Bug: eventless transitions in parallel states not taken anymore when starting interpreter from given state

[fparga]

Description

Eventless transitions in parallel state are not taken anymore when interpreter is started from a given state.

Expected result

Eventless transitions should always be taken.

For example, in the linked reproduction sandbox, the expected result is:

state.value == {"b":{"x":"bar","y":{}}} 

This is the result obtained with xstate version < 4.33.0

Actual result

The eventless transition in example is not taken anymore with xstate version >= 4.33.0.

Instead, we get:

state.value == {"b":{"x":"foo","y":{}}} 

Reproduction

https://codesandbox.io/s/affectionate-thunder-esq8rn?file=/src/index.js

Additional context

It looks like a regression introduced in version 4.33.0.

[Andarist]

Thanks for the repro case! We really appreciate it - I'm gonna take a look at this soon.

[Andarist]

I've found the culprit behind this regression. It seems that this case here actually has been implicitly relying on a shared reference to configuration. Your issue depends on the resolved~ configuration but the algorithm mutates entrySet here (they were pointing to the same array prior 4.33)

I'll try to figure out an improved algorithm for this.

[fparga]

Awesome, thank you @Andarist!