Importing a Git tree into a Subversion repository

Recently I worked on some new project, and as always I created a local Git repository as a start. After working on it several days, creating lots of commits, I had to publish it into the central Subversion repository (which is one of the VCSs we got). I could have done this by creating a new folder in SVN and add the latest version of all files of the project to it, but that way all history would be gone, which I didn’t like.

Git has a feature to work with SVN repositories, git-svn, but that’s intended to check out existing code from SVN and work on it, not publishing an existing Git tree into a Subversion repository.

A first rather naive approach didn’t work out (as somewhat expected), but then I figured out how to achieve this anyway.

As a test, let’s first create an empty SVN repository and a Git repository with some commits:

$ svnadmin create repo
$ svn co file:///Users/nicolas/Temp/git_to_svn/repo svn_repo
Checked out revision 0.
$ cd svn_repo
$ svn mkdir trunk tags branches
A         trunk
A         tags
A         branches
$ svn commit -m "Create repository structure"
Adding         branches
Adding         tags
Adding         trunk

Committed revision 1.
$ cd ..

$ mkdir project; cd project
$ git init
Initialized empty Git repository in /Users/nicolas/Temp/git_to_svn/project/.git/
$ echo "foo" > test.txt; git add test.txt; git commit -m "Initial version"
master (root-commit) 88464cf] Initial version
 1 files changed, 1 insertions(+), 0 deletions(-)
 create mode 100644 test.txt
$ echo "bar" > test.txt; git commit test.txt -m "Second version"
master cb62866] Second version
 1 files changed, 1 insertions(+), 1 deletions(-)

We now can set up git-svn:

$ git svn init -s file:///Users/nicolas/Temp/git_to_svn/repo/
$ git svn fetch
r1 = 741ab63aea786882eafd38dc74369e651f554c9c (trunk)

Depending on the layout of your SVN project, you might need to drop the -s parameter and add -t, -T or -b flags, see the git-svn manpage.

A little naive we could try to push everything to the SVN repository now:

$ git svn dcommit
Unable to determine upstream SVN information from HEAD history.
Perhaps the repository is empty. at /opt/local/libexec/git-core/git-svn line 439.

This fails since the git svn command can’t figure out which commits to push: there’s no link between our original Git repository and the Subversion heads.

To fix this, we can use a Git graft to link them. We’ll tell Git the commit which created the SVN folder in which we want to store the project is the parent commit of the first commit in our Git repository:

$ git show-ref trunk
741ab63aea786882eafd38dc74369e651f554c9c refs/remotes/trunk
$ git log --pretty=oneline master | tail -n1
88464cfdf549a82b30ee7c52e53e2b310f0d9ec4 Initial version
$ echo "88464cfdf549a82b30ee7c52e53e2b310f0d9ec4 741ab63aea786882eafd38dc74369e651f554c9c" >> .git/info/grafts

If now you execute git log, you’ll see the “Create repository structure” SVN commit is displayed after our “Initial version” commit.

Pushing to SVN now works fine:

$ git svn dcommit
Committing to file:///Users/nicolas/Temp/git_to_svn/repo/trunk ...
	A	test.txt
Committed r2
	A	test.txt
r2 = 8c72757dd3a7d550ed8ef393bb74c0350d22dbac (trunk)
No changes between current HEAD and refs/remotes/trunk
Resetting to the latest refs/remotes/trunk
test.txt: locally modified
	M	test.txt
Committed r3
	M	test.txt
r3 = ca0fc06d477bcd4dd5c6f6d2ae6d94356b510280 (trunk)
No changes between current HEAD and refs/remotes/trunk
Resetting to the latest refs/remotes/trunk

All set