code: def apply_injectables(self, targets):
      
      target_types = {type(t) for t in targets}
      target_subsystem_deps = {s for s in itertools.chain(*(t.subsystems() for t in target_types))}
      for subsystem in target_subsystem_deps:
        # TODO: The is_initialized() check is primarily for tests and would be nice to do away with.
        if issubclass(subsystem, InjectablesMixin) and subsystem.is_initialized():
          subsystem.global_instance().injectables(self)
docs: Given an iterable of `Target` instances, apply their transitive injectables.