class ForbiddenSourcesField(MultipleSourcesField):
    expected_num_files = 0
    default_glob_match_error_behavior = GlobMatchErrorBehavior.ignore

    @property
    def default(self):
        return self.globs


class ForbiddenFiles(Target):
    alias = "forbidden_files"
    help = "A target whose sources shouldn't exist."
    core_fields = (ForbiddenSourcesField,)