Revert "Disallow reading context during useMemo etc" (#14651)

* Revert "Add test coverage for readContext() on the server (#14649)"
This reverts commit fe2ecd2.
* Revert "Warn about incorrect use of useImperativeHandle() (#14647)"
This reverts commit 8f45a7f.
* Revert "Disallow reading context during useMemo etc (#14648)"
This reverts commit 1fcbd22.

Author: gaearon

packages/react-reconciler/src/ReactFiberClassComponent.js

@@ -20,6 +20,7 @@ import {
 importReactStrictModeWarningsfrom'./ReactStrictModeWarnings';
 import{isMounted}from'react-reconciler/reflection';
 import{getasgetInstance,setassetInstance}from'shared/ReactInstanceMap';
+importReactSharedInternalsfrom'shared/ReactSharedInternals';
 importshallowEqualfrom'shared/shallowEqual';
 importgetComponentNamefrom'shared/getComponentName';
 importinvariantfrom'shared/invariant';
@@ -47,14 +48,20 @@ import {
 hasContextChanged,
 emptyContextObject,
 }from'./ReactFiberContext';
-import{readContext}from'./ReactFiberNewContext';
 import{
 requestCurrentTime,
 computeExpirationForFiber,
 scheduleWork,
 flushPassiveEffects,
 }from'./ReactFiberScheduler';
 
+constReactCurrentDispatcher=ReactSharedInternals.ReactCurrentDispatcher;
+
+functionreadContext(contextType: any): any{
+constdispatcher=ReactCurrentDispatcher.current;
+returndispatcher.readContext(contextType);
+}
+
 constfakeInternalInstance={};
 constisArray=Array.isArray;
 

packages/react-reconciler/src/ReactFiberDispatcher.js

@@ -7,8 +7,8 @@
  * @flow
  */
 
+import{readContext}from'./ReactFiberNewContext';
 import{
-readContext,
 useCallback,
 useContext,
 useEffect,

packages/react-reconciler/src/ReactFiberHooks.js

@@ -14,7 +14,7 @@ import type {HookEffectTag} from './ReactHookEffectTags';
 
 import{NoWork}from'./ReactFiberExpirationTime';
 import{enableHooks}from'shared/ReactFeatureFlags';
-import{readContextasreadContextWithoutCheck}from'./ReactFiberNewContext';
+import{readContext}from'./ReactFiberNewContext';
 import{
 UpdateasUpdateEffect,
 PassiveasPassiveEffect,
@@ -284,7 +284,7 @@ export function resetHooks(): void {
 
 // This is used to reset the state of this module when a component throws.
 // It's also called inside mountIndeterminateComponent if we determine the
-// component is a module-style component, and also in readContext() above.
+// component is a module-style component.
 renderExpirationTime=NoWork;
 currentlyRenderingFiber=null;
 
@@ -394,7 +394,7 @@ export function useContext<T>(
  // Ensure we're in a function component (class components support only the
  // .unstable_read() form)
  resolveCurrentlyRenderingFiber();
- return readContextWithoutCheck(context, observedBits);
+ return readContext(context, observedBits);
 }
 
 exportfunctionuseState<S>(
@@ -785,29 +785,6 @@ export function useMemo<T>(
 returnnextValue;
 }
 
-exportfunctionreadContext<T>(
- context: ReactContext<T>,
- observedBits: void | number | boolean,
-): T {
-// Forbid reading context inside Hooks.
-// The outer check tells us whether we're inside a Hook like useMemo().
-// However, it would also be true if we're rendering a class.
-if(currentlyRenderingFiber===null){
-// The inner check tells us we're currently in renderWithHooks() phase
-// rather than, for example, in a class or a context consumer.
-// Then we know it should be an error.
-if(renderExpirationTime!==NoWork){
-invariant(
-false,
-'Context can only be read inside the body of a component. '+
-'If you read context inside a Hook like useMemo or useReducer, '+
-'move the call directly into the component body.',
-);
-}
-}
-returnreadContextWithoutCheck(context,observedBits);
-}
-
 functiondispatchAction<S,A>(
  fiber: Fiber,
  queue: UpdateQueue<S,A>,

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

@@ -672,88 +672,6 @@ describe('ReactHooks', () => {
 expect(root.toJSON()).toEqual('123');
 });
 
-it('throws when reading context inside useMemo',()=>{
-const{useMemo, createContext}=React;
-constReactCurrentDispatcher=
-React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED
-.ReactCurrentDispatcher;
-
-constThemeContext=createContext('light');
-functionApp(){
-returnuseMemo(()=>{
-returnReactCurrentDispatcher.current.readContext(ThemeContext);
-},[]);
-}
-
-expect(()=>ReactTestRenderer.create(<App/>)).toThrow(
-'Context can only be read inside the body of a component',
-);
-});
-
-it('throws when reading context inside useEffect',()=>{
-const{useEffect, createContext}=React;
-constReactCurrentDispatcher=
-React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED
-.ReactCurrentDispatcher;
-
-constThemeContext=createContext('light');
-functionApp(){
-useEffect(()=>{
-ReactCurrentDispatcher.current.readContext(ThemeContext);
-});
-returnnull;
-}
-
-constroot=ReactTestRenderer.create(<App/>);
-expect(()=>root.update(<App/>)).toThrow(
-// The exact message doesn't matter, just make sure we don't allow this
-"Cannot read property 'readContext' of null",
-);
-});
-
-it('throws when reading context inside useLayoutEffect',()=>{
-const{useLayoutEffect, createContext}=React;
-constReactCurrentDispatcher=
-React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED
-.ReactCurrentDispatcher;
-
-constThemeContext=createContext('light');
-functionApp(){
-useLayoutEffect(()=>{
-ReactCurrentDispatcher.current.readContext(ThemeContext);
-});
-returnnull;
-}
-
-expect(()=>ReactTestRenderer.create(<App/>)).toThrow(
-// The exact message doesn't matter, just make sure we don't allow this
-"Cannot read property 'readContext' of null",
-);
-});
-
-it('throws when reading context inside useReducer',()=>{
-const{useReducer, createContext}=React;
-constReactCurrentDispatcher=
-React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED
-.ReactCurrentDispatcher;
-
-constThemeContext=createContext('light');
-functionApp(){
-useReducer(
-()=>{
-ReactCurrentDispatcher.current.readContext(ThemeContext);
-},
-null,
-{},
-);
-returnnull;
-}
-
-expect(()=>ReactTestRenderer.create(<App/>)).toThrow(
-'Context can only be read inside the body of a component.',
-);
-});
-
 it('throws when calling hooks inside useReducer',()=>{
 const{useReducer, useRef}=React;
 functionApp(){