def METHOD_NAME(self) -> Set[str]:
    if not self.__stage_packages:
        processor = GrammarProcessor(
            arch=self._arch,
            target_arch=self._target_arch,
            checker=self._repo.build_package_is_valid,
            transformer=package_transformer,
        )
        self.__stage_packages = set(
            processor.process(
                grammar=self._get_property("stage-packages"),
            )
        )
    return self.__stage_packages