adding b b hg commit m Small example for file removal hg remove a hg status Ra hg remove b OF 4A OF UY U removing b b After you hg remove a file Mercurial will no longer track changes to that file even if you recreate a file with the same name in your working directory If you do recreate a file with the same name and want Mercurial to track the new file simply hg add it Mercurial will know that the newly added file is not related to the old file of the same name 5 2 1 Removing a file does not affect its history It is important to understand that removing a file has only two effects e It rem
207. it with an error if any is The order in which patches are folded is significant hg qfold a b means apply the current topmost patch followed by a followed by b The comments from the folded patches are appended to the comments of the destination patch with each block of comments separated by three asterisk characters Use the e option to edit the commit message for the combined patch changeset after the folding has completed 174 Options e Edit the commit message and patch description for the newly folded patch 1 Use the contents of the given file as the new commit message and patch description for the folded patch m Use the given text as the new commit message and patch description for the folded patch B 1 6 hg gheader display the header description of a patch The hg gheader command prints the header or description of a patch By default it prints the header of the topmost applied patch Given an argument it prints the header of the named patch B 1 7 hg qimport import a third party patch into the queue The hg gimport command adds an entry for an external patch to the series file and copies the patch into the hg patches directory It adds the entry immediately after the topmost applied patch but does not push the patch If the hg patches directory is a repository hg qimport automatically does an hg add of the imported patch B 1 8 hg qinit prepare a r
208. ith by default If you have a repository that contains thousands of files you will rarely want to know about files that Mercurial is tracking but that have not changed You can still get this information we ll return to this later Once you add a file Mercurial doesn t do anything with it immediately Instead it will take a snapshot of the file s state the next time you perform a commit It will then continue to track the changes you make to the file every time you commit until you remove the file 5 1 1 Explicit versus implicit file naming A useful behaviour that Mercurial has is that if you pass the name of a directory to a command every Mercurial command will treat this as I want to operate on every file in this directory and its subdirectories 5 5 5 5 5 mkdir b echo b gt b b echo c gt b c mkdir b d echo d gt b d d 47 hg add b adding b b adding b c adding b d d hg commit m Added all files in subdirectory Notice in this example that Mercurial printed the names of the files it added whereas it didn t do so when we added the file named a in the earlier example What s going on is that in the former case we explicitly named the file to add on the command line so the assumption that Mercurial makes in such cases is that you know what you were doing and it doesn t print any output However when we imply the names of files by giving the name of a directory Mercurial takes t
209. ithout these performance degrades while space usage grows rapidly A server that contains many Git repositories that are not rigorously and frequently repacked will become heavily disk bound during backups and there have been instances of daily backups taking far longer than 24 hours as a result A freshly packed Git repository is slightly smaller than a Mercurial repository but an unpacked repository is several orders of magnitude larger The core of Git is written in C Many Git commands are implemented as shell or Perl scripts and the quality of these scripts varies widely I have encountered a number of instances where scripts charged along blindly in the presence of errors that should have been fatal 1 6 3 CVS CVS is probably the most widely used revision control tool in the world Due to its age and internal untidiness it has been essentially unmaintained for many years It has a centralised client server architecture It does not group related file changes into atomic commits making it easy for people to break the build one person can successfully commit part of a change and then be blocked by the need for a merge causing other people to see only a portion of the work they intended to do This also affects how you work with project history If you want to see all of the modifications someone made as part of a task you will need to manually inspect the descriptions and timestamps of the changes made to each file involved if you even
210. itory string with the complete path to the repository you want to serve up At this point when you try to reload the page you should be presented with a nice HTML view of your repository s history Whew Configuring lighttpd To be exhaustive in my experiments I tried configuring the increasingly popular lighttpd web server to serve the same repository as I described with Apache above I had already overcome all of the problems I outlined with Apache many of which are not server specific As a result I was fairly sure that my file and directory permissions were good and that my hgweb cgi script was properly edited Once I had Apache running getting lighttpd to serve the repository was a snap in other words even if you re trying to use lighttpd you should read the Apache section I first had to edit the mod_access section of its config file to enable mod_cgi and mod_userdir both of which were disabled by default on my system I then added a few lines to the end of the config file to configure these modules userdir path public_html cgi assign cgi gt With this done lighttpd ran immediately for me If I had configured lighttpd before Apache I d almost certainly have run into many of the same system level configuration problems as I did with Apache However I found lighttpd to be noticeably easier to configure than Apache even though I ve used Apache for over a decade and this was my first exposur
211. ject 1 0 1 2 files updated 0 files merged 0 files removed 0 files unresolved Afterwards if someone needs to work on a bug fix that ought to go into an upcoming 1 0 1 minor release they clone the myproject 1 0 1 repository make their changes and push them back 82 hg clone myproject 1 0 1 my 1 0 1 bugfix files updated 0 files merged 0 files removed 0 files unresolved cd my 1 0 1 bugfix echo I fixed a bug using only echo gt gt myfile hg commit m Important fix for 1 0 1 hg push pushing to tmp branch repo8JmRu myproject 1 0 1 searching for changes adding changesets adding manifests adding file changes UY A 4 4 N wm added 1 changesets with 1 changes to 1 files Meanwhile development for the next major release can continue isolated and unabated in the myproject repository cd hg clone myproject my feature files updated 0 files merged 0 files removed 0 files unresolved cd my feature echo This sure is an exciting new feature gt mynewfile hg commit A m New feature adding mynewfile hg push pushing to tmp branch repo8JmRu myproject searching for changes adding changesets adding manifests adding file changes added 1 changesets with 1 changes to 1 files UY 14 4 N wm Ur 8 4 Don t repeat yourself merging across branches In many cases if you have a bug to fix on a maintenance branch the chances are good that the bug exists on your
212. k header it just runs the hunks together with a few lines of context between modifications Each line of context begins with a space character Within the hunk a line that begins with means remove this line while a line that begins with means insert this line For example a line that is modified is represented by one deletion and one insertion We will return to some of the more subtle aspects of patches later in section 12 6 but you should have enough information now to use MQ 12 5 Getting started with Mercurial Queues Because MQ is implemented as an extension you must explicitly enable before you can use it You don t need to download anything MQ ships with the standard Mercurial distribution To enable MQ edit your hgrc file and add the lines in figure 12 5 Once the extension is enabled it will make a number of new commands available To verify that the extension is working you can use hg help to see if the hg qinit command is now available see the example in figure 12 3 139 N extensions hgext mq Figure 12 2 Contents to add to hgrc to enable the MQ extension hg help qinit hg qinit c init a new queue repository options c create repo create queue repository use hg v help qinit to show global options The queue repository is unversioned by default If c is specified qinit will create a separate nested repository for patches
213. l back a group of changesets if they modify forbidden files Example hooks pretxnchangegroup acl python hgext acl hook The acl extension is configured using three sections The acl section has only one entry sources which lists the sources of incoming changesets that the hook should pay attention to You don t normally need to configure this section serve Control incoming changesets that are arriving from a remote repository over http or ssh This is the default value of sources and usually the only setting you ll need for this configuration item 114 cat hg hgre hooks pretxncommit whitespace hg check_whitespace py echo a gt gt a hg commit A m add new line with trailing whitespace a line 2 trailing whitespace added commit message saved to hg commit save abort pretxncommit whitespace hook exited with status 1 transaction abort rollback completed sed i s a hg commit A m trimmed trailing whitespace a line 2 trailing whitespace added commit message saved to hg commit save abort pretxncommit whitespace hook exited with status 1 transaction abort rollback completed Figure 10 6 A better trailing whitespace hook pull Control incoming changesets that are arriving via a pull from a local repository push Control incoming changesets that are arriving via a push from a local repository bundle Control incoming changesets that are
214. l has a consistent and straightforward approach to dealing with the options that you can pass to commands It follows the conventions for options that are common to modern Linux and Unix systems e Every option has a long name For example as we ve already seen the hg log command accepts a rev option 16 e Most options have short names too Instead of rev we can use r The reason that some options don t have short names is that the options in question are rarely used e Long options start with two dashes e g rev while short options start with one e g r e Option naming and usage is consistent across commands For example every command that lets you specify a changeset ID or revision number accepts both r and rev arguments In the examples throughout this book I use short options instead of long This just reflects my own preference so don t read anything significant into it Most commands that print output of some kind will print more output when passed a v or verbose option and less when passed q or quiet 2 6 Making and reviewing changes Now that we have a grasp of viewing history in Mercurial let s take a look at making some changes and examining them The first thing we ll do is isolate our experiment in a repository of its own We use the hg clone command but we don t need to clone a copy of the remote repository Since we already have a copy of it locally we can just clo
215. l you re targeting The less obtrusive the patch the easier it will be to understand and maintain If you re writing a collection of backport patches to avoid the rat s nest effect of lots of ifdefs hunks of source code that are only used conditionally in your code don t introduce version dependent ifdefs into the patches Instead write several patches each of which makes unconditional changes and control their application using guards There are two reasons to divide backport patches into a distinct group away from the regular patches whose effects they modify The first is that intermingling the two makes it more difficult to use a tool like the patchbomb extension to automate the process of submitting the patches to an upstream maintainer The second is that a backport patch could perturb the context in which a subsequent regular patch is applied making it impossible to apply the regular patch cleanly without the earlier backport patch already being applied 13 9 Useful tips for developing with MQ 13 9 1 Organising patches in directories If you re working on a substantial project with MQ it s not difficult to accumulate a large number of patches For example I have one patch repository that contains over 250 patches If you can group these patches into separate logical categories you can if you like store them in different directo ries MQ has no problems with patch names that contain path separators 13 9 2 Viewi
216. lated sets of changes hg heads changeset 3 93c44e38d2f2 tag tip parent 1 92480a09996c user Bryan O Sullivan lt bos serpentine com gt date Wed Jun 06 15 10 43 2007 0000 summary back out second change changeset 2 b5b85d3d30ee user Bryan O Sullivan lt bos serpentine com gt date Wed Jun 06 15 10 43 2007 0000 summary third change Let s think about what we expect to see as the contents of my file now The first change should be present because we ve never backed it out The second change should be missing as that s the change we backed out Since the history graph shows the third change as a separate head we don t expect to see the third change present in myfile cat myfile first change To get the third change back into the file we just do a normal merge of our two heads hg merge merging myfile 0 files updated 1 files merged 0 files removed 0 files unresolved branch merge don t forget to commit hg commit m merged backout with previous tip cat myfile first change third change Afterwards the graphical history of our repository looks like figure 9 4 9 3 5 Why hg backout works as it does Here s a brief description of how the hg backout command works 1 It ensures that the working directory is clean i e that the output of hg status would be empty 98 6 T back out second change Figure 9 4
217. lation of artefacts introduced by the lossy compression process video encoders periodically insert a complete frame called a key frame into the video stream the next delta is generated against that frame This means that if the video signal gets interrupted it will resume once the next key frame is received Also the accumulation of encoding errors restarts anew with each key frame 4 2 4 Identification and strong integrity Along with delta or snapshot information a revlog entry contains a cryptographic hash of the data that it represents This makes it difficult to forge the contents of a revision and easy to detect accidental corruption Hashes provide more than a mere check against corruption they are used as the identifiers for revisions The changeset identification hashes that you see as an end user are from revisions of the changelog Although filelogs and the manifest also use hashes Mercurial only uses these behind the scenes Mercurial verifies that hashes are correct when it retrieves file revisions and when it pulls changes from another repository If it encounters an integrity problem it will complain and stop whatever it s doing In addition to the effect it has on retrieval efficiency Mercurial s use of periodic snapshots makes it more robust against partial data corruption If a revlog becomes partly corrupted due to a hardware error or system bug it s often possible to reconstruct some or most revisions from the u
218. les that obviously haven t changed Because obtaining file status is crucial to good performance the authors of Mercurial have optimised this code to within an inch of its life However there s no avoiding the fact that when you run hg status Mercurial is going to have to perform at least one expensive system call for each managed file to determine whether it s changed since the last time Mercurial checked For a sufficiently large repository this can take a long time To put a number on the magnitude of this effect I created a repository containing 150 000 managed files I timed hg status as taking ten seconds to run even when none of those files had been modified 164 Many modern operating systems contain a file notification facility If a program signs up to an appropriate service the operating system will notify it every time a file of interest is created modified or deleted On Linux systems the kernel component that does this is called inotify Mercurial s inotify extension talks to the kernel s inotify component to optimise hg status commands The extension has two components A daemon sits in the background and receives notifications from the inotify subsystem It also listens for connections from a regular Mercurial command The extension modifies Mercurial s behaviour so that instead of scanning the filesystem it queries the daemon Since the daemon has perfect information about the state of the repository
219. let s think about a project that has multiple concurrent pieces of work under development at once There might be a push for a new main release a new minor bugfix release to the last main release and an unexpected hot fix to an old release that is now in maintenance mode The usual way people refer to these different concurrent directions of development is as branches However we ve already seen numerous times that Mercurial treats all of history as a series of branches and merges Really what we have here is two ideas that are peripherally related but which happen to share a name e Big picture branches represent the sweep of a project s evolution people give them names and talk about them in conversation e Little picture branches are artefacts of the day to day activity of developing and merging changes They expose the narrative of how the code was developed 8 3 Managing big picture branches in repositories The easiest way to isolate a big picture branch in Mercurial is in a dedicated repository If you have an existing shared repository let s call it myproject that reaches a 1 0 milestone you can start to prepare for future maintenance releases on top of version 1 0 by tagging the revision from which you prepared the 1 0 release cd myproject hg tag v1 0 You can then clone a new shared myproject 1 0 1 repository as of that tag cd hg clone myproject mypro
220. lied in this repository again from oldest to newest most recently applied 12 5 4 Manipulating the patch stack The previous discussion implied that there must be a difference between known and applied patches and there is MQ can manage a patch without it being applied in the repository An applied patch has a corresponding changeset in the repository and the effects of the patch and changeset are visible in the working directory You can undo the application of a patch using the hg qpop command MQ still knows about or manages a popped patch but the patch no longer has a corresponding changeset in the repository and the working directory does not contain the changes made by the patch Figure 12 10 illustrates the difference between applied and tracked patches You can reapply an unapplied or popped patch using the hg qpush command This creates a new changeset to correspond to the patch and the patch s changes once again become present in the working directory See figure 12 11 for examples of hg qpop and hg qpush in action Notice that once we have popped a patch or two patches the output of hg qseries remains the same while that of hg qapplied has changed 12 5 5 Pushing and popping many patches While hg qpush and hg qpop each operate on a single patch at a time by default you can push and pop many patches in one go The a option to hg qpush causes it to push all u
221. like Apache or lighttpd will run under a user ID that is different to yours CGI scripts run by your server such as hgweb cgi will usually also run under that user ID If you add web items to your own personal hgrc file CGI scripts won t read that hgrc file Those settings will thus only affect the behaviour of the hg serve command when you run it To cause CGI scripts to see your settings either create a hgrc file in the home directory of the user ID that runs your web server or add those settings to a system wide hgrc file 72 Chapter 7 File names and pattern matching Mercurial provides mechanisms that let you work with file names in a consistent and expressive way 7 1 Simple file naming Mercurial uses a unified piece of machinery under the hood to handle file names Every command behaves uniformly with respect to file names The way in which commands work with file names is as follows If you explicitly name real files on the command line Mercurial works with exactly those files as you would expect hg add COPYING README examples simple py When you provide a directory name Mercurial will interpret this as operate on every file in this directory and its subdirectories Mercurial traverses the files and subdirectories in a directory in alphabetical order When it encounters a subdirectory it will traverse that subdirectory before continuing with the current directory hg status src src m
222. like a perfect candidate for automation so let s turn it into a shell function mytest gt if grep q i have a gub gt then gt result bad gt else gt result good gt fi gt echo this revision is result gt hg bisect result gt We can now run an entire test step with a single command mytest mytest this revision is good Testing changeset 19 58088bed60a7 6 changesets remaining 2 tests 3 files updated 0 files merged 0 files removed 0 files unresolved A few more invocations of our canned test step command and we re done mytest this revision is good Testing changeset 20 e698beb23ae9 3 changesets remaining 1 tests 1 files updated 0 files merged 0 files removed 0 files unresolved mytest this revision is good Testing changeset 21 ceeb735f58f3 2 changesets remaining 1 tests 1 files updated 0 files merged 0 files removed 0 files unresolved mytest this revision is good The first bad revision is changeset 22 8ef86493d946 user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 20 2007 0000 summary buggy changeset Even though we had 40 changesets to search through the bisect extension let us find the changeset that introduced our bug with only five tests Because the number of tests that the bisect extension grows logarithmically with the number of changesets to search the advantage that i
223. ling us that the hg update command won t do a merge it won t update the working directory when it thinks we might be wanting to do a merge unless we force it to do so Instead we use the hg merge command to merge the two heads hg merge merging hello c 0 files updated 1 files merged 0 files removed 0 files unresolved branch merge don t forget to commit Working directery during merge Repository after merge committed El s E tip tid bea Figure 3 3 Working directory and repository during merge and following commit This updates the working directory so that it contains changes from both heads which is reflected in both the output of hg parents and the contents of hello c hg parents changeset 5 06795fee8236 user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 05 52 2007 0000 summary A new hello for a new day changeset 6 fa1321bf0c80 tag tip parent 4 b57 9a090b62 user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 05 50 2007 0000 summary Added an extra line of output cat hello c Placed in the public domain by Bryan O Sullivan This program is not covered by patents in the United States or other countries 28 include lt stdio h gt int main int argc char argv printf once more hello n printf hello world printf hello again n return 0 3 1 3 Commit
224. lity and which are Mercurial s A test is something that you run when bisect chooses a changeset A probe is what bisect runs to tell whether a revision is good Finally we ll use the word bisect as both a noun and a verb to stand in for the phrase search using the bisect extension One simple way to automate the searching process would be simply to probe every changeset However this scales poorly If it took ten minutes to test a single changeset and you had 10 000 changesets in your repository the exhaustive approach would take on average 35 days to find the changeset that introduced a bug Even if you knew that the bug was introduced by one of the last 500 changesets and limited your search to those you d still be looking at over 40 hours to find the changeset that introduced your bug What the bisect extension does is use its knowledge of the shape of your project s revision history to perform a search in time proportional to the logarithm of the number of changesets to check the kind of search it performs is called a dichotomic search With this approach searching through 10 000 changesets will take less than two hours even at ten minutes per test Limit your search to the last 500 changesets and it will take less than an hour The bisect extension is aware of the branchy nature of a Mercurial project s revision history so it has no problems dealing with branches merges or multiple heads in a repoository
225. lo gt gt file in addition added a file with the helpful name at least i hope that some m hg log r1 template desc tabindent n expand cut c 76 added line to end of lt lt hello gt gt file in addition added a file with the helpful name at least i hope tha hg log r1 template node n ee709a2e8cd1224c94823aa7 402437b28a2bf2c 11 7 1 The simplest of style files Our simple style file contains just one line echo changeset rev rev n gt rev hg log 11 style rev rev 3 This tells Mercurial if you re printing a changeset use the text on the right as the template 11 7 2 Style file syntax The syntax rules for a style file are simple The file is processed one line at a time Leading and trailing white space are ignored Empty lines are skipped oo If a line starts with either of the characters 4 or the entire line is treated as a comment and skipped as if empty A line starts with a keyword This must start with an alphabetic character or underscore and can subsequently contain any alphanumeric character or underscore In regexp notation a keyword must match A Za z_ A Za z0 9_ 6699 The next element must be an character which can be preceded or followed by an arbitrary amount of white space If the rest of the line starts and ends with matching quote characters either single or double quote it is treated
226. lowing or forbidding pushes from specific users 10 7 2 bugzilla integration with Bugzilla The bugzilla extension adds a comment to a Bugzilla bug whenever it finds a reference to that bug ID in a commit comment You can install this hook on a shared server so that any time a remote user pushes changes to this server the hook gets run It adds a comment to the bug that looks like this you can configure the contents of the comment see below 1 Changeset aad8b264143a made by Joe User lt joe user domain com gt in 2 the frobnitz repository refers to this bug 4 For complete details see s http hg domain com frobnitz cmd changeset node aad8b264143a 7 Changeset description 8 Fix bug 10483 by guarding against some NULL pointers The value of this hook is that it automates the process of updating a bug any time a changeset refers to it If you configure the hook properly it makes it easy for people to browse straight from a Bugzilla bug to a changeset that refers to that bug You can use the code in this hook as a starting point for some more exotic Bugzilla integration recipes Here are a few possibilities e Require that every changeset pushed to the server have a valid bug ID in its commit comment In this case you d want to configure the hook as a pret xncommit hook This would allow the hook to reject changes that didn t contain bug IDs e Allow incoming changesets to automatically modify the state of a b
227. lp a single user to manage revisions of a single file Over the past few decades the scope of revision control tools has expanded greatly they now manage multiple files and help multiple people to work together The best modern revision control tools have no problem coping with thousands of people working together on projects that consist of hundreds of thousands of files 1 1 1 Why use revision control There are a number of reasons why you or your team might want to use an automated revision control tool for a project e It will track the history and evolution of your project so you don t have to For every change you ll have a log of who made it why they made it when they made it and what the change was e When you re working with other people revision control software makes it easier for you to collaborate For example when people more or less simultaneously make potentially incompatible changes the software will help you to identify and resolve those conflicts e It can help you to recover from mistakes If you make a change that later turns out to be in error you can revert to an earlier version of one or more files In fact a really good revision control tool will even help you to efficiently figure out exactly when a problem was introduced see section 9 5 for details e It will help you to work simultaneously on and manage the drift between multiple versions of your project Most of these reasons are equally valid at l
228. mand every few seconds with any resulting timestamps correspondingly spread out my automated example scripts run many commands in one second As an instance of this several consecutive commits in an example can show up as having occurred during the same second You can see this occur in the bisect example in section 9 5 for instance So when you re reading examples don t place too much weight on the dates or times you see in the output of commands But do be confident that the behaviour you re seeing is consistent and reproducible 0 3 Colophon this book is Free This book is licensed under the Open Publication License and is produced entirely using Free Software tools It is typeset with IATRX illustrations are drawn and rendered with Inkscape The complete source code for this book is published as a Mercurial repository at http hg serpentine com mercurial book Chapter 1 Introduction 1 1 About revision control Revision control is the process of managing multiple versions of a piece of information In its simplest form this is something that many people do by hand every time you modify a file save it under a new name that contains a number each one higher than the number of the preceding version Manually managing multiple versions of even a single file is an error prone task though so software tools to help automate this process have long been available The earliest automated revision control tools were intended to he
229. mation See also incoming section 10 9 3 prechangegroup section 10 9 5 pretxnchangegroup section 10 9 9 10 9 2 commit after a new changeset is created This hook is run after a new changeset has been created Parameters to this hook node A changeset ID The changeset ID of the newly committed changeset parentl A changeset ID The changeset ID of the first parent of the newly committed changeset parent2 A changeset ID The changeset ID of the second parent of the newly committed changeset See also precommit section 10 9 6 pretxncommit section 10 9 10 10 9 3 incoming after one remote changeset is added This hook is run after a pre existing changeset has been added to the repository for example via a hg push Ifa group of changesets was added in a single operation this hook is called once for each added changeset You can use this hook for the same purposes as the changegroup hook section 10 9 1 it s simply more conve nient sometimes to run a hook once per group of changesets while other times it s handier once per changeset Parameters to this hook 122 node A changeset ID The ID of the newly added changeset source A string The source of these changes See section 10 8 3 for details url A URL The location of the remote repository if known See section 10 8 3 for more information See also changegroup section 10 9 1 prechangegroup section 10 9 5 pretxnchangegroup section 10 9 9 10 9
230. me something that I can t figure out with a quick glance at the output of hg log patch 19 2 7 4 Aborting a commit If you decide that you don t want to commit while in the middle of editing a commit message simply exit from your editor without saving the file that it s editing This will cause nothing to happen to either the repository or the working directory If we run the hg commit command without any arguments it records all of the changes we ve made as reported by hg status and hg diff 2 7 5 Admiring our new handiwork Once we ve finished the commit we can use the hg tip command to display the changeset we just created This command produces output that is identical to hg log but it only displays the newest revision in the repository hg tip vp changeset 5 fal321bf0c80 tag tip user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 05 50 2007 0000 files hello c description Added an extra line of output diff r b57 9a090b62 r fal321bf0c80 hello c a hello c Tue Sep 06 15 43 07 2005 0700 b hello c Sun Jun 17 18 05 50 2007 0000 8 5 8 6 int main int argc char argv int main int argc char argv printf hello world printf hello again n return 0 We refer to the newest revision in the repository as the tip revision or simply the tip 2 8 Sharing changes We mentioned earlier that repositor
231. ment or presence of patches This presents the interesting possibility of managing the contents of the patch directory as a Mercurial repository in its own right This can be a useful way to work For example you can work on a patch for a while hg qrefresh it then hg commit the current state of the patch This lets you roll back to that version of the patch later on 149 20 21 22 23 24 25 26 27 28 29 30 31 32 fi se ch ta ta us da ch ta ta ta us da su He Se Se He e 0 di rst patch cond patch angeset g g er te summary angeset g g g er te mary hg export HG changese dev null b other c hg qapplied hg log r qbase qtip 1 3 76c4bf 9538 first patch qbase Bryan O Sullivan lt bos serpentine com gt Sun Jun 17 18 03 54 2007 0000 patch queue first patch 2 cef6f3dalf9f atip second patch tip Bryan O Sullivan lt bos serpentine com gt Sun Jun 17 18 03 55 2007 0000 patch queue second patch sec t pa ee 0 0 1 1 ee double u ond patch tch User Bryan O Sullivan lt bos serpentine com gt Date 1182103435 0 ode ID cef6f3dalf9fb6c151820d477957530780b621e5 Parent 3f76c4bf 95389e7963356db5d0c9bbe755c2 764 patch queue second patch ff r 3 76c4bf9538 r cef6f3dalf9f other c Thu Jan 01 00 00 00 1970 0000 Sun Jun 17 18 03 55 2007 0000 You can th
232. most of the time When I m applying the patches on top of a tree where the patches are already present I can turn this patch off and the patches that follow it will apply cleanly Patches that are finished but not yet submitted have no guards If I m applying the patch stack to a copy of the upstream tree I don t need to enable any guards in order to get a reasonably safe source tree Those patches that need reworking before being resubmitted are guarded with rework For those patches that are still under development I use devel A backport patch may have several guards one for each version of the kernel to which it applies For example a patch that backports a piece of code to 2 6 9 will have a 2 6 9 guard This variety of guards gives me considerable flexibility in qdetermining what kind of source tree I want to end up with For most situations the selection of appropriate guards is automated during the build process but I can manually tune the guards to use for less common circumstances 160 N 13 8 1 The art of writing backport patches Using MQ writing a backport patch is a simple process All such a patch has to do is modify a piece of code that uses a kernel feature not present in the older version of the kernel so that the driver continues to work correctly under that older version A useful goal when writing a good backport patch is to make your code look as if it was written for the older version of the kerne
233. n abort rollback completed hg commit A m long enough Figure 10 4 A hook that forbids overly short commit messages 10 6 2 Checking for trailing whitespace An interesting use of a commit related hook is to help you to write cleaner code A simple example of cleaner code is the dictum that a change should not add any new lines of text that contain trailing whitespace Trailing whitespace is a series of space and tab characters at the end of a line of text In most cases trailing whitespace is unnecessary invisible noise but it is occasionally problematic and people often prefer to get rid of it You can use either the precommit or pretxncommit hook to tell whether you have a trailing whitespace problem If you use the precommit hook the hook will not know which files you are committing so it will have to check every modified file in the repository for trailing white space If you want to commit a change to just the file foo but the file bar contains trailing whitespace doing a check in the precommit hook will prevent you from committing foo due to the problem with bar This doesn t seem right Should you choose the pret xncommit hook the check won t occur until just before the transaction for the commit completes This will allow you to check for problems only the exact files that are being committed However if you entered the commit message interactively and the hook fails the transaction will roll back
234. n an 80 column fixed font window fi1176 Any text Wrap the text to fit in 76 columns firstline Any text Yield the first line of text without any trailing newlines hgdate date keyword Render the date as a pair of readable numbers Yields a string like 1157407993 25200 isodate date keyword Render the date as a text string in ISO 8601 format Yields a string like 2006 09 04 15 13 13 0700 131 obfuscate Any text but most useful for the author keyword Yield the input text rendered as a sequence of XML entities This helps to defeat some particularly stupid screen scraping email harvesting spambots person Any text but most useful for the author keyword Yield the text before an email address For example Bryan O Sullivan lt bos serpentine com gt becomes Bryan O Sullivan rfc822date date keyword Render a date using the same format used in email headers Yields a string like Mon 04 Sep 2006 15 13 13 short Changeset hash Yield the short form of a changeset hash 1 e a 12 byte hexadecimal string shortdate date keyword Render the year month and day of the date Yields a string like 2006 09 04 strip Any text Strip all leading and trailing whitespace from the string tabindent Any text Yield the text with every line except the first starting with a tab character urlescape Any text Escape all characters that are considered special by URL parsers For example foo bar becomes
235. n unmodified form hg revert a 5 cat a a hg status 5 2 3 Aside why tell Mercurial explicitly to remove a file You might wonder why Mercurial requires you to explicitly tell it that you are deleting a file Early during the development of Mercurial it let you delete a file however you pleased Mercurial would notice the absence of the file automatically when you next ran a hg commit and stop tracking the file In practice this made it too easy to accidentally remove a file without noticing 5 2 4 Useful shorthand adding and removing files in one step Mercurial offers a combination command hg addremove that adds untracked files and marks missing files as removed hg init addremove example cd addremove example echo a gt a echo b gt b hg addremove adding a adding b The hg commit command also provides a A option that performs this same add and remove immediately followed by a commit echo c gt c hg commit A m Commit with addremove adding c 5 3 Copying files Mercurial provides a hg copy command that lets you make a new copy of a file When you copy a file using this command Mercurial makes a record of the fact that the new file is a copy of the original file It treats these copied files specially when you merge your work with someone else s 5 3 1 The results of copying during a merge What happens during a merge is tha
236. napplied patches while the a option to hg apop causes it to pop all applied patches For some more ways to push and pop many patches see section 12 7 below 142 echo line 3 gt gt filel hg status filel hg qrefresh hg tip style compact patch qtip first patch tip qbase 403df3ef5eca 2007 06 17 18 03 0000 bos patch queue first patch Rx ur uu diff r 93d314596e46 r 403df3ef5ecd filel a filel Sun Jun 17 18 03 56 2007 0000 b filel Sun Jun 17 18 03 57 2007 0000 1 1 1 3 line 1 line 1 line 2 line 3 Figure 12 7 Refresh a patch many times to accumulate changes 12 5 6 Safety checks and overriding them Several MQ commands check the working directory before they do anything and fail if they find any modifications They do this to ensure that you won t lose any changes that you have made but not yet incorporated into a patch Figure 12 13 illustrates this the hg qnew command will not create a new patch if there are outstanding changes caused in this case by the hg add of file3 Commands that check the working directory all take an I know what I m doing option which is always named f The exact meaning of f depends on the command For example hg qnew will incorporate any outstanding changes into the new patch it creates but hg qpop will revert modifications to any files affected by the patch that it is popping Be sure to read the d
237. ncorrupted sections of the revlog both before and after the corrupted section This would not be possible with a delta only storage model 4 3 Revision history branching and merging Every entry in a Mercurial revlog knows the identity of its immediate ancestor revision usually referred to as its parent In fact a revision contains room for not one parent but two Mercurial uses a special hash called the null ID to represent the idea there is no parent here This hash is simply a string of zeroes In figure 4 4 you can see an example of the conceptual structure of a revlog Filelogs manifests and changelogs all have this same structure they differ only in the kind of data stored in each delta or snapshot The first revision in a revlog at the bottom of the image has the null ID in both of its parent slots For a normal revision its first parent slot contains the ID of its parent revision and its second contains the null ID indicating that the revision has only one real parent Any two revisions that have the same parent ID are branches A revision that represents a merge between branches has two normal revision IDs in its parent slots 4 4 The working directory In the working directory Mercurial stores a snapshot of the files from the repository as of a particular changeset The working directory knows which changeset it contains When you update the working directory to contain a particular changeset Mercuri
238. nded for a single target The trouble with this approach is that you must maintain iron discipline in the flow of changes between repositories A new feature or bug fix must start life in a pristine repository then percolate out to every backport repository Backport changes are more limited in the branches they should propagate to a backport change that is applied to a branch where it doesn t belong will probably stop the driver from compiling The second is to maintain a single source tree filled with conditional statements that turn chunks of code on or off depending on the intended target Because these ifdefs are not allowed in the Linux kernel tree a manual or 156 automatic process must be followed to strip them out and yield a clean tree A code base maintained in this fashion rapidly becomes a rat s nest of conditional blocks that are difficult to understand and maintain Neither of these approaches is well suited to a situation where you don t own the canonical copy of a source tree In the case of a Linux driver that is distributed with the standard kernel Linus s tree contains the copy of the code that will be treated by the world as canonical The upstream version of my driver can be modified by people I don t know without me even finding out about it until after the changes show up in Linus s tree These approaches have the added weakness of making it difficult to generate well formed patches to submit u
239. ne that instead This is much faster than cloning over the network and cloning a local repository uses less disk space in most cases too cd hg clone hello my hello 2 files updated 0 files merged 0 files removed 0 files unresolved cd my hello As an aside it s often good practice to keep a pristine copy of a remote repository around which you can then make temporary clones of to create sandboxes for each task you want to work on This lets you work on multiple tasks in parallel each isolated from the others until it s complete and you re ready to integrate it back Because local clones are so cheap there s almost no overhead to cloning and destroying repositories whenever you want In our my hello repository we have a file hello c that contains the classic hello world program Let s use the ancient and venerable sed command to edit this file so that it prints a second line of output I m only using sed to do this because it s easy to write a scripted example this way Since you re not under the same constraint you probably won t want to use sed simply use your preferred text editor to do the same thing sed i printf a tprintf hello again n hello c Mercurial s hg status command will tell us what Mercurial knows about the files in the repository ls Makefile hello c hg status M hello c The hg status command prints no output fo
240. ne of output And the hg push command does the actual push hg push hello push pushing to hello push searching for changes adding changesets adding manifests adding file changes added 1 changesets with 1 changes to 1 files As with hg pull the hg push command does not update the working directory in the repository that it s pushing changes into Unlike hg pull hg push does not provide a u option that updates the other repository s working directory What happens if we try to pull or push changes and the receiving repository already has those changes Nothing too exciting hg push hello push pushing to hello push searching for changes no changes found 2 8 4 Sharing changes over a network The commands we have covered in the previous few sections are not limited to working with local repositories Each works in exactly the same fashion over a network connection simply pass in a URL instead of a local path hg outgoing http hg serpentine com tutorial hello comparing with http hg serpentine com tutorial hello searching for changes changeset 5 fal321bf0c80 23 tag tip user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 05 50 2007 0000 summary Added an extra line of output In this example we can see what changes we could push to the remote repository but the repository is understandably not set up t
241. ng a local administrator to modify the repository Parameters to this hook source A string The source of these changes See section 10 8 3 for details url A URL The location of the remote repository if known See section 10 8 3 for more information See also changegroup section 10 9 1 incoming section 10 9 3 pret xnchangegroup section 10 9 9 10 9 6 precommit before starting to commit a changeset This hook is run before Mercurial begins to commit a new changeset It is run before Mercurial has any of the metadata for the commit such as the files to be committed the commit message or the commit date One use for this hook is to disable the ability to commit new changesets while still allowing incoming changesets Another is to run a build or test and only allow the commit to begin if the build or test succeeds Parameters to this hook parentl A changeset ID The changeset ID of the first parent of the working directory parent2 A changeset ID The changeset ID of the second parent of the working directory If the commit proceeds the parents of the working directory will become the parents of the new changeset See also commit section 10 9 2 pretxncommit section 10 9 10 123 10 9 7 preoutgoing before starting to propagate changesets This hook is invoked before Mercurial knows the identities of the changesets to be transmitted One use for this hook is to prevent changes from being transmitted to another repo
242. ng open source software developers Quilt manages a stack of patches on top of a directory tree To begin you tell quilt to manage a directory tree and tell it which files you want to manage it stores away the names and contents of those files To fix a bug you create a new patch using a single command edit the files you need to fix then refresh the patch The refresh step causes quilt to scan the directory tree it updates the patch with all of the changes you have made You can create another patch on top of the first which will track the changes required to modify the tree from tree with one patch applied to tree with two patches applied You can change which patches are applied to the tree If you pop a patch the changes made by that patch will vanish from the directory tree Quilt remembers which patches you have popped though so you can push a popped patch again and the directory tree will be restored to contain the modifications in the patch Most importantly you can run the refresh command at any time and the topmost applied patch will be updated This means that you can at any time change both which patches are applied and what modifications those patches make Quilt knows nothing about revision control tools so it works equally well on top of an unpacked tarball or a Subversion repository 12 2 2 From patchwork quilt to Mercurial Queues In mid 2005 Chris Mason took the features of quilt an
243. ng the history of a patch If you re developing a set of patches over a long time it s a good idea to maintain them in a repository as discussed in section 12 11 If you do so you ll quickly discover that using the hg diff command to look at the history of changes to a patch is unworkable This is in part because you re looking at the second derivative of the real code a diff of a diff but also because MQ adds noise to the process by modifying time stamps and directory names when it updates a patch However you can use the extdiff extension which is bundled with Mercurial to turn a diff of two versions of a patch into something readable To do this you will need a third party package called patchutils Wau This provides a command named interdiff which shows the differences between two diffs as a diff Used on two versions of the same diff 1t generates a diff that represents the diff from the first to the second version You can enable the extdiff extension in the usual way by adding a line to the extensions section of your hgrc extensions extdiff The interdiff command expects to be passed the names of two files but the extdiff extension passes the program it runs a pair of directories each of which can contain an arbitrary number of files We thus need a small program that will run interdiff on each pair of files in these two directories This program is available as hg interdiff in the examples directory
244. ngesets Simplified a little the merging process goes like this for every file in the manifests of both changesets e If neither changeset has modified a file do nothing with that file 39 e If one changeset has modified a file and the other hasn t create the modified copy of the file in the working directory e If one changeset has removed a file and the other hasn t or has also deleted it delete the file from the working directory e If one changeset has removed a file but the other has modified the file ask the user what to do keep the modified file or remove it e If both changesets have modified a file invoke an external merge program to choose the new contents for the merged file This may require input from the user e If one changeset has modified a file and the other has renamed or copied the file make sure that the changes follow the new name of the file There are more details merging has plenty of corner cases but these are the most common choices that are involved in a merge As you can see most cases are completely automatic and indeed most merges finish automatically without requiring your input to resolve any conflicts When you re thinking about what happens when you commit after a merge once again the working directory is the changeset I m about to commit After the hg merge command completes the working directory has two parents these will become the parents of the new changeset Me
245. not currently provide a filter that counts the number of items it is passed It took me no more than a minute or two of work to replace literal text from an example of Subversion s output with some keywords and filters to give the template above The style file simply refers to the template cat svn style Reader 6S 22 797997291 O RO a eS n n changeset svn template We could have included the text of the template file directly in the style file by enclosing it in quotes and replacing the newlines with n sequences but it would have made the style file too difficult to read Readability is a good guide when you re trying to decide whether some text belongs in a style file or in a template file that the style file points to If the style file will look too big or cluttered if you insert a literal piece of text drop it into a template instead 136 Chapter 12 Managing change with Mercurial Queues 12 1 The patch management problem Here is a common scenario you need to install a software package from source but you find a bug that you must fix in the source before you can start using the package You make your changes forget about the package for a while and a few months later you need to upgrade to a newer version of the package If the newer version of the package still has the bug you must extract your fix from the older source tree and apply it against the newer version This is a tedious task and it
246. ntine com gt 86 date Sun Jun 17 18 03 43 2007 0000 summary Third commit If we go back to the foo branch and then run hg update it will keep us on foo not move us to the tip of bar hg update foo files updated 0 files merged 1 files removed 0 files unresolved hg update O GO UY files updated 0 files merged 0 files removed 0 files unresolved Committing a new change on the foo branch introduces a new head echo something gt somefile hg commit A m New file adding somefile hg heads changeset 3 5b570081d902 branch foo tag tip parent 1 3af68d4362fb user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 43 2007 0000 summary New file changeset 2 4 00549a48el branch bar user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 43 2007 0000 summary Third commit We can no longer update from foo to bar without going sideways in history so Mercurial forces us to provide the C option to hg update hg update bar abort update spans branches use hg merge or hg update C to lose changes hg update C bar 1 files updated 0 files merged 1 files removed 0 files unresolved 8 7 Branch names and merging As you ve probably noticed merges in Mercurial are not symmetrical Let s say our repository has two heads 17 and 23 If I hg update to 17 and then hg merge with
247. ntine com gt date Sun Jun 17 18 04 00 2007 0000 summary Added tag v1 1 for changeset a78de6396931 8 1 1 Handling tag conflicts during a merge You won t often need to care about the hgtags file but it sometimes makes its presence known during a merge The format of the file is simple it consists of a series of lines Each line starts with a changeset hash followed by a space followed by the name of a tag If you re resolving a conflict in the hgtags file during a merge there s one twist to modifying the hgtags file when Mercurial is parsing the tags in a repository it never reads the working copy of the hgtags file Instead it reads the most recently committed revision of the file An unfortunate consequence of this design is that you can t actually verify that your merged hgtags file is correct until after you ve committed a change So if you find yourself resolving a conflict on hgtags during a merge be sure to run hg tags after you commit If it finds an error in the hgtags file it will report the location of the error which you can then fix and commit You should then run hg tags again just to be sure that your fix is correct 8 1 2 Tags and cloning You may have noticed that the hg clone command has a r option that lets you clone an exact copy of the repository as of a particular changeset The new clone will not contain any project history that comes after the revision you specified Th
248. o let anonymous users push to it hg push http hg serpentine com tutorial hello pushing to http hg serpentine com tutorial hello searching for changes ssl required 24 Chapter 3 A tour of Mercurial merging work We ve now covered cloning a repository making changes in a repository and pulling or pushing changes from one repository into another Our next step is merging changes from separate repositories 3 1 Merging streams of work Merging is a fundamental part of working with a distributed revision control tool e Alice and Bob each have a personal copy of a repository for a project they re collaborating on Alice fixes a bug in her repository Bob adds a new feature in his They want the shared repository to contain both the bug fix and the new feature e I frequently work on several different tasks for a single project at once each safely isolated in its own repository Working this way means that I often need to merge one piece of my own work with another Because merging is such a common thing to need to do Mercurial makes it easy Let s walk through the process We ll begin by cloning yet another repository see how often they spring up and making a change in it cd hg clone hello my new hello 2 files updated 0 files merged 0 files removed 0 files unresolved cd my new hello sed i printf i tprintf once more hello n hello c hg commit m A new hello for
249. o obtain much of the information that a hook requires by using the Mercurial API than by running Mercurial commands If you are comfortable with Python or require high performance writing your hooks in Python may be a good choice However when you have a straightforward hook to write and you don t need to care about performance probably the majority of hooks a shell script is perfectly fine 111 10 5 2 Hook parameters Mercurial calls each hook with a set of well defined parameters In Python a parameter is passed as a keyword argument to your hook function For an external program a parameter is passed as an environment variable Whether your hook is written in Python or as a shell script the hook specific parameter names and values will be the same A boolean parameter will be represented as a boolean value in Python but as the number 1 for true or 0 for false as an environment variable for an external hook If a hook parameter is named foo the keyword argument for a Python hook will also be named foo while the environment variable for an external hook will be named HG_FOO 10 5 3 Hook return values and activity control A hook that executes successfully must exit with a status of zero if external or return boolean false if in process Failure is indicated with a non zero exit status from an external hook or an in process hook returning boolean true If an in process hook raises an exception the hook is
250. oExec lt Limit GET POST OPTIONS gt Order allow deny Allow from all lt Limit gt lt LimitExcept GET POST OPTIONS gt Order deny allow Deny from all lt LimitExcept gt lt Directory gt If you find a similar looking Directory group in your Apache configuration the directive to look at inside it is Options Add ExecCGI to the end of this list if it s missing and restart the web server If you find that Apache serves you the text of the CGI script instead of executing it you may need to either uncomment if already present or add a directive like this AddHandler cgi script cgi 68 The next possibility is that you might be served with a colourful Python backtrace claiming that it can t import a mercurial related module This is actually progress The server is now capable of executing your CGI script This error is only likely to occur if you re running a private installation of Mercurial instead of a system wide version Remember that the web server runs the CGI program without any of the environment variables that you take for granted in an interactive session If this error happens to you edit your copy of hgweb cgi and follow the directions inside it to correctly set your PYTHONPATH environment variable Finally you are certain to by served with another colourful Python backtrace this one will complain that it can t find path to repository Edit your hgweb cgi script and replace the path to repos
251. ocumentation for a command s f option before you use it 12 5 7 Working on several patches at once The hg grefresh command always refreshes the topmost applied patch This means that you can suspend work on one patch by refreshing it pop or push to make a different patch the top and work on that patch for a while Here s an example that illustrates how you can use this ability Let s say you re developing a new feature as two patches The first is a change to the core of your software and the second layered on top of the first changes the user interface to use the code you just added to the core If you notice a bug in the core while you re working on the UI patch it s easy to fix the core Simply hg qrefresh the UI patch to save your in progress changes and hg apop down to the core patch Fix the core bug hg qrefresh the core patch and hg qpush back to the UI patch to continue where you left off 12 6 More about patches MQ uses the GNU patch command to apply patches so it s helpful to know a few more detailed aspects of how patch works and about patches themselves 12 6 1 The strip count If you look at the file headers in a patch you will notice that the pathnames usually have an extra component on the front that isn t present in the actual path name This is a holdover from the way that people used to generate patches 143 20 21 22 23 24 25 26 27 28
252. ol n aa e a a 44654 A bee Pees bees 8 2 A tour of Mercurial the basics 10 2 1 Installs Mercurial On Your Syst m a o e socn a ko a E a a Sw a 10 2 LIUR eci eR EA RO A EA ke ae ee Rha e a a ee A 10 22 OLMIS oir e eS A Ege bow A Be Bley Boe i 10 DLI MacOSX lt 64 44 02 Cru 0 4 24 RRR ERA wee eee ee bee Ee eS 11 Bil ADO 2 hos s adie a eer Goa 2 ee a boo A ewe oie Bale Hae sd Le ewes 11 2 MSG Stated sos ge ee Se eR ok eh Eee Ba ee ee ae ee eee oS ai 11 221 Bult mpelp 23 4 pe 240 25 54946 PERE A BE EA EE RRS N 11 2a Working WIN arepas occ SA A ae eGR Re WE RES Bee a Boe 12 231 Making a localcopy obarepostaty lt lt 4 06 44 24 Ged Ve BENS Ea POSE Bees S 12 2 02 WHATS UM ATEPOSIOLY cosa a ee a a te Re we lt BOS 12 24 A tobr throuphimstory s s cesme mekon ee ee Pew eee E ea A 13 2 4 1 Changesets revisions and talking to other people o 14 24 2 Viewing sp cific revisions gt eec ceses Me ee BAe eee ee es 14 243 More detailed information risa eo a GR ORS As 16 29 Allabout command Gpuons ia 8 2 bea ee Rew da ee eS 16 20 Making and reviewing Changes oeo u coe Tar m a EEE EEE SAA we LEER EE DAS 17 2 7 Recording changes im a new changeset o osos marisma a A a a Be 24 Ll SEIS UPA USCMAM io e eee hee ee Ba 2 22 Witing commit MESSAGE s c ocurrio sa A ee 243 WII a Pood commit message s v o coesa ee E RACER ee s A LA IE MECO DARA A Hee Ee Bees eae RS Zro Admine QUE new handiwork
253. om the stable branch The stable branch remains unaffected by these changes 60 6 2 5 Feature branches For larger projects an effective way to manage change is to break up a team into smaller groups Each group has a shared branch of its own cloned from a single master branch used by the entire project People working on an individual branch are typically quite isolated from developments on other branches Figure 6 1 Feature branches When a particular feature is deemed to be in suitable shape someone on that feature team pulls and merges from the master branch into the feature branch then pushes back up to the master branch 6 2 6 The release train Some projects are organised on a train basis a release is scheduled to happen every few months and whatever features are ready when the train is ready to leave are allowed in This model resembles working with feature branches The difference is that when a feature branch misses a train someone on the feature team pulls and merges the changes that went out on that train release into the feature branch and the team continues its work on top of that release so that their feature can make the next release 6 2 7 The Linux kernel model The development of the Linux kernel has a shallow hierarchical structure surrounded by a cloud of apparent chaos Because most Linux developers use git a distributed revision control tool with capabilities similar to Mercurial it s u
254. on control data to where it s actually needed Collaboration over the Internet has moved from constrained by technology to a matter of choice and consensus Modern tools can operate offline indefinitely and autonomously with a network connection only needed when syncing changes with another repository 1 4 A few of the advantages of distributed revision control Even though distributed revision control tools have for several years been as robust and usable as their previous generation counterparts people using older tools have not yet necessarily woken up to their advantages There are a number of ways in which distributed tools shine relative to centralised ones For an individual developer distributed tools are almost always much faster than centralised tools This is for a simple reason a centralised tool needs to talk over the network for many common operations because most metadata is stored in a single copy on the central server A distributed tool stores all of its metadata locally All else being equal talking over the network adds overhead to a centralised tool Don t underestimate the value of a snappy responsive tool you re going to spend a lot of time interacting with your revision control software Distributed tools are indifferent to the vagaries of your server infrastructure again because they replicate metadata to so many locations If you use a centralised system and your server catches fire you d better hope that your ba
255. on stored in the changelog Each revision of the changelog contains a pointer to a single revision of the manifest A revision of the manifest stores a pointer to a single revision of each filelog tracked when that changeset was created These relationships are illustrated in figure 4 2 Figure 4 2 Metadata relationships As the illustration shows there is not a one to one relationship between revisions in the changelog manifest or filelog If the manifest hasn t changed between two changesets the changelog entries for those changesets will point to the same revision of the manifest If a file that Mercurial tracks hasn t changed between two changesets the entry for that file in the two revisions of the manifest will point to the same revision of its filelog 4 2 Safe efficient storage The underpinnings of changelogs manifests and filelogs are provided by a single structure called the revlog 36 4 2 1 Efficient storage The revlog provides efficient storage of revisions using a delta mechanism Instead of storing a complete copy of a file for each revision it stores the changes needed to transform an older revision into the new revision For many kinds of file data these deltas are typically a fraction of a percent of the size of a full copy of a file Some obsolete revision control systems can only work with deltas of text files They must either store binary files as complete snapshots or encoded into a text representation b
256. onds Clearly MQ is well suited to working in large trees but there are a few tricks you can use to get the best perfor mance of it 147 First of all try to batch operations together Every time you run hg qpush or hg apop these com mands scan the working directory once to make sure you haven t made some changes and then forgotten to run hg grefresh On a small tree the time that this scan takes is unnoticeable However on a medium sized tree containing tens of thousands of files it can take a second or more The hg qpush and hg qpop commands allow you to push and pop multiple patches at a time You can identify the destination patch that you want to end up at When you hg qpush with a destination specified 1t will push patches until that patch is at the top of the applied stack When you hg qpop to a destination MQ will pop patches until the destination patch is at the top You can identify a destination patch using either the name of the patch or by number If you use numeric address ing patches are counted from zero this means that the first patch is zero the second is one and so on 12 8 Updating your patches when the underlying code changes It s common to have a stack of patches on top of an underlying repository that you don t modify directly If you re working on changes to third party code or on a feature that is taking longer to develop than the rate of change o
257. ong the same lines some commands normally print file names relative to the root of the repository even if you re invoking them from a subdirectory Such a command will print file names relative to your subdirectory if you give it explicit names Here we re going to run hg status from a subdirectory and get it to operate on the entire working directory while printing file names relative to our subdirectory by passing it the output of the hg root command hg status COPYING README examples simple py MANIFEST in examples performant py setup py src main py src watcher _watcher c src watcher watcher py src xyzzy txt hg status hg root COPYING README examples simple py MANIFEST in setup py main py watcher _watcher c watcher watcher py xyzzy txt VV VY Vw Vv PP PN vv vv dy vu wv PP Pm examples performant py 7 3 Telling you what s going on The hg add example in the preceding section illustrates something else that s helpful about Mercurial commands If acommand operates on a file that you didn t name explicitly on the command line it will usually print the name of the file so that you will not be surprised what s going on 74 The principle here is of least surprise If you ve exactly named a file on the command line there s no point in repeating it back at you If Mercurial is acting on a file implicitly because you provided no names or a directory or a patt
258. oning a copy of this repository They can pull changes from it whenever they need to and some perhaps all developers have permission to push a change back when they re ready for other people to see it Under this model it can still often make sense for people to pull changes directly from each other without going through the central repository Consider a case in which I have a tentative bug fix but I am worried that if I were to publish it to the central repository it might subsequently break everyone else s trees as they pull it To reduce the potential for damage I can ask you to clone my repository into a temporary repository of your own and test it This lets us put off publishing the potentially unsafe change until it has had a little testing In this kind of scenario people usually use the ssh protocol to securely push changes to the central repository as documented in section 6 5 It s also usual to publish a read only copy of the repository over HTTP using CGI as in section 6 6 Publishing over HTTP satisfies the needs of people who don t have push access and those who want to use web browsers to browse the repository s history 6 2 4 Working with multiple branches Projects of any significant size naturally tend to make progress on several fronts simultaneously In the case of soft ware it s common for a project to go through periodic official releases A release might then go into maintenance mode for a while after
259. op which the patches apply should be a snapshot of a very recent upstream tree This best facilitates the development of patches that can easily be submitted upstream with few or no modifications 13 7 Dividing up the series file I categorise the patches in the series file into a number of logical groups Each section of like patches begins with a block of comments that describes the purpose of the patches that follow The sequence of patch groups that I maintain follows The ordering of these groups is important I ll describe why after I introduce the groups 159 The accepted group Patches that the development team has submitted to the maintainer of the Infiniband subsystem and which he has accepted but which are not present in the snapshot that the tiny repository is based on These are read only patches present only to transform the tree into a similar state as it is in the upstream maintainer s repository The rework group Patches that I have submitted but that the upstream maintainer has requested modifications to before he will accept them The pending group Patches that I have not yet submitted to the upstream maintainer but which we have finished working on These will be read only for a while If the upstream maintainer accepts them upon submission I 11 move them to the end of the accepted group If he requests that I modify any 111 move them to the beginning of the rework group
260. ormance advantage you ll see The inotify daemon makes status operations almost instantaneous on repositories of all sizes If you like you can manually start a status daemon using the hg inserve command This gives you slightly finer control over how the daemon ought to run This command will of course only be available when the inotify extension is enabled When you re using the inot ify extension you should notice no difference at all in Mercurial s behaviour with the sole exception of status related commands running a whole lot faster than they used to You should specifically expect that commands will not print different output neither should they give different results If either of these situations occurs please report a bug 14 2 Flexible diff support with the extdi ff extension Mercurial s built in hg diff command outputs plaintext unified diffs hg diff diff r 271c4b32e6fb myfile a myfile Sun Jun 17 18 03 49 2007 0000 b myfile Sun Jun 17 18 03 49 2007 0000 1 1 1 2 QQ The first line The first line The second line If you would like to use an external tool to display modifications you ll want to use the ext diff extension This will let you use for example a graphical diff tool The extdiff extension is bundled with Mercurial so it s easy to set up In the extensions section of your hgrc simply add a one line entry to enable the extension 166 extensions
261. ory it will automatically hg add every patch that you create and import Finally MQ provides a shortcut command hg acommit that runs hg commit in the hg patches directory This saves some cumbersome typing 12 11 2 A few things to watch out for MQ s support for working with a repository full of patches is limited in a few small respects MQ cannot automatically detect changes that you make to the patch directory If you hg pull manually edit or hg update changes to patches or the series file you will have to hg apop a and then hg qpush a in the underlying repository to see those changes show up there If you forget to do this you can confuse MQ s idea of which patches are applied 12 12 Third party tools for working with patches Once you ve been working with patches for a while you ll find yourself hungry for tools that will help you to under stand and manipulate the patches you re dealing with The diffstat command Dic generates a histogram of the modifications made to each file in a patch It provides a good way to get a sense of a patch which files it affects and how much change it introduces to each file and as a whole I find that it s a good idea to use diffstat s p option as a matter of course as otherwise it will try to do clever things with prefixes of file names that inevitably confuse at least me The patchutils package Wau is invaluable It provi
262. ository The reason for this is simple a hook is a completely arbitrary piece of executable code It runs under your user identity with your privilege level on your machine It would be extremely reckless for any distributed revision control system to implement revision controlled hooks as this would offer an easily exploitable way to subvert the accounts of users of the revision control system Since Mercurial does not propagate hooks if you are collaborating with other people on a common project you should not assume that they are using the same Mercurial hooks as you are or that theirs are correctly configured You should document the hooks you expect people to use In a corporate intranet this is somewhat easier to control as you can for example provide a standard installation of Mercurial on an NFS filesystem and use a site wide hgrc file to define hooks that all users will see However this too has its limits see below 10 2 3 Hooks can be overridden Mercurial allows you to override a hook definition by redefining the hook You can disable it by setting its value to the empty string or change its behaviour as you wish If you deploy a system or site wide hgrc file that defines some hooks you should thus understand that your users can disable or override those hooks 10 2 4 Ensuring that critical hooks are run Sometimes you may want to enforce a policy that you do not want others to be able to work around For example yo
263. oted above the date keyword does not produce human readable output so we must treat it specially This involves using a filter about which more in section 11 6 1 hg log r1 template date date n date 1182103440 00 3 hg log r1 template date date isodate n 4 date 2007 06 17 18 04 0000 N 11 5 Escape sequences Mercurial s templating engine recognises the most commonly used escape sequences in strings When it sees a back slash character it looks at the following character and substitutes the two characters with a single replacement as described below 130 Backslash ASCII 134 n Newline ASCII 12 Xr Carriage return ASCII 15 Xt Tab ASCII 11 Av Vertical tab ASCII 13 Open curly brace ASCII 173 Close curly brace ASCII 175 As indicated above if you want the expansion of a template to contain a literal A or character you must escape it 11 6 Filtering keywords to change their results Some of the results of template expansion are not immediately easy to use Mercurial lets you specify an optional chain of filters to modify the result of expanding a keyword You have already seen a common filter isodate in action above to make a date readable Below is a list of the most commonly used filters that Mercurial supports While some filters can be applied to any text others can only be used in specific ci
264. oth of which are wasteful approaches Mercurial can efficiently handle deltas of files with arbitrary binary contents it doesn t need to treat text as special 4 2 2 Safe operation Mercurial only ever appends data to the end of a revlog file It never modifies a section of a file after it has written it This is both more robust and efficient than schemes that need to modify or rewrite data In addition Mercurial treats every write as part of a transaction that can span a number of files A transaction is atomic either the entire transaction succeeds and its effects are all visible to readers in one go or the whole thing is undone This guarantee of atomicity means that if you re running two copies of Mercurial where one is reading data and one is writing it the reader will never see a partially written result that might confuse it The fact that Mercurial only appends to files makes it easier to provide this transactional guarantee The easier it is to do stuff like this the more confident you should be that it s done correctly 4 2 3 Fast retrieval Mercurial cleverly avoids a pitfall common to all earlier revision control systems the problem of inefficient retrieval Most revision control systems store the contents of a revision as an incremental series of modifications against a snapshot To reconstruct a specific revision you must first read the snapshot and then every one of the revisions between the snapshot and your target rev
265. our bug with a file that contains the text i have a gub for if el gt gt gt gt gt gt gt fi gt buggy _change 22 i 0 i lt 35 i do i buggy_change then echo i have a gub gt myfile i hg commit q A m buggy changeset se echo nothing to see here move along gt myfile i hg commit q A m normal changeset The next thing that we d like to do is figure out how to use the bisect extension We can use Mercurial s normal built in help mechanism for this To use as bad as bad If you bad good help init next reset hg help bisect hg bisect help init reset next good bad Dichotomic search in the DAG of changesets This extension helps to find changesets which cause problems as good Bisect will update your working directory to a revision for testing Once you have performed tests mark the working directory changeset or announce that it has found the bad revision Note bisect expects bad revisions to be descendants of good revisions the problem free state bad and the problematic state good For subcommands see hg bisect help use hg v help bisect to show global options hg bisect help list of subcommands for the bisect extension mark the earliest changeset you know introduces the problem then mark the latest changeset which is free from the problem or good and bisect will either update
266. our idea of I deleted this file looks like every line of this file was deleted in a patch It treats the addition of a file as a diff between the empty file and the file to be added So in a patch your idea of I added this file looks like every line of this file was added It treats a renamed file as the removal of the old name and the addition of the new name This means that renamed files have a big footprint in patches Note also that Mercurial does not currently try to infer when files have been renamed or copied in a patch patch cannot represent empty files so you cannot use a patch to represent the notion I added this empty file to the tree 12 6 4 Beware the fuzz While applying a hunk at an offset or with a fuzz factor will often be completely successful these inexact techniques naturally leave open the possibility of corrupting the patched file The most common cases typically involve applying a patch twice or at an incorrect location in the file If patch or hg qpush ever mentions an offset or fuzz factor you should make sure that the modified files are correct afterwards 146 echo file 3 line 1 gt gt file3 hg qnew add file3 patch hg qnew f add file3 patch abort patch add file3 patch already exists Figure 12 13 Forcibly creating a patch It s often a good idea to refresh a patch that has applied with an offset or fuzz factor refreshing the patch genera
267. oves the current version of the file from the working directory e It stops Mercurial from tracking changes to the file from the time of the next commit Removing a file does not in any way alter the history of the file If you update the working directory to a changeset in which a file that you have removed was still tracked it will reappear in the working directory with the contents it had when you committed that changeset If you then update the working directory to a later changeset in which the file had been removed Mercurial will once again remove the file from the working directory 5 2 2 Missing files Mercurial considers a file that you have deleted but not used hg remove to delete to be missing A missing file is represented with in the output of hg status Mercurial commands will not generally do anything with missing files hg init missing example cd missing example echo a gt a hg add a hg commit m File about to be missing rma hg status a e AO E SE SO AOS MA If your repository contains a file that hg status reports as missing and you want the file to stay gone you can run hg remove after at any time later on to tell Mercurial that you really did mean to remove the file 49 hg remove after a hg status Ra On the other hand if you deleted the missing file by accident use hg revert filename to recover the file It will reappear i
268. p stream In principle Mercurial Queues seems like a good candidate to manage a development scenario such as the above While this is indeed the case MQ contains a few added features that make the job more pleasant 13 2 Conditionally applying patches with guards Perhaps the best way to maintain sanity with so many targets is to be able to choose specific patches to apply for a given situation MQ provides a feature called guards which originates with quilt s guards command that does just this To start off let s create a simple repository for experimenting in hg qinit hg qnew hello patch echo hello gt hello hg add hello hg qrefresh hg qnew goodbye patch echo goodbye gt goodbye hg add goodbye hg qrefresh Wt tf AA Ur OR A UE This gives us a tiny repository that contains two patches that don t have any dependencies on each other because they touch different files The idea behind conditional application is that you can tag a patch with a guard which is simply a text string of your choosing then tell MQ to select specific guards to use when applying patches MQ will then either apply or skip over a guarded patch depending on the guards that you have selected A patch can have an arbitrary number of guards each one is positive apply this patch if this guard is selected or negative skip this patch if this guard is selected A patch with no guards is always applied 13 3 Con
269. pen Publication works or a portion of an Open Publication work with other works or pro grams on the same media shall not cause this license to apply to those other works The aggregate work shall contain a notice specifying the inclusion of the Open Publication material and appropriate copyright notice Severability If any part of this license is found to be unenforceable in any jurisdiction the remaining portions of the license remain in force No warranty Open Publication works are licensed and provided as is without warranty of any kind express or implied including but not limited to the implied warranties of merchantability and fitness for a particular purpose or a warranty of non infringement 180 D 4 Requirements on modified works All modified versions of documents covered by this license including translations anthologies compilations and partial documents must meet the following requirements 1 2 The modified version must be labeled as such The person making the modifications must be identified and the modifications dated Acknowledgement of the original author and publisher if applicable must be retained according to normal aca demic citation practices The location of the original unmodified document must be identified The original author s or authors name s may not be used to assert or imply endorsement of the resulting document without the original author s or authors permission
270. r some files but a line starting with M for hello c Unless you tell it to hg status will not print any output for files that have not been modified The M indicates that Mercurial has noticed that we modified hello c We didn t need to inform Mercurial that we were going to modify the file before we started or that we had modified the file after we were done it was able to figure this out itself It s a little bit helpful to know that we ve modified hello c but we might prefer to know exactly what changes we ve made to it To do this we use the hg diff command 17 hg diff diff r b57 9a090b62 hello c a hello c Tue Sep 06 15 43 07 2005 0700 b hello c Sun Jun 17 18 05 50 2007 0000 8 5 8 6 int main int argc char argv int main int argc char argv printf hello world printf hello again n return 0 2 7 Recording changes in a new changeset We can modify files build and test our changes and use hg status and hg diff to review our changes until we re satisfied with what we ve done and arrive at a natural stopping point where we want to record our work in a new changeset The hg commit command lets us create a new changeset we ll usually refer to this as making a commit or committing 2 7 1 Setting up a username When you try to run hg commit for the first time it is not guaranteed to succeed Mercurial re
271. rcumstances The name of each filter is followed first by an indication of where it can be used then a description of its effect addbreaks Any text Add an XHTML lt br gt tag before the end of every line except the last For example foo nbar becomes foo lt br gt nbar age date keyword Render the age of the date relative to the current time Yields a string like 10 minutes basename Any text but most useful for the files keyword and its relatives Treat the text as a path and return the basename For example foo bar baz becomes baz date date keyword Render a date in a similar format to the Unix date command but with timezone included Yields a string like Mon Sep 04 15 13 13 2006 0700 domain Any text but most useful for the author keyword Finds the first string that looks like an email address and extract just the domain component For example Bryan O Sullivan lt bos serpentine com gt becomes serpentine com email Any text but most useful for the author keyword Extract the first string that looks like an email address For example Bryan O Sullivan lt bos serpentine com gt becomes bos serpentine com escape Any text Replace the special XML XHTML characters s lt and gt with XML entities fi1168 Any text Wrap the text to fit in 68 columns This is useful before you pass text through the tabindent filter and still want it to fit i
272. rcurial s repository storage mechanism is case safe However once they try to hg update the working directory to that changeset or hg merge with that changeset Mercurial will spot the conflict between the two file names that the filesystem would treat as the same and forbid the update or merge from occurring 7 7 3 Fixing a case conflict If you are using Windows or a Mac in a mixed environment where some of your collaborators are using Linux or Unix and Mercurial reports a case folding conflict when you try to hg update or hg merge the procedure to fix the problem is simple Just find a nearby Linux or Unix box clone the problem repository onto it and use Mercurial s hg rename command to change the names of any offending files or directories so that they will no longer cause case folding conflicts Commit this change hg pull or hg push it across to your Windows or MacOS system and hg update to the revision with the non conflicting names The changeset with case conflicting names will remain in your project s history and you still won t be able to hg update your working directory to that changeset on a Windows or MacOS system but you can continue development unimpeded Note Prior to version 0 9 3 Mercurial did not use a case safe repository storage mechanism and did not detect case folding conflicts If you are using an older ver sion of Mercurial on Windows or MacOS I strongly
273. rcurial lets you perform multiple merges but you must commit the results of each individual merge as you go This is necessary because Mercurial only tracks two parents for both revisions and the working directory While 1t would be technically possible to merge multiple changesets at once the prospect of user confusion and making a terrible mess of a merge immediately becomes overwhelming 4 5 Other interesting design features In the sections above I ve tried to highlight some of the most important aspects of Mercurial s design to illustrate that it pays careful attention to reliability and performance However the attention to detail doesn t stop there There are a number of other aspects of Mercurial s construction that I personally find interesting I ll detail a few of them here separate from the big ticket items above so that if you re interested you can gain a better idea of the amount of thinking that goes into a well designed system 4 5 1 Clever compression When appropriate Mercurial will store both snapshots and deltas in compressed form It does this by always trying to compress a snapshot or delta but only storing the compressed version if it s smaller than the uncompressed version This means that Mercurial does the right thing when storing a file whose native form is compressed such as a zip archive or a JPEG image When these types of files are compressed a second time the resulting file is usually bigg
274. re already in subbdirectory foo if you want to match files under this directory your pattern must start with foo One thing to note if you re familiar with Perl style regexps is that Mercurial s are rooted That is a regexp starts matching against the beginning of a string it doesn t look for a match anywhere within the string To match anywhere in a string start your pattern with 7 5 Filtering files Not only does Mercurial give you a variety of ways to specify files it lets you further winnow those files using filters Commands that work with file names accept two filtering options e I or include lets you specify a pattern that file names must match in order to be processed 76 e X or exclude gives you a way to avoid processing files if they match this pattern You can provide multiple I and X options on the command line and intermix them as you please Mercurial interprets the patterns you provide using glob syntax by default but you can use regexps if you need to You can read a I filter as process only the files that match this filter hg status I in MANIFEST in The X filter is best read as process only the files that don t match this pattern hg status X x py src src watcher _watcher c src xyzzy txt 7 6 Ignoring unwanted files and directories XXX 7 7 Case sensitivity If you re working in a mixed development env
275. re the remote repository is but it may know where the client is connecting from In such cases the URL will take one of the following forms e remote ssh ip address remote ssh client at the given IP address e remote http ip address tremote http client at the given IP address If the client is using SSL this will be of the form remote https ip address e Empty no information could be discovered about the remote client 10 9 Hook reference 10 9 1 changegroup after remote changesets added This hook is run after a group of pre existing changesets has been added to the repository for example via a hg pull or hg unbundle This hook is run once per operation that added one or more changesets This is in contrast to the incoming hook which is run once per changeset regardless of whether the changesets arrive in a group Some possible uses for this hook include kicking off an automated build or test of the added changesets updating a bug database or notifying subscribers that a repository contains new changes Parameters to this hook node A changeset ID The changeset ID of the first changeset in the group that was added All changesets between this and tip inclusive were added by a single hg pull hg push or hg unbundle source A string The source of these changes See section 10 8 3 for details url A URL The location of the remote repository if known See section 10 8 3 for more infor
276. rents of the working directory become the parents of the new changeset This new changeset has no children so it becomes the new tip And the repository now contains two changesets that have no children we call these heads You can see the structure that this creates in figure 4 8 Note If you re new to Mercurial you should keep in mind a common error which is to use the hg pull command without any options By default the hg pull command does not update the working directory so you ll bring new changesets into your repository but the working directory will stay synced at the same changeset as before the pull If you make some changes and commit after wards you 1l thus create a new head because your working directory isn t synced to whatever the current tip is I put the word error in quotes because all that you need to do to rectify this situation is hg merge then hg commit In other words this almost never has negative consequences it just surprises people 1 11 discuss other ways to avoid this behaviour and why Mercurial behaves in this initially surprising way later on 4 4 3 Merging heads When you run the hg merge command Mercurial leaves the first parent of the working directory unchanged and sets the second parent to the changeset you re merging with as shown in figure 4 9 Mercurial also has to modify the working directory to merge the files managed in the two cha
277. riented portion of the web interface is available String A free form but preferably brief string identifying the person or group in charge of the repository This often contains the name and email address of a person or mailing list It often makes sense to place this entry in a repository s own hg hgrc file but it can make sense to use in a global hgrc if every repository has a single maintainer Integer The default maximum number of changesets to display in a single page of output Integer The default maximum number of modified files to display in a single page of output Integer If the web interface displays alternating stripes to make it easier to visually align rows when you are looking at a table this number controls the number of rows in each stripe Controls the template Mercurial uses to display the web interface Mercurial ships with two web templates named default and gitweb the latter is much more visually attractive You can also specify a custom template of your own see chapter 11 for details Here you can see how to enable the gitweb style web style gitweb Path The directory in which to search for template files By default Mercurial searches in the directory in which it was installed If you are using hgwebdir cgi you can place a few configuration items in a web section of the hgweb config file instead of a hgrc file for convenience These items are motd and style Options spec
278. ropriate If a snapshot is of revision a631aca1083f the directory will be named foo a63lacal083f A snapshot of the working directory won t have a changeset ID appended so it would just be foo in this example To see what this looks like in practice look again at the hg extdiff example above Notice that the diff has the snapshot directory names embedded in its header The hg extdiff command accepts two important options The p option lets you choose a program to view differences with instead of diff With the o option you can change the options that hg extdiff passes to the program by default these options are Npru which only make sense if you re running diff In other respects the hg extdiff command acts similarly to the built in hg diff command you use the same option names syntax and arguments to specify the revisions you want the files you want and so on As an example here s how to run the normal system diff command getting it to generate context diffs using the c option instead of unified diffs and five lines of context instead of the default three passing 5 as the argument to the C option hg extdiff o NprcC5 making snapshot of 1 files from rev 271c4b32e6fb making snapshot of 1 files from working dir diff NprcC5 a 271c4b32e6fb myfile a myfile a 271c4b32e6fb myfile Sun Jun 17 18 03 49 2007 a myfile Sun Jun 17 18 03 49 2007 KEKKKKKEKKKKKKKK kkk i KKK a iit
279. rust or read it In the ideal world you should be able to run the following command successfully and it should print exactly one line of output the current date and time ssh myserver date If on your server you have login scripts that print banners or other junk even when running non interactive commands like this you should fix them before you continue so that they only print output if they re run interactively Otherwise these banners will at least clutter up Mercurial s output Worse they could potentially cause problems with running Mercurial commands remotely Mercurial makes tries to detect and ignore banners in non interactive ssh sessions but it is not foolproof If you re editing your login scripts on your server the usual way to see if a login script is running in an interactive shell is to check the return code from the command tty s Once you ve verified that plain old ssh is working with your server the next step is to ensure that Mercurial runs on the server The following command should run successfully ssh myserver hg version If you see an error message instead of normal hg version output this is usually because you haven t installed Mercurial to usr bin Don t worry if this is the case you don t need to do that But you should check for a few possible problems e Is Mercurial really installed on the server at all I know this sounds trivial but it s worth checking e
280. ry Options a Pop all applied patches This returns the repository to its state before you applied any patches f Forcibly revert any modifications to the working directory when popping n Pop a patch from the named queue The hg qpop command removes one line from the end of the status file for each patch that it pops B 1 12 hg qprev print the name of the previous patch The hg qprev command prints the name of the patch in the series file that comes before the topmost applied patch This will become the topmost applied patch if you run hg qpop B 1 13 hg qpush push patches onto the stack The hg qpush command adds patches onto the applied stack By default it adds only one patch This command creates a new changeset to represent each applied patch and updates the working directory to apply the effects of the patches The default data used when creating a changeset are as follows e The commit date and time zone are the current date and time zone Because these data are used to compute the identity of a changeset this means that if you hg apop a patch and hg qpush it again the changeset that you push will have a different identity than the changeset you popped e The author is the same as the default used by the hg commit command e The commit message is any text from the patch file that comes before the first diff header If there is no such text a default commit message
281. s The Linux kernel changes rapidly and has never been internally stable developers frequently make drastic changes between releases This means that a version of the driver that works well with a particular released version of the kernel will not even compile correctly against typically any other version To maintain a driver we have to keep a number of distinct versions of Linux in mind e One target is the main Linux kernel development tree Maintenance of the code is in this case partly shared by other developers in the kernel community who make drive by modifications to the driver as they develop and refine kernel subsystems We also maintain a number of backports to older versions of the Linux kernel to support the needs of cus tomers who are running older Linux distributions that do not incorporate our drivers To backport a piece of code is to modify it to work in an older version of its target environment than the version it was developed for Finally we make software releases on a schedule that is necessarily not aligned with those used by Linux distributors and kernel developers so that we can deliver new features to customers without forcing them to upgrade their entire kernels or distributions 13 1 1 Tempting approaches that don t work well There are two standard ways to maintain a piece of software that has to target many different environments The first is to maintain a number of branches each inte
282. s There s a one to one relationship between branches you re working in and directo ries on your system This lets you use normal non Mercurial aware tools to work on files within a branch repository If you re more in the power user category and your collaborators are too there is an alternative way of handling branches that you can consider I ve already mentioned the human level distinction between small picture and big picture branches While Mercurial works with multiple small picture branches in a repository all the time for example after you pull changes in but before you merge them it can also work with multiple big picture branches The key to working this way is that Mercurial lets you assign a persistent name to a branch There always exists a branch named default Even before you start naming branches yourself you can find traces of the default branch if you look for them As an example when you run the hg commit command and it pops up your editor so that you can enter a commit message look for a line that contains the text HG branch default at the bottom This is telling you that your commit will occur on the branch named default To start working with named branches use the hg branches command This command lists the named branches already present in your repository telling you which changeset is the tip of each hg tip changeset 0 7070a49b08e8 tag tip user
283. s a lot of history has its filelog stored in separate data d suffix and index i suffix files For small files without much history the revision data and index are combined in a single i file The correspondence between a file in the working directory and the filelog that tracks its history in the repository is illustrated in figure 4 1 4 1 2 Managing tracked files Mercurial uses a structure called a manifest to collect together information about the files that it tracks Each entry in the manifest contains information about the files present in a single changeset An entry records which files are present in the changeset the revision of each file and a few other pieces of file metadata 4 1 3 Recording changeset information The changelog contains information about each changeset Each revision records who committed a change the changeset comment other pieces of changeset related information and the revision of the manifest to use 4 1 4 Relationships between revisions Within a changelog a manifest or a filelog each revision stores a pointer to its immediate parent or to its two parents if it s a merge revision As I mentioned above there are also relationships between revisions across these structures 35 Figure 4 1 Relationships between files in working directory and filelogs in repository and they are hierarchical in nature For every changeset in a repository there is exactly one revisi
284. s control for parts of a repository o o e e 114 10 7 2 bugzilla mtesration with Bugzilla ccc ti ea p eee i Ba a eee BR eS 116 10 7 3 notify send email notifications dp eedi ee ee 119 10 8 Information for Writers of hooks 2 6 ee da ee ee we ee 120 10 8 1 In process hook execution 6 copo Re RR o a aa i 120 10 8 2 External hook EXECUION s c e A ewe A be ee eS 121 10 8 3 Finding out where champesets come from ww Re a 121 109 Hook feterence cie be bi Se bee oe a Ga ee web eee ee bea 122 10 9 1 changegroup after remote changesets added o o 0 00002 2 eee 122 10 9 2 commit after a new changeset is Created 2 2 2 ee eee ee 122 10 9 3 incoming after one remote changeset is added o o 122 10 9 4 outgoing after changesets are propagated ee ee ee 123 10 9 5 prechangegroup before starting to add remote changesets 123 10 9 6 precommit before starting to commit a changeset o o o 123 10 9 7 preoutgoing before starting to propagate changesets o e 124 10 9 8 pretag before tagging a changeset eee eee eee 124 10 9 9 pretxnchangegroup before completing addition of remote changesets 124 10 9 10 pret xncommit before completing commit of new changeset 125 10 9 11 preupdate before updating or merging working directory
285. se templates to generate specific output for a single command or to customise the entire appearance of the built in web interface 11 1 Using precanned output styles Packaged with Mercurial are some output styles that you can use immediately A style is simply a precanned template that someone wrote and installed somewhere that Mercurial can find Before we take a look at Mercurial s bundled styles let s review its normal output hg log r1 changeset l ee709a2e8cd1 tag mytag user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 04 00 2007 0000 summary added line to end of lt lt hello gt gt file This is somewhat informative but it takes up a lot of space five lines of output per changeset The compact style reduces this to three lines presented in a sparse manner hg log style compact 3 tip 921354c5e6bb 2007 06 17 18 04 000 Added tag v0 1 for changeset ba526719a3b3 o bos 2 v0 1 ba526719a3b3 2007 06 17 18 04 0000 bos Added tag mytag for changeset ee709a2e8cdl 1 mytag ee709a2e8cd1 2007 06 17 18 04 0000 bos added line to end of lt lt hello gt gt file 0 c4ff58d082b6 2007 06 17 18 04 0000 bos added hello The changelog style hints at the expressive power of Mercurial s templating engine This style attempts to follow the GNU Project s changelog guidelines RS 127 hg log style changelog 2007 06 17 Bryan O Sullivan lt bos serpentin
286. se to me but that caused a considerable amount of consternation and strife within my development team In spite of my attempts to explain why we needed a complex set of branches and how changes ought to flow between them a few team members revolted Even though they were smart people they didn t want to pay attention to the constraints we were operating under or face the consequences of those constraints in the details of the model that I was advocating Don t sweep foreseeable social or technical problems under the rug Whatever scheme you put into effect you should plan for mistakes and problem scenarios Consider adding automated machinery to prevent or quickly recover from trouble that you can anticipate As an example if you intend to have a branch with not for release changes in it you d do well to think early about the possibility that someone might accidentally merge those changes into a release branch You could avoid this particular problem by writing a hook that prevents changes from being merged from an inappropriate branch 6 2 2 Informal anarchy I wouldn t suggest an anything goes approach as something sustainable but it s a model that s easy to grasp and it works perfectly well in a few unusual situations As one example many projects have a loose knit group of collaborators who rarely physically meet each other Some groups like to overcome the isolation of working at a distance by organising occasional sprints
287. seful to describe the way work flows in that environment if you like the ideas the approach translates well across tools At the center of the community sits Linus Torvalds the creator of Linux He publishes a single source repository that is considered the authoritative current tree by the entire developer community Anyone can clone Linus s tree but he is very choosy about whose trees he pulls from Linus has a number of trusted lieutenants As a general rule he pulls whatever changes they publish in most cases without even reviewing those changes Some of those lieutenants are generally agreed to be maintainers responsible for specific subsystems within the kernel If a random kernel hacker wants to make a change to a subsystem that they want to end up in Linus s tree they must find out who the subsystem s maintainer is and ask that maintainer to take their change If the maintainer reviews their changes and agrees to take them they ll pass them along to Linus in due course Individual lieutenants have their own approaches to reviewing accepting and publishing changes and for deciding when to feed them to Linus In addition there are several well known branches that people use for different purposes For example a few people maintain stable repositories of older versions of the kernel to which they apply critical fixes as needed Some maintainers publish multiple trees one for experimental changes one for c
288. serpentine com gt date Sun Jun 17 18 03 59 2007 0000 summary Added tag v1 0 for changeset 37cc3lacedcl changeset 0 37cc3lacedcl tag v1 0 user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 59 2007 0000 summary Initial commit Any time you need to provide a revision ID to a Mercurial command the command will accept a tag name in its place Internally Mercurial will translate your tag name into the corresponding revision ID then use that echo goodbye gt myfile2 hg commit A m Second commit adding myfile2 hg log r v1 0 changeset 0 37cc3lacedcl tag v1 0 user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 59 2007 0000 summary Initial commit There s no limit on the number of tags you can have in a repository or on the number of tags that a single revision can have As a practical matter it s not a great idea to have too many a number which will vary from project to project simply because tags are supposed to help you to find revisions If you have lots of tags the ease of using them to identify revisions diminishes rapidly For example if your project has milestones as frequent as every few days it s perfectly reasonable to tag each one of those But if you have a continuous build system that makes sure every revision can be built cleanly you d be introducing a lot of noise if you were to tag every clean build Instead
289. sitory Parameters to this hook source A string The source of the operation that is attempting to obtain changes from this repository see sec tion 10 8 3 See the documentation for the source parameter to the outgoing hook in section 10 9 4 for possible values of this parameter url A URL The location of the remote repository if known See section 10 8 3 for more information See also outgoing section 10 9 4 10 9 8 pretag before tagging a changeset This controlling hook is run before a tag is created If the hook succeeds creation of the tag proceeds If the hook fails the tag is not created Parameters to this hook local A boolean Whether the tag is local to this repository instance i e stored in hg localtags or managed by Mercurial stored in hgtags node A changeset ID The ID of the changeset to be tagged tag A string The name of the tag to be created If the tag to be created is revision controlled the precommit and pretxncommit hooks sections 10 9 2 and 10 9 10 will also be run See also tag section 10 9 12 10 9 9 pretxnchangegroup before completing addition of remote changesets This controlling hook is run before a transaction that manages the addition of a group of new changesets from outside the repository completes If the hook succeeds the transaction completes and all of the changesets become permanent within this repository If the hook fails the transaction is rolled back and the
290. small and easy to deal with Some extensions add new commands that you can use from the command line while others work behind the scenes for example adding capabilities to the server The fet ch extension adds a new command called not surprisingly hg fetch This extension acts as a combi nation of hg pull hg update and hg merge It begins by pulling changes from another repository into the current repository If it finds that the changes added a new head to the repository it begins a merge then commits the result of the merge with an automatically generated commit message If no new heads were added it updates the working directory to the new tip changeset Enabling the fetch extension is easy Edit your hgrc and either go to the extensions section or create an extensions section Then add a line that simply reads fetch extensions fetch 6699 Normally on the right hand side of the would appear the location of the extension but since the fetch extension is in the standard distribution Mercurial knows where to search for it 33 letter txt base C8 rvc lt gt lettertxt File Edit Directory Movement a a dlo a E Difview Merge Window Settings Help Flo max an vay F A Base tmp letter td base C8 rvc Top line 1 B fhome bos scamilet Greetings Greetings Nigerian dictator Sani Abacha Nigerian dicta Ta Output home bos scam Letter t
291. sources of problems and to handle them appropriately 9 1 Erasing local history 9 1 1 The accidental commit I have the occasional but persistent problem of typing rather more quickly than I can think which sometimes results in me committing a changeset that is either incomplete or plain wrong In my case the usual kind of incomplete changeset is one in which I ve created a new source file but forgotten to hg add it A plain wrong changeset is not as common but no less annoying 9 1 2 Rolling back a transaction In section 4 2 2 I mentioned that Mercurial treats each modification of a repository as a transaction Every time you commit a changeset or pull changes from another repository Mercurial remembers what you did You can undo or roll back exactly one of these actions using the hg rollback command See section 9 1 4 for an important caveat about the use of this command Here s a mistake that I often find myself making committing a change in which I ve created a new file but forgotten to hg ada it hg status Ma echo b gt b hg commit m Add file b Looking at the output of hg status after the commit immediately confirms the error hg status 2b hg tip changeset 1 cbe28556f1a4 tag tip user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 59 2007 0000 89 summary Add file b The commit captured the changes to t
292. stand I have several times worked on and hg qrefresh ed a patch other than the one I intended and it s often tricky to migrate changes into the right patch after making them in the wrong one For this reason it is very much worth investing a little time to learn how to use some of the third party tools I described in section 12 12 particularly diffstat and filterdiff The former will give you a quick idea of what changes your patch is making while the latter makes it easy to splice hunks selectively out of one patch and into another 151 20 21 22 23 5 e module_init aul100fb_init diffstat p1 remove redundant null checks patch drivers char agp sgi agp c 5 4 drivers char hvcs c 11 drivers message fusion mptfc c 6 drivers message fusion mptsas c 3 drivers net fs_enet fs_enet mii c 3 drivers net wireless ipw2200 c 22 FPE 7 77 drivers scsi libata scsi c 4 drivers video aull00fb c 3 8 files changed 19 insertions 38 deletions filterdiff i video remove redundant null checks patch a drivers video aul100fb c remove redundant null checks before free in drivers a drivers video aul100fb c 743 8 743 7 void _ exit aull00fb_cleanup void driver_unregister amp aul100fb_driver if drv_info opt_mode kfree drv_info opt_mode kfree drv_info opt_mode Figure 12 15 The diffstat fil
293. succeeded If it returns a boolean true value or raises an exception it is considered to have failed A useful way to think of the calling convention is tell me if you fail Note that changeset IDs are passed into Python hooks as hexadecimal strings not the binary hashes that Mercurial s APIs normally use To convert a hash from hex to binary use the mercurial node bin function 10 8 2 External hook execution An external hook is passed to the shell of the user running Mercurial Features of that shell such as variable substitu tion and command redirection are available The hook is run in the root directory of the repository unlike in process hooks which are run in the same directory that Mercurial was run in Hook parameters are passed to the hook as environment variables Each environment variable s name is converted in upper case and prefixed with the string HG_ For example if the name of a parameter is node the name of the environment variable representing that parameter will be HG_NODE A boolean parameter is represented as the string 1 for true 0 for false If an environment variable is named HG_NODE HG_PARENT1 or HG_PARENT2 it contains a changeset ID represented as a hexadecimal string The empty string is used to represent null changeset ID instead of a string of zeroes If an environment variable is named HG_URL it will contain the URL of a remote repository if that
294. t 11168 11 7 From templates to styles A command line template provides a quick and simple way to format some output Templates can become verbose though and it s useful to be able to give a template a name A style file is a template with a name stored in a file More than that using a style file unlocks the power of Mercurial s templating engine in ways that are not possible using the command line template option 132 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 52 53 54 55 56 58 59 60 hg log r1 template author n Bryan O Sullivan lt bos serpentine com gt hg log r1 template author domain n serpentine com hg log r1 template author email n bos serpentine com hg log r1 template author obfuscate n cut c 76 amp 66 amp 114 amp 121 amp 97 amp 110 amp 32 79 amp 39 amp 83 amp 117 amp 108 amp 108 amp 105 amp 11 hg log r1 template fauthor person in Bryan O Sullivan hg log r1 template author user n bos hg log r1 template looks almost right but actually garbage date n looks almost right but actually garbage 1182103440 00 hg log r1 template date age n 2 seconds hg log r1 template date date n Sun Jun 17 18 04 00 2007 0000 hg
295. t s say your software crashes at revision 100 and worked correctly at revision 50 Unknown to you someone else introduced a different crashing bug at revision 60 and fixed it at revision 80 This could distort your results in one of several ways It is possible that this other bug completely masks yours which is to say that it occurs before your bug has a chance to manifest itself If you can t avoid that other bug for example it prevents your project from building and so can t tell whether your bug is present in a particular changeset the bisect extension cannot help you directly Instead you ll need to manually avoid the changesets where that bug is present and do separate searches around it A different problem could arise if your test for a bug s presence is not specific enough If you check for my program crashes then both your crashing bug and an unrelated crashing bug that masks it will look like the same thing and mislead bisect 105 9 6 5 Bracket your search lazily Choosing the first good and bad changesets that will mark the end points of your search is often easy but it bears a little discussion nevertheless From the perspective of bisect the newest changeset is conventionally bad and the older changeset is good If you re having trouble remembering when a suitable good change was so that you can tell bisect you could do worse than testing changesets at random
296. t changes follow a copy To best illustrate what this means let s create an example We ll start with the usual tiny repository that contains a single file 50 hg init my copy cd my copy echo line gt file hg add file hg commit m Added a file GW Ur Uk U We need to do some work in parallel so that we ll have something to merge So let s clone our repository cd hg clone my copy your copy 1 files updated 0 files merged 0 files removed 0 files unresolved Back in our initial repository let s use the hg copy command to make a copy of the first file we created ed my copy hg copy file new file If we look at the output of the hg status command afterwards the copied file looks just like a normal added file hg status A new file But if we pass the C option to hg status it prints another line of output this is the file that our newly added file was copied from hg status C A new file file hg commit m Copied file Now back in the repository we cloned let s make a change in parallel We ll add a line of content to the original file that we created ed your copy echo new contents gt gt file hg commit m Changed file Now we have a modified file in this repository When we pull the changes from the first repository and merge the two heads Mercurial will propagate
297. t data is erased This hook can access the metadata associated with the almost new changeset but it should not do anything perma nent with this data It must also not modify the working directory While this hook is running if other Mercurial processes access this repository they will be able to see the almost new changeset as if it is permanent This may lead to race conditions if you do not take steps to avoid them Parameters to this hook node A changeset ID The changeset ID of the newly committed changeset parentl A changeset ID The changeset ID of the first parent of the newly committed changeset parent2 A changeset ID The changeset ID of the second parent of the newly committed changeset See also precommit section 10 9 6 10 9 11 preupdate before updating or merging working directory This controlling hook is run before an update or merge of the working directory begins It is run only if Mercurial s normal pre update checks determine that the update or merge can proceed If the hook succeeds the update or merge may proceed if it fails the update or merge does not start Parameters to this hook parent1 A changeset ID The ID of the parent that the working directory is to be updated to If the working directory is being merged it will not change this parent parent2 A changeset ID Only set if the working directory is being merged The ID of the revision that the working directory is being merged with See also
298. t has over the brute force search approach increases with every changeset you add 9 5 2 Cleaning up after your search When you re finished using the bisect extension in a repository you can use the hg bisect reset command to drop the information it was using to drive your search The extension doesn t use much space so it doesn t matter if you forget to run this command However bisect won t let you start a new search in that repository until you do a hg bisect reset hg bisect reset 104 9 6 Tips for finding bugs effectively 9 6 1 Give consistent input The bisect extension requires that you correctly report the result of every test you perform If you tell it that a test failed when it really succeeded it might be able to detect the inconsistency If it can identify an inconsistency in your reports it will tell you that a particular changeset is both good and bad However it can t do this perfectly it s about as likely to report the wrong changeset as the source of the bug 9 6 2 Automate as much as possible When I started using the bisect extension I tried a few times to run my tests by hand on the command line This is an approach that I at least am not suited to After a few tries I found that I was making enough mistakes that I was having to restart my searches several times before finally getting correct results My initial problems with driving the bisect extension by hand o
299. tches you name in the order you name them into the topmost applied patch and concatenates their descriptions onto the end of its description The patches that you fold must be unapplied before you fold them The order in which you fold patches matters If your topmost applied patch is foo and you hg gqfold bar and quux into it you will end up with a patch that has the same effect as if you applied first foo then bar followed by quux 12 14 3 Merging part of one patch into another Merging part of one patch into another is more difficult than combining entire patches If you want to move changes to entire files you can use filterdiff s i and x options to choose the modifica tions to snip out of one patch concatenating its output onto the end of the patch you want to merge into You usually won t need to modify the patch you ve merged the changes from Instead MQ will report some rejected hunks when you hg qpush it from the hunks you moved into the other patch and you can simply hg qrefresh the patch to drop the duplicate hunks If you have a patch that has multiple hunks modifying a file and you only want to move a few of those hunks the job becomes more messy but you can still partly automate it Use lsdiff nvv to print some metadata about the patch lsdiff nvv remove redundant null checks patch 22 File 1 a drivers char agp
300. teeing that a reader won t see a partial write If you recall figure 4 2 revisions in the changelog point to revisions in the manifest and revisions in the manifest point to revisions in filelogs This hierarchy is deliberate A writer starts a transaction by writing filelog and manifest data and doesn t write any changelog data until those are finished A reader starts by reading changelog data then manifest data followed by filelog data Since the writer has always finished writing filelog and manifest data before it writes to the changelog a reader will never read a pointer to a partially written manifest revision from the changelog and it will never read a pointer to a partially written filelog revision from the manifest 4 5 3 Concurrent access The read write ordering and atomicity guarantees mean that Mercurial never needs to lock a repository when it s reading data even if the repository is being written to while the read is occurring This has a big effect on scalability you can have an arbitrary number of Mercurial processes safely reading data from a repository safely all at once no matter whether it s being written to or not The lockless nature of reading means that if you re sharing a repository on a multi user system you don t need to grant other local users permission to write to your repository in order for them to be able to clone it or pull changes from it they only need read permission This is not a common feature
301. ter in the 1980s Dick Grune used RCS as a building block for a set of shell scripts he initially called cmt but then renamed to CVS Concurrent Versions System The big innovation of CVS was that it let developers work simultaneously and somewhat independently in their own personal workspaces The personal workspaces prevented developers from stepping on each other s toes all the time as was common with SCCS and RCS Each developer had a copy of every project file and could modify their copies independently They had to merge their edits prior to committing changes to the central repository Brian Berliner took Grune s original scripts and rewrote them in C releasing in 1989 the code that has since devel oped into the modern version of CVS CVS subsequently acquired the ability to operate over a network connection giving it a client server architecture CVS s architecture is centralised only the server has a copy of the history of the project Client workspaces just contain copies of recent versions of the project s files and a little metadata to tell them where the server is CVS has been enormously successful it is probably the world s most widely used revision control system In the early 1990s Sun Microsystems developed an early distributed revision control system called Team Ware A TeamWare workspace contains a complete copy of the project s history TeamWare has no notion of a central repository CVS relied upon RCS for its his
302. ter txt 7 hg commit m 419 scam first draft We ll clone the repository and make a change to the file cd hg clone scam scam cousin files updated 0 files merged 0 files removed 0 files unresolved cd scam cousin cat gt letter txt lt lt EOF Greetings I am Shehu Musa Abacha cousin to the former Nigerian dictator Sani Abacha EOF hg commit m 419 scam with cousin w NY V VV Vn Rm DH And another clone to simulate someone else making a change to the file This hints at the idea that it s not all that unusual to merge with yourself when you isolate tasks in separate repositories and indeed to find and resolve conflicts while doing so cd hg clone scam scam son files updated 0 files merged 0 files removed 0 files unresolved cd scam son cat gt letter txt lt lt EOF Greetings I am Alhaji Abba Abacha son of the former Nigerian dictator Sani Abacha EOF hg commit m 419 scam with son w NY V VV Vn Rm DH Having created two different versions of the file we 1l set up an environment suitable for running our merge cd hg clone scam cousin scam merge files updated 0 files merged 0 files removed 0 files unresolved cd scam merge hg pull u scam son 6 pulling from scam son 7 searching for changes s adding changesets adding manifests 1 adding file changes 1 added 1 changesets with 1 changes to 1 files 1 heads 2 not
303. terdiff and 1sdiff commands 12 14 MQ cookbook 12 14 1 Manage trivial patches Because the overhead of dropping files into a new Mercurial repository is so low it makes a lot of sense to manage patches this way even if you simply want to make a few changes to a source tarball that you downloaded Begin by downloading and unpacking the source tarball and turning it into a Mercurial repository 5 5 5 5 5 5 1 download netplug 1 2 5 tar bz2 tar jxf netplug 1 2 5 tar bz2 cd netplug 1 2 5 hg init hg commit q addremove message netplug 1 2 5 cd hg clone netplug 1 2 5 netplug 8 files updated 0 files merged 0 files removed 0 files unresolved Continue by creating a patch stack and making your changes SA UF LO SUR EQ UE cd netplug hg qinit hg qnew m fix build problem with gcc 4 build fix patch perl pi e s int addr_len socklen_t addr_len netlink c hg qrefresh hg tip p 152 20 21 22 23 24 25 26 27 28 changeset 1 6llbef1 3551 tag qtip tag build fix patch tag tip tag qbase user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 55 2007 0000 summary fix build problem with gcc 4 diff r 273662f32ddd r 611bef1f 3551 netlink c a netlink c Sun Jun 17 18 03 55 2007 0000 b netlink c Sun Jun 17 18 03 55 2007 0000 275 7 275 7 netlink_open void exit 1 int addr_len sizeof ad
304. tes Both ssh and plink accept a C option which turns on compression You can easily edit your hgrc to enable compression for all of Mercurial s uses of the ssh protocol ui ssh ssh C If you use ssh you can configure it to always use compression when talking to your server To do this edit your ssh config file which may not yet exist as follows 66 N N Host hg Compression yes HostName hg example com This defines an alias hg When you use it on the ssh command line or in a Mercurial ssh protocol URL it will cause ssh to connect to hg example com and use compression This gives you both a shorter name to type and compression each of which is a good thing in its own right 6 6 Serving over HTTP using CGI Depending on how ambitious you are configuring Mercurial s CGI interface can take anything from a few moments to several hours We ll begin with the simplest of examples and work our way towards a more complex configuration Even for the most basic case you re almost certainly going to need to read and modify your web server s configuration Note Configuring a web server is a complex fiddly and highly system dependent activity I can t possibly give you instructions that will cover anything like all of the cases you will encounter Please use your discretion and judgment in following the sections below Be prepared to make plenty of mistakes and to spend a lot of time reading
305. tes new context information that will make it apply cleanly I say often not always because sometimes refreshing a patch will make it fail to apply against a different revision of the underlying files In some cases such as when you re maintaining a patch that must sit on top of multiple versions of a source tree it s acceptable to have a patch apply with some fuzz provided you ve verified the results of the patching process in such cases 12 6 5 Handling rejection If hg qpush fails to apply a patch it will print an error message and exit If it has left rej files behind it is usually best to fix up the rejected hunks before you push more patches or do any further work If your patch used to apply cleanly and no longer does because you ve changed the underlying code that your patches are based on Mercurial Queues can help see section 12 8 for details Unfortunately there aren t any great techniques for dealing with rejected hunks Most often you ll need to view the rej file and edit the target file applying the rejected hunks by hand If you re feeling adventurous Neil Brown a Linux kernel hacker wrote a tool called wiggle Bro which is more vigorous than patch in its attempts to make a patch apply Another Linux kernel hacker Chris Mason the author of Mercurial Queues wrote a similar tool called mpat ch Mas which takes a simple approach to automating the application of hunks rejected by patch Th
306. the changes that we made locally to file into its copy new file hg pull my copy pulling from my copy searching for changes adding changesets adding manifests adding file changes added 1 changesets with 1 changes to 1 files 1 heads run hg heads to see heads hg merge to merge hg merge merging file and new file 51 N 0 files updated 1 files merged 0 files removed 0 files unresolved branch merge don t forget to commit cat new file line new contents 5 3 2 Why should changes follow copies This behaviour of changes to a file propagating out to copies of the file might seem esoteric but in most cases it s highly desirable First of all remember that this propagation only happens when you merge So if you hg copy a file and subsequently modify the original file during the normal course of your work nothing will happen The second thing to know is that modifications will only propagate across a copy as long as the repository that you re pulling changes from doesn t know about the copy The reason that Mercurial does this is as follows Let s say I make an important bug fix in a source file and commit my changes Meanwhile you ve decided to hg copy the file in your repository without knowing about the bug or having seen the fix and you have started hacking on your copy of the file If you pulled and merged my changes and Mercurial didn t propagate changes
307. ting the results of the merge Whenever we ve done a merge hg parents will display two parents until we hg commit the results of the merge hg commit m Merged changes We now have a new tip revision notice that it has both of our former heads as its parents These are the same revisions that were previously displayed by hg parents hg tip changeset 7 1138dc84f30b tag tip parent 5 06795fee8236 parent 6 fa1321bf0c80 user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 05 52 2007 0000 summary Merged changes In figure 3 3 you can see a representation of what happens to the working directory during the merge and how this affects the repository when the commit happens During the merge the working directory has two parent changesets and these become the parents of the new changeset 3 2 Merging conflicting changes Most merges are simple affairs but sometimes you ll find yourself merging changes where each modifies the same portions of the same files Unless both modifications are identical this results in a conflict where you have to decide how to reconcile the different changes into something coherent Figure 3 4 illustrates an instance of two conflicting changes to a document We started with a single version of the file then we made some changes while someone else made different changes to the same text Our task in resolving the conflicting changes
308. tory storage TeamWare used SCCS As the 1990s progressed awareness grew of a number of problems with CVS It records simultaneous changes to multiple files individually instead of grouping them together as a single logically atomic operation It does not manage its file hierarchy well it is easy to make a mess of a repository by renaming files and directories Worse its source code is difficult to read and maintain which made the pain level of fixing these architectural problems prohibitive In 2001 Jim Blandy and Karl Fogel two developers who had worked on CVS started a project to replace it with a tool that would have a better architecture and cleaner code The result Subversion does not stray from CVS s centralised client server model but it adds multi file atomic commits better namespace management and a number of other features that make it a generally better tool than CVS Since its initial release it has rapidly grown in popularity More or less simultaneously Graydon Hoare began working on an ambitious distributed revision control system that he named Monotone While Monotone addresses many of CVS s design flaws and has a peer to peer architecture it goes beyond earlier and subsequent revision control tools in a number of innovative ways It uses cryptographic hashes as identifiers and has an integral notion of trust for code from different sources Mercurial began life in 2005 While a few aspects of its design
309. trol tools listed below in most cases for several years at a time 1 6 1 Subversion Subversion is a popular revision control tool developed to replace CVS It has a centralised client server architecture Subversion and Mercurial have similarly named commands for performing the same operations so it is easy for a person who is familiar with one to learn to use the other Both tools are portable to all popular operating systems Subversion lacks a history aware merge capability forcing its users to manually track exactly which revisions have been merged between branches If users fail to do this or make mistakes they face the prospect of manually resolving merges with unnecessary conflicts Mercurial has a substantial performance advantage over Subversion on every revision control operation I have benchmarked I have measured its advantage as ranging from a factor of two to a factor of six when compared with Subversion 1 4 3 s ra_local file store which is the fastest access method available In more realistic deployments involving a network based store Subversion will be at a substantially larger disadvantage Because many Subversion commands must talk to the server and Subversion does not have useful replication facilities server capacity becomes a bottleneck for modestly large projects Additionally Subversion incurs a substantial storage overhead to avoid network transactions for a few common operations such as finding modified files st
310. trolling the guards on a patch The hg qguard command lets you determine which guards should apply to a patch or display the guards that are already in effect Without any arguments it displays the guards on the current topmost patch hg qguard goodbye patch unguarded To set a positive guard on a patch prefix the name of the guard with a hg qguard foo hg qguard goodbye patch foo gt To set a negative guard on a patch prefix the name of the guard with a 157 N hg qguard hello patch quux hg qguard hello patch hello patch quux Note The hg qguard command sets the guards on a patch it doesn t modify them What this means is that if you run hg qguard a b on a patch then hg qguard c on the same patch the only guard that will be set on it afterwards is c Mercurial stores guards in the series file the form in which they are stored is easy both to understand and to edit by hand In other words you don t have to use the hg aguard command if you don t want to it s okay to simply edit the series file cat hg patches series hello patch quux goodbye patch foo 13 4 Selecting the guards to use The hg qselect command determines which guards are active at a given time The effect of this is to determine which patches MQ will apply the next time you run hg qpush It has no other e
311. ty e7639888bb2f E ke 7b064d8bac5e lt Tb064d8bac5e 000000000000 Figure 4 7 The working directory updated to an older changeset Nowly created head and tip Parente of working directary e7639888bb2f ffb20e170lea Th064d8bacSe 000000000000 Figure 4 8 After a commit made while synced to an older changeset 45 Newly created head and tip Parente of working directary t parent unchanged ffb20e170lea e7639888bb2f 000000000000 Figure 4 9 Merging two heads 46 Chapter 5 Mercurial in daily use 5 1 Telling Mercurial which files to track Mercurial does not work with files in your repository unless you tell it to manage them The hg status command will tell you which files Mercurial doesn t know about it uses a 9 to display such files To tell Mercurial to track a file use the hg add command Once you have added a file the entry in the output of hg status for that file changes from to A UY UY gt 747 Y LU uu hg init add example cd add example echo a gt a hg status a hg add a hg status a hg commit m Added one file hg status After you run a hg commit the files that you added before the commit will no longer be listed in the output of hg status The reason for this is that hg status only tells you about interesting files those that you have modified or told Mercurial to do something w
312. u may have a requirement that every changeset must pass a rigorous set of tests Defining this requirement via a hook in a site wide hgrc won t work for remote users on laptops and of course local users can subvert it at will by overriding the hook Instead you can set up your policies for use of Mercurial so that people are expected to propagate changes through a well known canonical server that you have locked down and configured appropriately One way to do this is via a combination of social engineering and technology Set up a restricted access account users can push changes over the network to repositories managed by this account but they cannot log into the account 108 and run normal shell commands In this scenario a user can commit a changeset that contains any old garbage they want When someone pushes a changeset to the server that everyone pulls from the server will test the changeset before it accepts it as permanent and reject it if it fails to pass the test suite If people only pull changes from this filtering server it will serve to ensure that all changes that people pull have been automatically vetted 10 3 Care with pretxn hooks in a shared access repository If you want to use hooks to do some automated work in a repository that a number of people have shared access to you need to be careful in how you do this Mercurial only locks a repository when it is writing to the repository and only the parts of Mercuri
313. u specify patterns using regular expressions also known as regexps By the way in the examples that follow notice that I m careful to wrap all of my patterns in quote characters so that they won t get expanded by the shell before Mercurial sees them 7 4 1 Shell style glob patterns This is an overview of the kinds of patterns you can use when you re matching on glob patterns The character matches any string within a single directory hg add glob py adding main py The pattern matches any string and crosses directory boundaries It s not a standard Unix glob token but it s accepted by several popular Unix shells and is very useful Sed hg status glob x py A examples simple py A src main py examples performant py gt setup py src watcher watcher py The pattern matches any single character hg status glob x src watcher _watcher c 75 The character begins a character class This matches any single character within the class The class ends with a character A class may contain multiple ranges of the form a f which is shorthand for abcdef hg status glob x nr t MANIFEST in src xyzzy txt gt Tf the first character after the in a character class is a not in the class A begins a group of subpatterns where the whole group matches if any subpatt
314. u start a command like hg update or hg pull u It will update the working directory to the tip of this branch no matter what the repo wide tip is To update to a revision that s on a different named branch you may need to use the C option to hg update This behaviour is a little subtle so let s see it in action First let s remind ourselves what branch we re currently on and what branches are in our repository hg parents changeset 2 4 00549a48el branch bar tag tip user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 43 2007 0000 summary Third commit hg branches bar 2 4 00549a48el foo 1 3af68d4362fb default 0 7070a49b08e8 We re on the bar branch but there also exists an older hg foo branch We can hg update back and forth between the tips of the foo and bar branches without needing to use the C option because this only involves going backwards and forwards linearly through our change history hg update foo 0 files updated 0 files merged 1 files removed 0 files unresolved hg parents changeset 1 3af68d4362fb branch foo user Bryan O Sullivan lt bos serpentine com gt date Sun Jun 17 18 03 42 2007 0000 summary Second commit hg update bar 1 files updated 0 files merged 0 files removed 0 files unresolved hg parents changeset 2 4 00549a48el branch bar tag tip user Bryan O Sullivan lt bos serpe
315. ug as well as simply adding a comment For example the hook could recognise the string fixed bug 31337 as indicating that it should update the state of bug 31337 to requires testing Configuring the bugzilla hook You should configure this hook in your server s hgrc as an incoming hook for example as follows 1 hooks 2 incoming bugzilla python hgext bugzilla hook Because of the specialised nature of this hook and because Bugzilla was not written with this kind of integration in mind configuring this hook is a somewhat involved process Before you begin you must install the MySQL bindings for Python on the host s where you ll be running the hook If this is not available as a binary package for your system you can download it from Dus Configuration information for this hook lives in the bugzilla section of your hgrc version The version of Bugzilla installed on the server The database schema that Bugzilla uses changes occasionally so this hook has to know exactly which schema to use At the moment the only version supported is 2 16 host The hostname of the MySQL server that stores your Bugzilla data The database must be configured to allow connections from whatever host you are running the bugzilla hook on 116 user The username with which to connect to the MySQL server The database must be configured to allow this user to connect from whatever host you are running the bugzilla hook on This
316. un it first with the n option This will show you what the command would send without actually sending anything Once you ve had a quick glance over the changes and verified that you are sending the right ones you can rerun the same command with the n option removed The hg email command accepts the same kind of revision syntax as every other Mercurial command For example this command will send every revision between 7 and tip inclusive hg email n 7 tip You can also specify a repository to compare with If you provide a repository but no revisions the hg email command will send all revisions in the local repository that are not present in the remote repository If you additionally specify revisions or a branch name the latter using the b option this will constrain the revisions sent It s perfectly safe to run the hg email command without the names of the people you want to send to if you do this it will just prompt you for those values interactively If you re using a Linux or Unix like system you should have enhanced readline style editing capabilities when entering those headers too which is useful When you are sending just one revision the hg email command will by default use the first line of the changeset description as the subject of the single email message it sends If you send multiple revisions the hg email command will usually send one message per changeset It will pref
317. ure hgwebdir cgi is with a section named collections This will automatically publish every repository under the directories you name The section should look like this 69 1 collections my root my root N cc_o Mercurial interprets this by looking at the directory name on the right hand side of the sign finding repositories in that directory hierarchy and using the text on the left to strip off matching text from the names it will actually list in the web interface The remaining component of a path after this stripping has occurred is called a virtual path Given the example above if we have a repository whose local path is my root this repo the CGI script will strip the leading my root from the name and publish the repository with a virtual path of this repo If the base URL for our CGI script is http myhostname myuser hgwebdir cgi the complete URL for that repository will be http myhostname myuser hgwebdir cgi this repo If we replace my root on the left hand side of this example with my then hgwebdir cgi will only strip off my from the repository name and will give us a virtual path of root this repo instead of this repo The hgwebdir cgi script will recursively search each directory listed in the collections section of its configu ration file but it will not recurse into the repositories it finds The collections mechanism makes it easy to publish many repositories in a fire and forget m
318. urial through its normal internal tag machin ery you don t need to type in the entire name of a patch when you want to identify it by name Another nice consequence of representing patch names as tags is that when you run the hg log command it will display a patch s name as a tag simply as part of its normal output This makes it easy to visually distinguish applied patches from underlying normal revisions Figure 12 14 shows a few normal Mercurial commands in use with applied patches 12 10 Useful things to know about There are a number of aspects of MQ usage that don t fit tidily into sections of their own but that are good to know Here they are in one place e Normally when you hg apop a patch and hg qpush it again the changeset that represents the patch af ter the pop push will have a different identity than the changeset that represented the hash beforehand See section B 1 13 for information as to why this is e It s not a good idea to hg merge changes from another branch with a patch changeset at least if you want to maintain the patchiness of that changeset and changesets below it on the patch stack If you try to do this it will appear to succeed but MQ will become confused 12 11 Managing patches in a repository Because MQ s hg patches directory resides outside a Mercurial repository s working directory the underlying Mercurial repository knows nothing about the manage
319. user must be able to access and modify Bugzilla tables The default value of this item is bugs which is the standard name of the Bugzilla user in a MySQL database password The MySQL password for the user you configured above This is stored as plain text so you should make sure that unauthorised users cannot read the hgrc file where you store this information db The name of the Bugzilla database on the MySQL server The default value of this item is bugs which is the standard name of the MySQL database where Bugzilla stores its data notify If you want Bugzilla to send out a notification email to subscribers after this hook has added a comment to a bug you will need this hook to run a command whenever it updates the database The command to run depends on where you have installed Bugzilla but it will typically look something like this if you have Bugzilla installed in var www html bugzilla 1 cd var www html bugzilla amp amp processmail s nobody nowhere com The Bugzilla processmail program expects to be given a bug ID the hook replaces s with the bug ID and an email address It also expects to be able to write to some files in the directory that it runs in If Bugzilla and this hook are not installed on the same machine you will need to find a way to run processmail on the server where Bugzilla is installed Mapping committer names to Bugzilla user names By default the bugzilla hook tries to use the email
320. which is run once per group of changesets brought in This is run after a group of changesets has been transmitted from this repository This is run before starting to bring a group of changesets into the repository Controlling This is run before starting a commit Controlling This is run before starting to transmit a group of changesets from this repository Controlling This is run before creating a tag Controlling This is run after a group of changesets has been brought into the local repository from another but before the transaction completes that will make the changes permanent in the repository Controlling This is run after a new changeset has been created in the local repository but before the transaction completes that will make it permanent Controlling This is run before starting an update or merge of the working directory This is run after a tag is created This is run after an update or merge of the working directory has finished Each of the hooks whose description begins with the word Controlling has the ability to determine whether an activity can proceed If the hook succeeds the activity may proceed if it fails the activity is either not permitted or undone depending on the hook 107 10 2 Hooks and security 10 2 1 Hooks are run with your privileges When you run a Mercurial command in a repository and the command causes a hook to run that hook runs on your system under your user account with
321. will If you don t like a patch you can drop it If a patch isn t quite as you want it to be simply fix it as many times as you need to until you have refined it into the form you desire As an example the integration of patches with revision control makes understanding patches and debugging their effects and their interplay with the code they re based on enormously easier Since every applied patch has an associated changeset you can use hg log filename to see which changesets and patches affected a file You can use the bisect extension to binary search through all changesets and applied patches to see where a bug got introduced or fixed You can use the hg annotate command to see which changeset or patch modified a particular line of a source file And so on 138 12 4 Understanding patches Because MQ doesn t hide its patch oriented nature it is helpful to understand what patches are and a little about the tools that work with them The traditional Unix diff command compares two files and prints a list of differences between them The patch command understands these differences as modifications to make to a file Take a look at figure 12 1 for a simple example of these commands in action echo this is my first line gt oldfile echo my first line is here gt newfile diff u oldfile newfile gt tiny patch cat tiny patch oldfile 2007 06 17 18 03 54 000000000 0000 newfile 2007
322. with that repository or any other unless you tell it to What this means for now is that we re free to experiment with our repository safe in the knowledge that it s a private sandbox that won t affect anyone else 2 3 2 What s in a repository When we take a more detailed look inside a repository we can see that it contains a directory named hg This is where Mercurial keeps all of its metadata for the repository cd hello ls a hg Makefile hello c 12 The contents of the hg directory and its subdirectories are private to Mercurial Every other file and directory in the repository is yours to do with as you please To introduce a little terminology the hg directory is the real repository and all of the files and directories that coexist with it are said to live in the working directory An easy way to remember the distinction is that the repository contains the history of your project while the working directory contains a snapshot of your project at a particular point in history 2 4 A tour through history One of the first things we might want to do with a new unfamiliar repository is understand its history The hg log command gives us a view of history 1 hg log 2 changeset 4 b57 9a090b62 3 tag tip 4 user Bryan O Sullivan lt bos serpentine com gt 5 date Tue Sep 06 15 43 07 2005 0700 6 summary Trim comments s changeset 3 5d7b70a2a9 user Br
323. xpensive than even a comparatively large read operation This is why for example the dirstate is stored in a single file If there were a dirstate file per directory that Mercurial tracked the disk would seek once per directory Instead Mercurial reads the entire single dirstate file in one step Mercurial also uses a copy on write scheme when cloning a repository on local storage Instead of copying every revlog file from the old repository into the new repository it makes a hard link which is a shorthand way to say these two names point to the same file When Mercurial is about to write to one of a revlog s files it checks to see if the number of names pointing at the file is greater than one If it is more than one repository is using the file so Mercurial makes a new copy of the file that is private to this repository A few revision control developers have pointed out that this idea of making a complete private copy of a file is not very efficient in its use of storage While this is true storage is cheap and this method gives the highest performance while deferring most book keeping to the operating system An alternative scheme would most likely 41 reduce performance and increase the complexity of the software each of which is much more important to the feel of day to day use 4 5 5 Other contents of the dirstate Because Mercurial doesn t force you to tell it when you re modifying a file it uses the d
324. xt Greetings zl eases dictator Sani Abacha 34 Ca AS AN AA AAA O FA Mumber of remaining unsolved conflicts 1 of which 0 are whitespace Chapter 4 Behind the scenes Unlike many revision control systems the concepts upon which Mercurial is built are simple enough that it s easy to understand how the software really works Knowing this certainly isn t necessary but I find it useful to have a mental model of what s going on This understanding gives me confidence that Mercurial has been carefully designed to be both safe and efficient And just as importantly if it s easy for me to retain a good idea of what the software is doing when I perform a revision control task I m less likely to be surprised by its behaviour In this chapter we ll initially cover the core concepts behind Mercurial s design then continue to discuss some of the interesting details of its implementation 4 1 Mercurial s historical record 4 1 1 Tracking the history of a single file When Mercurial tracks modifications to a file it stores the history of that file in a metadata object called a filelog Each entry in the filelog contains enough information to reconstruct one revision of the file that is being tracked Filelogs are stored as files in the hg store data directory A filelog contains two kinds of information revision data and an index to help Mercurial to find a revision efficiently A file that is large or ha
325. y the file and hunk you want to extract Once you have this hunk you can concatenate it onto the end of your destination patch and continue with the remainder of section 12 14 2 12 15 Differences between quilt and MQ If you are already familiar with quilt MQ provides a similar command set There are a few differences in the way that 1t works You will already have noticed that most quilt commands have MQ counterparts that simply begin with a q The exceptions are quilt s add and remove commands the counterparts for which are the normal Mercurial hg add and hg remove commands There is no MQ equivalent of the quilt edit command 155 Chapter 13 Advanced uses of Mercurial Queues While it s easy to pick up straightforward uses of Mercurial Queues use of a little discipline and some of MQ s less frequently used capabilities makes it possible to work in complicated development environments In this chapter I will use as an example a technique I have used to manage the development of an Infiniband device driver for the Linux kernel The driver in question is large at least as drivers go with 25 000 lines of code spread across 35 source files It is maintained by a small team of developers While much of the material in this chapter is specific to Linux the same principles apply to any code base for which you re not the primary owner and upon which you need to do a lot of development 13 1 The problem of many target
326. yan O Sullivan lt bos serpentine com gt lo date Tue Sep 06 13 15 58 2005 0700 1 summary Get make to generate the final binary from a o file 3 changeset 2 05743c2d823c 4 user Bryan O Sullivan lt bos serpentine com gt 15 date Tue Sep 06 13 15 43 2005 0700 16 summary Introduce a typo into hello c is changeset 1 82e55d328c8c 19 user mpm selenic com 2 date Fri Aug 26 01 21 28 2005 0700 21 summary Create a makefile 22 23 changeset 0 0a04b987be5a 24 user mpm selenic com 2 date Fri Aug 26 01 20 50 2005 0700 26 summary Create a standard hello world program 27 By default this command prints a brief paragraph of output for each change to the project that was recorded In Mercurial terminology we call each of these recorded events a changeset because it can contain a record of changes to several files The fields in a record of output from hg log are as follows changeset This field has the format of a number followed by a colon followed by a hexadecimal string These are identifiers for the changeset There are two identifiers because the number is shorter and easier to type than the hex string user The identity of the person who created the changeset This is a free form field but it most often contains a person s name and email address 13 date The date and time on which the changeset was created and the timezone in which it was created The date and tim
327. you ll need to edit your Mercurial ini file to tell Mercurial where to find the actual client command For example if you re using PuTTY you ll need to use the plink command as a command line ssh client ui ssh C path to plink exe ssh i C path to my private key Note The path to plink shouldn t contain any whitespace characters or Mercu rial may not be able to run it correctly so putting it in C Program Files is probably not a good idea 6 5 3 Generating a key pair To avoid the need to repetitively type a password every time you need to use your ssh client I recommend generating a key pair On a Unix like system the ssh keygen command will do the trick On Windows if you re using PuTTY the puttygen command is what you ll need When you generate a key pair it s usually highly advisable to protect it with a passphrase The only time that you might not want to do this id when you re using the ssh protocol for automated tasks on a secure network Simply generating a key pair isn t enough however You ll need to add the public key to the set of authorised keys for whatever user you re logging in remotely as For servers using OpenSSH the vast majority this will mean adding the public key to a list in a file called authorized_keys in their ssh directory On a Unix like system your public key will have a pub extension If you re using putt ygen on Windows you can save the public
328. you can see you can run an arbitrary shell command in a hook Mercurial passes extra information to the hook using environment variables look for HG_NODE in the example 10 4 1 Performing multiple actions per event Quite often you will want to define more than one hook for a particular kind of event as shown in example 10 2 Mercurial lets you do this by adding an extension to the end of a hook s name You extend a hook s name by giving the name of the hook followed by a full stop the character followed by some more text of your choosing For example Mercurial will run both commit foo and commit bar when the commit event occurs echo commit when echo n date of commit date gt gt hg hgre echo a gt gt a hg commit m i have two hooks committed 16b1cd3b5d79a599d53 5162099bab5d9d984eb8 date of commit Sun Jun 17 18 03 51 GMT 2007 Figure 10 2 Defining a second commit hook To give a well defined order of execution when there are multiple hooks defined for an event Mercurial sorts hooks by extension and executes the hook commands in this sorted order In the above example it will execute commit bar before commit foo and commit before both It is a good idea to use a somewhat descriptive extension when you define a new hook This will help you to remember what the hook was for If the hook fails you ll get an error message that contains the hook name and extension so using
329. your privilege level Since hooks are arbitrary pieces of executable code you should treat them with an appropriate level of suspicion Do not install a hook unless you are confident that you know who created it and what it does In some cases you may be exposed to hooks that you did not install yourself If you work with Mercurial on an unfamiliar system Mercurial will run hooks defined in that system s global hgrc file If you are working with a repository owned by another user Mercurial can run hooks defined in that user s reposi tory but it will still run them as you For example if you hg pull from that repository and its hg hgrc defines a local out going hook that hook will run under your user account even though you don t own that repository Note This only applies if you are pulling from a repository on a local or network filesystem If you re pulling over http or ssh any outgoing hook will run under whatever account is executing the server process on the server XXX To see what hooks are defined in a repository use the hg config hooks command If you are working in one repository but talking to another that you do not own e g using hg pull or hg incoming remember that it is the other repository s hooks you should be checking not your own 10 2 2 Hooks do not propagate In Mercurial hooks are not revision controlled and do not propagate when you clone or pull from a rep
330. ystem command 66 import command 144 173 incoming command 21 63 108 128 incoming hook 107 116 122 124 init command 151 174 inotify extension 164 166 inserve command 166 inserve command inotify extension 166 interdiff system command 161 163 168 isodate template filter 131 132 kdiff 3 system command 30 34 167 168 locate command 153 log command 13 16 19 20 80 81 85 94 128 129 138 149 patch option 16 rev option 14 16 17 template option 129 132 p option 16 r option 14 17 1sdiff command 154 1sdiff system command 152 mercurial localrepo module localrepository class 113 121 mercurial node module bin function 121 ercurial ui module ui class 113 121 erge command 28 33 39 40 78 87 149 172 erge system command 31 32 patch system command 147 mq extension 165 168 gapplied command 142 145 151 174 qcommit command 151 174 adelete command 174 adel command f option 174 adiff command 174 afold command 154 174 e option 174 175 1 option 175 m option 175 aguard command 157 158 aheader command 175 gimport command 144 175 ginit command 139 140 150 174 175 178 c option 150 151 174 175 178 qnew command 140 141 143 144 175 f option 143 175 m option 175 aqnext command 175 apop command 142 143 148 149 176 a option 142 147 148 151 176 f option 143 176 n option 148 176 aprev command 176 apush command 142 143
331. ython Note There are two Python inotify binding libraries One of them is called bindings to the inotify subsystem pyinotify and is packaged by some Linux distributions as python inotify This is not the one you ll need as it is too buggy and inefficient to be practical Note If you follow the instructions below you ll be To get going it s best to already have a functioning copy of Mercurial installed any existing installation of Mercurial that you might alr bleeding edge Mercurial code Don t say you weren t 1 Clone the Python inotify binding repository Build and install it 1 hg clone http hg kublai com python inotify cd inotify 3 python setup py build force 4 sudo python setup py install skip build N 2 Clone the crew Mercurial repository Clone the inotify patch repository so that Mercurial Queues will be able to apply patches to your cope of the crew repository hg clone http hg intevation org mercurial crew 2 hg clone crew inotify hg clone http hg kublai com mercurial patches inotify inotify hg patches 3 Make sure that you have the Mercurial Queues extension mq enabled If you ve never used MQ read sec tion 12 5 to get started quickly 4 Go into the inotify repo and apply all of the inotify patches using the a option to the hg qpush com mand 165 1 cd inotify 2 hg qpush a If you get an error mess

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