DCE hooks code when flag is off

packages/react-dom/src/server/ReactPartialRenderer.js

@@ -25,6 +25,7 @@ import describeComponentFrame from 'shared/describeComponentFrame';
 import ReactSharedInternals from 'shared/ReactSharedInternals';
 import {
   warnAboutDeprecatedLifecycles,
+  enableHooks,
   enableSuspenseServerRenderer,
 } from 'shared/ReactFeatureFlags';
 
@@ -52,6 +53,7 @@ import {
   prepareToUseHooks,
   finishHooks,
   Dispatcher,
+  DispatcherWithoutHooks,
 } from './ReactPartialRendererHooks';
 import {
   Namespaces,
@@ -819,7 +821,11 @@ class ReactDOMServerRenderer {
       return null;
     }
 
-    ReactCurrentOwner.currentDispatcher = Dispatcher;
+    if (enableHooks) {
+      ReactCurrentOwner.currentDispatcher = Dispatcher;
+    } else {
+      ReactCurrentOwner.currentDispatcher = DispatcherWithoutHooks;
+    }
     try {
       let out = '';
       while (out.length < bytes) {

packages/react-dom/src/server/ReactPartialRendererHooks.js

@@ -350,3 +350,6 @@ export const Dispatcher = {
   // Effects are not run in the server environment.
   useEffect: noop,
 };
+export const DispatcherWithoutHooks = {
+  readContext,
+};

packages/react-reconciler/src/ReactFiberCommitWork.js

@@ -22,6 +22,7 @@ import type {SuspenseState} from './ReactFiberSuspenseComponent';
 import type {FunctionComponentUpdateQueue} from './ReactFiberHooks';
 
 import {
+  enableHooks,
   enableSchedulerTracing,
   enableProfilerTimer,
 } from 'shared/ReactFeatureFlags';
@@ -278,6 +279,9 @@ function commitHookEffectList(
   mountTag: number,
   finishedWork: Fiber,
 ) {
+  if (!enableHooks) {
+    return;
+  }
   const updateQueue: FunctionComponentUpdateQueue | null = (finishedWork.updateQueue: any);
   let lastEffect = updateQueue !== null ? updateQueue.lastEffect : null;
   if (lastEffect !== null) {

packages/react-reconciler/src/ReactFiberDispatcher.js

@@ -34,3 +34,6 @@ export const Dispatcher = {
   useRef,
   useState,
 };
+export const DispatcherWithoutHooks = {
+  readContext,
+};

packages/react-reconciler/src/ReactFiberHooks.js

@@ -13,6 +13,7 @@ import type {ExpirationTime} from './ReactFiberExpirationTime';
 import type {HookEffectTag} from './ReactHookEffectTags';
 
 import {NoWork} from './ReactFiberExpirationTime';
+import {enableHooks} from 'shared/ReactFeatureFlags';
 import {readContext} from './ReactFiberNewContext';
 import {
   Snapshot as SnapshotEffect,
@@ -124,6 +125,9 @@ export function prepareToUseHooks(
   workInProgress: Fiber,
   nextRenderExpirationTime: ExpirationTime,
 ): void {
+  if (!enableHooks) {
+    return;
+  }
   renderExpirationTime = nextRenderExpirationTime;
   currentlyRenderingFiber = workInProgress;
   firstCurrentHook = current !== null ? current.memoizedState : null;
@@ -147,6 +151,10 @@ export function finishHooks(
   children: any,
   refOrContext: any,
 ): any {
+  if (!enableHooks) {
+    return children;
+  }
+
   // This must be called after every function component to prevent hooks from
   // being used in classes.
 
@@ -206,6 +214,10 @@ export function finishHooks(
 }
 
 export function resetHooks(): void {
+  if (!enableHooks) {
+    return;
+  }
+
   // This is called instead of `finishHooks` if the component throws. It's also
   // called inside mountIndeterminateComponent if we determine the component
   // is a module-style component.

packages/react-reconciler/src/ReactFiberScheduler.js

@@ -56,6 +56,7 @@ import {
   SimpleMemoComponent,
 } from 'shared/ReactWorkTags';
 import {
+  enableHooks,
   enableSchedulerTracing,
   enableProfilerTimer,
   enableUserTimingAPI,
@@ -164,7 +165,7 @@ import {
   commitDetachRef,
   commitPassiveHookEffects,
 } from './ReactFiberCommitWork';
-import {Dispatcher} from './ReactFiberDispatcher';
+import {Dispatcher, DispatcherWithoutHooks} from './ReactFiberDispatcher';
 
 export type Thenable = {
   then(resolve: () => mixed, reject?: () => mixed): mixed,
@@ -504,7 +505,7 @@ function commitAllLifeCycles(
       commitAttachRef(nextEffect);
     }
 
-    if (effectTag & Passive) {
+    if (enableHooks && effectTag & Passive) {
       rootWithPendingPassiveEffects = finishedRoot;
     }
 
@@ -768,7 +769,11 @@ function commitRoot(root: FiberRoot, finishedWork: Fiber): void {
     }
   }
 
-  if (firstEffect !== null && rootWithPendingPassiveEffects !== null) {
+  if (
+    enableHooks &&
+    firstEffect !== null &&
+    rootWithPendingPassiveEffects !== null
+  ) {
     // This commit included a passive effect. These do not need to fire until
     // after the next paint. Schedule an callback to fire them in an async
     // event. To ensure serial execution, the callback will be flushed early if
@@ -1192,7 +1197,11 @@ function renderRoot(root: FiberRoot, isYieldy: boolean): void {
   flushPassiveEffects();
 
   isWorking = true;
-  ReactCurrentOwner.currentDispatcher = Dispatcher;
+  if (enableHooks) {
+    ReactCurrentOwner.currentDispatcher = Dispatcher;
+  } else {
+    ReactCurrentOwner.currentDispatcher = DispatcherWithoutHooks;
+  }
 
   const expirationTime = root.nextExpirationTimeToWorkOn;