python error UnboundLocalError in jit/frontend.py

[arvrmd]

🐛 Bug

One of the error cases in the function build_param_list uses ctx_range without defining it, in the following context:

    if not PY2 and py_args.kw_defaults:
        raise NotSupportedError(ctx_range, _vararg_kwarg_err)

To Reproduce

Steps to reproduce the behavior:

I was using torch.jit.script() on a large module, and since it's the error reporting that's failing I don't have a line reference. By inspection, however, I believe the unsupported feature was the asterisk in the following function definition:

    @torch.jit.export
    def initState(self, *, n_tokens: int, device_name: str) -> None:

Expected behavior

Relevant error message should be reported.

cc @suo

[suo]

cc @driazati can you take a look?