Extract subproject from git repository by grafting commits onto the corresponding files

1-GraftNextCommitIfAny.sh

# CONTRACT
# SOURCE_SUBPRPOJECT_ROOT points to the "same" directory tree
# as TARGET_PROJECT_ROOT. We're extracting the directory tree
# at SOURCE_SUBPROJECT_ROOT into TARGET_PROJECT_ROOT.
#
# There must be a single, linear history in the SOURCE repository.

# Graft the current commit into the target
pushd "$SOURCE_SUBPROJECT_ROOT"
commit_comment="$(git log -1 --pretty=%B)"
rsync $RSYNC_OPTIONS --delete -aiP "$SOURCE_SUBPROJECT_ROOT/" "$TARGET_PROJECT_ROOT"
pushd "$TARGET_PROJECT_ROOT"
git add -A
git commit --allow-empty -m "${commit_comment}"
popd

# Decide what to do next
next_commit_sha1="$(git log --reverse --ancestry-path HEAD..master --pretty=%H | head -n 1)"
if [ -n "${next_commit_sha1}" ];
then
    git checkout ${next_commit_sha1}
    echo "Keep going."
else
    echo "Done!"
fi
popd

Thanks for a nice bit of bash! I learnt new things reading it (pushd/popd and that -1 is applied before --reverse).

I don't understand the use-case for the script. Why not filter-branch or cherry pick?

You might want to use rev-list instead of log --pretty=%H

I didn't think I could cherry-pick because the TARGET project's file tree is inside a subtree of the SOURCE project, and I didn't know any other way to say "apply these changes, but remove /a/b/c/ from the beginning of every file path (and also ignore incidental changes to files outside of the tree /a/b/c/". If filter-branch or cherry-pick could do that, then that's something for me to learn.

Good to know about rev-list! There are always many ways to do it. :)

Sounds like you are re-implementing subtree modules. bbl with some research :).

One more ting though, how does the target repo look like? Is it empty or does it already have some history?

so what you might want is this git push ../tmp $(git subtree split --prefix=src):refs/heads/new_branch where ../tmp is a new git repo and new_branch is the branch you want to create with the subtree in src

ah, there was a command for that :P git subtree push --prefix=src ../tmp newer_branch doeas (i think) the same as the one above.

Excellent! I'll have to try it to see whether it does what I expected. I hope I remember that in case there is a next time. :)