def METHOD_NAME(func):
    """
    Replace 'package' parameter as 'anchor' and warn about the change.
    Other errors should fall through.
    >>> files('a', 'b')
    Traceback (most recent call last):
    TypeError: files() takes from 0 to 1 positional arguments but 2 were given
    """
    undefined = object()
    @functools.wraps(func)
    def wrapper(anchor=undefined, package=undefined):
        if package is not undefined:
            if anchor is not undefined:
                return func(anchor, package)
            warnings.warn(
                "First parameter to files is renamed to 'anchor'",
                DeprecationWarning,
                stacklevel=2,
            )
            return func(package)
        elif anchor is undefined:
            return func()
        return func(anchor)
    return wrapper