Apply facebook#20778 to new fork, too (facebook#20782)

* Apply facebook#20778 to new fork, too

* Fix tests that use runWithPriority

Where possible, I tried to rewrite in terms of an idiomatic API.

For DOM tests, we should be dispatching an event with the desired
priority level.

For Idle updates (very unstable feature), probably need an unstable
API like ReactDOM.unstable_IdleUpdates.

Some of these fixes are not great, but we can replace them once we've
landed the more of our planned changes to the layering between
Scheduler, the reconciler, and the renderer.

packages/react-dom/src/__tests__/ReactDOMServerSelectiveHydration-test.internal.js

@@ -92,6 +92,21 @@ function dispatchClickEvent(target) {
   return target.dispatchEvent(mouseOutEvent);
 }
 
+// TODO: There's currently no React DOM API to opt into Idle priority updates,
+// and there's no native DOM event that maps to idle priority, so this is a
+// temporary workaround. Need something like ReactDOM.unstable_IdleUpdates.
+function TODO_scheduleIdleDOMSchedulerTask(fn) {
+  Scheduler.unstable_runWithPriority(Scheduler.unstable_IdlePriority, () => {
+    const prevEvent = window.event;
+    window.event = {type: 'message'};
+    try {
+      fn();
+    } finally {
+      window.event = prevEvent;
+    }
+  });
+}
+
 describe('ReactDOMServerSelectiveHydration', () => {
   beforeEach(() => {
     jest.resetModuleRegistry();
@@ -889,12 +904,10 @@ describe('ReactDOMServerSelectiveHydration', () => {
       expect(Scheduler).toFlushAndYieldThrough(['App', 'Commit']);
 
       // Render an update at Idle priority that needs to update A.
-      Scheduler.unstable_runWithPriority(
-        Scheduler.unstable_IdlePriority,
-        () => {
-          root.render(<App a="AA" />);
-        },
-      );
+
+      TODO_scheduleIdleDOMSchedulerTask(() => {
+        root.render(<App a="AA" />);
+      });
 
       // Start rendering. This will force the first boundary to hydrate
       // by scheduling it at one higher pri than Idle.

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

@@ -41,6 +41,7 @@ export const {
   deferredUpdates,
   unbatchedUpdates,
   discreteUpdates,
+  idleUpdates,
   flushDiscreteUpdates,
   flushSync,
   flushPassiveEffects,

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

@@ -41,6 +41,7 @@ export const {
   deferredUpdates,
   unbatchedUpdates,
   discreteUpdates,
+  idleUpdates,
   flushDiscreteUpdates,
   flushSync,
   flushPassiveEffects,

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

@@ -27,6 +27,7 @@ import {
   LegacyRoot,
 } from 'react-reconciler/src/ReactRootTags';
 
+import {enableNativeEventPriorityInference} from 'shared/ReactFeatureFlags';
 import ReactSharedInternals from 'shared/ReactSharedInternals';
 import enqueueTask from 'shared/enqueueTask';
 const {IsSomeRendererActing} = ReactSharedInternals;
@@ -392,7 +393,7 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
     resetAfterCommit(): void {},
 
     getCurrentEventPriority() {
-      return NoopRenderer.DefaultEventPriority;
+      return currentEventPriority;
     },
 
     now: Scheduler.unstable_now,
@@ -587,6 +588,8 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
   const roots = new Map();
   const DEFAULT_ROOT_ID = '<default>';
 
+  let currentEventPriority = NoopRenderer.DefaultEventPriority;
+
   function childToJSX(child, text) {
     if (text !== null) {
       return text;
@@ -925,6 +928,23 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
 
     discreteUpdates: NoopRenderer.discreteUpdates,
 
+    idleUpdates<T>(fn: () => T): T {
+      if (enableNativeEventPriorityInference) {
+        const prevEventPriority = currentEventPriority;
+        currentEventPriority = NoopRenderer.IdleEventPriority;
+        try {
+          fn();
+        } finally {
+          currentEventPriority = prevEventPriority;
+        }
+      } else {
+        return Scheduler.unstable_runWithPriority(
+          Scheduler.unstable_IdlePriority,
+          fn,
+        );
+      }
+    },
+
     flushDiscreteUpdates: NoopRenderer.flushDiscreteUpdates,
 
     flushSync(fn: () => mixed) {

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

@@ -70,7 +70,7 @@ const RetryLanePriority: LanePriority = 5;
 const SelectiveHydrationLanePriority: LanePriority = 4;
 
 const IdleHydrationLanePriority: LanePriority = 3;
-const IdleLanePriority: LanePriority = 2;
+export const IdleLanePriority: LanePriority = 2;
 
 const OffscreenLanePriority: LanePriority = 1;
 
@@ -275,6 +275,7 @@ export function getNextLanes(root: FiberRoot, wipLanes: Lanes): Lanes {
 
   // Check if any work has expired.
   if (expiredLanes !== NoLanes) {
+    // TODO: Should entangle with SyncLane
     nextLanes = expiredLanes;
     nextLanePriority = return_highestLanePriority = SyncLanePriority;
   } else {

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

@@ -70,7 +70,7 @@ const RetryLanePriority: LanePriority = 5;
 const SelectiveHydrationLanePriority: LanePriority = 4;
 
 const IdleHydrationLanePriority: LanePriority = 3;
-const IdleLanePriority: LanePriority = 2;
+export const IdleLanePriority: LanePriority = 2;
 
 const OffscreenLanePriority: LanePriority = 1;
 
@@ -275,6 +275,7 @@ export function getNextLanes(root: FiberRoot, wipLanes: Lanes): Lanes {
 
   // Check if any work has expired.
   if (expiredLanes !== NoLanes) {
+    // TODO: Should entangle with SyncLane
     nextLanes = expiredLanes;
     nextLanePriority = return_highestLanePriority = SyncLanePriority;
   } else {

packages/react-reconciler/src/ReactFiberReconciler.js

@@ -55,6 +55,7 @@ import {
   DefaultEventPriority as DefaultEventPriority_old,
   DiscreteEventPriority as DiscreteEventPriority_old,
   ContinuousEventPriority as ContinuousEventPriority_old,
+  IdleEventPriority as IdleEventPriority_old,
 } from './ReactFiberReconciler.old';
 
 import {
@@ -98,6 +99,7 @@ import {
   DefaultEventPriority as DefaultEventPriority_new,
   DiscreteEventPriority as DiscreteEventPriority_new,
   ContinuousEventPriority as ContinuousEventPriority_new,
+  IdleEventPriority as IdleEventPriority_new,
 } from './ReactFiberReconciler.new';
 
 export const createContainer = enableNewReconciler
@@ -183,6 +185,9 @@ export const DiscreteEventPriority = enableNewReconciler
 export const ContinuousEventPriority = enableNewReconciler
   ? ContinuousEventPriority_new
   : ContinuousEventPriority_old;
+export const IdleEventPriority = enableNewReconciler
+  ? IdleEventPriority_new
+  : IdleEventPriority_old;
 
 //TODO: "psuedo" is spelled "pseudo"
 export const createHasPsuedoClassSelector = enableNewReconciler

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

@@ -101,6 +101,7 @@ export {
   InputDiscreteLanePriority as DiscreteEventPriority,
   InputContinuousLanePriority as ContinuousEventPriority,
   DefaultLanePriority as DefaultEventPriority,
+  IdleLanePriority as IdleEventPriority,
 } from './ReactFiberLane.new';
 
 export {registerMutableSourceForHydration} from './ReactMutableSource.new';

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

@@ -101,6 +101,7 @@ export {
   InputDiscreteLanePriority as DiscreteEventPriority,
   InputContinuousLanePriority as ContinuousEventPriority,
   DefaultLanePriority as DefaultEventPriority,
+  IdleLanePriority as IdleEventPriority,
 } from './ReactFiberLane.old';
 
 export {registerMutableSourceForHydration} from './ReactMutableSource.new';

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

@@ -465,15 +465,7 @@ export function requestUpdateLane(fiber: Fiber): Lane {
   } else {
     if (enableNativeEventPriorityInference) {
       const eventLanePriority = getCurrentEventPriority();
-      if (eventLanePriority === DefaultLanePriority) {
-        // TODO: move this case into the ReactDOM host config.
-        const schedulerLanePriority = schedulerPriorityToLanePriority(
-          schedulerPriority,
-        );
-        lane = findUpdateLane(schedulerLanePriority, currentEventWipLanes);
-      } else {
-        lane = findUpdateLane(eventLanePriority, currentEventWipLanes);
-      }
+      lane = findUpdateLane(eventLanePriority, currentEventWipLanes);
     } else {
       const schedulerLanePriority = schedulerPriorityToLanePriority(
         schedulerPriority,