Move priorities to separate import to break cycle (#21060)

The event priority constants exports 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.

packages/react-art/src/ReactARTHostConfig.js

@@ -7,17 +7,11 @@
 
 import Transform from 'art/core/transform';
 import Mode from 'art/modes/current';
-import {enableNewReconciler} from 'shared/ReactFeatureFlags';
 import invariant from 'shared/invariant';
 
 import {TYPES, EVENT_TYPES, childrenAsString} from './ReactARTInternals';
 
-import {DefaultLanePriority as DefaultLanePriority_old} from 'react-reconciler/src/ReactFiberLane.old';
-import {DefaultLanePriority as DefaultLanePriority_new} from 'react-reconciler/src/ReactFiberLane.new';
-
-const DefaultLanePriority = enableNewReconciler
-  ? DefaultLanePriority_new
-  : DefaultLanePriority_old;
+import {DefaultEventPriority} from 'react-reconciler/src/ReactEventPriorities';
 
 const pooledTransform = new Transform();
 
@@ -347,7 +341,7 @@ export function shouldSetTextContent(type, props) {
 }
 
 export function getCurrentEventPriority() {
-  return DefaultLanePriority;
+  return DefaultEventPriority;
 }
 
 // The ART renderer is secondary to the React DOM renderer.

packages/react-dom/src/client/ReactDOMHostConfig.js

@@ -67,17 +67,11 @@ import {
   enableSuspenseServerRenderer,
   enableCreateEventHandleAPI,
   enableScopeAPI,
-  enableNewReconciler,
 } from 'shared/ReactFeatureFlags';
 import {HostComponent, HostText} from 'react-reconciler/src/ReactWorkTags';
 import {listenToAllSupportedEvents} from '../events/DOMPluginEventSystem';
 
-import {DefaultLanePriority as DefaultLanePriority_old} from 'react-reconciler/src/ReactFiberLane.old';
-import {DefaultLanePriority as DefaultLanePriority_new} from 'react-reconciler/src/ReactFiberLane.new';
-
-const DefaultLanePriority = enableNewReconciler
-  ? DefaultLanePriority_new
-  : DefaultLanePriority_old;
+import {DefaultEventPriority} from 'react-reconciler/src/ReactEventPriorities';
 
 export type Type = string;
 export type Props = {
@@ -385,7 +379,7 @@ export function createTextInstance(
 export function getCurrentEventPriority(): * {
   const currentEvent = window.event;
   if (currentEvent === undefined) {
-    return DefaultLanePriority;
+    return DefaultEventPriority;
   }
   return getEventPriority(currentEvent.type);
 }

packages/react-dom/src/events/ReactDOMEventListener.js

@@ -14,6 +14,7 @@ import type {
 } from 'react-reconciler/src/ReactInternalTypes';
 import type {Container, SuspenseInstance} from '../client/ReactDOMHostConfig';
 import type {DOMEventName} from '../events/DOMEventNames';
+import type {LanePriority} from 'react-reconciler/src/ReactFiberLane.new';
 
 import {
   isReplayableDiscreteEvent,
@@ -49,18 +50,13 @@ import {
 
 import {
   InputContinuousLanePriority as InputContinuousLanePriority_old,
-  DefaultLanePriority as DefaultLanePriority_old,
   getCurrentUpdateLanePriority as getCurrentUpdateLanePriority_old,
   setCurrentUpdateLanePriority as setCurrentUpdateLanePriority_old,
 } from 'react-reconciler/src/ReactFiberLane.old';
 import {
   InputContinuousLanePriority as InputContinuousLanePriority_new,
-  DefaultLanePriority as DefaultLanePriority_new,
   getCurrentUpdateLanePriority as getCurrentUpdateLanePriority_new,
   setCurrentUpdateLanePriority as setCurrentUpdateLanePriority_new,
-  SyncLanePriority,
-  IdleLanePriority,
-  NoLanePriority,
 } from 'react-reconciler/src/ReactFiberLane.new';
 import {getCurrentPriorityLevel as getCurrentPriorityLevel_old} from 'react-reconciler/src/SchedulerWithReactIntegration.old';
 import {
@@ -71,14 +67,16 @@ import {
   NormalPriority as NormalSchedulerPriority,
   UserBlockingPriority as UserBlockingSchedulerPriority,
 } from 'react-reconciler/src/SchedulerWithReactIntegration.new';
-import type {LanePriority} from 'react-reconciler/src/ReactFiberLane.new';
+import {
+  DiscreteEventPriority,
+  ContinuousEventPriority,
+  DefaultEventPriority,
+  IdleEventPriority,
+} from 'react-reconciler/src/ReactEventPriorities';
 
 const InputContinuousLanePriority = enableNewReconciler
   ? InputContinuousLanePriority_new
   : InputContinuousLanePriority_old;
-const DefaultLanePriority = enableNewReconciler
-  ? DefaultLanePriority_new
-  : DefaultLanePriority_old;
 const getCurrentUpdateLanePriority = enableNewReconciler
   ? getCurrentUpdateLanePriority_new
   : getCurrentUpdateLanePriority_old;
@@ -94,17 +92,17 @@ function schedulerPriorityToLanePriority(
 ): LanePriority {
   switch (schedulerPriorityLevel) {
     case ImmediateSchedulerPriority:
-      return SyncLanePriority;
+      return DiscreteEventPriority;
     case UserBlockingSchedulerPriority:
-      return InputContinuousLanePriority;
+      return ContinuousEventPriority;
     case NormalSchedulerPriority:
     case LowSchedulerPriority:
       // TODO: Handle LowSchedulerPriority, somehow. Maybe the same lane as hydration.
-      return DefaultLanePriority;
+      return DefaultEventPriority;
     case IdleSchedulerPriority:
-      return IdleLanePriority;
+      return IdleEventPriority;
     default:
-      return NoLanePriority;
+      return DefaultEventPriority;
   }
 }
 
@@ -142,13 +140,13 @@ export function createEventListenerWrapperWithPriority(
   const eventPriority = getEventPriority(domEventName);
   let listenerWrapper;
   switch (eventPriority) {
-    case SyncLanePriority:
+    case DiscreteEventPriority:
       listenerWrapper = dispatchDiscreteEvent;
       break;
-    case InputContinuousLanePriority:
+    case ContinuousEventPriority:
       listenerWrapper = dispatchContinuousEvent;
       break;
-    case DefaultLanePriority:
+    case DefaultEventPriority:
     default:
       listenerWrapper = dispatchEvent;
       break;
@@ -407,7 +405,7 @@ export function getEventPriority(domEventName: DOMEventName): * {
     case 'popstate':
     case 'select':
     case 'selectstart':
-      return SyncLanePriority;
+      return DiscreteEventPriority;
     case 'drag':
     case 'dragenter':
     case 'dragexit':
@@ -427,7 +425,7 @@ export function getEventPriority(domEventName: DOMEventName): * {
     // eslint-disable-next-line no-fallthrough
     case 'mouseenter':
     case 'mouseleave':
-      return InputContinuousLanePriority;
+      return ContinuousEventPriority;
     case 'message': {
       // We might be in the Scheduler callback.
       // Eventually this mechanism will be replaced by a check
@@ -436,6 +434,6 @@ export function getEventPriority(domEventName: DOMEventName): * {
       return schedulerPriorityToLanePriority(schedulerPriority);
     }
     default:
-      return DefaultLanePriority;
+      return DefaultEventPriority;
   }
 }

packages/react-native-renderer/src/ReactFabricHostConfig.js

@@ -21,17 +21,11 @@ import type {
 import {mountSafeCallback_NOT_REALLY_SAFE} from './NativeMethodsMixinUtils';
 import {create, diff} from './ReactNativeAttributePayload';
 
-import {enableNewReconciler} from 'shared/ReactFeatureFlags';
 import invariant from 'shared/invariant';
 
 import {dispatchEvent} from './ReactFabricEventEmitter';
 
-import {DefaultLanePriority as DefaultLanePriority_old} from 'react-reconciler/src/ReactFiberLane.old';
-import {DefaultLanePriority as DefaultLanePriority_new} from 'react-reconciler/src/ReactFiberLane.new';
-
-const DefaultLanePriority = enableNewReconciler
-  ? DefaultLanePriority_new
-  : DefaultLanePriority_old;
+import {DefaultEventPriority} from 'react-reconciler/src/ReactEventPriorities';
 
 // Modules provided by RN:
 import {
@@ -349,7 +343,7 @@ export function shouldSetTextContent(type: string, props: Props): boolean {
 }
 
 export function getCurrentEventPriority(): * {
-  return DefaultLanePriority;
+  return DefaultEventPriority;
 }
 
 // The Fabric renderer is secondary to the existing React Native renderer.

packages/react-native-renderer/src/ReactNativeHostConfig.js

@@ -10,7 +10,6 @@
 import type {TouchedViewDataAtPoint} from './ReactNativeTypes';
 
 import invariant from 'shared/invariant';
-import {enableNewReconciler} from 'shared/ReactFeatureFlags';
 
 // Modules provided by RN:
 import {
@@ -27,12 +26,7 @@ import {
 } from './ReactNativeComponentTree';
 import ReactNativeFiberHostComponent from './ReactNativeFiberHostComponent';
 
-import {DefaultLanePriority as DefaultLanePriority_old} from 'react-reconciler/src/ReactFiberLane.old';
-import {DefaultLanePriority as DefaultLanePriority_new} from 'react-reconciler/src/ReactFiberLane.new';
-
-const DefaultLanePriority = enableNewReconciler
-  ? DefaultLanePriority_new
-  : DefaultLanePriority_old;
+import {DefaultEventPriority} from 'react-reconciler/src/ReactEventPriorities';
 
 const {get: getViewConfigForType} = ReactNativeViewConfigRegistry;
 
@@ -268,7 +262,7 @@ export function shouldSetTextContent(type: string, props: Props): boolean {
 }
 
 export function getCurrentEventPriority(): * {
-  return DefaultLanePriority;
+  return DefaultEventPriority;
 }
 
 // -------------------

packages/react-noop-renderer/src/createReactNoop.js

@@ -27,6 +27,9 @@ import ReactSharedInternals from 'shared/ReactSharedInternals';
 import enqueueTask from 'shared/enqueueTask';
 const {IsSomeRendererActing} = ReactSharedInternals;
 
+// TODO: Publish public entry point that exports the event priority constants
+const DefaultEventPriority = 8;
+
 type Container = {
   rootID: string,
   children: Array<Instance | TextInstance>,
@@ -587,7 +590,7 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
   const roots = new Map();
   const DEFAULT_ROOT_ID = '<default>';
 
-  let currentEventPriority = NoopRenderer.DefaultEventPriority;
+  let currentEventPriority = DefaultEventPriority;
 
   function childToJSX(child, text) {
     if (text !== null) {

packages/react-reconciler/README.md

@@ -219,10 +219,16 @@ This is a property (not a function) that should be set to `true` if your rendere
 To implement this method, you'll need some constants available on the _returned_ `Renderer` object:
 
 ```js
+import {
+  DiscreteEventPriority,
+  ContinuousEventPriority,
+  DefaultEventPriority,
+} from './ReactFiberReconciler/src/ReactEventPriorities';
+
 const HostConfig = {
   // ...
   getCurrentEventPriority() {
-    return MyRenderer.DefaultEventPriority;
+    return DefaultEventPriority;
   },
   // ...
 }
@@ -232,11 +238,11 @@ const MyRenderer = Reconciler(HostConfig);
 
 The constant you return depends on which event, if any, is being handled right now. (In the browser, you can check this using `window.event && window.event.type`).
 
-* **Discrete events:** If the active event is _directly caused by the user_ (such as mouse and keyboard events) and _each event in a sequence is intentional_ (e.g. `click`), return `MyRenderer.DiscreteEventPriority`. This tells React that they should interrupt any background work and cannot be batched across time.
+* **Discrete events:** If the active event is _directly caused by the user_ (such as mouse and keyboard events) and _each event in a sequence is intentional_ (e.g. `click`), return `DiscreteEventPriority`. This tells React that they should interrupt any background work and cannot be batched across time.
 
-* **Continuous events:** If the active event is _directly caused by the user_ but _the user can't distinguish between individual events in a sequence_ (e.g. `mouseover`), return `MyRenderer.ContinuousEventPriority`. This tells React they should interrupt any background work but can be batched across time.
+* **Continuous events:** If the active event is _directly caused by the user_ but _the user can't distinguish between individual events in a sequence_ (e.g. `mouseover`), return `ContinuousEventPriority`. This tells React they should interrupt any background work but can be batched across time.
 
-* **Other events / No active event:** In all other cases, return `MyRenderer.DefaultEventPriority`. This tells React that this event is considered background work, and interactive events will be prioritized over it.
+* **Other events / No active event:** In all other cases, return `DefaultEventPriority`. This tells React that this event is considered background work, and interactive events will be prioritized over it.
 
 You can consult the `getCurrentEventPriority()` implementation in `ReactDOMHostConfig.js` for a reference implementation.
 

packages/react-reconciler/src/ReactEventPriorities.js

@@ -0,0 +1,37 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+import {enableNewReconciler} from 'shared/ReactFeatureFlags';
+
+import {
+  DiscreteEventPriority as DiscreteEventPriority_old,
+  ContinuousEventPriority as ContinuousEventPriority_old,
+  DefaultEventPriority as DefaultEventPriority_old,
+  IdleEventPriority as IdleEventPriority_old,
+} from './ReactEventPriorities.old';
+
+import {
+  DiscreteEventPriority as DiscreteEventPriority_new,
+  ContinuousEventPriority as ContinuousEventPriority_new,
+  DefaultEventPriority as DefaultEventPriority_new,
+  IdleEventPriority as IdleEventPriority_new,
+} from './ReactEventPriorities.new';
+
+export const DiscreteEventPriority = enableNewReconciler
+  ? DiscreteEventPriority_new
+  : DiscreteEventPriority_old;
+export const ContinuousEventPriority = enableNewReconciler
+  ? ContinuousEventPriority_new
+  : ContinuousEventPriority_old;
+export const DefaultEventPriority = enableNewReconciler
+  ? DefaultEventPriority_new
+  : DefaultEventPriority_old;
+export const IdleEventPriority = enableNewReconciler
+  ? IdleEventPriority_new
+  : IdleEventPriority_old;

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

@@ -0,0 +1,15 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+export {
+  SyncLanePriority as DiscreteEventPriority,
+  InputContinuousLanePriority as ContinuousEventPriority,
+  DefaultLanePriority as DefaultEventPriority,
+  IdleLanePriority as IdleEventPriority,
+} from './ReactFiberLane.new';

packages/react-reconciler/src/ReactEventPriorities.old.js

@@ -0,0 +1,15 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+export {
+  SyncLanePriority as DiscreteEventPriority,
+  InputContinuousLanePriority as ContinuousEventPriority,
+  DefaultLanePriority as DefaultEventPriority,
+  IdleLanePriority as IdleEventPriority,
+} from './ReactFiberLane.old';

packages/react-reconciler/src/ReactFiberReconciler.js

@@ -52,10 +52,6 @@ import {
   registerMutableSourceForHydration as registerMutableSourceForHydration_old,
   runWithPriority as runWithPriority_old,
   getCurrentUpdateLanePriority as getCurrentUpdateLanePriority_old,
-  DefaultEventPriority as DefaultEventPriority_old,
-  DiscreteEventPriority as DiscreteEventPriority_old,
-  ContinuousEventPriority as ContinuousEventPriority_old,
-  IdleEventPriority as IdleEventPriority_old,
 } from './ReactFiberReconciler.old';
 
 import {
@@ -96,10 +92,6 @@ import {
   registerMutableSourceForHydration as registerMutableSourceForHydration_new,
   runWithPriority as runWithPriority_new,
   getCurrentUpdateLanePriority as getCurrentUpdateLanePriority_new,
-  DefaultEventPriority as DefaultEventPriority_new,
-  DiscreteEventPriority as DiscreteEventPriority_new,
-  ContinuousEventPriority as ContinuousEventPriority_new,
-  IdleEventPriority as IdleEventPriority_new,
 } from './ReactFiberReconciler.new';
 
 export const createContainer = enableNewReconciler
@@ -176,18 +168,6 @@ export const createPortal = enableNewReconciler
 export const createComponentSelector = enableNewReconciler
   ? createComponentSelector_new
   : createComponentSelector_old;
-export const DefaultEventPriority = enableNewReconciler
-  ? DefaultEventPriority_new
-  : DefaultEventPriority_old;
-export const DiscreteEventPriority = enableNewReconciler
-  ? DiscreteEventPriority_new
-  : DiscreteEventPriority_old;
-export const ContinuousEventPriority = enableNewReconciler
-  ? ContinuousEventPriority_new
-  : ContinuousEventPriority_old;
-export const IdleEventPriority = enableNewReconciler
-  ? IdleEventPriority_new
-  : IdleEventPriority_old;
 
 //TODO: "psuedo" is spelled "pseudo"
 export const createHasPseudoClassSelector = enableNewReconciler