Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

[Flight] Support (Async) Generator ServerComponent #28849

Merged
merged 1 commit into from
Apr 21, 2024
Merged

[Flight] Support (Async) Generator ServerComponent #28849

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
65 changes: 44 additions & 21 deletions packages/react-client/src/__tests__/ReactFlight-test.js
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -295,6 +295,33 @@ describe('ReactFlight', () => {
expect(Array.from(result)).toEqual([]);
});

it('can render a Generator Server Component as a fragment', async () => {
function ItemListClient(props) {
return <span>{props.children}</span>;
}
const ItemList = clientReference(ItemListClient);

function* Items() {
yield 'A';
yield 'B';
yield 'C';
}

const model = (
<ItemList>
<Items />
</ItemList>
);

const transport = ReactNoopFlightServer.render(model);

await act(async () => {
ReactNoop.render(await ReactNoopFlightClient.read(transport));
});

expect(ReactNoop).toMatchRenderedOutput(<span>ABC</span>);
});

it('can render undefined', async () => {
function Undefined() {
return undefined;
Expand Down Expand Up @@ -2151,16 +2178,9 @@ describe('ReactFlight', () => {
}
const Stateful = clientReference(StatefulClient);

function ServerComponent({item, initial}) {
// While the ServerComponent itself could be an async generator, single-shot iterables
// are not supported as React children since React might need to re-map them based on
// state updates. So we create an AsyncIterable instead.
return {
async *[Symbol.asyncIterator]() {
yield <Stateful key="a" initial={'a' + initial} />;
yield <Stateful key="b" initial={'b' + initial} />;
},
};
async function* ServerComponent({item, initial}) {
yield <Stateful key="a" initial={'a' + initial} />;
yield <Stateful key="b" initial={'b' + initial} />;
}

function ListClient({children}) {
Expand All @@ -2172,6 +2192,11 @@ describe('ReactFlight', () => {
expect(fragment.type).toBe(React.Fragment);
const fragmentChildren = [];
const iterator = fragment.props.children[Symbol.asyncIterator]();
if (iterator === fragment.props.children) {
console.error(
'AyncIterators are not valid children of React. It must be a multi-shot AsyncIterable.',
);
}
for (let entry; !(entry = React.use(iterator.next())).done; ) {
fragmentChildren.push(entry.value);
}
Expand Down Expand Up @@ -2316,23 +2341,21 @@ describe('ReactFlight', () => {
let resolve;
const iteratorPromise = new Promise(r => (resolve = r));

function ThirdPartyAsyncIterableComponent({item, initial}) {
// While the ServerComponent itself could be an async generator, single-shot iterables
// are not supported as React children since React might need to re-map them based on
// state updates. So we create an AsyncIterable instead.
return {
async *[Symbol.asyncIterator]() {
yield <span>Who</span>;
yield <span>dis?</span>;
resolve();
},
};
async function* ThirdPartyAsyncIterableComponent({item, initial}) {
yield <span>Who</span>;
yield <span>dis?</span>;
resolve();
}

function ListClient({children: fragment}) {
// TODO: Unwrap AsyncIterables natively in React. For now we do it in this wrapper.
const resolvedChildren = [];
const iterator = fragment.props.children[Symbol.asyncIterator]();
if (iterator === fragment.props.children) {
console.error(
'AyncIterators are not valid children of React. It must be a multi-shot AsyncIterable.',
);
}
for (let entry; !(entry = React.use(iterator.next())).done; ) {
resolvedChildren.push(entry.value);
}
Expand Down
103 changes: 89 additions & 14 deletions packages/react-server/src/ReactFlightServer.js
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -865,20 +865,95 @@ function renderFunctionComponent<Props>(
} else {
result = Component(props, secondArg);
}
if (
typeof result === 'object' &&
result !== null &&
typeof result.then === 'function'
) {
// When the return value is in children position we can resolve it immediately,
// to its value without a wrapper if it's synchronously available.
const thenable: Thenable<any> = result;
if (thenable.status === 'fulfilled') {
return thenable.value;
}
// TODO: Once we accept Promises as children on the client, we can just return
// the thenable here.
result = createLazyWrapperAroundWakeable(result);
if (typeof result === 'object' && result !== null) {
if (typeof result.then === 'function') {
// When the return value is in children position we can resolve it immediately,
// to its value without a wrapper if it's synchronously available.
const thenable: Thenable<any> = result;
if (thenable.status === 'fulfilled') {
return thenable.value;
}
// TODO: Once we accept Promises as children on the client, we can just return
// the thenable here.
result = createLazyWrapperAroundWakeable(result);
}

// Normally we'd serialize an Iterator/AsyncIterator as a single-shot which is not compatible
// to be rendered as a React Child. However, because we have the function to recreate
// an iterable from rendering the element again, we can effectively treat it as multi-
// shot. Therefore we treat this as an Iterable/AsyncIterable, whether it was one or not, by
// adding a wrapper so that this component effectively renders down to an AsyncIterable.
const iteratorFn = getIteratorFn(result);
if (iteratorFn) {
const iterableChild = result;
result = {
[Symbol.iterator]: function () {
const iterator = iteratorFn.call(iterableChild);
if (__DEV__) {
// If this was an Iterator but not a GeneratorFunction we warn because
// it might have been a mistake. Technically you can make this mistake with
// GeneratorFunctions and even single-shot Iterables too but it's extra
// tempting to try to return the value from a generator.
if (iterator === iterableChild) {
const isGeneratorComponent =
// $FlowIgnore[method-unbinding]
Object.prototype.toString.call(Component) ===
'[object GeneratorFunction]' &&
// $FlowIgnore[method-unbinding]
Object.prototype.toString.call(iterableChild) ===
'[object Generator]';
if (!isGeneratorComponent) {
console.error(
'Returning an Iterator from a Server Component is not supported ' +
'since it cannot be looped over more than once. ',
);
}
}
}
return (iterator: any);
},
};
if (__DEV__) {
(result: any)._debugInfo = iterableChild._debugInfo;
}
} else if (
enableFlightReadableStream &&
typeof (result: any)[ASYNC_ITERATOR] === 'function' &&
(typeof ReadableStream !== 'function' ||
!(result instanceof ReadableStream))
) {
const iterableChild = result;
result = {
[ASYNC_ITERATOR]: function () {
const iterator = (iterableChild: any)[ASYNC_ITERATOR]();
if (__DEV__) {
// If this was an AsyncIterator but not an AsyncGeneratorFunction we warn because
// it might have been a mistake. Technically you can make this mistake with
// AsyncGeneratorFunctions and even single-shot AsyncIterables too but it's extra
// tempting to try to return the value from a generator.
if (iterator === iterableChild) {
const isGeneratorComponent =
// $FlowIgnore[method-unbinding]
Object.prototype.toString.call(Component) ===
'[object AsyncGeneratorFunction]' &&
// $FlowIgnore[method-unbinding]
Object.prototype.toString.call(iterableChild) ===
'[object AsyncGenerator]';
if (!isGeneratorComponent) {
console.error(
'Returning an AsyncIterator from a Server Component is not supported ' +
'since it cannot be looped over more than once. ',
);
}
}
}
return iterator;
},
};
if (__DEV__) {
(result: any)._debugInfo = iterableChild._debugInfo;
}
}
}
// Track this element's key on the Server Component on the keyPath context..
const prevKeyPath = task.keyPath;
Expand Down