/// Read HEAD without mistaking an unborn branch for an I/O error.
fn head_info(repo: &gix::Repository) -> Result<HeadInfo> {
    let head = repo.head().map_err(|e| error("HEAD", e))?;
    Ok(HeadInfo { detached: head.is_detached(), unborn: head.is_unborn(),
        branch: head.referent_name().map(|name| name.as_bstr().to_str_lossy().into_owned()),
        id: head.id().map(|id| id.to_string()) })
}