like git-cherry-pick, but with more sledgehammer
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git-import-commit.xcodeproj
libgit2
README.markdown
git-import-commit.c
git-import-commit_Prefix.pch

README.markdown

git-import-commit

git-import-commit is a small command-line tool that imports a source repo's commit (and all its associated trees and blobs) into a destination repo as a "new" commit (it updates the given branch's head).

Unlike git-cherry-pick, the commit itself is not rewritten in any way (it's copied wholesale) and the imported commit's tree can be entirely different than what's currently in the destination repo. The imported commit will have a different SHA, however, since its parent ID is different than it was in the source repo.

Purpose

I wrote this tool after I migrated a ten-year-old CVS repo to git for client and then logged a few hundred commits before I realized I botched the initial migration (I used multiple cvs2git ... module invocations when I should have used a single cvs2git ... cvsroot on the entire repo (the dir with the CVSROOT dir in it) and lost most of the tags).

I was able to redo the initial migration and restore the tags (thanks backups+paranoia), but I still had those 200+ commits from the "future". I couldn't just merge them in since none of the parent commit IDs matched.

So I did something like this:

$ cd bad-repo
$ git rev-list HEAD|sed '1!G;h;$!d'|bbedit #sed magic to reverse lines
(...edit out commit IDs from original migrated repo...)

That yielded a reverse-chronological listing of commits IDs to be imported into the newly migrated repo. I turned it into a dumb .sh script full of git-import-commit invocations that I ran:

git-import-commit project-migration2/.git refs/heads/develop project-botched-base/.git 31a7fd5117d11fc4db6f19e8e52219cee5a7ec87 --quiet
git-import-commit project-migration2/.git refs/heads/develop project-botched-base/.git e321b08b83cd194a477951f95b84d7ed52fbaf68 --quiet
git-import-commit project-migration2/.git refs/heads/develop project-botched-base/.git 50b8f1939e1ae1c49fc281abaf90cdbf7efc253b --quiet
git-import-commit project-migration2/.git refs/heads/develop project-botched-base/.git 8a89f790cd2049766ddbae0696af01c45703cfe8 --quiet
...

When run in default verbose mode, git-import-commit prints the commit tree. It prefixes each dir and file with either an equal sign (=) or a plus (+). The equal sign means the dir/tree or file/blob was already found in the destination repo and didn't need to be copied over, while the plus indicates a copy was needed.

All that said, you probably won't ever need this tool unless you're up against a similar wall.

Dependancies

git-import-commit relies on libgit2, which is included as a submodule.

FIXME

There's a bunch of limitations that I didn't bother to deal with since they didn't bite me:

  • Tags aren't imported.

  • Commits with multiple parents are flattened down to one parent, losing information.

  • It would be cool to stream blobs when copying instead of buffering their entirety into memory.

  • Argument handling is pathetic (should use getopt or some such).

  • While the code should be pretty much cross-platform, only an .xcodeproj file is provided.