Friday, October 08, 2010

Git+SVN #5: Centralized Git-SVN Mirror

This post is part of a series on Git and Subversion. To see all the related posts, screencasts and other resources, please click here

Another episode on how to live with Git and Subversion in parallel:

Only a few days left till GearConf, where I will be repeating the exercise, adding all sorts of useful hints and tips on the way.

NOTE: At the end of the cast, I presented this little shell-script that I normally use for committing:

git update-ref refs/remotes/git-svn refs/remotes/origin/master
git svn dcommit

Some more background:

git svn dcommit actually updates the refs/remotes/git-svn

However, in the case that I first do a git pull from the bare repo, getting the new commits via the "pure" git command, no svn refs are updated! Example:

Let's say bob commits a change. John then updates his repo:

tfnico@flint:~/john/website/>git pull --rebase
remote: Counting objects: 8, done.
remote: Compressing objects: 100% (4/4), done.
remote: Total 6 (delta 2), reused 0 (delta 0)
Unpacking objects: 100% (6/6), done.
From /Users/tfnico/john/../git-repos/website
884f657..1cb7f98 master -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 1cb7f98dbcc6fd9351108021e3ab9aa29a6bcb6a.
tfnico@flint:~/john/website/>vim README.txt
tfnico@flint:~/john/website/>git commit -a -m "Fixed readme again."
tfnico@flint:~/john/website/>git svn dcommit
Committing to file:///Users/tfnico/svn-repos/company-repo/website ...
Transaction is out of date: File '/website/' is out of date at /opt/local/libexec/git-core/git-svn line 572

See? We can't push back to SVN, because the ref is out of date. This is where the update-ref comes into play:

tfnico@flint:~/john/website/>git update-ref refs/remotes/git-svn refs/remotes/origin/master
tfnico@flint:~/john/website/>git svn dcommit
Partial-rebuilding .git/svn/refs/remotes/git-svn/.rev_map.748a8128-3b48-42b3-854a-26eb1451c56d ...
Currently at 8 = fe775358fcec6db0cc130f2377549c1cc5668400
r9 = a72a3e8c37f3fa174c5ec7464ab97a8fddbf4652
r10 = 1cb7f98dbcc6fd9351108021e3ab9aa29a6bcb6a
Done rebuilding .git/svn/refs/remotes/git-svn/.rev_map.748a8128-3b48-42b3-854a-26eb1451c56d
Committing to file:///Users/tfnico/svn-repos/company-repo/website ...
Committed r11
r11 = c019fc06ad36b06ef644518e85085da653335fb9 (refs/remotes/git-svn)
No changes between current HEAD and refs/remotes/git-svn
Resetting to the latest refs/remotes/git-svn

The dcommit was now successful. Remember: If you pull normal git style, nothing happens with the svn refs even if we pull changes from SVN. Perhaps this is a fault in git-pull, but we'll have to do this work-around for now.

Another important note: The reason why John uses --rebase for his pull is that he has local commits, and he wants to keep history linear for the sake of Subversion, like we discussed in previous episodes. If you have local commits, always pull from the bare repo with --rebase.