git-moving-commit-history.md

Moving commit history from one repo to another

1. Split out a subset of commits that affect a directory

eg: to move all commits in an old repo affecting files in scala/ to a new repo

In the old repo

# create a scala branch with full commit history, but containing only changes to files in the scala/ directory
git checkout master
# the files in the new subtree commits with be unprefixed, ie: in the root directory
git subtree split --prefix scala --branch scala

2. Import the commits into the new repo

In the new repo, to import the branch from the old repo

# fetch the scala branch from the old repo
git fetch ~/projects/oldrepo scala
# create the branch scala from the fetch
git checkout FETCH_HEAD -b scala

The new repo will now have a scala branch containing all commits, but files will have the scala/ prefix removed.

3. Merge into master with a directory prefix

To create a merge commit on master, merging the scala branch in and prefixing all files with scala211/:

git checkout master
git subtree add -P scala211 -m "merged scala branch under directory scala211/" scala