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Posponing directly inside a Suspense boundary needs a special case
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It's like a combination of ReplaySuspenseBoundary and ResumeElement.
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@sebmarkbage
sebmarkbage committed Sep 14, 2023
1 parent cf125d2 commit 5b276c6
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Showing 2 changed files with 226 additions and 26 deletions.
39 changes: 39 additions & 0 deletions packages/react-dom/src/__tests__/ReactDOMFizzStaticBrowser-test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -624,6 +624,45 @@ describe('ReactDOMFizzStaticBrowser', () => {
);
});

// @gate enablePostpone
it('supports postponing in lazy as a direct child', async () => {
let prerendering = true;
const Hole = React.lazy(async () => {
React.unstable_postpone();
});
function Postpone() {
return prerendering ? Hole : 'Hello';
}

function App() {
return (
<div>
<Suspense fallback="Loading...">
<Postpone key="key" />
</Suspense>
</div>
);
}

const prerendered = await ReactDOMFizzStatic.prerender(<App />);
expect(prerendered.postponed).not.toBe(null);

prerendering = false;

const resumed = await ReactDOMFizzServer.resume(
<App />,
prerendered.postponed,
);

await readIntoContainer(prerendered.prelude);

expect(getVisibleChildren(container)).toEqual(<div>Loading...</div>);

await readIntoContainer(resumed);

expect(getVisibleChildren(container)).toEqual(<div>Hello</div>);
});

// @gate enablePostpone
it('only emits end tags once when resuming', async () => {
let prerendering = true;
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213 changes: 187 additions & 26 deletions packages/react-server/src/ReactFizzServer.js
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Original file line number Diff line number Diff line change
Expand Up @@ -168,7 +168,8 @@ export type KeyNode = [
const REPLAY_NODE = 0;
const REPLAY_SUSPENSE_BOUNDARY = 1;
const RESUME_ELEMENT = 2;
const RESUME_SLOT = 3;
const RESUME_SUSPENSE_BOUNDARY = 3;
const RESUME_SLOT = 4;

type ReplaySuspenseBoundary = [
1, // REPLAY_SUSPENSE_BOUNDARY
Expand All @@ -188,6 +189,14 @@ type ReplayNode =
]
| ReplaySuspenseBoundary;

type ResumeSuspenseBoundary = [
3, // RESUME_SUSPENSE_BOUNDARY
string | null /* name */,
string | number /* key */,
SuspenseBoundaryID /* id */,
number /* rootSegmentID */,
];

type ResumeElement = [
2, // RESUME_ELEMENT
string | null /* name */,
Expand All @@ -196,12 +205,16 @@ type ResumeElement = [
];

type ResumeSlot = [
3, // RESUME_SLOT
4, // RESUME_SLOT
number /* index */,
number /* segment id */,
];

type ResumableNode = ReplayNode | ResumeElement | ResumeSlot;
type ResumableNode =
| ReplayNode
| ResumeElement
| ResumeSuspenseBoundary
| ResumeSlot;

type PostponedHoles = {
workingMap: Map<KeyNode, ReplayNode>,
Expand Down Expand Up @@ -1053,6 +1066,109 @@ function replaySuspenseBoundary(
popComponentStackInDEV(task);
}

function resumeSuspenseBoundary(
request: Request,
task: ReplayTask,
props: Object,
replayNode: ResumeSuspenseBoundary,
): void {
pushBuiltInComponentStackInDEV(task, 'Suspense');

const previousReplaySet: ReplaySet = task.replay;

const parentBoundary = task.blockedBoundary;

const content: ReactNodeList = props.children;

const fallbackAbortSet: Set<Task> = new Set();
const resumedBoundary = createSuspenseBoundary(
request,
fallbackAbortSet,
task.keyPath,
);
resumedBoundary.parentFlushed = true;
// We restore the same id of this boundary as was used during prerender.
resumedBoundary.id = replayNode[3];
resumedBoundary.rootSegmentID = replayNode[4];

const resumedSegment = createPendingSegment(
request,
0,
null,
task.formatContext,
false,
false,
);
resumedSegment.parentFlushed = true;
resumedSegment.id = replayNode[4];

// We can reuse the current context and task to render the content immediately without
// context switching. We just need to temporarily switch which boundary and replay node
// we're writing to. If something suspends, it'll spawn new suspended task with that context.
task.blockedBoundary = resumedBoundary;
if (enableFloat) {
// Does this even matter for replaying?
setCurrentlyRenderingBoundaryResourcesTarget(
request.renderState,
resumedBoundary.resources,
);
}
try {
// Convert the current ReplayTask to a RenderTask.
const renderTask: RenderTask = (task: any);
renderTask.replay = null;
renderTask.blockedSegment = resumedSegment;
// We use the safe form because we don't handle suspending here. Only error handling.
renderNode(request, task, content, -1);
resumedSegment.status = COMPLETED;
queueCompletedSegment(resumedBoundary, resumedSegment);
if (
resumedBoundary.pendingTasks === 0 &&
resumedBoundary.status === PENDING
) {
resumedBoundary.status = COMPLETED;
request.completedBoundaries.push(resumedBoundary);
}
} catch (error) {
resumedBoundary.status = CLIENT_RENDERED;
let errorDigest;
if (
enablePostpone &&
typeof error === 'object' &&
error !== null &&
error.$$typeof === REACT_POSTPONE_TYPE
) {
const postponeInstance: Postpone = (error: any);
logPostpone(request, postponeInstance.message);
// TODO: Figure out a better signal than a magic digest value.
errorDigest = 'POSTPONE';
} else {
errorDigest = logRecoverableError(request, error);
}
resumedBoundary.errorDigest = errorDigest;
if (__DEV__) {
captureBoundaryErrorDetailsDev(resumedBoundary, error);
}

// We don't need to decrement any task numbers because we didn't spawn any new task.
// We don't need to schedule any task because we know the parent has written yet.
// We do need to fallthrough to create the fallback though.
} finally {
if (enableFloat) {
setCurrentlyRenderingBoundaryResourcesTarget(
request.renderState,
parentBoundary ? parentBoundary.resources : null,
);
}
task.blockedBoundary = parentBoundary;
// Restore to a ReplayTask
task.blockedSegment = null;
task.replay = previousReplaySet;
}
// TODO: Should this be in the finally?
popComponentStackInDEV(task);
}

function renderBackupSuspenseBoundary(
request: Request,
task: Task,
Expand Down Expand Up @@ -2029,6 +2145,25 @@ function replayElement(
}
continue;
}
case RESUME_SUSPENSE_BOUNDARY: {
const node: ResumeSuspenseBoundary = candidate;
if (keyOrIndex === node[2]) {
// Let's double check that the component name matches as a precaution.
if (type !== REACT_SUSPENSE_TYPE) {
throw new Error(
'Expected to see a Suspense boundary in this slot. ' +
"The tree doesn't match so React will fallback to client rendering.",
);
}
// Matched a resumable suspense boundary.
resumeSuspenseBoundary(request, task, props, node);

// We finished rendering this node, so now we can consume this
// slot. This must happen after in case we rerender this task.
replayNodes.splice(i, 1);
}
continue;
}
// For RESUME_SLOT we ignore them here and assume we've handled them
// separately already.
}
Expand Down Expand Up @@ -2437,8 +2572,13 @@ function trackPostpone(
segment: Segment,
): void {
segment.status = POSTPONED;
// We know that this will leave a hole so we might as well assign an ID now.
segment.id = request.nextSegmentId++;

const keyPath = task.keyPath;
if (keyPath === null) {
throw new Error(
'It should not be possible to postpone at the root. This is a bug in React.',
);
}

const boundary = task.blockedBoundary;
if (boundary !== null && boundary.status === PENDING) {
Expand All @@ -2457,29 +2597,52 @@ function trackPostpone(
'It should not be possible to postpone at the root. This is a bug in React.',
);
}
const children: Array<ResumableNode> = [];
const boundaryNode: ReplaySuspenseBoundary = [
REPLAY_SUSPENSE_BOUNDARY,
boundaryKeyPath[1],
boundaryKeyPath[2],
children,
boundary.id,
boundary.rootSegmentID,
];
trackedPostpones.workingMap.set(boundaryKeyPath, boundaryNode);
addToReplayParent(boundaryNode, boundaryKeyPath[0], trackedPostpones);

if (boundaryKeyPath === keyPath && task.childIndex === -1) {
// Since we postponed directly in the Suspense boundary we can't have written anything
// to its segment. Therefore this will end up becoming the root segment.
segment.id = boundary.rootSegmentID;
// We postponed directly inside the Suspense boundary so we mark this for resuming.
const boundaryNode: ResumeSuspenseBoundary = [
RESUME_SUSPENSE_BOUNDARY,
boundaryKeyPath[1],
boundaryKeyPath[2],
boundary.id,
boundary.rootSegmentID,
];
addToReplayParent(boundaryNode, boundaryKeyPath[0], trackedPostpones);
return;
} else {
const children: Array<ResumableNode> = [];
const boundaryNode: ReplaySuspenseBoundary = [
REPLAY_SUSPENSE_BOUNDARY,
boundaryKeyPath[1],
boundaryKeyPath[2],
children,
boundary.id,
boundary.rootSegmentID,
];
trackedPostpones.workingMap.set(boundaryKeyPath, boundaryNode);
addToReplayParent(boundaryNode, boundaryKeyPath[0], trackedPostpones);
// Fall through to add the child node.
}
}

const keyPath = task.keyPath;
if (keyPath === null) {
throw new Error(
'It should not be possible to postpone at the root. This is a bug in React.',
);
// We know that this will leave a hole so we might as well assign an ID now.
// We might have one already if we had a parent that gave us its ID.
if (segment.id === -1) {
if (segment.parentFlushed && boundary !== null) {
// If this segment's parent was already flushed, it means we really just
// skipped the parent and this segment is now the root.
segment.id = boundary.rootSegmentID;
} else {
segment.id = request.nextSegmentId++;
}
}

if (task.childIndex === -1) {
// Resume at the position before the first array
const resumableElement = [
// Resume starting from directly inside the previous parent element.
const resumableElement: ResumeElement = [
RESUME_ELEMENT,
keyPath[1],
keyPath[2],
Expand Down Expand Up @@ -2919,9 +3082,7 @@ function queueCompletedSegment(
if (
segment.chunks.length === 0 &&
segment.children.length === 1 &&
segment.children[0].boundary === null &&
// Typically the id would not be assigned yet but if it's a postponed segment it might be.
segment.children[0].id === -1
segment.children[0].boundary === null
) {
// This is an empty segment. There's nothing to write, so we can instead transfer the ID
// to the child. That way any existing references point to the child.
Expand Down

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