How to use the ghstack.diff function in ghstack

return self._search_group(RE_RAW_AUTHOR, "name")

    def author_email(self) -> str:
        return self._search_group(RE_RAW_AUTHOR, "email")

    def commit_msg(self) -> str:
        return '\n'.join(
            m.group("line")
            for m in RE_RAW_COMMIT_MSG_LINE.finditer(self.raw_header))


def split_header(s: str) -> List[CommitHeader]:
    return list(map(CommitHeader, s.split("\0")[:-1]))


class GitPatch(ghstack.diff.Patch):
    h: CommitHeader

    def __init__(self, h: CommitHeader):
        self.h = h

    def apply(self, sh: ghstack.shell.Shell, base_tree: GitTreeHash) -> GitTreeHash:
        expected_tree = sh.git("rev-parse", self.h.commit_id() + "~^{tree}")
        assert expected_tree == base_tree, \
            "expected_tree = {}, base_tree = {}".format(expected_tree, base_tree)
        return self.h.tree()


def parse_header(s: str) -> List[ghstack.diff.Diff]:
    def convert(h: CommitHeader) -> ghstack.diff.Diff:
        parents = h.parents()
        if len(parents) != 1: