Git/Conversion

This page discusses efforts to convert away from our current Subversion repository to Git, immediately affecting MediaWiki core and extensions used on Wikimedia sites. The current plan as of February 2012 is to do this by the end of March 2012.

Rationale
Our current Subversion-based version control system has served us well, but we're in need of a more suitable version control system for our development effort. Our community is very distributed, with many parallel efforts and needs to integrate many different feature efforts. After long consideration, we've decided to move from Subversion to Git.

Some advantages of git:


 * "I love git just because it allows me to commit locally (and offline)." - Guillaume Paumier
 * "[Y]ou can create commits locally and push them to the server later (great for working without wifi), you can tell it 'save my work so I can go do something else now' in one command, and it'll allow us to review changes before they go into "trunk" (master).... without human intervention in merging things into trunk. Gerrit automates this process." - Roan Kattouw

Affected development projects
MediaWiki Core (/trunk/phase3/) and MediaWiki extensions that WMF deploys will move to git in March 2012. Afterwards, any other extensions, tools, or projects that wish to move can do so. These might include operations, fundraising, pywikipediabot, etc.

We will leave some codebases in Subversion and not bother migrating them, because those extensions or tools have been abandoned. Some developers will choose to move their projects to Github or some other git site. We will also leave svn.wikimedia.org up for at least multiple years; for the subdirectories holding projects that have moved to git, the repository will be read-only.

The Git conversion team will publicize any changeover date with at least 2 weeks' notice. As of right now (1 Feb 2011) there are no specific cutover dates set.

Chad would like to gradually migrate all projects currently on Wikimedia's Subversion repository so that he can make all of svn.wikimedia.org read-only by the middle of 2013. They could move to WMF's git repo, or to another host; Chad can help them decide and migrate.


 * MediaWiki extensions (not used by WMF)
 * Starting in March or April 2012, Chad will move alphabetically through all extensions (that are not deployed on Wikimedia Foundation sites) and offer each of them choices as to when and whether to shift.


 * Pywikipediabot
 * The pywikipediabot community has not yet decided on whether to move, but is strongly leaning towards staying with SVN for now. Sumana Harihareswara, Wikimedia Foundation Volunteer Development Coordinator 00:23, 8 February 2012 (UTC)


 * Wikimedia Foundation fundraising
 * Fundraising extensions (including DonationInterface, FundraiserLandingPage, ContributionReporting, et al) can move along with core
 * Fundraising stuff in the Wikimedia repository can move on a timeline TBD


 * Wikimedia Foundation operations
 * Ops is pretty much aware of this since they've already started the git move. Happening piecemeal by them as they're ready.


 * Ariel Glenn's dumps infrastructure
 * Just two paths, /trunk/backups and /branches/ariel/. Should be pretty trivial, history's not complicated.
 * Can convert: as soon as we're ready, just give Ariel a day's notice or so.
 * Moved to operations/dumps.git on 15-Feb-2012. svn made r/o.


 * Wikimedia Foundation data mining and analytics, including Community Department


 * Toolserver internationalisation


 * Daniel Kinzler's WikiWord project
 * Per IRC: No rush, will move casually after main migration. Not under active development right now.


 * mwdumper
 * Not being actively developed right now. Can move this whenever.
 * Has been moved to mediawiki/tools/mwdumper.git on 15-Feb-2012. svn made r/o.


 * WM planet configuration
 * Was moved into operations/puppet.git (in files/planet) by Dzhan. This whole system needs redoing anyway (see bug 27208, GSoC 2012 project idea), but it'll do for now.
 * Should probably make svn r/o for this.


 * Wikimedia Mobile
 * Currently being done on github -- moving will be easy, just have to talk to mobile team about adjusting their workflow.

December 2011

 * Preliminary test conversions early in month ✅, December 5ish
 * Git workflow architecture review ✅, December 19
 * Agree on implementation strategies regarding remaining development process questions, e.g. how to handle multi-repo commits ✅ as of 1 Feb

January 2012

 * CI tests and linting get run when a developer chooses to push to the stage between their branch and the mainline branch (see Ideal Workflow Document and https://labsconsole.wikimedia.org/wiki/Git-review ) (still in progess as of 24 Feb -- Antoine is working on this)

February 2012

 * Finish code review on trunk (progress at Code Review stats and MediaWiki 1.19/Revision report) Code review backlog went back up at the end of the month.
 * Cut 1.19 release branch - ✅, Branched at r110996 on 9th February, 2012
 * Ask people to stop creating new extensions in Subversion now - ✅, 11 Feb
 * Communicate to larger community about migration
 * techblog post - ✅, 15 Febuary 2012
 * Make Gerrit behave like we want it to -- TODO [in progress, see March]
 * (work on permissions and hooks)
 * Training documentation and interactive training
 * Update Git/Workflow ✅
 * Video training. Set up a test repo, tell 3 people to submit patches simultaneously, walk them through that, then walk them through reviewing it ✅

March 2012
(Chad Horohoe will be unavailable March 10th-19th; Antoine Musso is his backup.) schedule, first of many...1.20wmf2, 1.20wmf3, etc) [Week of 12 March]
 * Finish up specific Git management scripts / changes
 * to support WMF workflow
 * stage git-based tree on fenari (Aaron S to work on fenari git stuff; this blocks 1.20 deployment/release)
 * update documentation
 * i18n updates
 * Automate the translators' process as much as possible--it currently takes about 20mins/day for Raymond to do and that's a huge timesink. Chad to follow up.  This has to be ready before ANY migration of core to git starts.
 * MediaWiki 1.19RC1 release from Subversion. [Week of 5 March]
 * Code review stats goal by end-of-week: 20 new on phase3, 100 new on phase3+extensions WMF deploys.
 * 2 weeks before migration of MediaWiki core, start communicating about cutover date -- give date & links to all the documentation with the 3 most frequently asked questions [Week of 5 March]
 * wikitech-l, mediawiki-l [ongoing]
 * add !gitconversion to mw-bot
 * MediaWiki 1.19.0 release from Subversion. Possibly even 1.20wmf1 (first mini deployment untethered to release
 * Code review stats goal by end-of-week: as close to zero as possible in phase3+extensions WMF deploys.
 * Make Gerrit behave like we want it to -- TODO
 * Making permissions right [Mostly done - want some help here to double check]
 * Allow anyone to create a gerrit account without needing human intervention from a gatekeeper [in discussion]
 * Making hooks correct [In progress - Antoine]
 * Documentation and training
 * Chad to update the code review guides, with help from Guillaume, before the migration of core. This will include:
 * docs on how current SVN committers can link their LDAP accounts, get passwords put on them, and thus get gerrit accounts (currently on labs, need improvement)
 * procedure for adding and removing people from gerrit project owner groups, including for WMF deployment branch and WMF master
 * change links on mediawiki.org
 * Developer Hub
 * How to become a MediaWiki hacker
 * Commit access
 * Code review guide
 * Download from SVN
 * templates for extensions
 * Writing an extension for deployment
 * Subversion
 * and more!
 * Git migration -- core & extensions [scheduled for Wednesday, March 21]
 * Make trunk/phase3 & trunk/extensions read-only
 * do deauth of SVN as a pre-commit hook to output an informative error message in case someone tries to commit to MW core -- "Subversion is dead, we have moved to git, read Git/Conversion"
 * pre-commit hooks are in puppet, when someone does this (probably Chad)

April 2012

 * 2 weeks before migration of MediaWiki extensions not deployed on WMF sites, start communicating about cutover date to extensions developers -- give date & links to all the documentation with the 3 most frequently asked questions (wikitech-l, mediawiki-l)
 * Git migration -- ANYTHING ELSE
 * Make paths read-only on case-by-case basis.
 * Ongoing, slow process.
 * Move towards git-based development and release process
 * First deployment from git mainline development branch
 * Move towards continuous integration via git, goalpost: weekly deployment
 * Jenkins (Testswarm/PHPUnit tests) on git branches
 * MediaWiki 1.20, first deployment and release from git mainline development branch

Unscheduled items
Other cool things to do:
 * ❌ Convert the Bugzilla code to recognize the new SHA-1 commits. Come up with a shorthand to autolink from BZ to gerrit changeset
 * Would Mark H. mind looking into this, since Bugzilla is his baby?
 * ❌ Create database of SVN revision ids -> Git SHA-1's for useful lookups.
 * Info is included in Git commits, just need to make a DB mapping of them. Good weekend project after the conversion is complete if someone is feeling bored.
 * ❌ Rusty and Roan's effort to turn every Bugzilla patch into a git pull request.
 * ❌ Bump gerrit ids to some big number (eg. 200000) greater than the largest svn revision (so that they could be treated as 'logical' revisions, without conflicting the svn ones).
 * Not easy -- we've already started using gerrit in a production setting and we've got over 2k changesets.
 * We can live with those 2k changesets having the same number of MW ones, as they are different repos. For the actual change, it seems as easy as running ALTER TABLE tbl_name AUTO_INCREMENT = N.
 * ❌ Get native packages on Windows and Mac for git-review since it's so much easier and better than the manual commit messages hook process.
 * ❌ Change the configs of automatic bots -- when I commit, where will it spit out?
 * ❌ change MediaWiki CR to readonly, no new comments or statuschanges. This is in the very long run: how to write redirects for viewvc -> gitweb?  But that can wait till like 2013.
 * ❌ Keep Extension:ExtensionDistributor working.

Split up and convert repositories
A naïve  conversion of the entire repository (with branches) weighs in at around 7.8GB (November 2011). It makes no sense to make one Git MediaWiki repository, it should be split up.

In Subversion everything gets squashed into one giant repository. In Git repositories are split at the boundaries over which code does not cross.

Splitting
We have a test repository up, but in February 2012 will redo the split to create a permanent git repo.


 * MediaWiki will go in mediawiki/core.git
 * Extensions will go in mediawiki/extensions/foo.git
 * Two meta-repos, mediawiki/extensions-all.git and mediawiki/extensions-wmf.git will be repos using submodules to maintain "all" or "wmf" extensions.
 * Other things across SVN need to find new homes in Git

/Splitting tests

Converting

 * ✅ Every commit needs to be rewritten to give name/email pairs to SVN users. We are using username@users.mediawiki.org for a unified e-mail address scheme for all old commits.
 * Only for those without a known mailaddress or all?
 * What about username@svn.wikimedia.org instead?

Ideal state
This is what we'd love to see:

History

 * See history of MediaWiki version control

Working on the conversion

 * User:^demon

Would like to see it happen

 * 
 * Aryeh Gregor
 * Ashar Voultoiz (already use git locally)
 * Daniel Friesen
 * Gregory Varnum

Documents

 * User requirements:
 * Specifications: https://labsconsole.wikimedia.org/wiki/Gerrit_bugs_that_matter
 * Software design document:
 * Test plan:
 * Documentation plan:
 * User interface design docs: https://labsconsole.wikimedia.org/wiki/Gerrit_bugs_that_matter
 * Schedule: see Timeline above
 * Task management: Task list from Bugzilla (bug 22596)
 * Release management plan:
 * Communications plan:
 * Status updates

Communications

 * draft plan
 * announcement of test repository
 * "git boot camp" from October 2011 NOLA hackathon GitBootcamp
 * https://blog.wikimedia.org/2012/02/15/wikimedia-engineering-moving-from-subversion-to-git/
 * Git, Gerrit, and You! or, Gerrit training available starting Monday 27 February
 * Postponing Git migration until March 21