opened
mwu-tow
username_0
### General Summary
If the visualization sets preprocessor code that yields an error, this error is not reported in any way to IDE.

This is really troublesome, as developing or debugging visualizations when there is something wrong in the preprocessor code becomes guesswork.

### Steps to Reproduce
Create a visualization that sets nonsensical preprocessor expression. Wait for updates.

See the example request IDE makes under such condition and the reply:

```json
{
    "jsonrpc": "2.0",
    "id": 18,
    "method": "executionContext/attachVisualisation",
    "params": {
        "expressionId": "1f9ca20f-5143-4010-819d-7b4a4768e477",
        "visualisationConfig": {
            "executionContextId": "38358e93-60ef-400f-bb25-c084e51af57d",
            "expression": "hey -> this is pure nonsense",
            "visualisationModule": "Unnamed.Main"
        },
        "visualisationId": "a1cced79-1e4b-47f6-a85d-73f766325372"
    }
}

{
    "jsonrpc": "2.0",
    "id": 18,
    "result": null
}
```


### Expected Result

1) if expression can feasibly be proven to be incorrect, attaching should fail;
2) if expression's validity depends on runtime conditions, the error should be reported through appropriate channels (binary connection?).

Basically, IDE needs to observe some results of visualization, be it correct values or errors on whatever stage.

### Actual Result
Attaching succeeds but visualization never receives any data. No error nor diagnostics are provided to explain this silence.

In the logs one can find line 
```
[warn] [2021-03-08T17:28:42.928Z] [org.enso.languageserver.protocol.json.JsonConnectionController] Received unknown message: VisualisationEvaluationFailed(38358e93-60ef-400f-bb25-c084e51af57d,Compile error: Variable `is` is not defined.)
``` 
but it is not easily accessible.

### Enso Version
0.2.6
Visualization Errors Are Not Reported
issue
closed
4e6
username_1
issue