Tracking Moodle CVS with git

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Introduction

If you plan on doing complicated or sustained development on Moodle, you will benefit from a local revision control system. Centralized systems like CVS and SVN have limited capabilities for tracking vendor branches. For the ultimate experience you will want to use a system with distributed capabilities like git. Alternative tools for this include Mercurial, Darcs and SVK.

GIT was developed by Linus Torvalds specifically for the Linux Kernel team. It is fast, fast, fast. Its usage is slightly different from CVS/SVN, but, if kernel developers can handle it Moodle developers will find it easy  ;-)

Caveat: Git is not particularly easy to use or understand beyond trivial use. It was designed with a great deal of flexibility in mind and you will never get one answer to "how do I....". It is well worth spending some time to understand the basics of how git works. It will pay many times over. There are some very good online resources (see the end of this article).

Git is packaged for most major operating systems and an up to date list of packages can be found on git.or.cz.

Obtaining git

You'll want:

  • Git (and its deps). It includes gitk, a very good UI for visualising project history.

You might also find the additional git porcelain (frontend) useful:

  • qgit a nice GUI to view the project history, make commits, etc. Recommended! Note: qgit is tricky to compile by hand, get a .deb or an .rpm
  • stgit (StackedGIT is mainly for users doing heavy cherry picking. Only recommended for very advanced SCM users.)

Git is still developing very quickly, but good mature versions are already available in packaged format. This guide is written with GIT v1.5.3 in mind. Earlier versions work somewhat differently and you are unlikely to have a positive experience. You can check your version in the usual manner:

   git --version

Downloading Moodle CVS History for git

There are currently two methods of retrieving Moodle CVS history for git:

Creating a Working Copy

In order to use your repository you must clone yourself a working copy using git clone.

(Let's assume your destination directory is ~/src/moodle)

git clone git://git.moodle.org/moodle.git ~/src/moodle

This will clone the moodle git repostitory into a local working copy that you may make changes to and commit to. This initial clone will take some time, but note that once you have cloned this repository, you will have the complete moodle source code history locally and can easily browse and checkout any commit in moodle history without a network connection.

Using git effectively with Moodle

Git can be used to intelligently track changes for creating client installs based off your own local, base, customisations which in turn tracks changes to the main Moodle CVS.

If you have a local git copy of the Moodle CVS repository you will have a number of heads such as: MOODLE_15_STABLE, MOODLE_16_STABLE, and so on. If you wish to create a new branch for your local customisations, you can base it off an existing HEAD (one of the CVS branches that exist in the main Moodle repository). If you wish to create a new local branch, mymoodle, based off the current stable 1.6 code you would:

cd ~/src/moodle
git branch mymoodle origin/MOODLE_16_STABLE
git branch # lists all the current branches, should show mymoodle
git checkout mymoodle # you are now working on the mymoodle branch
# add some new files (i.e. themes, blocks, etc.)
git add  .
git status # Will list your uncommited files
git commit -m "Added base customisations."

To return to the master HEAD, equivalent to the main Moodle CVS HEAD branch, you would have to use:

git branch master

To get updated from cvs/catalyst

cd ~/src/moodle
git fetch # fetches changes from upstream repostiroy
git checkout mymoodle
git merge origin/MOODLE_16_STABLE # merges changes from upstream

If you wanted to use this custom local branch to create a new client install, you could use:

git clone ~/src/moodle /home/someclient/public_html/
cd /home/someclient/public_html/
git branch mymoodle origin/mymoodle
git checkout mymoodle 

This would create a new git repository from your branch that could be used to do a client install which can, in turn, have the client's custom files added to it. This entire process can be automated so that your mymoodle branch is tracking upstream changes from the Moodle CVS (MOODLE_16_STABLE in this example) and your client installs are tracking changes against your local branch.

Merging a patch from GIT into CVS

If you have cvs access, you can use the git-cvsexportcommit command to merge or cherry pick individual patches into upstream.

git-cvsexportcommit was initially written to do merges of NZOSVLE bugfixes into Moodle. Several tools and patches to GIT and Cogito come from the NZOSVLE team. Martin Langhoff 14:55, 19 July 2006 (WST)

If the patches merge cleanly, future updates will recognise the already-applied patch. In that sense the merger in git is smarter than the merger in Cogito, consider using git-pull rather than cg-update. Note that if you see conflicts using git-pull you will have to work a bit harder to resolve them. Make sure you are familiar with handling merge conflicts with pure git before trying this.

This is how I use git-cvsexportcommit: I have two directories - one with my Moodle git clone, the second with the CVS checkout. I commit a patch on a branch in git. Then I go into the CVS checkout directory and use something like

$ GIT_DIR=../moodle-19/.git git cvsexportcommit b38cb61
$ cvs commit -F .msg 'file1.php' 'path/to/file2.php'

Here "b38cb61" is the commit id I want to merge into CVS. See the cvsexportcommit output as it tells you what parameters to use during cvs commit.

Preparing to merge large patch series or porting over to the next Moodle release

When you have a large set of patches to apply to CVS, or a large set of custom patches to apply on top of the next release of Moodle, you can use git-format-patch to see what are your unmerged patches. git-format-patch tries hard to spot already-merged patches and skip them.

If you are applying patches to CVS, you can then use git-cvsexportcommit or plain old patch -p1 filename. If you are applying them to a new git branch (as you would to merge them on top of a new Moodle release) then you want to be on that new branch, and use git-am -3 -k filename.

If you are using git-am, make sure you learn how to deal with merge conflicts, and the use of git-update-index.

IDE support for git

Eclipse

NetBeans

See also Setting up Netbeans#Git with NetBeans.

TortoiseGit

Git Tips

Helpful Documentation

Moodle Forum Discussions