def METHOD_NAME(filename: str, slug: str) -> str:
    """
    Look for a source file location.
    If the location is found, return a string location suitable for GDB's
    break command. Raise a RuntimeError otherwise.
    :param filename: Target source file name.
    :param slug: Source file excerpt for the location. For instance, a
        specific string that is in a comment.
    :return: String location suitable for GDB's break command.
    """
    with open(filename, "r") as f:
        for i, line in enumerate(f, 1):
            if slug in line:
                return "{}:{}".format(filename, i)
    raise RuntimeError(
        "Could not find location in {} for {}".format(filename, slug)
    )