improve wasm error message

[natasha41575]

Fix #3763

It looks like there is a flaky function in our wasm fnruntime library. Specifically this line is looking problematic:

https://github.com/GoogleContainerTools/kpt/blob/5a7e65fa4bf03f7948ec1365d4a4a0c30a59b889/internal/fnruntime/wasmtime.go#L145

It's supposed to populate result with the output ResourceList, but for me, maybe 1/20 times it is returning very odd-looking strings like s(<nil>) or s(float64=4.0474e-320. This currently results in kyaml throwing its very unhelpful Error: wrong Node Kind for expected: MappingNode was ScalarNode: value: {s(float64=5.565e-320} error.

This PR doesn't fix the flake, but it is trying to at least improve the error message to make it more obvious where it came from. I filed a separate issue for addressing the flake: #3782

[yuwenma]

That's fair. Thank you for the change!

[droot]

maybe 1/20 times it is returning very odd-looking strings like

I am making a wild guess. Since wasm runtime is using js based bridge, it might be a symptom of that js bridge not ready yet when the function was invoked. So just a retry might help. You could try adding a retry (just once) around that function and see if retry succeed (if you have a reproducible setup).

Improving the error is anyway helpful.

[natasha41575]

Thanks for the feedback! Looked like the user attempted a retry and is still running into the issue. I will merge this PR and we can use the other issue I filed for further tracking.