Unhelpful traceback

[numpde]

The following grim traceback was caused by writing button(disabled=mutation) instead of ...=mutation.loading, and it's representative of a fairly common set. It would be great to have a pointer to near the origin of the error.

Exception inside application: Object of type Mutation is not JSON serializable
Traceback (most recent call last):
  File "REPO/venv-3.11/lib/python3.11/site-packages/django/contrib/staticfiles/handlers.py", line 101, in __call__
    return await self.application(scope, receive, send)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "REPO/venv-3.11/lib/python3.11/site-packages/channels/routing.py", line 62, in __call__
    return await application(scope, receive, send)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "REPO/venv-3.11/lib/python3.11/site-packages/channels/sessions.py", line 47, in __call__
    return await self.inner(dict(scope, cookies=cookies), receive, send)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "REPO/venv-3.11/lib/python3.11/site-packages/channels/sessions.py", line 263, in __call__
    return await self.inner(wrapper.scope, receive, wrapper.send)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "REPO/venv-3.11/lib/python3.11/site-packages/channels/sessions.py", line 47, in __call__
    return await self.inner(dict(scope, cookies=cookies), receive, send)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "REPO/venv-3.11/lib/python3.11/site-packages/channels/sessions.py", line 263, in __call__
    return await self.inner(wrapper.scope, receive, wrapper.send)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "REPO/venv-3.11/lib/python3.11/site-packages/channels/auth.py", line 185, in __call__
    return await super().__call__(scope, receive, send)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "REPO/venv-3.11/lib/python3.11/site-packages/channels/middleware.py", line 24, in __call__
    return await self.inner(scope, receive, send)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "REPO/venv-3.11/lib/python3.11/site-packages/channels/routing.py", line 116, in __call__
    return await application(
           ^^^^^^^^^^^^^^^^^^
  File "REPO/venv-3.11/lib/python3.11/site-packages/channels/consumer.py", line 94, in app
    return await consumer(scope, receive, send)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "REPO/venv-3.11/lib/python3.11/site-packages/channels/consumer.py", line 62, in __call__
    await await_many_dispatch([receive], self.dispatch)
  File "REPO/venv-3.11/lib/python3.11/site-packages/channels/utils.py", line 50, in await_many_dispatch
    await dispatch(result)
  File "REPO/venv-3.11/lib/python3.11/site-packages/channels/consumer.py", line 73, in dispatch
    await handler(message)
  File "REPO/venv-3.11/lib/python3.11/site-packages/channels/generic/websocket.py", line 238, in websocket_disconnect
    await self.disconnect(message["code"])
  File "REPO/venv-3.11/lib/python3.11/site-packages/django_idom/websocket/consumer.py", line 48, in disconnect
    await self._idom_dispatcher_future
  File "REPO/venv-3.11/lib/python3.11/site-packages/django_idom/websocket/consumer.py", line 124, in _run_dispatch_loop
    await serve_layout(
  File "REPO/venv-3.11/lib/python3.11/site-packages/idom/core/serve.py", line 41, in serve_layout
    async with create_task_group() as task_group:
  File "REPO/venv-3.11/lib/python3.11/site-packages/anyio/_backends/_asyncio.py", line 662, in __aexit__
    raise exceptions[0]
  File "REPO/venv-3.11/lib/python3.11/site-packages/idom/core/serve.py", line 52, in _single_outgoing_loop
    await send(await layout.render())
  File "REPO/venv-3.11/lib/python3.11/site-packages/channels/generic/websocket.py", line 271, in send_json
    await super().send(text_data=await self.encode_json(content), close=close)
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "REPO/venv-3.11/lib/python3.11/site-packages/channels/generic/websocket.py", line 279, in encode_json
    return json.dumps(content)
           ^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/json/__init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/json/encoder.py", line 200, in encode
    chunks = self.iterencode(o, _one_shot=True)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/json/encoder.py", line 258, in iterencode
    return _iterencode(o, 0)
           ^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/json/encoder.py", line 180, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type Mutation is not JSON serializable

[rmorshea]

Agreed. Would it be acceptable if we only reported a more proximal error when in debug mode (for the sake of performance)? If we do this, then it probably makes sense to catch serialization errors and suggest running in debug mode to get a more useful traceback.

[numpde]

Makes sense.

[rmorshea]

#930