Remove disableSchedulerTimeoutInWorkLoop flag (#19902)

We found and mitigated the root cause of the regression that led us to
temporarily revert this change. So now I'm un-reverting it.

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

@@ -30,7 +30,6 @@ import {
   enableSchedulingProfiler,
   enableScopeAPI,
   skipUnmountedBoundaries,
-  disableSchedulerTimeoutInWorkLoop,
   enableDoubleInvokingEffects,
 } from 'shared/ReactFeatureFlags';
 import ReactSharedInternals from 'shared/ReactSharedInternals';
@@ -745,7 +744,7 @@ function ensureRootIsScheduled(root: FiberRoot, currentTime: number) {
 
 // This is the entry point for every concurrent task, i.e. anything that
 // goes through Scheduler.
-function performConcurrentWorkOnRoot(root, didTimeout) {
+function performConcurrentWorkOnRoot(root) {
   // Since we know we're in a React event, we can clear the current
   // event time. The next update will compute a new event time.
   currentEventTime = NoTimestamp;
@@ -785,18 +784,6 @@ function performConcurrentWorkOnRoot(root, didTimeout) {
     return null;
   }
 
-  // TODO: We only check `didTimeout` defensively, to account for a Scheduler
-  // bug we're still investigating. Once the bug in Scheduler is fixed,
-  // we can remove this, since we track expiration ourselves.
-  if (!disableSchedulerTimeoutInWorkLoop && didTimeout) {
-    // Something expired. Flush synchronously until there's no expired
-    // work left.
-    markRootExpired(root, lanes);
-    // This will schedule a synchronous callback.
-    ensureRootIsScheduled(root, now());
-    return null;
-  }
-
   let exitStatus = renderRootConcurrent(root, lanes);
 
   if (

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

@@ -30,7 +30,6 @@ import {
   enableSchedulingProfiler,
   enableScopeAPI,
   skipUnmountedBoundaries,
-  disableSchedulerTimeoutInWorkLoop,
 } from 'shared/ReactFeatureFlags';
 import ReactSharedInternals from 'shared/ReactSharedInternals';
 import invariant from 'shared/invariant';
@@ -739,7 +738,7 @@ function ensureRootIsScheduled(root: FiberRoot, currentTime: number) {
 
 // This is the entry point for every concurrent task, i.e. anything that
 // goes through Scheduler.
-function performConcurrentWorkOnRoot(root, didTimeout) {
+function performConcurrentWorkOnRoot(root) {
   // Since we know we're in a React event, we can clear the current
   // event time. The next update will compute a new event time.
   currentEventTime = NoTimestamp;
@@ -779,18 +778,6 @@ function performConcurrentWorkOnRoot(root, didTimeout) {
     return null;
   }
 
-  // TODO: We only check `didTimeout` defensively, to account for a Scheduler
-  // bug we're still investigating. Once the bug in Scheduler is fixed,
-  // we can remove this, since we track expiration ourselves.
-  if (!disableSchedulerTimeoutInWorkLoop && didTimeout) {
-    // Something expired. Flush synchronously until there's no expired
-    // work left.
-    markRootExpired(root, lanes);
-    // This will schedule a synchronous callback.
-    ensureRootIsScheduled(root, now());
-    return null;
-  }
-
   let exitStatus = renderRootConcurrent(root, lanes);
 
   if (

packages/shared/ReactFeatureFlags.js

@@ -135,6 +135,4 @@ export const enableDiscreteEventFlushingChange = false;
 
 export const enableEagerRootListeners = true;
 
-export const disableSchedulerTimeoutInWorkLoop = false;
-
 export const enableDoubleInvokingEffects = false;

packages/shared/forks/ReactFeatureFlags.native-fb.js

@@ -50,7 +50,6 @@ export const deferRenderPhaseUpdateToNextBatch = true;
 export const decoupleUpdatePriorityFromScheduler = false;
 export const enableDiscreteEventFlushingChange = false;
 export const enableEagerRootListeners = true;
-export const disableSchedulerTimeoutInWorkLoop = false;
 
 export const enableDoubleInvokingEffects = false;
 

packages/shared/forks/ReactFeatureFlags.native-oss.js

@@ -49,7 +49,6 @@ export const deferRenderPhaseUpdateToNextBatch = true;
 export const decoupleUpdatePriorityFromScheduler = false;
 export const enableDiscreteEventFlushingChange = false;
 export const enableEagerRootListeners = true;
-export const disableSchedulerTimeoutInWorkLoop = false;
 
 export const enableDoubleInvokingEffects = false;
 

packages/shared/forks/ReactFeatureFlags.test-renderer.js

@@ -49,7 +49,6 @@ export const deferRenderPhaseUpdateToNextBatch = true;
 export const decoupleUpdatePriorityFromScheduler = false;
 export const enableDiscreteEventFlushingChange = false;
 export const enableEagerRootListeners = true;
-export const disableSchedulerTimeoutInWorkLoop = false;
 
 export const enableDoubleInvokingEffects = false;
 

packages/shared/forks/ReactFeatureFlags.test-renderer.native.js

@@ -49,7 +49,6 @@ export const deferRenderPhaseUpdateToNextBatch = true;
 export const decoupleUpdatePriorityFromScheduler = false;
 export const enableDiscreteEventFlushingChange = false;
 export const enableEagerRootListeners = true;
-export const disableSchedulerTimeoutInWorkLoop = false;
 
 export const enableDoubleInvokingEffects = false;
 

packages/shared/forks/ReactFeatureFlags.test-renderer.www.js

@@ -49,7 +49,6 @@ export const deferRenderPhaseUpdateToNextBatch = true;
 export const decoupleUpdatePriorityFromScheduler = false;
 export const enableDiscreteEventFlushingChange = false;
 export const enableEagerRootListeners = true;
-export const disableSchedulerTimeoutInWorkLoop = false;
 
 export const enableDoubleInvokingEffects = false;
 

packages/shared/forks/ReactFeatureFlags.testing.js

@@ -49,7 +49,6 @@ export const deferRenderPhaseUpdateToNextBatch = true;
 export const decoupleUpdatePriorityFromScheduler = false;
 export const enableDiscreteEventFlushingChange = false;
 export const enableEagerRootListeners = true;
-export const disableSchedulerTimeoutInWorkLoop = false;
 
 export const enableDoubleInvokingEffects = false;
 

packages/shared/forks/ReactFeatureFlags.testing.www.js

@@ -49,7 +49,6 @@ export const deferRenderPhaseUpdateToNextBatch = true;
 export const decoupleUpdatePriorityFromScheduler = false;
 export const enableDiscreteEventFlushingChange = true;
 export const enableEagerRootListeners = true;
-export const disableSchedulerTimeoutInWorkLoop = false;
 
 export const enableDoubleInvokingEffects = false;
 

packages/shared/forks/ReactFeatureFlags.www-dynamic.js

@@ -47,6 +47,5 @@ export const replayFailedUnitOfWorkWithInvokeGuardedCallback = __DEV__;
 // to __VARIANT__.
 export const enableTrustedTypesIntegration = false;
 export const disableSchedulerTimeoutBasedOnReactExpirationTime = false;
-export const disableSchedulerTimeoutInWorkLoop = __VARIANT__;
 
 export const enableDoubleInvokingEffects = false;

packages/shared/forks/ReactFeatureFlags.www.js

@@ -28,7 +28,6 @@ export const {
   enableDebugTracing,
   skipUnmountedBoundaries,
   enableEagerRootListeners,
-  disableSchedulerTimeoutInWorkLoop,
   enableDoubleInvokingEffects,
 } = dynamicFeatureFlags;