Git Submodule from Existing Path with Branches

This article will show you how you can migrate an existing path within an existing project into a new project, then add that new project as submodule to the original project, while keeping all tags and branches. Typically, branches are lost in migration, but not with this little addition.

Fill a New Repository With a Complete Sub Path of Another Repository

You clone the original project, then filter to the path you want to extract, change the origin and push everything to the new origin. But with only that, this will not copy all the existing branches. Only if you first checkout all branches, then they will also be pushed to the new location. This is what the for-loop does for you.

git clone git@server.url:path/to/original-project.git
cd original-project
git filter-branch --tag-name-filter cat --subdirectory-filter path/to/submodule -- --all
for b in $(git branch -r); do
    git checkout ${b#origin/}
    git reset --hard $b
    git fetch
    git reset --hard ${b#origin/}
done
git remote remove origin
git remote add origin git@server.url:path/to/new-sub-project.git
git push origin --all

Now you have a new repository that contains only a part of the previous one.

Replace a Path with a Submodule

Next step is to replace the path in the old repository by the new repository as a submodule. Clone the original project again (delete the previous clone).

git clone git@server.url:path/to/original-project.git
cd original-project
git rm -rf path/to/submodule
git commit -am "remove old path/to/submodule"
git submodule add git@server.url:path/to/new-sub-project.git path/to/submodule

Now you have replaced path/to/submodule by a new submodule.