git-svn, and thoughts on Subversion

We use Subversion for our revision control system, and it’s great. It’s certainly not the most advanced thing out there, but it has perhaps the best client support on every platform out there, and when you need to work with non-coders on Windows, Linux and Mac OS X, there’s a lot of better things to do than explain how to use the command-line to people who’ve never heard of it before.

However, I also really need to work offline. My usual modus operandi is working at a café without Internet access (thanks for still being in the stone-age when it comes to data access, Australia), which pretty rules out using Subversion, because I can’t do commits when I do the majority of my work. So, I used svk for quite a long time, and everything was good.

Then, about a month ago, I got annoyed with svk screwing up relatively simple pushes and pulls for the last time. svk seems to work fine if you only track one branch and all you ever do is use its capabilities to commit offline, but the moment you start doing anything vaguely complicated like merges, or track both the trunk and a branch or two, it’ll explode. Workmates generally don’t like it when they see 20 commits arrive the next morning that totally FUBAR your repository.

So, I started using git-svn instead. People who know me will understand that I have a hatred of crap user interfaces, and I have a special hatred of UIs that are different “just because”, which applies to git rather well. I absolutely refused to use tla for that reason—which thankfully never seems to be mentioned in distributed revision control circles anymore—and I stayed away from git for a long time because of its refusal to use conventional revision control terminology. git-svn in particular suffered more much from (ab)using different terminology than git, because you were intermixing Subversion jargon with git jargon. Sorry, you use checkout to revert a commit? And checkout also switches between branches? revert is like a merge? WTF? The five or ten tutorials that I found on the ‘net helped quite a lot, but since a lot of them told me to do things in different ways and I didn’t know what the subtle differences between the commands were, I went back to tolerating svk until it screwed up a commit for the very last time. I also tried really hard to use bzr-svn since I really like Bazaar (and the guys behind Bazaar), but it was clear that git-svn was stable and ready to use right now, whereas bzr-svn still had some very rough edges around it and isn’t quite ready for production yet.

However, now that I’ve got my head wrapped around git’s jargon, I’m very happy to say that it was well worth the time for my brain to learn it. Linus elevated himself from “bloody good” to “true genius” in my eyes for writing that thing in a week, and I now have a very happy workflow using git to integrate with svn.

So, just to pollute the Intertubes more, here’s my own git-svn cheatsheet. I don’t know if this is the most correct way to do things (is there any “correct” way to do things in git?), but it certainly works for me:

* initial repository import (svk sync):
git-svn init -T trunk -b branches -t tags
git checkout -b work trunk

* pulling from upstream (svk pull):
git-svn rebase

* pulling from upstream when there's new branches/tags/etc added:
git-svn fetch

* switching between branches:
git checkout branchname

* svk/svn diff -c NNNN:
git diff NNNN^!

* commiting a change:
git add
git commit

* reverting a change:
git checkout path

* pushing changes upstream (svk push):
git-svn dcommit

* importing svn:ignore:
(echo; git-svn show-ignore) >> .git/info/exclude

* uncommit:
git reset <SHA1 to reset to>

Drop me an email if you have suggestions to improve those. About the only thing that I miss from svk was the great feature of being able to delete a filename from the commit message, which would unstage it from the commit. That was tremendously useful; it meant that you could git commit -a all your changes except one little file, which was simply deleting one line. It’s much easier than tediously trying to git add thirteen files in different directories just you can omit one file.

One tip for git: if your repository has top-level trunk/branches/tags directories, like this:


That layout makes switching between the trunk and a branch of a project quite annoying, because while you can “switch” to (checkout) branches/foo-experimental/, git won’t let you checkout trunk/foo; it’ll only let you checkout trunk. This isn’t a big problem, but it does mean that your overall directory structure keeps changing because switching to trunk means that you have foo/ and bar/ directories, while switching to a foo-experimental or bar-experimental omits those directories. This ruins your git excludes and tends to cause general confusion with old files being left behind when switching branches.

Since many of us will only want to track one particular project in a Subversion repository rather than an entire tree (i.e. switch between trunk/foo and branches/foo-experimental), change your .git/config file from this:

[svn-remote "svn"]
    url =
    fetch = trunk:refs/remotes/trunk
    branches = branches/*:refs/remotes/*
    tags = tags/*:refs/remotes/tags/*

to this:

[svn-remote "svn"]
    url =
    fetch = trunk/foo:refs/remotes/trunk
     ; ^ change "trunk" to "trunk/foo" as the first part of the fetch
    branches = branches/*:refs/remotes/*
    tags = tags/*:refs/remotes/tags/*

Doing that will make git’s “trunk” branch track trunk/foo/ on your server rather than just trunk/, which is probably what you want. If you want to track other projects in the tree, it’s probably better to git-svn init another directory. Update: Oops, I forgot to thank Mark Rowe for help with this. Thanks Mark!

As an aside, while I believe that distributed version control systems look like a great future for open-source projects, it’s interesting that DVCS clients are now starting to support Subversion, which now forms some form of lowest common denominator. (I’d call it the FAT32 of revision control systems, but that’d be a bit unkind… worse-is-better, perhaps?) Apart from the more “official” clients such as command-line svn and TortoiseSVN, it’s also supported by svk, Git, Bazaar, Mercurial, and some great other GUI clients on Mac OS X and Windows. Perhaps Subversion will become a de-facto repository format that everyone else can push and pull between, since it has the widest range of client choice.

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