annotate class variables using `typing.ClassVar` about sphinx HOT 1 OPEN

class SphinxI18nReader(SphinxBaseReader):
    """
    A document reader for i18n.

    This returns the source line number of original text as current source line number
    to let users know where the error happened.
    Because the translated texts are partial and they don't have correct line numbers.
    """

    def setup(self, app: Sphinx) -> None:
        super().setup(app)

        self.transforms = self.transforms + app.registry.get_transforms()
        unused = [PreserveTranslatableMessages, Locale, RemoveTranslatableInline,
                  AutoIndexUpgrader, SphinxDomains, DoctreeReadEvent,
                  UIDTransform]
        for transform in unused:
            if transform in self.transforms:
                self.transforms.remove(transform)