Add feature flag to disable yielding (#15119)

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

@@ -10,6 +10,7 @@
 'use strict';
 
 const React = require('react');
+const Fragment = React.Fragment;
 let ReactFeatureFlags = require('shared/ReactFeatureFlags');
 
 let ReactDOM;
@@ -659,4 +660,55 @@ describe('ReactDOMFiberAsync', () => {
       expect(formSubmitted).toBe(true);
     });
   });
+
+  describe('Disable yielding', () => {
+    beforeEach(() => {
+      jest.resetModules();
+      ReactFeatureFlags = require('shared/ReactFeatureFlags');
+      ReactFeatureFlags.disableYielding = true;
+      ReactFeatureFlags.debugRenderPhaseSideEffectsForStrictMode = false;
+      ReactDOM = require('react-dom');
+      Scheduler = require('scheduler');
+    });
+
+    it('wont yield during a render if yielding is disabled', () => {
+      class A extends React.Component {
+        render() {
+          Scheduler.yieldValue('A');
+          return <div>{this.props.children}</div>;
+        }
+      }
+
+      class B extends React.Component {
+        render() {
+          Scheduler.yieldValue('B');
+          return <div>{this.props.children}</div>;
+        }
+      }
+
+      class C extends React.Component {
+        render() {
+          Scheduler.yieldValue('C');
+          return <div>{this.props.children}</div>;
+        }
+      }
+
+      let root = ReactDOM.unstable_createRoot(container);
+
+      root.render(
+        <Fragment>
+          <A />
+          <B />
+          <C />
+        </Fragment>,
+      );
+
+      expect(Scheduler).toHaveYielded([]);
+
+      Scheduler.unstable_flushNumberOfYields(2);
+      // Even though we just flushed two yields, we should have rendered
+      // everything without yielding when the flag is on.
+      expect(Scheduler).toHaveYielded(['A', 'B', 'C']);
+    });
+  });
 });

packages/react-reconciler/src/ReactFiberScheduler.js

@@ -63,6 +63,7 @@ import {
   replayFailedUnitOfWorkWithInvokeGuardedCallback,
   warnAboutDeprecatedLifecycles,
   enableSuspenseServerRenderer,
+  disableYielding,
 } from 'shared/ReactFeatureFlags';
 import getComponentName from 'shared/getComponentName';
 import invariant from 'shared/invariant';
@@ -2019,7 +2020,7 @@ function onSuspend(
   msUntilTimeout: number,
 ): void {
   root.expirationTime = rootExpirationTime;
-  if (msUntilTimeout === 0 && !shouldYield()) {
+  if (msUntilTimeout === 0 && (disableYielding || !shouldYield())) {
     // Don't wait an additional tick. Commit the tree immediately.
     root.pendingCommitExpirationTime = suspendedExpirationTime;
     root.finishedWork = finishedWork;
@@ -2233,7 +2234,11 @@ function performAsyncWork(didTimeout) {
       } while (root !== firstScheduledRoot);
     }
   }
-  performWork(NoWork, true);
+  let isYieldy = true;
+  if (disableYielding) {
+    isYieldy = false;
+  }
+  performWork(NoWork, isYieldy);
 }
 
 function performSyncWork() {

packages/shared/ReactFeatureFlags.js

@@ -45,6 +45,9 @@ export function addUserTimingListener() {
 // Disable javascript: URL strings in href for XSS protection.
 export const disableJavaScriptURLs = false;
 
+// Disables yielding during render in Concurrent Mode. Used for debugging only.
+export const disableYielding = false;
+
 // React Fire: prevent the value and checked attributes from syncing
 // with their related DOM properties
 export const disableInputAttributeSyncing = false;

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

@@ -25,6 +25,7 @@ export const warnAboutShorthandPropertyCollision = false;
 export const enableSchedulerDebugging = false;
 export const debugRenderPhaseSideEffectsForStrictMode = true;
 export const disableJavaScriptURLs = false;
+export const disableYielding = false;
 export const disableInputAttributeSyncing = false;
 export const replayFailedUnitOfWorkWithInvokeGuardedCallback = __DEV__;
 export const warnAboutDeprecatedLifecycles = true;

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

@@ -21,6 +21,7 @@ export const enableProfilerTimer = __PROFILE__;
 export const enableSchedulerTracing = __PROFILE__;
 export const enableSuspenseServerRenderer = false;
 export const disableJavaScriptURLs = false;
+export const disableYielding = false;
 export const disableInputAttributeSyncing = false;
 export const enableStableConcurrentModeAPIs = false;
 export const warnAboutShorthandPropertyCollision = false;

packages/shared/forks/ReactFeatureFlags.persistent.js

@@ -21,6 +21,7 @@ export const enableProfilerTimer = __PROFILE__;
 export const enableSchedulerTracing = __PROFILE__;
 export const enableSuspenseServerRenderer = false;
 export const disableJavaScriptURLs = false;
+export const disableYielding = false;
 export const disableInputAttributeSyncing = false;
 export const enableStableConcurrentModeAPIs = false;
 export const warnAboutShorthandPropertyCollision = false;

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

@@ -21,6 +21,7 @@ export const enableProfilerTimer = false;
 export const enableSchedulerTracing = false;
 export const enableSuspenseServerRenderer = false;
 export const disableJavaScriptURLs = false;
+export const disableYielding = false;
 export const disableInputAttributeSyncing = false;
 export const enableStableConcurrentModeAPIs = false;
 export const warnAboutShorthandPropertyCollision = false;

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

@@ -24,6 +24,7 @@ export const enableStableConcurrentModeAPIs = false;
 export const enableSchedulerDebugging = false;
 export const warnAboutDeprecatedSetNativeProps = false;
 export const disableJavaScriptURLs = false;
+export const disableYielding = false;
 export const enableEventAPI = true;
 
 // Only used in www builds.

packages/shared/forks/ReactFeatureFlags.www.js

@@ -17,6 +17,7 @@ export const {
   replayFailedUnitOfWorkWithInvokeGuardedCallback,
   warnAboutDeprecatedLifecycles,
   disableJavaScriptURLs,
+  disableYielding,
   disableInputAttributeSyncing,
   warnAboutShorthandPropertyCollision,
   warnAboutDeprecatedSetNativeProps,