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[eclipse-dev] Platform/JDT/PDE Committers Please Read: Git development process

Now that we are becoming more familiar with Git, we should have a discussion about our team development processes and consider changes that are more suitable to our new tools. In particular, our existing release process of tagging and map files were designed for the CVS world where moving code between branches was painful. This process is not adapting well to Git. For example, you can't reliably checkout a branch or tag that matches what was in a given build, and there is no clear way to apply release tags such as "R3_7_1" because no single commit is guaranteed to represent the built contents of all bundles in that repository.

If you think about it, our map files effectively superimposed another branch on HEAD, with the precise contents of that branch defined by the map tags for each project. This allowed us to do things like proceed with new work in HEAD without disrupting rebuilds, or revert a change by altering the map file (because backing out changes that span multiple files in CVS is painful). With Git, the more natural _expression_ of this setup is to have two branches: one for integration builds and one for ongoing work that we want to test and share with other teams but not submit to a build. It turns out that there is a popular Git development process similar to this, called git-flow [1]. I think a simplified form of git-flow would match our current development practices:

- Two main branches called "develop" and "master"
- All major feature work is first released to "develop"
- Each team periodically merges "develop" into master after performing their appropriate checks and tests (similar to our current weekly tag and release process)
- Integration builds automatically tag and build the contents of "master"

With this approach each tag on master represents a build. This makes it easy for anyone to checkout the contents of any particular build even if it spans multiple Git repositories. This also allows you to revert a build submission or make a surgical fix for a rebuild without disrupting the ongoing work in the develop branch. We could also adopt other aspects of git-flow such as release branches for our end-game period, although I'm not convinced we need it.

After that long-winded explanation, my request is that all teams think about their development practices and how they can be adjusted or improved in our new Git setup. Read up on git-flow and think about how it applies to our development process. If you're interested you might also want to look at other processes such as github-flow [2] for an alternate viewpoint. Talk about it within your team, and we'll aim to have a general discussion about it at next week's planning call (Wednesday October 19th, 11am EDT). If you don't normally join that call, send feedback to your team lead, or you're welcome to join next week's call to chime in. I don't think we'll arrive at a perfect development process overnight, but we can start to make changes and refine it as we go forward.

[1] http://nvie.com/posts/a-successful-git-branching-model/
[2] scottchacon.com/2011/08/31/github-flow.html

John