Function die_path_inside_submodule_when_disabled 

pub fn die_path_inside_submodule_when_disabled(
    git_dir: &Path,
    work_tree: &Path,
    new_path: &str,
    index: Option<&Index>,
) -> Result<()>

Fails when submodulePathConfig is off and new_path would nest inside an existing submodule.

index is optional; when set, checked gitlinks match Git’s die_path_inside_submodule.