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Git-SVN

If you work on a project that’s been around for a while, chances are it might still be using SVN for version control. Even if you can’t get buy-in from Management or Ops to move to Git, you can still get most of the benefits by learning the ins and outs of the git svn sub command.

Initial Clone

$ git svn clone --stdlayout svn://svn.example.com/project

Using --stdlayout tells Git that your project follows the common layout for trunk, branches, and tags. This allows you to leave off the /trunk when cloning and is important for the branching strategy I’ll mention later.

Alternatively, you could only clone trunk (and have to separately clone every branch or tag you work with) or use separate options to specify the directory structure of your project’s trunk, branches, and tags.

Commits and Branching

Now you can work with the repo as if it were a normal Git repo: commit at will, create and merge local branches, etc. When you want to sync remote changes on trunk to your local master, run:

$ git svn rebase

If you’re unfamiliar with rebasing, you should spend some time reading up on the Git concept itself. Conceptually, Git will remove any local changes you’ve made, sync master with trunk, then reapply your changes over top of the new master.

When you’re satisfied with your local changeset, you can publish your work back to trunk with:

$ git svn dcommit

This will make your local commits one-for-one as SVN commits on trunk. It uses these commits and their messages as-is, so make sure git log shows exactly what you want to publish before you execute this.

Both of these commands require a clean working directory. Later, you’ll see a shortcut for using git stash to get around this limitation.

Branches which you create with a simple git checkout -b foo will be local-only branches. They have no relationship with any SVN branches and you must not try to dcommit or rebase when on these branches.

Master obviously has a relationship to trunk and you can checkout and work with other remote SVN branches similarly with:

$ git checkout -b foo_local foo

Where foo is an SVN branch. Adding the _local suffix is my convention, you can use anything that’s unambiguous.

When on this branch, any rebase or dcommit you do will be interacting with that SVN remote branch.

If branches are added in SVN since your initial clone, you won’t be able to check them out until you let your local repo know about them:

$ git svn fetch

This effectively does a rebase of all branches as part of the update.

At any time, you can a list of all remote branches with:

$ git branch -r

Example Workflow

For non-trivial project work, I’ll typically make a local topic-branch. This allows me to jump back onto master and re-branch if I need to shift gears. It also gives me a chance to fiddle with the commits during the merge to master before I publish it out to SVN.

The simplest case of this would be using a “squash” merge:

$ git checkout -b fix-123
$ ...
$ git commit -am 'fix this thing'
$ ...
$ git commit -am 'fix that other thing'
$ ...
$ git commit -am 'change how I did this or that'
$ ...
$ git commit -am 'add test coverage ;)'

With a branch full of messy commits but a nice clean change-set, I can make all that as one SVN commit:

$ git checkout master
$ git merge --squash fix-123
$ git commit -m 'Fix Issue #123 ...'
$ git svn dcommit

There are more complicated rewrites and rebasings you could do, but this is the workflow I find myself using most often.

Aliases

I’m still coming up with these as needed, but here are a few aliases that should make things easier. Just dump them into a .gitconfig.

[alias]
  sha = svn log --show-commit --oneline -r
  spull = !git stash && git svn rebase && git stash apply
  spush = !git stash && git svn dcommit && git stash apply

The latter two should be fairly obvious, but the first allows you to print the SHA for a given revision; very useful when talking to team members who use plain SVN:

$ git sha 34961
r34961 | b6a9f38 | Fix the thingy #123

16 Jan 2013, tagged with git