[Flight] Dedupe suspense boundaries when it has already been found earlier

packages/react-dom/src/__tests__/ReactDOMFizzStaticBrowser-test.js

@@ -840,4 +840,51 @@ describe('ReactDOMFizzStaticBrowser', () => {
  </div>,
  ]);
  });
+
+ // @gate enablePostpone
+ it('can postpone a boundary after it has already been added', async () => {
+ let prerendering = true;
+ function Postpone() {
+ if (prerendering) {
+ React.unstable_postpone();
+ }
+ return 'Hello';
+ }
+
+ function App() {
+ return (
+ <div>
+ <Suspense fallback="Loading...">
+ <Suspense fallback="Loading...">
+ <Postpone />
+ </Suspense>
+ <Postpone />
+ <Postpone />
+ </Suspense>
+ </div>
+ );
+ }
+
+ const prerendered = await ReactDOMFizzStatic.prerender(<App />);
+ expect(prerendered.postponed).not.toBe(null);
+
+ prerendering = false;
+
+ console.log(JSON.stringify(prerendered.postponed, null, 2));
+
+ const resumed = await ReactDOMFizzServer.resume(
+ <App />,
+ JSON.parse(JSON.stringify(prerendered.postponed)),
+ );
+
+ await readIntoContainer(prerendered.prelude);
+
+ expect(getVisibleChildren(container)).toEqual(<div>Loading...</div>);
+
+ await readIntoContainer(resumed);
+
+ expect(getVisibleChildren(container)).toEqual(
+ <div>{['Hello', 'Hello', 'Hello']}</div>,
+ );
+ });
 });

packages/react-server/src/ReactFizzServer.js

@@ -2490,15 +2490,23 @@ function trackPostpone(
  addToReplayParent(boundaryNode, boundaryKeyPath[0], trackedPostpones);
  return;
  } else {
- const boundaryNode: ReplaySuspenseBoundary = [
- boundaryKeyPath[1],
- boundaryKeyPath[2],
- children,
- null,
- boundary.rootSegmentID,
- ];
- trackedPostpones.workingMap.set(boundaryKeyPath, boundaryNode);
- addToReplayParent(boundaryNode, boundaryKeyPath[0], trackedPostpones);
+ let boundaryNode: void | ReplayNode =
+ trackedPostpones.workingMap.get(boundaryKeyPath);
+ if (boundaryNode === undefined) {
+ boundaryNode = [
+ boundaryKeyPath[1],
+ boundaryKeyPath[2],
+ children,
+ null,
+ boundary.rootSegmentID,
+ ];
+ trackedPostpones.workingMap.set(boundaryKeyPath, boundaryNode);
+ addToReplayParent(boundaryNode, boundaryKeyPath[0], trackedPostpones);
+ } else {
+ // Upgrade to ReplaySuspenseBoundary.
+ ((boundaryNode: any): ReplaySuspenseBoundary)[4] =
+ boundary.rootSegmentID;
+ }
  // Fall through to add the child node.
  }
  }