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[DevTools] Stop mounting empty roots #34467

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Merged
merged 3 commits into from
Sep 11, 2025
Merged

[DevTools] Stop mounting empty roots #34467

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591c2d3
[DevTools] Stop mounting empty roots
eps1lon Sep 11, 2025
999f2fb
Use same terminology as in other similar checks
eps1lon Sep 11, 2025
badf59c
error copy
eps1lon Sep 11, 2025
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5 changes: 4 additions & 1 deletion 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 @@ -2489,7 +2489,7 @@ describe('Store', () => {
withErrorsOrWarningsIgnored(['test-only:'], async () => {
await act(() => render(<React.Fragment />));
});
expect(store).toMatchInlineSnapshot(`[root]`);
expect(store).toMatchInlineSnapshot(``);
expect(store.componentWithErrorCount).toBe(0);
expect(store.componentWithWarningCount).toBe(0);
});
Expand Down Expand Up @@ -3083,6 +3083,9 @@ describe('Store', () => {

it('should handle an empty root', async () => {
await actAsync(() => render(null));
expect(store).toMatchInlineSnapshot(``);

await actAsync(() => render(<span />));
expect(store).toMatchInlineSnapshot(`[root]`);
});
});
45 changes: 20 additions & 25 deletions packages/react-devtools-shared/src/backend/fiber/renderer.js
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Original file line number Diff line number Diff line change
Expand Up @@ -5322,12 +5322,12 @@ export function attach(
root: FiberRoot,
priorityLevel: void | number,
) {
const current = root.current;
const nextFiber = root.current;

let prevFiber: null | Fiber = null;
let rootInstance = rootToFiberInstanceMap.get(root);
if (!rootInstance) {
rootInstance = createFiberInstance(current);
rootInstance = createFiberInstance(nextFiber);
rootToFiberInstanceMap.set(root, rootInstance);
idToDevToolsInstanceMap.set(rootInstance.id, rootInstance);
} else {
Expand Down Expand Up @@ -5366,30 +5366,25 @@ export function attach(
};
}

if (prevFiber !== null) {
// TODO: relying on this seems a bit fishy.
const wasMounted =
prevFiber.memoizedState != null &&
prevFiber.memoizedState.element != null;
const isMounted =
current.memoizedState != null && current.memoizedState.element != null;
if (!wasMounted && isMounted) {
// Mount a new root.
setRootPseudoKey(currentRoot.id, current);
mountFiberRecursively(current, false);
} else if (wasMounted && isMounted) {
// Update an existing root.
updateFiberRecursively(rootInstance, current, prevFiber, false);
} else if (wasMounted && !isMounted) {
// Unmount an existing root.
unmountInstanceRecursively(rootInstance);
removeRootPseudoKey(currentRoot.id);
rootToFiberInstanceMap.delete(root);
}
} else {
const nextIsMounted = nextFiber.child !== null;
const prevWasMounted = prevFiber !== null && prevFiber.child !== null;
if (!prevWasMounted && nextIsMounted) {
// Mount a new root.
setRootPseudoKey(currentRoot.id, current);
mountFiberRecursively(current, false);
setRootPseudoKey(currentRoot.id, nextFiber);
mountFiberRecursively(nextFiber, false);
} else if (prevWasMounted && nextIsMounted) {
if (prevFiber === null) {
throw new Error(
'Expected a previous Fiber when updating an existing root.',
);
}
// Update an existing root.
updateFiberRecursively(rootInstance, nextFiber, prevFiber, false);
} else if (prevWasMounted && !nextIsMounted) {
// Unmount an existing root.
unmountInstanceRecursively(rootInstance);
removeRootPseudoKey(currentRoot.id);
rootToFiberInstanceMap.delete(root);
}

if (isProfiling && isProfilingSupported) {
Expand Down
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