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I am planning a svn to git migration of a bunch of repositories. Two of them are in a particular state.

A project has been developped in a svn repo. Due to various constraints, the project has been forked at some point. The fork has been made by duplicating the svn repo. After that point, the two projects evolved separately. No branches or tags exist in either repo besides the trunk.

A significant functionality has been developed for the original project and needs to be ported to the fork. In the current situation this could be done by creating a patch from the various revisions and applying it on the forked project. This has the advantage of short term simplicity in the current situation but has a number of unwieldy consequences on the long term.

We could have two distinct git repos and do cross-fork porting via pull requests, but this could lack usability (we're not using github). Besides there may come a time where we might want to reintegrate the fork into the parent project thanks to modular design refactoring. Another approach would be to merge the two svn repositories into a single git repository as distinct branches, and manage subsequent merges from there (with all the advantages that it gives).

Ideally I'd like to recreate the true history of the project, that is have a git repo with:

  • a single branch comprised of commits up to the fork
  • two distinct branches comprised of parent and fork commits up to HEADs

An interesting fact that might help, the following command produces identical SHA1s for the common commits:

git svn clone -s -A svn.authors --no-metadata http://subversion.foo.local/repo/path git_migration

I don't care about --no-metadata because it's a one-way migration.

How could I achieve such a result, if even possible?

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2 Answers 2

Reset to default
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Since you have a way to clone the SVN repos with identical hashes for common commits, this should work.

git svn clone -s -A svn.authors --no-metadata http://subversion.foo.local/repo1/path git_migration git svn clone -s -A svn.authors --no-metadata http://subversion.foo.local/repo2/path git_migration-2 cd git_migration git branch repo1 # Branch for first repo git reset --hard <highest_common_hash> # To have only common history on master git checkout -b repo2 # Branch for second repo git pull ../git_migration-2 master

Now you must have common history in master and 2 branches for the different SVN repos.

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5 Comments

I came up with this quick and dirty command to find the highest common hash: cd git_migration, git log | grep 'commit' | cut -f2 -d' ' | while read hash; do (cd ../git_migration-2; git log | grep "$hash"); done | head -1. No bailing out on match, so use Ctrl+C liberally. Watch out, it's a O(m*n) complexity (we have ~2000 revs and it's a one shot so we could care less).
@Lloeki: have a look at git merge-base, I think it can do these things.
git remote add -f -t master migration2 ../git_migration-2 then git merge-base $(cat .git/refs/heads/master) $(cat .git/refs/remotes/migration2/master) produced the same commit as my hack, only much (much!) faster. Thanks @sehe.
@Lloeki: And it'll be even shorter if you just say git merge-base master migration2/master :) (the symbolic names - called refs - will be automatically resolved; see git rev-parse)
Duh. How could I have overlooked that? I still got a long way I guess :)
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Joining history to a single root in general can usually be done using git Graft Points

Il refer you to

https://git.wiki.kernel.org/index.php/GraftPoint

In simplistic terms, you just tell git which revisions share a certain parent revision (a magic 'merge' result if you will). Once you're happy you can cast it in stone using git filter-branch

Sample from man git-filter-branch

echo "$commit-id $graft-id" >> .git/info/grafts git filter-branch $graft-id..HEAD
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1 Comment

Although only partial and quite a brutal answer to my problem it struck me as interesting whenever I want to force-record merges from the git-svn side.

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