Bug: [5.25.0] typing issue when using assertEvent and generics

[jlowcs]

XState version

XState version 5

Description

function test(event: InspectionEvent) {
	assertEvent(event, '@xstate.event');
	// eslint-disable-next-line no-console
	console.log(event.event);
}

function test2<TEVENT extends InspectionEvent>(event: TEVENT) {
	assertEvent(event, '@xstate.event');
	// eslint-disable-next-line no-console
	console.log(event.event);
}

test2 results in a type error:

Expected result

no error, asserts works as expected

Actual result

error, cannot use assertEvent with generics.

Reproduction

https://codesandbox.io/p/devbox/nifty-cloud-wnzqnr

Additional context

I was able to avoid the typing issue by doing this, but I'm not sure if there's a better option:

function test2<TEVENT extends InspectionEvent>(eventP: TEVENT) {
	const event: InspectionEvent = eventP;
	assertEvent(event, '@xstate.event');
	// eslint-disable-next-line no-console
	console.log(event.event);
}

[jlowcs]

Another issue that could be related:

if (event.type === '@xstate.event' && event.event.type === 'continue') {
	assertEvent(event.event, 'continue');
	const currentSnapshot = actorRef.getSnapshot();
	const [nextSnapshot] = transition(machine, currentSnapshot, event.event);
}

Typing issue on event.event in transition(machine, currentSnapshot, event.event).

In 5.24.0, event.event was inferred by assertEvent as AnyEventObject & { type: 'continue' }. In 5.25.0 it is inferred as just AnyEventObject.

[davidkpiano]

For this specific use-case, I recommend just checking if (event.type === '…') - it will do the type narrowing properly.