Move priorities to separate import to break cycle

[acdlite]

Doesn't change any behavior. Just moves stuff around.

---

The event priority constants exported by the reconciler package are meant to be used by the reconciler (host config) itself. So it doesn't make sense to export them from a module that requires them.

To break the cycle, we can move them to a separate module and import that. This looks like a "deep import" of an internal module, which we try to avoid, but conceptually these are part of the public interface of the reconciler module. So, no different than importing from the main react-reconciler.

We do need to be careful about not mixing these types of imports with implementation details. Those are the ones to really avoid.

An unintended benefit of the reconciler fork infra is that it makes deep imports harder. Any module that we treat as "public", like this one, needs to account for the enableNewReconciler flag and forward to the correct implementation.

[rickhanlonii]

Works for me

[sizebot]

Comparing: 25bfa28...0557a49

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	122.80 kB	122.80 kB	=	39.50 kB	39.50 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	129.21 kB	129.21 kB	=	41.50 kB	41.50 kB
facebook-www/ReactDOM-prod.classic.js	=	408.57 kB	408.57 kB	=	75.63 kB	75.62 kB
facebook-www/ReactDOM-prod.modern.js	=	396.83 kB	396.83 kB	=	73.70 kB	73.70 kB
facebook-www/ReactDOMForked-prod.classic.js	=	408.58 kB	408.57 kB	=	75.63 kB	75.62 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-experimental/react-noop-renderer/cjs/react-noop-renderer.development.js	+0.26%	36.25 kB	36.34 kB	+0.56%	8.18 kB	8.23 kB
oss-stable/react-noop-renderer/cjs/react-noop-renderer.development.js	+0.26%	36.25 kB	36.34 kB	+0.56%	8.18 kB	8.23 kB
oss-experimental/react-noop-renderer/cjs/react-noop-renderer-persistent.development.js	+0.26%	36.26 kB	36.36 kB	+0.56%	8.19 kB	8.23 kB
oss-stable/react-noop-renderer/cjs/react-noop-renderer-persistent.development.js	+0.26%	36.26 kB	36.36 kB	+0.56%	8.19 kB	8.23 kB

Generated by 🚫 dangerJS against 0557a49

[gaearon]

This used to be NoLane, now it's DefaultLane. Any differences?

[acdlite]

I think that was just a mistake before. NoLanePriority would get passed to findUpdateLane, which would throw:

react/packages/react-reconciler/src/ReactFiberLane.new.js

Lines 544 to 571 in 25bfa28

	export function findUpdateLane(lanePriority: LanePriority): Lane {
	switch (lanePriority) {
	case NoLanePriority:
	break;
	case SyncLanePriority:
	return SyncLane;
	case SyncBatchedLanePriority:
	return SyncBatchedLane;
	case InputContinuousLanePriority:
	return InputContinuousLane;
	case DefaultLanePriority:
	return DefaultLane;
	case TransitionPriority: // Should be handled by findTransitionLane instead
	case RetryLanePriority: // Should be handled by findRetryLane instead
	break;
	case IdleLanePriority:
	return IdleLane;
	default:
	// The remaining priorities are not valid for updates
	break;
	}
	invariant(
	false,
	'Invalid update priority: %s. This is a bug in React.',
	lanePriority,
	);
	}

I suppose we never hit this internally because we don't have any native event handlers that aren't part of the big switch.

I'll add a regression test as a follow up.

[acdlite]

Actually I'll address this in the next PR. We're about to remove the LanePriority type in favor of returning a lane directly.

[gaearon]

We currently reference these values in README. If we're removing them, can you update the README with a recommendation of what to do? E.g. just hardcoding numbers or telling people to look at this particular file. https://github.com/facebook/react/blob/master/packages/react-reconciler/README.md#getcurrenteventpriority

[gaearon]

Hmm. How does this work? It doesn't exist in the open source npm package. Should this suggest to copy-paste from our repo?

[gaearon]

I'll send a follow-up PR

[gaearon]

#21062

[gaearon]

This sentence is no longer true