Automatically synchronizing a Subversion repository and a Git repository

Question

My project has a Subversion repository on a network file system, and a new team would like to access it using Git, and be able to commit to it and get updates from it.

W

Answer 1

Here is what I've come up with:

1. Create the git-svn repository if it doesn't exist already:

   git svn init --std-layout <svn_url> <git-svn_path>
   

   The master branch is created automatically to track the trunk.

2. To avoid name ambiguities with Subversion-tracking branches, make the original Subversion branches show as remotes/svn/<branch name>: go to the newly-created git-svn repository and run

   git config svn-remote.svn.fetch trunk:refs/remotes/svn/trunk
   git config svn-remote.svn.branches branches/*:refs/remotes/svn/*
   git config svn-remote.svn.tags tags/*:refs/remotes/svn/tags/*
   
   rm .git/refs/remotes/*
   git svn fetch
   

3. Create a Subversion-tracking branch for each Subversion branch:

   for BRANCH in $(svn ls <svn_url>/branches/); do
       git branch $BRANCH remotes/svn/$BRANCH
   done
   

4. Make sure no non-Subversion-tracking branches are created on the central Git repository:

   # Used by hooks/update:
   git config hooks.denyCreateBranch true
   git config hooks.allowDeleteBranch false
   
   cp .git/hooks/update.sample .git/hooks/update
   chmod +x .git/hooks/update
   

5. Allow pushing to the central Git repository:

   git config receive.denyCurrentBranch ignore
   git config receive.denyNonFastForwards true
   git config push.default current
   

   And create the post-receive hook to reset and send the commits to Subversion:

   cat .git/hooks/post-receive
   
       #!/bin/sh
   
       date >> receive.log
       git reset --quiet --hard
       while read LINE
       do
           BRANCH=${LINE##*/}
           echo Updating $BRANCH
           git checkout --quiet --force $BRANCH
           git svn dcommit
       done 2>&1 | tee -a receive.log
       git checkout --quiet --force master
   
   chmod +x .git/hooks/post-receive
   

   The reset is necessary, because otherwise the current branch is out-of-date after each receive.

6. Finally, create the hook to get updates from Subversion:

   cat .git/hooks/svn-rebase-all
   
       #!/bin/sh
   
       date >> .git/svn-rebase.log
       git reset --quiet --hard
       for REF in .git/refs/heads/*
       do
           BRANCH=${REF##*/}
           echo Updating $BRANCH
           git checkout --quiet --force $BRANCH
           git svn rebase
       done 2>&1 | tee -a .git/svn-rebase.log
       git checkout --quiet --force master
   
   chmod +x .git/hooks/svn-rebase-all
   

   And call it from the Subversion post-commit hook:

   cat <svn_path>/hooks/post-commit
   
       cd <git_path>
       . .git/hooks/svn-rebase-all
   
   chmod +x <svn_path>/hooks/post-commit
   

Instead of using a single git-svn central repository, one can use a bare central Git repository and an intermediate non-bare git-svn repository, as in this answer. I chose to use one non-bare git-svn repository which is also the central repository.

Anyone can work on the project using Git by cloning <git_path> and pushing to it, or using Subversion by checking out <svn_url> and committing to it.

Answer 2

You're better off with just having each developer learn to use git-svn directly. There's simply too much of an impedance mismatch between the git and SVN models to be able to robustly implement what you are looking for. The only way you could get it to work even nearly reliably would be to enact the same sort of restrictions that git-svn would have, but with more moving parts that could break. In my opinion, your revision control system is not the sort of thing that you want to be just partially reliable.

Alternatively just ditch SVN altogether and move all the way to git, if possible.