How can I create a gitsubtree of an existing repository?

Question

I'm trying to create a gitsubtree of an existing repository, for example:

-> projectA/projectB

Project A is the parent, i want to add project B as a git subtree.

git subtree -P projectB ssh://[email protected]/projectB.git master

But it fails, and shows the following message:

prefix 'projectB' already exists.

I don't want to download all the repository again, I just want to add this directory to my gitsubtree.

This directory project B isn't tracked by Project A git.

thanks in advance

Answer 1

You can add projectB as a subtree of projectA using vanilla git (you don't need git subtree).

cd projectA
git remote add projectB_remote [email protected]/projectB.git
git fetch projectB_remote
git checkout -b projectB_branch projectB_remote/master
git checkout master
git read-tree --prefix=projectB/ -u projectB_branch

Explanation

1. Enter the local projectA repo.
2. Add a new remote called projectB_remote with projectB's url.
3. Fetch projectB_remote without merging.
4. Create and checkout a projectB_branch; bring in the projectB_remote/master files.
5. Return to projectA/master.
6. Create a subtree in projectA/master that contains a checkout of the projectB_branch.

Resultant Directory Structure

projectA
    projectB
    other.txt
    project.txt
    A.txt
    files.txt

See http://www.git-scm.com/book/en/v1/Git-Tools-Subtree-Merging

Answer 2

When adding a subtree, it seems that the prefix (subdirectory in which you will add the subtree) cannot already exist.

I worked around this problem by checking-out to a commit before this subdirectory existed, doing the git subtree add, and then merging with the branch that contained my old subdirectory contents.