def file_reporter(
        self,
        filename: str,                  # pylint: disable=unused-argument
    ) -> FileReporter | str:      # str should be Literal["python"]
        """Get the :class:`FileReporter` class to use for a file.

        Plug-in type: file tracer.

        This will only be invoked if `filename` returns non-None from
        :meth:`file_tracer`.  It's an error to return None from this method.

        Returns a :class:`FileReporter` object to use to report on `filename`,
        or the string `"python"` to have coverage.py treat the file as Python.

        """
        _needs_to_implement(self, "file_reporter")
Get the :class:`FileReporter` class to use for a file.

        Plug-in type: file tracer.

        This will only be invoked if `filename` returns non-None from
        :meth:`file_tracer`.  It's an error to return None from this method.

        Returns a :class:`FileReporter` object to use to report on `filename`,
        or the string `"python"` to have coverage.py treat the file as Python.

        
coverage/plugin.py