docs: def set_loader(fxn):
      """Set __loader__ on the returned module.
      This function is deprecated.
      """
      @functools.wraps(fxn)
      def set_loader_wrapper(self, *args, **kwargs):
          warnings.warn('The import system now takes care of this automatically.',
                        DeprecationWarning, stacklevel=2)
          module = fxn(self, *args, **kwargs)
          if getattr(module, '__loader__', None) is None:
              module.__loader__ = self
          return module
      return set_loader_wrapper