def METHOD_NAME(self) -> Set[str]:
    if not self.__stage_snaps:
        processor = GrammarProcessor(
            arch=self._arch,
            target_arch=self._target_arch,
            checker=repo.snaps.SnapPackage.is_valid_snap,
        )
        self.__stage_snaps = set(
            processor.process(grammar=self._get_property("stage-snaps"))
        )
    return self.__stage_snaps