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[DevTools] Handle reorders when resuspending while fallback contains Suspense #34225

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Aug 19, 2025
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[DevTools] Handle reorders when resuspending while fallback contains Suspense #34225

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189 changes: 189 additions & 0 deletions packages/react-devtools-shared/src/__tests__/store-test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2775,4 +2775,193 @@ describe('Store', () => {
<Suspense name="content" rects={[{x:1,y:2,width:4,height:1}]}>
`);
});

// @reactVersion >= 18.0
it('can reconcile resuspended Suspense with Suspense in fallback positions', async () => {
let resolveHeadFallback;
let resolveHeadContent;
let resolveMainFallback;
let resolveMainContent;

function Component({children, promise}) {
if (promise) {
React.use(promise);
}
return <div>{children}</div>;
}

function WithSuspenseInFallback({fallbackPromise, contentPromise, name}) {
return (
<React.Suspense
name={name}
fallback={
<React.Suspense
name={`${name}-fallback`}
fallback={
<Component key={`${name}-fallback-fallback`}>
Loading fallback...
</Component>
}>
<Component
key={`${name}-fallback-content`}
promise={fallbackPromise}>
Loading...
</Component>
</React.Suspense>
}>
<Component key={`${name}-content`} promise={contentPromise}>
done
</Component>
</React.Suspense>
);
}

function App({
headFallbackPromise,
headContentPromise,
mainContentPromise,
mainFallbackPromise,
tailContentPromise,
tailFallbackPromise,
}) {
return (
<>
<WithSuspenseInFallback
fallbackPromise={headFallbackPromise}
contentPromise={headContentPromise}
name="head"
/>
<WithSuspenseInFallback
fallbackPromise={mainFallbackPromise}
contentPromise={mainContentPromise}
name="main"
/>
</>
);
}

const initialHeadContentPromise = new Promise(resolve => {
resolveHeadContent = resolve;
});
const initialHeadFallbackPromise = new Promise(resolve => {
resolveHeadFallback = resolve;
});
const initialMainContentPromise = new Promise(resolve => {
resolveMainContent = resolve;
});
const initialMainFallbackPromise = new Promise(resolve => {
resolveMainFallback = resolve;
});
await actAsync(() =>
render(
<App
headFallbackPromise={initialHeadFallbackPromise}
headContentPromise={initialHeadContentPromise}
mainContentPromise={initialMainContentPromise}
mainFallbackPromise={initialMainFallbackPromise}
/>,
),
);

expect(store).toMatchInlineSnapshot(`
[root]
▾ <App>
▾ <WithSuspenseInFallback>
▾ <Suspense name="head">
▾ <Suspense name="head-fallback">
<Component key="head-fallback-fallback">
▾ <WithSuspenseInFallback>
▾ <Suspense name="main">
▾ <Suspense name="main-fallback">
<Component key="main-fallback-fallback">
[shell]
<Suspense name="head" rects={null}>
<Suspense name="head-fallback" rects={null}>
<Suspense name="main" rects={null}>
<Suspense name="main-fallback" rects={null}>
`);

await actAsync(() => {
resolveHeadFallback();
resolveMainFallback();
resolveHeadContent();
resolveMainContent();
});

expect(store).toMatchInlineSnapshot(`
[root]
▾ <App>
▾ <WithSuspenseInFallback>
▾ <Suspense name="head">
<Component key="head-content">
▾ <WithSuspenseInFallback>
▾ <Suspense name="main">
<Component key="main-content">
[shell]
<Suspense name="head" rects={[{x:1,y:2,width:4,height:1}]}>
<Suspense name="main" rects={[{x:1,y:2,width:4,height:1}]}>
`);

// Resuspend head content
const nextHeadContentPromise = new Promise(resolve => {
resolveHeadContent = resolve;
});
await actAsync(() =>
render(
<App
headFallbackPromise={initialHeadFallbackPromise}
headContentPromise={nextHeadContentPromise}
mainContentPromise={initialMainContentPromise}
mainFallbackPromise={initialMainFallbackPromise}
/>,
),
);

expect(store).toMatchInlineSnapshot(`
[root]
▾ <App>
▾ <WithSuspenseInFallback>
▾ <Suspense name="head">
▾ <Suspense name="head-fallback">
<Component key="head-fallback-content">
▾ <WithSuspenseInFallback>
▾ <Suspense name="main">
<Component key="main-content">
[shell]
<Suspense name="head" rects={[{x:1,y:2,width:4,height:1}]}>
<Suspense name="head-fallback" rects={[{x:1,y:2,width:10,height:1}]}>
<Suspense name="main" rects={[{x:1,y:2,width:4,height:1}]}>
`);

// Resuspend head fallback
const nextHeadFallbackPromise = new Promise(resolve => {
resolveHeadFallback = resolve;
});
await actAsync(() =>
render(
<App
headFallbackPromise={nextHeadFallbackPromise}
headContentPromise={nextHeadContentPromise}
mainContentPromise={initialMainContentPromise}
mainFallbackPromise={initialMainFallbackPromise}
/>,
),
);

expect(store).toMatchInlineSnapshot(`
[root]
▾ <App>
▾ <WithSuspenseInFallback>
▾ <Suspense name="head">
▾ <Suspense name="head-fallback">
<Component key="head-fallback-fallback">
▾ <WithSuspenseInFallback>
▾ <Suspense name="main">
<Component key="main-content">
[shell]
<Suspense name="head" rects={[{x:1,y:2,width:4,height:1}]}>
<Suspense name="head-fallback" rects={[{x:1,y:2,width:10,height:1}]}>
<Suspense name="main" rects={[{x:1,y:2,width:4,height:1}]}>
`);
});
});
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