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Revert "Disallow reading context during useMemo etc" #14651

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merged 3 commits into from
Jan 21, 2019
Merged

Revert "Disallow reading context during useMemo etc" #14651

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16189d5
Revert "Add test coverage for readContext() on the server (#14649)"
gaearon Jan 21, 2019
8a5b243
Revert "Warn about incorrect use of useImperativeHandle() (#14647)"
gaearon Jan 21, 2019
820445c
Revert "Disallow reading context during useMemo etc (#14648)"
gaearon Jan 21, 2019
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9 changes: 8 additions & 1 deletion packages/react-reconciler/src/ReactFiberClassComponent.js
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@ import {
import ReactStrictModeWarnings from './ReactStrictModeWarnings';
import {isMounted} from 'react-reconciler/reflection';
import {get as getInstance, set as setInstance} from 'shared/ReactInstanceMap';
import ReactSharedInternals from 'shared/ReactSharedInternals';
import shallowEqual from 'shared/shallowEqual';
import getComponentName from 'shared/getComponentName';
import invariant from 'shared/invariant';
Expand Down Expand Up @@ -47,14 +48,20 @@ import {
hasContextChanged,
emptyContextObject,
} from './ReactFiberContext';
import {readContext} from './ReactFiberNewContext';
import {
requestCurrentTime,
computeExpirationForFiber,
scheduleWork,
flushPassiveEffects,
} from './ReactFiberScheduler';

const ReactCurrentDispatcher = ReactSharedInternals.ReactCurrentDispatcher;

function readContext(contextType: any): any {
const dispatcher = ReactCurrentDispatcher.current;
return dispatcher.readContext(contextType);
}

const fakeInternalInstance = {};
const isArray = Array.isArray;

Expand Down
2 changes: 1 addition & 1 deletion packages/react-reconciler/src/ReactFiberDispatcher.js
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Expand Up @@ -7,8 +7,8 @@
* @flow
*/

import {readContext} from './ReactFiberNewContext';
import {
readContext,
useCallback,
useContext,
useEffect,
Expand Down
29 changes: 3 additions & 26 deletions packages/react-reconciler/src/ReactFiberHooks.js
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Expand Up @@ -14,7 +14,7 @@ import type {HookEffectTag} from './ReactHookEffectTags';

import {NoWork} from './ReactFiberExpirationTime';
import {enableHooks} from 'shared/ReactFeatureFlags';
import {readContext as readContextWithoutCheck} from './ReactFiberNewContext';
import {readContext} from './ReactFiberNewContext';
import {
Update as UpdateEffect,
Passive as PassiveEffect,
Expand Down Expand Up @@ -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;

Expand Down Expand Up @@ -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);
}

export function useState<S>(
Expand Down Expand Up @@ -771,29 +771,6 @@ export function useMemo<T>(
return nextValue;
}

export function readContext<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.',
);
}
}
return readContextWithoutCheck(context, observedBits);
}

function dispatchAction<S, A>(
fiber: Fiber,
queue: UpdateQueue<S, A>,
Expand Down
82 changes: 0 additions & 82 deletions packages/react-reconciler/src/__tests__/ReactHooks-test.internal.js
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Expand Up @@ -633,88 +633,6 @@ describe('ReactHooks', () => {
expect(root.toJSON()).toEqual('123');
});

it('throws when reading context inside useMemo', () => {
const {useMemo, createContext} = React;
const ReactCurrentDispatcher =
React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED
.ReactCurrentDispatcher;

const ThemeContext = createContext('light');
function App() {
return useMemo(() => {
return ReactCurrentDispatcher.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;
const ReactCurrentDispatcher =
React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED
.ReactCurrentDispatcher;

const ThemeContext = createContext('light');
function App() {
useEffect(() => {
ReactCurrentDispatcher.current.readContext(ThemeContext);
});
return null;
}

const root = 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;
const ReactCurrentDispatcher =
React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED
.ReactCurrentDispatcher;

const ThemeContext = createContext('light');
function App() {
useLayoutEffect(() => {
ReactCurrentDispatcher.current.readContext(ThemeContext);
});
return null;
}

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;
const ReactCurrentDispatcher =
React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED
.ReactCurrentDispatcher;

const ThemeContext = createContext('light');
function App() {
useReducer(
() => {
ReactCurrentDispatcher.current.readContext(ThemeContext);
},
null,
{},
);
return null;
}

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;
function App() {
Expand Down