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Implement useSyncExternalStore on server #22347

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merged 1 commit into from
Sep 20, 2021
Merged

Implement useSyncExternalStore on server #22347

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1 change: 1 addition & 0 deletions packages/react-debug-tools/src/ReactDebugHooks.js
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Original file line number Diff line number Diff line change
Expand Up @@ -258,6 +258,7 @@ function useMemo<T>(
function useSyncExternalStore<T>(
subscribe: (() => void) => () => void,
getSnapshot: () => T,
getServerSnapshot?: () => T,
): T {
// useSyncExternalStore() composes multiple hooks internally.
// Advance the current hook index the same number of times
Expand Down
157 changes: 157 additions & 0 deletions packages/react-dom/src/__tests__/ReactDOMFizzServer-test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,8 @@ let ReactDOM;
let ReactDOMFizzServer;
let Suspense;
let SuspenseList;
let useSyncExternalStore;
let useSyncExternalStoreExtra;
let PropTypes;
let textCache;
let document;
Expand All @@ -39,6 +41,9 @@ describe('ReactDOMFizzServer', () => {
Stream = require('stream');
Suspense = React.Suspense;
SuspenseList = React.SuspenseList;
useSyncExternalStore = React.unstable_useSyncExternalStore;
useSyncExternalStoreExtra = require('use-sync-external-store/extra')
.useSyncExternalStoreExtra;
PropTypes = require('prop-types');

textCache = new Map();
Expand Down Expand Up @@ -1478,4 +1483,156 @@ describe('ReactDOMFizzServer', () => {
// We should've been able to display the content without waiting for the rest of the fallback.
expect(getVisibleChildren(container)).toEqual(<div>Hello</div>);
});

// @gate supportsNativeUseSyncExternalStore
// @gate experimental
it('calls getServerSnapshot instead of getSnapshot', async () => {
const ref = React.createRef();

function getServerSnapshot() {
return 'server';
}

function getClientSnapshot() {
return 'client';
}

function subscribe() {
return () => {};
}

function Child({text}) {
Scheduler.unstable_yieldValue(text);
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noob q: I see we use this everywhere in tests, why is it needed?

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Oh is it just as a way to avoid relying on implementation details for testing if a codepath executed?

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It's a common testing pattern we use. yieldValue pushes something into a log, and then we later assert the output of that log.

The reason it's a Scheduler API is that we also use it to perform some partial work and then yield right after, to test concurrent tasks:

scheduleSomeWork(); // e.g. a React update
expect(Scheduler).toFlushAndYieldThrough([
  'child 1',
  'child 2,'
]);

// The work is paused. Do something concurrent, like an interleaved input event.

// Then flush the rest of the work
expect(Scheduler).toFlushAndYield([
  'child 3',
  'child 4,'
]);

// Assert on final result

It's probably not the most intuitive name; it's inspired by the yield keyword for generator functions since that's roughly the way it's used.

return text;
}

function App() {
const value = useSyncExternalStore(
subscribe,
getClientSnapshot,
getServerSnapshot,
);
return (
<div ref={ref}>
<Child text={value} />
</div>
);
}

const loggedErrors = [];
await act(async () => {
const {startWriting} = ReactDOMFizzServer.pipeToNodeWritable(
<Suspense fallback="Loading...">
<App />
</Suspense>,
writable,
{
onError(x) {
loggedErrors.push(x);
},
},
);
startWriting();
});
expect(Scheduler).toHaveYielded(['server']);

const serverRenderedDiv = container.getElementsByTagName('div')[0];

ReactDOM.hydrateRoot(container, <App />);

// The first paint uses the server snapshot
expect(Scheduler).toFlushUntilNextPaint(['server']);
expect(getVisibleChildren(container)).toEqual(<div>server</div>);
// Hydration succeeded
expect(ref.current).toEqual(serverRenderedDiv);

// Asynchronously we detect that the store has changed on the client,
// and patch up the inconsistency
expect(Scheduler).toFlushUntilNextPaint(['client']);
expect(getVisibleChildren(container)).toEqual(<div>client</div>);
expect(ref.current).toEqual(serverRenderedDiv);
});

// The selector implementation uses the lazy ref initialization pattern
// @gate !(enableUseRefAccessWarning && __DEV__)
// @gate supportsNativeUseSyncExternalStore
// @gate experimental
it('calls getServerSnapshot instead of getSnapshot (with selector and isEqual)', async () => {
// Same as previous test, but with a selector that returns a complex object
// that is memoized with a custom `isEqual` function.
const ref = React.createRef();

function getServerSnapshot() {
return {env: 'server', other: 'unrelated'};
}

function getClientSnapshot() {
return {env: 'client', other: 'unrelated'};
}

function selector({env}) {
return {env};
}

function isEqual(a, b) {
return a.env === b.env;
}

function subscribe() {
return () => {};
}

function Child({text}) {
Scheduler.unstable_yieldValue(text);
return text;
}

function App() {
const {env} = useSyncExternalStoreExtra(
subscribe,
getClientSnapshot,
getServerSnapshot,
selector,
isEqual,
);
return (
<div ref={ref}>
<Child text={env} />
</div>
);
}

const loggedErrors = [];
await act(async () => {
const {startWriting} = ReactDOMFizzServer.pipeToNodeWritable(
<Suspense fallback="Loading...">
<App />
</Suspense>,
writable,
{
onError(x) {
loggedErrors.push(x);
},
},
);
startWriting();
});
expect(Scheduler).toHaveYielded(['server']);

const serverRenderedDiv = container.getElementsByTagName('div')[0];

ReactDOM.hydrateRoot(container, <App />);

// The first paint uses the server snapshot
expect(Scheduler).toFlushUntilNextPaint(['server']);
expect(getVisibleChildren(container)).toEqual(<div>server</div>);
// Hydration succeeded
expect(ref.current).toEqual(serverRenderedDiv);

// Asynchronously we detect that the store has changed on the client,
// and patch up the inconsistency
expect(Scheduler).toFlushUntilNextPaint(['client']);
expect(getVisibleChildren(container)).toEqual(<div>client</div>);
expect(ref.current).toEqual(serverRenderedDiv);
});
});
10 changes: 9 additions & 1 deletion packages/react-dom/src/server/ReactPartialRendererHooks.js
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Original file line number Diff line number Diff line change
Expand Up @@ -464,8 +464,16 @@ export function useCallback<T>(
function useSyncExternalStore<T>(
subscribe: (() => void) => () => void,
getSnapshot: () => T,
getServerSnapshot?: () => T,
): T {
throw new Error('Not yet implemented');
if (getServerSnapshot === undefined) {
invariant(
false,
'Missing getServerSnapshot, which is required for ' +
'server-rendered content. Will revert to client rendering.',
);
}
return getServerSnapshot();
}

function useDeferredValue<T>(value: T): T {
Expand Down
97 changes: 67 additions & 30 deletions packages/react-reconciler/src/ReactFiberHooks.new.js
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Original file line number Diff line number Diff line change
Expand Up @@ -938,23 +938,64 @@ function rerenderReducer<S, I, A>(
function mountSyncExternalStore<T>(
subscribe: (() => void) => () => void,
getSnapshot: () => T,
getServerSnapshot?: () => T,
): T {
const fiber = currentlyRenderingFiber;
const hook = mountWorkInProgressHook();
// Read the current snapshot from the store on every render. This breaks the
// normal rules of React, and only works because store updates are
// always synchronous.
const nextSnapshot = getSnapshot();
if (__DEV__) {
if (!didWarnUncachedGetSnapshot) {
if (nextSnapshot !== getSnapshot()) {
console.error(
'The result of getSnapshot should be cached to avoid an infinite loop',
);
didWarnUncachedGetSnapshot = true;

let nextSnapshot;
const isHydrating = getIsHydrating();
if (isHydrating) {
if (getServerSnapshot === undefined) {
invariant(
false,
'Missing getServerSnapshot, which is required for ' +
'server-rendered content. Will revert to client rendering.',
);
}
nextSnapshot = getServerSnapshot();
if (__DEV__) {
if (!didWarnUncachedGetSnapshot) {
if (nextSnapshot !== getServerSnapshot()) {
console.error(
'The result of getServerSnapshot should be cached to avoid an infinite loop',
);
didWarnUncachedGetSnapshot = true;
}
}
}
} else {
nextSnapshot = getSnapshot();
if (__DEV__) {
if (!didWarnUncachedGetSnapshot) {
if (nextSnapshot !== getSnapshot()) {
console.error(
'The result of getSnapshot should be cached to avoid an infinite loop',
);
didWarnUncachedGetSnapshot = true;
}
}
}
// Unless we're rendering a blocking lane, schedule a consistency check.
// Right before committing, we will walk the tree and check if any of the
// stores were mutated.
//
// We won't do this if we're hydrating server-rendered content, because if
// the content is stale, it's already visible anyway. Instead we'll patch
// it up in a passive effect.
const root: FiberRoot | null = getWorkInProgressRoot();
invariant(
root !== null,
'Expected a work-in-progress root. This is a bug in React. Please file an issue.',
);
if (!includesBlockingLane(root, renderLanes)) {
pushStoreConsistencyCheck(fiber, getSnapshot, nextSnapshot);
}
}

// Read the current snapshot from the store on every render. This breaks the
// normal rules of React, and only works because store updates are
// always synchronous.
hook.memoizedState = nextSnapshot;
const inst: StoreInstance<T> = {
value: nextSnapshot,
Expand All @@ -980,24 +1021,13 @@ function mountSyncExternalStore<T>(
null,
);

// Unless we're rendering a blocking lane, schedule a consistency check. Right
// before committing, we will walk the tree and check if any of the stores
// were mutated.
const root: FiberRoot | null = getWorkInProgressRoot();
invariant(
root !== null,
'Expected a work-in-progress root. This is a bug in React. Please file an issue.',
);
if (!includesBlockingLane(root, renderLanes)) {
pushStoreConsistencyCheck(fiber, getSnapshot, nextSnapshot);
}

return nextSnapshot;
}

function updateSyncExternalStore<T>(
subscribe: (() => void) => () => void,
getSnapshot: () => T,
getServerSnapshot?: () => T,
): T {
const fiber = currentlyRenderingFiber;
const hook = updateWorkInProgressHook();
Expand Down Expand Up @@ -2235,10 +2265,11 @@ if (__DEV__) {
useSyncExternalStore<T>(
subscribe: (() => void) => () => void,
getSnapshot: () => T,
getServerSnapshot?: () => T,
): T {
currentHookNameInDev = 'useSyncExternalStore';
mountHookTypesDev();
return mountSyncExternalStore(subscribe, getSnapshot);
return mountSyncExternalStore(subscribe, getSnapshot, getServerSnapshot);
},
useOpaqueIdentifier(): OpaqueIDType | void {
currentHookNameInDev = 'useOpaqueIdentifier';
Expand Down Expand Up @@ -2366,10 +2397,11 @@ if (__DEV__) {
useSyncExternalStore<T>(
subscribe: (() => void) => () => void,
getSnapshot: () => T,
getServerSnapshot?: () => T,
): T {
currentHookNameInDev = 'useSyncExternalStore';
updateHookTypesDev();
return mountSyncExternalStore(subscribe, getSnapshot);
return mountSyncExternalStore(subscribe, getSnapshot, getServerSnapshot);
},
useOpaqueIdentifier(): OpaqueIDType | void {
currentHookNameInDev = 'useOpaqueIdentifier';
Expand Down Expand Up @@ -2497,10 +2529,11 @@ if (__DEV__) {
useSyncExternalStore<T>(
subscribe: (() => void) => () => void,
getSnapshot: () => T,
getServerSnapshot?: () => T,
): T {
currentHookNameInDev = 'useSyncExternalStore';
updateHookTypesDev();
return updateSyncExternalStore(subscribe, getSnapshot);
return updateSyncExternalStore(subscribe, getSnapshot, getServerSnapshot);
},
useOpaqueIdentifier(): OpaqueIDType | void {
currentHookNameInDev = 'useOpaqueIdentifier';
Expand Down Expand Up @@ -2629,10 +2662,11 @@ if (__DEV__) {
useSyncExternalStore<T>(
subscribe: (() => void) => () => void,
getSnapshot: () => T,
getServerSnapshot?: () => T,
): T {
currentHookNameInDev = 'useSyncExternalStore';
updateHookTypesDev();
return updateSyncExternalStore(subscribe, getSnapshot);
return updateSyncExternalStore(subscribe, getSnapshot, getServerSnapshot);
},
useOpaqueIdentifier(): OpaqueIDType | void {
currentHookNameInDev = 'useOpaqueIdentifier';
Expand Down Expand Up @@ -2774,11 +2808,12 @@ if (__DEV__) {
useSyncExternalStore<T>(
subscribe: (() => void) => () => void,
getSnapshot: () => T,
getServerSnapshot?: () => T,
): T {
currentHookNameInDev = 'useSyncExternalStore';
warnInvalidHookAccess();
mountHookTypesDev();
return mountSyncExternalStore(subscribe, getSnapshot);
return mountSyncExternalStore(subscribe, getSnapshot, getServerSnapshot);
},
useOpaqueIdentifier(): OpaqueIDType | void {
currentHookNameInDev = 'useOpaqueIdentifier';
Expand Down Expand Up @@ -2921,11 +2956,12 @@ if (__DEV__) {
useSyncExternalStore<T>(
subscribe: (() => void) => () => void,
getSnapshot: () => T,
getServerSnapshot?: () => T,
): T {
currentHookNameInDev = 'useSyncExternalStore';
warnInvalidHookAccess();
updateHookTypesDev();
return updateSyncExternalStore(subscribe, getSnapshot);
return updateSyncExternalStore(subscribe, getSnapshot, getServerSnapshot);
},
useOpaqueIdentifier(): OpaqueIDType | void {
currentHookNameInDev = 'useOpaqueIdentifier';
Expand Down Expand Up @@ -3069,11 +3105,12 @@ if (__DEV__) {
useSyncExternalStore<T>(
subscribe: (() => void) => () => void,
getSnapshot: () => T,
getServerSnapshot?: () => T,
): T {
currentHookNameInDev = 'useSyncExternalStore';
warnInvalidHookAccess();
updateHookTypesDev();
return updateSyncExternalStore(subscribe, getSnapshot);
return updateSyncExternalStore(subscribe, getSnapshot, getServerSnapshot);
},
useOpaqueIdentifier(): OpaqueIDType | void {
currentHookNameInDev = 'useOpaqueIdentifier';
Expand Down
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