Noop unstable_batchedUpdates (#28120)

## Overview

`unstable_batchedUpdates` is effectively a no-op outside of legacy mode,
this PR makes it an actual no-op outside legacy mode.

packages/react-dom/index.classic.fb.js

@@ -23,7 +23,6 @@ export {
   findDOMNode,
   flushSync,
   unmountComponentAtNode,
-  unstable_batchedUpdates,
   unstable_createEventHandle,
   unstable_renderSubtreeIntoContainer,
   unstable_runWithPriority, // DO NOT USE: Temporarily exposed to migrate off of Scheduler.runWithPriority.
@@ -38,6 +37,11 @@ export {
   version,
 } from './src/client/ReactDOM';
 
-export {createRoot, hydrateRoot, render} from './src/client/ReactDOMRootFB';
+export {
+  createRoot,
+  hydrateRoot,
+  render,
+  unstable_batchedUpdates,
+} from './src/client/ReactDOMRootFB';
 
 export {Internals as __SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED};

packages/react-dom/src/__tests__/ReactLegacyMount-test.js

@@ -248,7 +248,7 @@ describe('ReactMount', () => {
     expect(calls).toBe(5);
   });
 
-  // @gate !disableLegacyMode
+  // @gate !disableLegacyMode && classic
   it('initial mount of legacy root is sync inside batchedUpdates, as if it were wrapped in flushSync', () => {
     const container1 = document.createElement('div');
     const container2 = document.createElement('div');

packages/react-dom/src/__tests__/ReactLegacyUpdates-test.js

@@ -32,7 +32,7 @@ describe('ReactLegacyUpdates', () => {
     assertLog = InternalTestUtils.assertLog;
   });
 
-  // @gate !disableLegacyMode
+  // @gate !disableLegacyMode && classic
   it('should batch state when updating state twice', () => {
     let updateCount = 0;
 
@@ -63,7 +63,7 @@ describe('ReactLegacyUpdates', () => {
     expect(updateCount).toBe(1);
   });
 
-  // @gate !disableLegacyMode
+  // @gate !disableLegacyMode && classic
   it('should batch state when updating two different state keys', () => {
     let updateCount = 0;
 
@@ -97,7 +97,7 @@ describe('ReactLegacyUpdates', () => {
     expect(updateCount).toBe(1);
   });
 
-  // @gate !disableLegacyMode
+  // @gate !disableLegacyMode && classic
   it('should batch state and props together', () => {
     let updateCount = 0;
 
@@ -131,7 +131,7 @@ describe('ReactLegacyUpdates', () => {
     expect(updateCount).toBe(1);
   });
 
-  // @gate !disableLegacyMode
+  // @gate !disableLegacyMode && classic
   it('should batch parent/child state updates together', () => {
     let parentUpdateCount = 0;
 
@@ -187,7 +187,7 @@ describe('ReactLegacyUpdates', () => {
     expect(childUpdateCount).toBe(1);
   });
 
-  // @gate !disableLegacyMode
+  // @gate !disableLegacyMode && classic
   it('should batch child/parent state updates together', () => {
     let parentUpdateCount = 0;
 
@@ -245,7 +245,7 @@ describe('ReactLegacyUpdates', () => {
     expect(childUpdateCount).toBe(1);
   });
 
-  // @gate !disableLegacyMode
+  // @gate !disableLegacyMode && classic
   it('should support chained state updates', () => {
     let updateCount = 0;
 
@@ -286,7 +286,7 @@ describe('ReactLegacyUpdates', () => {
     expect(updateCount).toBe(2);
   });
 
-  // @gate !disableLegacyMode
+  // @gate !disableLegacyMode && classic
   it('should batch forceUpdate together', () => {
     let shouldUpdateCount = 0;
     let updateCount = 0;
@@ -548,7 +548,7 @@ describe('ReactLegacyUpdates', () => {
     );
   });
 
-  // @gate !disableLegacyMode
+  // @gate !disableLegacyMode && classic
   it('should queue mount-ready handlers across different roots', () => {
     // We'll define two components A and B, then update both of them. When A's
     // componentDidUpdate handlers is called, B's DOM should already have been
@@ -849,7 +849,7 @@ describe('ReactLegacyUpdates', () => {
     expect(callbackCount).toBe(1);
   });
 
-  // @gate !disableLegacyMode
+  // @gate !disableLegacyMode && classic
   it('does not call render after a component as been deleted', () => {
     let renderCount = 0;
     let componentB = null;

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

@@ -32,7 +32,6 @@ import {
 import {createEventHandle} from 'react-dom-bindings/src/client/ReactDOMEventHandle';
 
 import {
-  batchedUpdates,
   flushSync as flushSyncWithoutWarningIfAlreadyRendering,
   isAlreadyRendering,
   injectIntoDevTools,
@@ -167,9 +166,16 @@ function flushSync<R>(fn: (() => R) | void): R | void {
 // Expose findDOMNode on internals
 Internals.findDOMNode = findDOMNode;
 
+function unstable_batchedUpdates<A, R>(fn: (a: A) => R, a: A): R {
+  // batchedUpdates was a legacy mode feature that is a no-op outside of
+  // legacy mode. In 19, we made it an actual no-op, but we're keeping it
+  // for now since there may be libraries that still include it.
+  return fn(a);
+}
+
 export {
   createPortal,
-  batchedUpdates as unstable_batchedUpdates,
+  unstable_batchedUpdates,
   flushSync,
   ReactVersion as version,
   // Disabled behind disableLegacyReactDOMAPIs
@@ -196,7 +202,7 @@ Internals.Events = [
   getFiberCurrentPropsFromNode,
   enqueueStateRestore,
   restoreStateIfNeeded,
-  batchedUpdates,
+  unstable_batchedUpdates,
 ];
 
 const foundDevTools = injectIntoDevTools({

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

@@ -42,6 +42,7 @@ import {
 } from 'react-dom-bindings/src/client/HTMLNodeType';
 
 import {
+  batchedUpdates,
   createContainer,
   createHydrationContainer,
   findHostInstanceWithNoPortals,
@@ -416,3 +417,5 @@ export function unstable_renderSubtreeIntoContainer(
     callback,
   );
 }
+
+export {batchedUpdates as unstable_batchedUpdates};

packages/react-reconciler/src/ReactFiberWorkLoop.js

@@ -39,6 +39,7 @@ import {
   disableLegacyContext,
   alwaysThrottleRetries,
   enableInfiniteRenderLoopDetection,
+  disableLegacyMode,
 } from 'shared/ReactFeatureFlags';
 import ReactSharedInternals from 'shared/ReactSharedInternals';
 import is from 'shared/objectIs';
@@ -1456,21 +1457,27 @@ export function deferredUpdates<A>(fn: () => A): A {
 }
 
 export function batchedUpdates<A, R>(fn: A => R, a: A): R {
-  const prevExecutionContext = executionContext;
-  executionContext |= BatchedContext;
-  try {
+  if (disableLegacyMode) {
+    // batchedUpdates is a no-op now, but there's still some internal react-dom
+    // code calling it, that we can't remove until we remove legacy mode.
     return fn(a);
-  } finally {
-    executionContext = prevExecutionContext;
-    // If there were legacy sync updates, flush them at the end of the outer
-    // most batchedUpdates-like method.
-    if (
-      executionContext === NoContext &&
-      // Treat `act` as if it's inside `batchedUpdates`, even in legacy mode.
-      !(__DEV__ && ReactCurrentActQueue.isBatchingLegacy)
-    ) {
-      resetRenderTimer();
-      flushSyncWorkOnLegacyRootsOnly();
+  } else {
+    const prevExecutionContext = executionContext;
+    executionContext |= BatchedContext;
+    try {
+      return fn(a);
+    } finally {
+      executionContext = prevExecutionContext;
+      // If there were legacy sync updates, flush them at the end of the outer
+      // most batchedUpdates-like method.
+      if (
+        executionContext === NoContext &&
+        // Treat `act` as if it's inside `batchedUpdates`, even in legacy mode.
+        !(__DEV__ && ReactCurrentActQueue.isBatchingLegacy)
+      ) {
+        resetRenderTimer();
+        flushSyncWorkOnLegacyRootsOnly();
+      }
     }
   }
 }