An activity call to a non-existent function should error-out

[davidmrdavid]

Currently, if we try to make an activity call to a non-existent function, the orchestrator simply sleeps indefinitely. We should instead validate that the function exists and error out if not.

Additionally, we should consider doing some basic typo-checking in case the function exists under a slightly different name. Think of Hello versus Hello1. The latter is a scenario that you can get into when using the plugin to create functions.

[davidmrdavid]

tagging @ConnorMcMahon and @cgillum for discussion on the typo-checking proposal.

[cgillum]

The fact that the orchestrator hangs indefinitely is definitely a bug that we should investigate and prioritize fixing. We can probably separate that issue into its own. At a minimum it should cause the orchestrator to transition into a Failed state.

I agree it would be idea if the callActivity and callSubOrchestrator APIs threw an error. The challenge we have is that the out-of-proc SDKs don't know about what activities exist today, only the extension knows this today. One potential solution would be to include the list of activity, orchestrator, and entity function names in the context payload and have the SDK validate against those lists.

I don't have a recommendation about typo-checking since I think that will need to be language-specifc. It would be great if we could have a custom linter check for this, similar to what we have with the C# analyzer. That would also make sense as a separate issue.