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Re: [] Moving to GIT

Hi all,

Axel: I think you volunteered to supervise the migration from CVS to GIT
after the Indigo release.

Axel: Have you had a chance to consider what might need to be done?

I see two sorts of things that need to happen:

- initial import: we have to make up our minds what we'd like to take with us. I suggest to have the entire history of the OCL project migrate from CVS to GIT. My understanding is that there is admin support on side assisting us with such a first-time migration.

- adjusting releng; in particular the Hudson job needs to be aware of the git repository and the branch to check out for building. I suggest I have a meeting with our eGit committers at SAP to get their recommendations. Perhaps we can afford to have more than one build job, for different branches, given how easy and convenient it is on git to branch/merge. According to my experience this can help avoiding broken builds for the master branch. For example, if Ed want to try some outrageously complicated refactoring for Pivot and still have the luxury of a central build, Ed would do so on a git branch and happily commit to that branch with Hudson building / testing that branch for him. Re-basing on master, one more build, then merge into master is then fairly easy.

- commit and CQ procedures: we briefly discussed this at EclipseCon, and I haven't received full clarification on this subject yet. I assume that ideally we can manage to have only commits by registered OCL committers in the commits that get pushed. I have to check the details of pushing multiple commits at once. This is how we usually work in our internal projects. Many committers doing many small commits locally. When their stuff looks halfway reasonable they push a whole series of commits to a branch that Hudson can build. If that looks ok they merge it into the master branch. Not sure we can get to something equivalent at Eclipse because someone mentioned that the procedures would suggest single-commit-pushes only which I would find somewhat unfortunate. Action item for me is to get clarification on this until after Indigo.

I briefly tried to access the Xtext GIT repository without success (very
brief, didn't read the guide).
But it did appear that I needed to set up multiple levels of redirection.

This might be good. Presumably I can set up my local repository on my
network RAID redirecting to the
Eclipse GIT. This could solve my laptop/tower workspace synchronisation

It most certainly will. You usually "git clone" some central repository to a local git. You can clone this again to other locations. Synchronizing between them happens by pushing / fetching the commits.

Axel: How do we migrate CVS? or is GIT an upper level continuing to use
CVS as its lower implementation?

There is a git-cvsimport utility that I'm using regularly to synchronize the OCL CVS into my local git and from there to github where we have our FURCAS development with branches that test our OCL contributions before we submit them to the Eclipse CVS. git-cvsimport has its shortcomings in day-to-day use but should be fine for a one-shot migration. For example, git-cvsimport is trying to group many CVS file commits into larger git commits, based on timestamp and commit log message. But that's guessing. And sometimes I experienced that git-cvsimport loses some commits which can get really nasty. But if we get's support in doing the one-time synch and have all committers commit to git only afterwards, that shouldn't be a problem. It means, however, that we should have releng more or less prepared before we do this, or we'd have to rely on git-cvsimport to do at least one more synch before we stop committing to CVS.

And, no, git does not use CVS as an underlying impl. GIT has a binary file-based repository underneath that has a structure fairly different from that of CVS which---being based on RCS---has a file-by-file view. GIT takes a commit-by-commit view where each commit holds the changes to one or more files which can include renames/moves, deletions, creations and so on. GIT commits also know their predecessor commits, so all branch/merge activities are recorded in the commits, too.

-- Axel

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