Object of type RequestError is not JSON serializable

[MetRonnie]

Description

(Tested on graphql-core v3 branch - #672)

A mutation error resulting in a RequestError does not get sent back to the GUI properly, instead it falls over at JSON serialization:

[E CylcUIServer] RequestError: Unknown argument "reloadGlobal" on field "reload" of type "Mutations".
    (Workflow is running in Cylc 8.4.3)
[E CylcHubApp tornado:420] Error: Object of type RequestError is not JSON serializable Traceback (most recent call last):
      File "~/cylc-uiserver/cylc/uiserver/graphql/tornado.py", line 163, in post
        await self.run("post")
      File "~/cylc-uiserver/cylc/uiserver/handlers.py", line 366, in run
        await TornadoGraphQLHandler.run(self, *args, **kwargs)
      File "~/cylc-uiserver/cylc/uiserver/graphql/tornado.py", line 185, in run
        result, status_code = await self.get_response(data)
                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "~/cylc-uiserver/cylc/uiserver/graphql/tornado.py", line 237, in get_response
        result = self.json_encode(response)
      File "~/cylc-uiserver/cylc/uiserver/graphql/tornado.py", line 248, in json_encode
        return json.dumps(d, separators=(",", ":"))
               ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "~/.conda/envs/gql-update/lib/python3.13/json/__init__.py", line 238, in dumps
        **kw).encode(obj)
              ~~~~~~^^^^^
      File "~/.conda/envs/gql-update/lib/python3.13/json/encoder.py", line 200, in encode
        chunks = self.iterencode(o, _one_shot=True)
      File "~/.conda/envs/gql-update/lib/python3.13/json/encoder.py", line 261, in iterencode
        return _iterencode(o, 0)
      File "~/.conda/envs/gql-update/lib/python3.13/json/encoder.py", line 180, in default
        raise TypeError(f'Object of type {o.__class__.__name__} '
                        f'is not JSON serializable')
    TypeError: Object of type RequestError is not JSON serializable

[dwsutherland]

The real problem here is that the cylc-flow end doesn't propagate this as an Error, and instead sets it as a result:

ExecutionResult(data={'reload': {'result': [RequestError('Unknown argument "reloadGlobal" on field "reload" of type "Mutations".', '8.4.4.dev')]}}, errors=None)

this should be:

ExecutionResult(data=None, errors=["'Unknown argument "reloadGlobal" on field "reload" of type "Mutations".', '8.4.4.dev'"])

However, I wouldn't want to change 8.4.x in this section of code (because it's likely changed at 8.5.0).. So the only thing I can think of doing is putting a back compat patch on the UIS end

[MetRonnie]

The multi_request method in uiserver seems to be the problem:

cylc-uiserver/cylc/uiserver/workflows_mgr.py

Line 360 in 6001b20

async def multi_request(

It was aggregating exceptions so they were not raised. But cylc-flow's mutator cannot do anything with this other than assume successful results.

See #672 (comment)