Function is_submodule_active 

pub fn is_submodule_active(
    repo: &Repository,
    path: &str,
) -> Result<bool, String>

Git is_submodule_active for the current repository and index (HEAD + .gitmodules mapping).

Returns Ok(true) / Ok(false) for normal checks, or Err when submodule.active has a bare entry (Git config_error_nonbool).