More git-svn fun: working with svn branches

September 16, 2009

So, last time I detailed using git to work with your svn trunk. But many of you asked, “But Ralph, my svn repo has many branches and many tags because developers love branches and tags! How can I work with that?” Well, since no one reads this blog and no one actually asked me that, also misspelling my name in the process, let’s just pretend that what I write is relevant.

So you want to work with multiple svn branches (not to be confused with git branches). What you have to do is clone the svn repository in a different way, like this:

    $ git svn clone https://somesvnrepo/svn/project -T trunk -b branches -t tags

This should work in most cases. The arguments to the -T, -b, and -t switches are the paths that the trunk, branches, and tags are in respectively. Typically, your branches and tags should be what I put above, but just in case it is different in your case, there you go.

Working with your shiny repo

After a short time in which humans achieve interstellar travel, git finishes cloning, and you have access to the entire svn repository. Now, let’s say you wanted to start working on trunk. Like before, you should checkout a branch, but this time it’s going to use trunk as it’s parent:

    $ git checkout -b BranchOfTrunk trunk

But Lo! You have the entire repo, so you can checkout that branch from whatever branch you have in subversion.

    $ git checkout -b BranchOfSubversionBranch subversion-branch

Now, you can switch between BranchOfTrunk and BranchOfSubversionBranch, and you’ll get all the code associated with trunk and subversion-branch respectively. No more checkout of a branch ever again, wasting precious keystrokes you could use to post to Facebook.

If a new svn branch is created on the server, make sure to run the following command to see it:

    $ git svn fetch
    . (updating blah blah)
    .
    .
    $ git branch -a

The last command will show you all the branches, local (your own branches) and remote (every dumb svn branch), for this repository.

NOTE: git svn fetch and git svn rebase are almost exactly the same. fetch will update the entire git repository with anything not received from svn. rebase is concerned only with the parent of the branch you have checked out. If you recall last time, git svn rebase was equivalent to svn update. Now you can work with the same workflow as I mentioned before, working, committing locally, rebasing, etc.

Merging from subversion branch to trunk? BALDERDASH!

Now, let’s say that you want to commit a series of changes into a subversion branch, but you also want to commit the same changes in trunk also. What I’m going to show you is the workflow that I go through most of the time. I think it’s the most effective way to accomplish it in git.

First, you can run a fake dcommit.

    $ git svn dcommit --dry-run
    Committing to https://svnserver/svn/project/branches/subversion-branch ...
    diff-tree b64fdc9250bbe04b3246214ade509e0b0d9d912d~1 b64fdc9250bbe04b3246214ade509e0b0d9d912d

The --dry-run is key here, for two reasons. First, you’ll be able to see what branch you are actually committing to in subversion. Not a bad idea, since you’re working in a git repo that has all your subversion branches.

Second, you’ll see a diff tree with some of the commit hashes, one corresponding to each time you did a commit locally, in order. You will want to keep the values of the hash around, because next we are going to cherry-pick them into trunk:

    $ git checkout BranchOfTrunk
    Switched to branch "BranchOfTrunk"
    $ git cherry-pick b64fdc9
    Finished one cherry-pick.
    Created commit e4a7971:  Your commit comments here
     12 files changed, 58 insertions(+), 66 deletions(-)

You’ll notice I only used the first 7 digits of the hash (b64fdc9) to do the cherry-pick. That’s all you need to use…git will pick out the revision from just those seven characters. What this does is pulls the change from the other branch into this branch. If you have more than one commit, you should do this multiple times, in the order of the commits. But then you have the things you did on the branch ready to be checked into trunk!

This is the way I usually work. You may decide that doing a subversion merge is easier for what you are trying to do (I sometimes do also). I’d also like to know if there is an easier way to do this. This doesn’t seem the easiest way, but was the easiest way I could find so far. And I googled for like…20 minutes.

Hopefully this helps…someone. One person, at least.