def METHOD_NAME(self) -> List[str]:
    """Returns a set of files that are not ignored by .lightningignore."""
    if self._non_ignored_files is None:
        if self.package_source:
            self._non_ignored_files = _copytree(self.path, "", ignore_functions=self.ignore_functions, dry_run=True)
        else:
            self._non_ignored_files = []
    return self._non_ignored_files