code: def missing_output_files(self):
          
          missing = self.check_output_files(return_found=False)
          ret_dict = {}
          for miss_file in missing:
              ret_dict[miss_file] = [self.linkname]
          return ret_dict
docs: Make and return a dictionary of the missing output files.
  
          This returns a dictionary mapping
          filepath to list of links that produce the file as output.