def _get_proto_filename(src):
    """Assemble the filename for a proto

    Args:
      src: the .proto <File>

    Returns:
      <string> of the filename.
    """
    parts = src.short_path.split("/")
    if len(parts) > 1 and parts[0] == "..":
        return "/".join(parts[2:])
    return src.short_path