Bug: throwing an error within onReceive in invoked callback service isn't being caught by onError

[koenoe]

Description

When throwing an error within onReceive in an invoked callback service, it's not caught. Thrown errors outside onReceive are caught properly. Therefore I'm forced to do something like callback({ type: 'ERROR', error }) in order to handle the error properly and transition to an error state in my state machine.

Expected result

I expect the error to be caught, so my callback service fails and I can transition to an error state properly.

Actual result

Error is not caught and state machine ends up in an invalid state.

Reproduction

https://codesandbox.io/s/pensive-curran-6p4vvx?file=/src/index.js

Additional context

Checked with @mattpocock on Stately Discord and seems to be a bug.

[Andarist]

This is somewhat related to: statelyai/rfcs#4 . We are planning to have strong guarantees about errors in v5.

[mattpocock]

This feels like its own thing - surely any error thrown inside an invoked callback should result in the onError transition being taken?

[Andarist]

It should but it also doesn't 😅 There are just a lot of errors that are currently swallowed in XState, for instance, onError won't usually be taken in the parent machine when a child machine errors somewhere (like in assign or whatever).

So while we could improve things in v4 bit by bit - I feel like it's better to focus on the algorithm overhaul and ship this improvement in v5. Merging v4 to v5 already has a non-trivial cost and any changes to the core logic like this have the potential of being problematic in this sense.

[mattpocock]

OK, boss 👍

[Andarist]

I believe that #4145 & #4492 addressed this issue.