def missing_input_files(self):
        """Make and return a dictionary of the missing input files.

        This returns a dictionary mapping
        filepath to list of `Link` that use the file as input.
        """
        missing = self.check_input_files(return_found=False)
        ret_dict = {}
        for miss_file in missing:
            ret_dict[miss_file] = [self.linkname]
        return ret_dict