[flags] Remove enableModernStrictMode (#31838)

This is enabled everywhere.

packages/react-reconciler/src/ReactFiberWorkLoop.js

@@ -32,7 +32,6 @@ import {
   enableSchedulingProfiler,
   enableUpdaterTracking,
   enableTransitionTracing,
-  useModernStrictMode,
   disableLegacyContext,
   alwaysThrottleRetries,
   enableInfiniteRenderLoopDetection,
@@ -4205,7 +4204,7 @@ function commitDoubleInvokeEffectsInDEV(
   hasPassiveEffects: boolean,
 ) {
   if (__DEV__) {
-    if (useModernStrictMode && (disableLegacyMode || root.tag !== LegacyRoot)) {
+    if (disableLegacyMode || root.tag !== LegacyRoot) {
       let doubleInvokeEffects = true;
 
       if (

packages/react-reconciler/src/__tests__/ActivityStrictMode-test.js

@@ -77,7 +77,7 @@ describe('Activity StrictMode', () => {
     ]);
   });
 
-  // @gate __DEV__ && enableActivity && useModernStrictMode
+  // @gate __DEV__ && enableActivity
   it('should not trigger strict effects when offscreen is hidden', async () => {
     await act(() => {
       ReactNoop.render(

packages/react-reconciler/src/__tests__/StrictEffectsMode-test.js

@@ -945,34 +945,25 @@ describe('StrictEffectsMode', () => {
       shouldSuspend = false;
     });
 
-    if (gate(flags => flags.useModernStrictMode)) {
-      expect(log).toEqual([
-        'Child rendered',
-        'Child rendered',
-        // !!! Committed, destroy and create effect.
-        // !!! The other effect is not destroyed and created
-        // !!! because the dep didn't change
-        'Child dep destroy',
-        'Child dep create',
+    expect(log).toEqual([
+      'Child rendered',
+      'Child rendered',
+      // !!! Committed, destroy and create effect.
+      // !!! The other effect is not destroyed and created
+      // !!! because the dep didn't change
+      'Child dep destroy',
+      'Child dep create',
 
-        // Double invoke both effects
-        'Child destroy',
-        'Child dep destroy',
-        'Child create',
-        'Child dep create',
-        // Fires setState
-        '-----------------------after setState',
-        'Child rendered',
-        'Child rendered',
-        'Child dep create',
-      ]);
-    } else {
-      expect(log).toEqual([
-        'Child rendered',
-        'Child rendered',
-        'Child dep destroy',
-        'Child dep create',
-      ]);
-    }
+      // Double invoke both effects
+      'Child destroy',
+      'Child dep destroy',
+      'Child create',
+      'Child dep create',
+      // Fires setState
+      '-----------------------after setState',
+      'Child rendered',
+      'Child rendered',
+      'Child dep create',
+    ]);
   });
 });

packages/react-reconciler/src/__tests__/StrictEffectsModeDefaults-test.internal.js

@@ -461,7 +461,6 @@ describe('StrictEffectsMode defaults', () => {
       expect(log).toEqual([]);
     });
 
-    //@gate useModernStrictMode
     it('disconnects refs during double invoking', async () => {
       const onRefMock = jest.fn();
       function App({text}) {

packages/shared/ReactFeatureFlags.js

@@ -186,12 +186,6 @@ export const disableLegacyContext = true;
  */
 export const disableLegacyContextForFunctionComponents = true;
 
-// Not ready to break experimental yet.
-// Modern <StrictMode /> behaviour aligns more with what components
-// components will encounter in production, especially when used With <Offscreen />.
-// TODO: clean up legacy <StrictMode /> once tests pass WWW.
-export const useModernStrictMode = true;
-
 // Enable the moveBefore() alternative to insertBefore(). This preserves states of moves.
 export const enableMoveBefore = false;
 

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

@@ -80,7 +80,6 @@ export const renameElementSymbol = false;
 export const retryLaneExpirationMs = 5000;
 export const syncLaneExpirationMs = 250;
 export const transitionLaneExpirationMs = 5000;
-export const useModernStrictMode = true;
 export const enableHydrationLaneScheduling = true;
 export const enableYieldingBeforePassive = false;
 

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

@@ -70,7 +70,6 @@ export const renameElementSymbol = true;
 export const retryLaneExpirationMs = 5000;
 export const syncLaneExpirationMs = 250;
 export const transitionLaneExpirationMs = 5000;
-export const useModernStrictMode = true;
 export const enableSiblingPrerendering = true;
 export const enableUseResourceEffectHook = false;
 

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

@@ -52,7 +52,6 @@ export const enableLegacyHidden = false;
 
 export const enableTransitionTracing = false;
 
-export const useModernStrictMode = true;
 export const enableDO_NOT_USE_disableStrictPassiveEffect = false;
 export const enableFizzExternalRuntime = true;
 export const enableDeferRootSchedulingToMicrotask = true;

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

@@ -65,7 +65,6 @@ export const renameElementSymbol = false;
 export const retryLaneExpirationMs = 5000;
 export const syncLaneExpirationMs = 250;
 export const transitionLaneExpirationMs = 5000;
-export const useModernStrictMode = true;
 export const enableFabricCompleteRootInCommitPhase = false;
 export const enableSiblingPrerendering = true;
 export const enableUseResourceEffectHook = true;

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

@@ -54,7 +54,6 @@ export const enableLegacyHidden = false;
 
 export const enableTransitionTracing = false;
 
-export const useModernStrictMode = true;
 export const enableDO_NOT_USE_disableStrictPassiveEffect = false;
 export const enableFizzExternalRuntime = false;
 export const enableDeferRootSchedulingToMicrotask = true;

packages/shared/forks/ReactFeatureFlags.www.js

@@ -106,7 +106,6 @@ export const disableClientCache = true;
 export const enableServerComponentLogs = true;
 
 export const enableReactTestRendererWarning = false;
-export const useModernStrictMode = true;
 
 export const disableLegacyMode = true;