Defer work scheduler work if we're inside a pending commit

Author: sebmarkbage

packages/react-reconciler/src/ReactFiberRootScheduler.js

@@ -44,6 +44,7 @@ import {
   getWorkInProgressRootRenderLanes,
   getRootWithPendingPassiveEffects,
   getPendingPassiveEffectsLanes,
+  hasPendingCommitEffects,
   isWorkLoopSuspendedOnData,
   performWorkOnRoot,
 } from './ReactFiberWorkLoop';
@@ -466,6 +467,19 @@ function performWorkOnRootViaSchedulerTask(
     trackSchedulerEvent();
   }
 
+  if (hasPendingCommitEffects()) {
+    // We are currently in the middle of an async committing (such as a View Transition).
+    // We could force these to flush eagerly but it's better to defer any work until
+    // it finishes. This may not be the same root as we're waiting on.
+    // TODO: This relies on the commit eventually calling ensureRootIsScheduled which
+    // always calls processRootScheduleInMicrotask which in turn always loops through
+    // all the roots to figure out. This is all a bit inefficient and if optimized
+    // it'll need to consider rescheduling a task for any skipped roots.
+    root.callbackNode = null;
+    root.callbackPriority = NoLane;
+    return null;
+  }
+
   // Flush any pending passive effects before deciding which lanes to work on,
   // in case they schedule additional work.
   const originalCallbackNode = root.callbackNode;

packages/react-reconciler/src/ReactFiberWorkLoop.js

@@ -657,6 +657,13 @@ export function getWorkInProgressRootRenderLanes(): Lanes {
   return workInProgressRootRenderLanes;
 }
 
+export function hasPendingCommitEffects(): boolean {
+  return (
+    pendingEffectsStatus !== NO_PENDING_EFFECTS &&
+    pendingEffectsStatus !== PENDING_PASSIVE_PHASE
+  );
+}
+
 export function getRootWithPendingPassiveEffects(): FiberRoot | null {
   return pendingEffectsStatus === PENDING_PASSIVE_PHASE
     ? pendingEffectsRoot