Moving Git patch streams between repos.

10 06 2008

I have 2 Git repositories mirroring SVN repositories, and I want to use git to replay all the patches I made in one of the repositories to the other. The added complication is one of the SVN repos that I am mirroring uses externals, the other does not. So my source is a single repo, with no externals, and the target has externals. Fortunately I want to make all my changes in one of the modules.

So I can use the patch generations capabilities of git to generate a stream of patches.
cd sdata; git log . tells me the stream of commits in the subdir.
Having located the commit I want to start from
git-format-patch -o patches --relative d649f550a43d8f94cbe91a7c735a4a68cab4ba14 .
generates a number sequence of patch emails in a directory gitrepobase/patches. The --relative is vital since it makes the patch set relative to working directory. Unfortunately there is a bug in the next git command that means you must have the correct path for the patch to work -p4 used to strip path elements from a patch in git-am does not work for new files.

Once the patch set is created, I dont need to email it, I can just run the patch set against the target repo from files on disk. git-am -i ../camtools-trunk/patches/*.patch will interactively apply patches to the target repo, asking me for each patch.

Once the patch operation is complete a git svn dcommit commits the changes back to the target svn repo

With a bit of scripting, it should be possible to build a complete patch set with moves and transfer it between detached repos, just as if the modifications where made to the target repo by hand.

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