[RFC] git submodule split

Hello,

I needed to convert a subdirectory of a repo to a submodule and have the histories of both repos linked together. I found that this was discussed few years back [1], but the code seemed quite complicated and was not merged.

[1]: http://git.661346.n2.nabble.com/RFC-What-s-the-best-UI-for-git-submodule-split-tp2318127.html

Now, the situation is better, because git subtree can already do most of the work. Below is a script that I used to split a submodule from my repo. It basically consist of a call to 'git subtree split' followed by 'git filter-branch' to link the histories together.

I'd like to get some initial feedback on it before attempting to integrate it with git sources (i.e. writing tests and doc). What do you think?

Thanks, -Michal

#!/bin/sh

set -e

. git-sh-setup

url=$1 dir=$2

test -d "$dir" || die "$dir is not a directory"

# Create subtree corresponding to the directory subtree=$(git subtree split --prefix="$dir")

subtree_tag=tmp/submodule-split-$$ git tag $subtree_tag $subtree superproject=$PWD export subtree subtree_tag superproject

# Replace the directory with submodule reference in the whole history
git filter-branch -f --index-filter "
    set -e
    # Check whether the $dir exists in this commit
    if git ls-files --error-unmatch '$dir' > /dev/null 2>&1; then

        # Find subtree commit corresponding to the commit in the
        # superproject (this could be made faster by not running git log
        # for every commit)
        subcommit=\$(git log --format='%T %H' $subtree |
     	    grep ^\$(git ls-tree \$GIT_COMMIT -- '$dir'|awk '{print \$3}') |
     	    awk '{print \$2}')

        # filter-branch runs the filter in an empty work-tree - create the
        # future submodule in it so that the 'git submodule add' below
        # does not try to clone it.
        if ! test -d '$dir'; then
     	    mkdir -p '$dir'
     	    ( cd '$dir' && clear_local_git_env && git init --quiet && git pull $superproject $subtree_tag )
        fi

        # Remove all files under $dir from index so that the 'git
        # submodule add' below does not complain.
        git ls-files '$dir'|git update-index --force-remove --stdin

        # Add the submodule - the goal here is to create/update .gitmodules
        git submodule add $url '$dir'

        # Update the submodule commit hash to the correct value
        echo \"160000 \$subcommit	$dir\"|git update-index --index-info
    fi
"

# Replace the directory in the working tree with the submodule ( cd "$dir" && find -mindepth 1 -delete && git init && git pull $superproject $subtree_tag )

# Clean up git tag --delete $subtree_tag