Function submodule_gitdir_outer_conflict 

pub fn submodule_gitdir_outer_conflict(
    git_dir: &Path,
    submodule_name: &str,
) -> Option<PathBuf>

When a proposed .git/modules/<name> path would sit inside another submodule’s git dir (e.g. names hippo and hippo/hooks), returns the outer git directory path (Git validate_submodule_legacy_git_dir).