git merge -s subtree seems to be broken.

At work, we recently updated from a massively old version of git (1.7.10) to 2.18. There are a few code bases that use subtrees, and they seem to have completely broke when trying to merge in updates.

I have confirmed that it works correctly in 1.7.10. The 2.18 behavior is clearly incorrect.

git init echo init > test git add test git commit -m init

git remote add tig https://github.com/jonas/tig.git git fetch tig git merge -s ours --no-commit --allow-unrelated-histories tig-2.3.0 git read-tree --prefix=src/ -u tig-2.3.0 git commit -m "Get upstream tig-2.3.0" # Notice how the history are merged, and that the source from the upstream repo is in src

echo update > test git commit -a -m "test"

git merge -s subtree tig-2.4.0 # Boom, in 2.18 instead of merging into the subtree, it just deletes everything in the repository, which is clearly the wrong behavior.