Fix: Don't call cWU if already unmounted

When a tree goes offscreen, we unmount all the effects just like we
would in a normal deletion. (Conceptually it _is_ a deletion; we keep
the fiber around so we can reuse its state if the tree mounts again.)

If an offscreen component gets deleted "for real", we shouldn't unmount
it again.

The fix is to track on the stack whether we're inside a hidden tree.

We already had a stack variable for this purpose, called
`offscreenSubtreeWasHidden`, in another part of the commit phase, so I
reused that variable instead of creating a new one. (The name is a bit
confusing: "was" refers to the current tree before this commit. So, the
"previous current".)

Co-authored-by: dan <dan.abramov@me.com>

packages/react-reconciler/src/ReactFiberCommitWork.new.js

@@ -1604,7 +1604,9 @@ function commitDeletionEffectsOnFiber(
   // that don't modify the stack.
   switch (deletedFiber.tag) {
     case HostComponent: {
-      safelyDetachRef(deletedFiber, nearestMountedAncestor);
+      if (!offscreenSubtreeWasHidden) {
+        safelyDetachRef(deletedFiber, nearestMountedAncestor);
+      }
       // Intentional fallthrough to next branch
     }
     // eslint-disable-next-line-no-fallthrough
@@ -1710,54 +1712,56 @@ function commitDeletionEffectsOnFiber(
     case ForwardRef:
     case MemoComponent:
     case SimpleMemoComponent: {
-      const updateQueue: FunctionComponentUpdateQueue | null = (deletedFiber.updateQueue: any);
-      if (updateQueue !== null) {
-        const lastEffect = updateQueue.lastEffect;
-        if (lastEffect !== null) {
-          const firstEffect = lastEffect.next;
+      if (!offscreenSubtreeWasHidden) {
+        const updateQueue: FunctionComponentUpdateQueue | null = (deletedFiber.updateQueue: any);
+        if (updateQueue !== null) {
+          const lastEffect = updateQueue.lastEffect;
+          if (lastEffect !== null) {
+            const firstEffect = lastEffect.next;
 
-          let effect = firstEffect;
-          do {
-            const {destroy, tag} = effect;
-            if (destroy !== undefined) {
-              if ((tag & HookInsertion) !== NoHookEffect) {
-                safelyCallDestroy(
-                  deletedFiber,
-                  nearestMountedAncestor,
-                  destroy,
-                );
-              } else if ((tag & HookLayout) !== NoHookEffect) {
-                if (enableSchedulingProfiler) {
-                  markComponentLayoutEffectUnmountStarted(deletedFiber);
-                }
-
-                if (
-                  enableProfilerTimer &&
-                  enableProfilerCommitHooks &&
-                  deletedFiber.mode & ProfileMode
-                ) {
-                  startLayoutEffectTimer();
+            let effect = firstEffect;
+            do {
+              const {destroy, tag} = effect;
+              if (destroy !== undefined) {
+                if ((tag & HookInsertion) !== NoHookEffect) {
                   safelyCallDestroy(
                     deletedFiber,
                     nearestMountedAncestor,
                     destroy,
                   );
-                  recordLayoutEffectDuration(deletedFiber);
-                } else {
-                  safelyCallDestroy(
-                    deletedFiber,
-                    nearestMountedAncestor,
-                    destroy,
-                  );
-                }
+                } else if ((tag & HookLayout) !== NoHookEffect) {
+                  if (enableSchedulingProfiler) {
+                    markComponentLayoutEffectUnmountStarted(deletedFiber);
+                  }
 
-                if (enableSchedulingProfiler) {
-                  markComponentLayoutEffectUnmountStopped();
+                  if (
+                    enableProfilerTimer &&
+                    enableProfilerCommitHooks &&
+                    deletedFiber.mode & ProfileMode
+                  ) {
+                    startLayoutEffectTimer();
+                    safelyCallDestroy(
+                      deletedFiber,
+                      nearestMountedAncestor,
+                      destroy,
+                    );
+                    recordLayoutEffectDuration(deletedFiber);
+                  } else {
+                    safelyCallDestroy(
+                      deletedFiber,
+                      nearestMountedAncestor,
+                      destroy,
+                    );
+                  }
+
+                  if (enableSchedulingProfiler) {
+                    markComponentLayoutEffectUnmountStopped();
+                  }
                 }
               }
-            }
-            effect = effect.next;
-          } while (effect !== firstEffect);
+              effect = effect.next;
+            } while (effect !== firstEffect);
+          }
         }
       }
 
@@ -1769,14 +1773,16 @@ function commitDeletionEffectsOnFiber(
       return;
     }
     case ClassComponent: {
-      safelyDetachRef(deletedFiber, nearestMountedAncestor);
-      const instance = deletedFiber.stateNode;
-      if (typeof instance.componentWillUnmount === 'function') {
-        safelyCallComponentWillUnmount(
-          deletedFiber,
-          nearestMountedAncestor,
-          instance,
-        );
+      if (!offscreenSubtreeWasHidden) {
+        safelyDetachRef(deletedFiber, nearestMountedAncestor);
+        const instance = deletedFiber.stateNode;
+        if (typeof instance.componentWillUnmount === 'function') {
+          safelyCallComponentWillUnmount(
+            deletedFiber,
+            nearestMountedAncestor,
+            instance,
+          );
+        }
       }
       recursivelyTraverseDeletionEffects(
         finishedRoot,
@@ -1796,6 +1802,27 @@ function commitDeletionEffectsOnFiber(
       );
       return;
     }
+    case OffscreenComponent: {
+      // If this offscreen component is hidden, we already unmounted it. Before
+      // deleting the children, track that it's already unmounted so that we
+      // don't attempt to unmount the effects again.
+      // TODO: If the tree is hidden, in most cases we should be able to skip
+      // over the nested children entirely. An exception is we haven't yet found
+      // the topmost host node to delete, which we already track on the stack.
+      // But the other case is portals, which need to be detached no matter how
+      // deeply they are nested. We should use a subtree flag to track whether a
+      // subtree includes a nested portal.
+      const prevOffscreenSubtreeWasHidden = offscreenSubtreeWasHidden;
+      offscreenSubtreeWasHidden =
+        prevOffscreenSubtreeWasHidden || deletedFiber.memoizedState !== null;
+      recursivelyTraverseDeletionEffects(
+        finishedRoot,
+        nearestMountedAncestor,
+        deletedFiber,
+      );
+      offscreenSubtreeWasHidden = prevOffscreenSubtreeWasHidden;
+      break;
+    }
     default: {
       recursivelyTraverseDeletionEffects(
         finishedRoot,
@@ -2203,13 +2230,21 @@ function commitMutationEffectsOnFiber(
       return;
     }
     case OffscreenComponent: {
+      const wasHidden = current !== null && current.memoizedState !== null;
+
+      // Before committing the children, track on the stack whether this
+      // offscreen subtree was already hidden, so that we don't unmount the
+      // effects again.
+      const prevOffscreenSubtreeWasHidden = offscreenSubtreeWasHidden;
+      offscreenSubtreeWasHidden = prevOffscreenSubtreeWasHidden || wasHidden;
       recursivelyTraverseMutationEffects(root, finishedWork, lanes);
+      offscreenSubtreeWasHidden = prevOffscreenSubtreeWasHidden;
+
       commitReconciliationEffects(finishedWork);
 
       if (flags & Visibility) {
         const newState: OffscreenState | null = finishedWork.memoizedState;
         const isHidden = newState !== null;
-        const wasHidden = current !== null && current.memoizedState !== null;
         const offscreenBoundary: Fiber = finishedWork;
 
         if (supportsMutation) {

packages/react-reconciler/src/ReactFiberCommitWork.old.js

@@ -1604,7 +1604,9 @@ function commitDeletionEffectsOnFiber(
   // that don't modify the stack.
   switch (deletedFiber.tag) {
     case HostComponent: {
-      safelyDetachRef(deletedFiber, nearestMountedAncestor);
+      if (!offscreenSubtreeWasHidden) {
+        safelyDetachRef(deletedFiber, nearestMountedAncestor);
+      }
       // Intentional fallthrough to next branch
     }
     // eslint-disable-next-line-no-fallthrough
@@ -1710,54 +1712,56 @@ function commitDeletionEffectsOnFiber(
     case ForwardRef:
     case MemoComponent:
     case SimpleMemoComponent: {
-      const updateQueue: FunctionComponentUpdateQueue | null = (deletedFiber.updateQueue: any);
-      if (updateQueue !== null) {
-        const lastEffect = updateQueue.lastEffect;
-        if (lastEffect !== null) {
-          const firstEffect = lastEffect.next;
+      if (!offscreenSubtreeWasHidden) {
+        const updateQueue: FunctionComponentUpdateQueue | null = (deletedFiber.updateQueue: any);
+        if (updateQueue !== null) {
+          const lastEffect = updateQueue.lastEffect;
+          if (lastEffect !== null) {
+            const firstEffect = lastEffect.next;
 
-          let effect = firstEffect;
-          do {
-            const {destroy, tag} = effect;
-            if (destroy !== undefined) {
-              if ((tag & HookInsertion) !== NoHookEffect) {
-                safelyCallDestroy(
-                  deletedFiber,
-                  nearestMountedAncestor,
-                  destroy,
-                );
-              } else if ((tag & HookLayout) !== NoHookEffect) {
-                if (enableSchedulingProfiler) {
-                  markComponentLayoutEffectUnmountStarted(deletedFiber);
-                }
-
-                if (
-                  enableProfilerTimer &&
-                  enableProfilerCommitHooks &&
-                  deletedFiber.mode & ProfileMode
-                ) {
-                  startLayoutEffectTimer();
+            let effect = firstEffect;
+            do {
+              const {destroy, tag} = effect;
+              if (destroy !== undefined) {
+                if ((tag & HookInsertion) !== NoHookEffect) {
                   safelyCallDestroy(
                     deletedFiber,
                     nearestMountedAncestor,
                     destroy,
                   );
-                  recordLayoutEffectDuration(deletedFiber);
-                } else {
-                  safelyCallDestroy(
-                    deletedFiber,
-                    nearestMountedAncestor,
-                    destroy,
-                  );
-                }
+                } else if ((tag & HookLayout) !== NoHookEffect) {
+                  if (enableSchedulingProfiler) {
+                    markComponentLayoutEffectUnmountStarted(deletedFiber);
+                  }
 
-                if (enableSchedulingProfiler) {
-                  markComponentLayoutEffectUnmountStopped();
+                  if (
+                    enableProfilerTimer &&
+                    enableProfilerCommitHooks &&
+                    deletedFiber.mode & ProfileMode
+                  ) {
+                    startLayoutEffectTimer();
+                    safelyCallDestroy(
+                      deletedFiber,
+                      nearestMountedAncestor,
+                      destroy,
+                    );
+                    recordLayoutEffectDuration(deletedFiber);
+                  } else {
+                    safelyCallDestroy(
+                      deletedFiber,
+                      nearestMountedAncestor,
+                      destroy,
+                    );
+                  }
+
+                  if (enableSchedulingProfiler) {
+                    markComponentLayoutEffectUnmountStopped();
+                  }
                 }
               }
-            }
-            effect = effect.next;
-          } while (effect !== firstEffect);
+              effect = effect.next;
+            } while (effect !== firstEffect);
+          }
         }
       }
 
@@ -1769,14 +1773,16 @@ function commitDeletionEffectsOnFiber(
       return;
     }
     case ClassComponent: {
-      safelyDetachRef(deletedFiber, nearestMountedAncestor);
-      const instance = deletedFiber.stateNode;
-      if (typeof instance.componentWillUnmount === 'function') {
-        safelyCallComponentWillUnmount(
-          deletedFiber,
-          nearestMountedAncestor,
-          instance,
-        );
+      if (!offscreenSubtreeWasHidden) {
+        safelyDetachRef(deletedFiber, nearestMountedAncestor);
+        const instance = deletedFiber.stateNode;
+        if (typeof instance.componentWillUnmount === 'function') {
+          safelyCallComponentWillUnmount(
+            deletedFiber,
+            nearestMountedAncestor,
+            instance,
+          );
+        }
       }
       recursivelyTraverseDeletionEffects(
         finishedRoot,
@@ -1796,6 +1802,27 @@ function commitDeletionEffectsOnFiber(
       );
       return;
     }
+    case OffscreenComponent: {
+      // If this offscreen component is hidden, we already unmounted it. Before
+      // deleting the children, track that it's already unmounted so that we
+      // don't attempt to unmount the effects again.
+      // TODO: If the tree is hidden, in most cases we should be able to skip
+      // over the nested children entirely. An exception is we haven't yet found
+      // the topmost host node to delete, which we already track on the stack.
+      // But the other case is portals, which need to be detached no matter how
+      // deeply they are nested. We should use a subtree flag to track whether a
+      // subtree includes a nested portal.
+      const prevOffscreenSubtreeWasHidden = offscreenSubtreeWasHidden;
+      offscreenSubtreeWasHidden =
+        prevOffscreenSubtreeWasHidden || deletedFiber.memoizedState !== null;
+      recursivelyTraverseDeletionEffects(
+        finishedRoot,
+        nearestMountedAncestor,
+        deletedFiber,
+      );
+      offscreenSubtreeWasHidden = prevOffscreenSubtreeWasHidden;
+      break;
+    }
     default: {
       recursivelyTraverseDeletionEffects(
         finishedRoot,
@@ -2203,13 +2230,21 @@ function commitMutationEffectsOnFiber(
       return;
     }
     case OffscreenComponent: {
+      const wasHidden = current !== null && current.memoizedState !== null;
+
+      // Before committing the children, track on the stack whether this
+      // offscreen subtree was already hidden, so that we don't unmount the
+      // effects again.
+      const prevOffscreenSubtreeWasHidden = offscreenSubtreeWasHidden;
+      offscreenSubtreeWasHidden = prevOffscreenSubtreeWasHidden || wasHidden;
       recursivelyTraverseMutationEffects(root, finishedWork, lanes);
+      offscreenSubtreeWasHidden = prevOffscreenSubtreeWasHidden;
+
       commitReconciliationEffects(finishedWork);
 
       if (flags & Visibility) {
         const newState: OffscreenState | null = finishedWork.memoizedState;
         const isHidden = newState !== null;
-        const wasHidden = current !== null && current.memoizedState !== null;
         const offscreenBoundary: Fiber = finishedWork;
 
         if (supportsMutation) {

packages/react-reconciler/src/__tests__/ReactSuspenseEffectsSemantics-test.js

@@ -1980,7 +1980,6 @@ describe('ReactSuspenseEffectsSemantics', () => {
 
           // Destroy layout and passive effects in the errored tree.
           'App destroy layout',
-          'ThrowsInWillUnmount componentWillUnmount',
           'Text:Fallback destroy layout',
           'Text:Outside destroy layout',
           'Text:Inside destroy passive',

packages/react-reconciler/src/__tests__/ReactSuspenseEffectsSemanticsDOM-test.js

@@ -10,18 +10,39 @@
 'use strict';
 
 let React;
+let ReactDOM;
 let ReactDOMClient;
+let Scheduler;
 let act;
+let container;
 
 describe('ReactSuspenseEffectsSemanticsDOM', () => {
   beforeEach(() => {
     jest.resetModules();
 
     React = require('react');
+    ReactDOM = require('react-dom');
     ReactDOMClient = require('react-dom/client');
+    Scheduler = require('scheduler');
     act = require('jest-react').act;
+
+    container = document.createElement('div');
+    document.body.appendChild(container);
   });
 
+  afterEach(() => {
+    document.body.removeChild(container);
+  });
+
+  async function fakeImport(result) {
+    return {default: result};
+  }
+
+  function Text(props) {
+    Scheduler.unstable_yieldValue(props.text);
+    return props.text;
+  }
+
   it('should not cause a cycle when combined with a render phase update', () => {
     let scheduleSuspendingUpdate;
 
@@ -63,7 +84,7 @@ describe('ReactSuspenseEffectsSemanticsDOM', () => {
     }
 
     act(() => {
-      const root = ReactDOMClient.createRoot(document.createElement('div'));
+      const root = ReactDOMClient.createRoot(container);
       root.render(<App />);
     });
 
@@ -71,4 +92,367 @@ describe('ReactSuspenseEffectsSemanticsDOM', () => {
       scheduleSuspendingUpdate();
     });
   });
+
+  it('does not destroy layout effects twice when hidden child is removed', async () => {
+    function ChildA({label}) {
+      React.useLayoutEffect(() => {
+        Scheduler.unstable_yieldValue('Did mount: ' + label);
+        return () => {
+          Scheduler.unstable_yieldValue('Will unmount: ' + label);
+        };
+      }, []);
+      return <Text text={label} />;
+    }
+
+    function ChildB({label}) {
+      React.useLayoutEffect(() => {
+        Scheduler.unstable_yieldValue('Did mount: ' + label);
+        return () => {
+          Scheduler.unstable_yieldValue('Will unmount: ' + label);
+        };
+      }, []);
+      return <Text text={label} />;
+    }
+
+    const LazyChildA = React.lazy(() => fakeImport(ChildA));
+    const LazyChildB = React.lazy(() => fakeImport(ChildB));
+
+    function Parent({swap}) {
+      return (
+        <React.Suspense fallback={<Text text="Loading..." />}>
+          {swap ? <LazyChildB label="B" /> : <LazyChildA label="A" />}
+        </React.Suspense>
+      );
+    }
+
+    const root = ReactDOMClient.createRoot(container);
+    act(() => {
+      root.render(<Parent swap={false} />);
+    });
+    expect(Scheduler).toHaveYielded(['Loading...']);
+
+    await LazyChildA;
+    expect(Scheduler).toFlushAndYield(['A', 'Did mount: A']);
+    expect(container.innerHTML).toBe('A');
+
+    // Swap the position of A and B
+    ReactDOM.flushSync(() => {
+      root.render(<Parent swap={true} />);
+    });
+    expect(Scheduler).toHaveYielded(['Loading...', 'Will unmount: A']);
+    expect(container.innerHTML).toBe('Loading...');
+
+    await LazyChildB;
+    expect(Scheduler).toFlushAndYield(['B', 'Did mount: B']);
+    expect(container.innerHTML).toBe('B');
+  });
+
+  it('does not destroy ref cleanup twice when hidden child is removed', async () => {
+    function ChildA({label}) {
+      return (
+        <span
+          ref={node => {
+            if (node) {
+              Scheduler.unstable_yieldValue('Ref mount: ' + label);
+            } else {
+              Scheduler.unstable_yieldValue('Ref unmount: ' + label);
+            }
+          }}>
+          <Text text={label} />
+        </span>
+      );
+    }
+
+    function ChildB({label}) {
+      return (
+        <span
+          ref={node => {
+            if (node) {
+              Scheduler.unstable_yieldValue('Ref mount: ' + label);
+            } else {
+              Scheduler.unstable_yieldValue('Ref unmount: ' + label);
+            }
+          }}>
+          <Text text={label} />
+        </span>
+      );
+    }
+
+    const LazyChildA = React.lazy(() => fakeImport(ChildA));
+    const LazyChildB = React.lazy(() => fakeImport(ChildB));
+
+    function Parent({swap}) {
+      return (
+        <React.Suspense fallback={<Text text="Loading..." />}>
+          {swap ? <LazyChildB label="B" /> : <LazyChildA label="A" />}
+        </React.Suspense>
+      );
+    }
+
+    const root = ReactDOMClient.createRoot(container);
+    act(() => {
+      root.render(<Parent swap={false} />);
+    });
+    expect(Scheduler).toHaveYielded(['Loading...']);
+
+    await LazyChildA;
+    expect(Scheduler).toFlushAndYield(['A', 'Ref mount: A']);
+    expect(container.innerHTML).toBe('<span>A</span>');
+
+    // Swap the position of A and B
+    ReactDOM.flushSync(() => {
+      root.render(<Parent swap={true} />);
+    });
+    expect(Scheduler).toHaveYielded(['Loading...', 'Ref unmount: A']);
+    expect(container.innerHTML).toBe(
+      '<span style="display: none;">A</span>Loading...',
+    );
+
+    await LazyChildB;
+    expect(Scheduler).toFlushAndYield(['B', 'Ref mount: B']);
+    expect(container.innerHTML).toBe('<span>B</span>');
+  });
+
+  it('does not call componentWillUnmount twice when hidden child is removed', async () => {
+    class ChildA extends React.Component {
+      componentDidMount() {
+        Scheduler.unstable_yieldValue('Did mount: ' + this.props.label);
+      }
+      componentWillUnmount() {
+        Scheduler.unstable_yieldValue('Will unmount: ' + this.props.label);
+      }
+      render() {
+        return <Text text={this.props.label} />;
+      }
+    }
+
+    class ChildB extends React.Component {
+      componentDidMount() {
+        Scheduler.unstable_yieldValue('Did mount: ' + this.props.label);
+      }
+      componentWillUnmount() {
+        Scheduler.unstable_yieldValue('Will unmount: ' + this.props.label);
+      }
+      render() {
+        return <Text text={this.props.label} />;
+      }
+    }
+
+    const LazyChildA = React.lazy(() => fakeImport(ChildA));
+    const LazyChildB = React.lazy(() => fakeImport(ChildB));
+
+    function Parent({swap}) {
+      return (
+        <React.Suspense fallback={<Text text="Loading..." />}>
+          {swap ? <LazyChildB label="B" /> : <LazyChildA label="A" />}
+        </React.Suspense>
+      );
+    }
+
+    const root = ReactDOMClient.createRoot(container);
+    act(() => {
+      root.render(<Parent swap={false} />);
+    });
+    expect(Scheduler).toHaveYielded(['Loading...']);
+
+    await LazyChildA;
+    expect(Scheduler).toFlushAndYield(['A', 'Did mount: A']);
+    expect(container.innerHTML).toBe('A');
+
+    // Swap the position of A and B
+    ReactDOM.flushSync(() => {
+      root.render(<Parent swap={true} />);
+    });
+    expect(Scheduler).toHaveYielded(['Loading...', 'Will unmount: A']);
+    expect(container.innerHTML).toBe('Loading...');
+
+    await LazyChildB;
+    expect(Scheduler).toFlushAndYield(['B', 'Did mount: B']);
+    expect(container.innerHTML).toBe('B');
+  });
+
+  it('does not destroy layout effects twice when parent suspense is removed', async () => {
+    function ChildA({label}) {
+      React.useLayoutEffect(() => {
+        Scheduler.unstable_yieldValue('Did mount: ' + label);
+        return () => {
+          Scheduler.unstable_yieldValue('Will unmount: ' + label);
+        };
+      }, []);
+      return <Text text={label} />;
+    }
+    function ChildB({label}) {
+      React.useLayoutEffect(() => {
+        Scheduler.unstable_yieldValue('Did mount: ' + label);
+        return () => {
+          Scheduler.unstable_yieldValue('Will unmount: ' + label);
+        };
+      }, []);
+      return <Text text={label} />;
+    }
+    const LazyChildA = React.lazy(() => fakeImport(ChildA));
+    const LazyChildB = React.lazy(() => fakeImport(ChildB));
+
+    function Parent({swap}) {
+      return (
+        <React.Suspense fallback={<Text text="Loading..." />}>
+          {swap ? <LazyChildB label="B" /> : <LazyChildA label="A" />}
+        </React.Suspense>
+      );
+    }
+
+    const root = ReactDOMClient.createRoot(container);
+    act(() => {
+      root.render(<Parent swap={false} />);
+    });
+    expect(Scheduler).toHaveYielded(['Loading...']);
+
+    await LazyChildA;
+    expect(Scheduler).toFlushAndYield(['A', 'Did mount: A']);
+    expect(container.innerHTML).toBe('A');
+
+    // Swap the position of A and B
+    ReactDOM.flushSync(() => {
+      root.render(<Parent swap={true} />);
+    });
+    expect(Scheduler).toHaveYielded(['Loading...', 'Will unmount: A']);
+    expect(container.innerHTML).toBe('Loading...');
+
+    // Destroy the whole tree, including the hidden A
+    ReactDOM.flushSync(() => {
+      root.render(<h1>Hello</h1>);
+    });
+    expect(Scheduler).toFlushAndYield([]);
+    expect(container.innerHTML).toBe('<h1>Hello</h1>');
+  });
+
+  it('does not destroy ref cleanup twice when parent suspense is removed', async () => {
+    function ChildA({label}) {
+      return (
+        <span
+          ref={node => {
+            if (node) {
+              Scheduler.unstable_yieldValue('Ref mount: ' + label);
+            } else {
+              Scheduler.unstable_yieldValue('Ref unmount: ' + label);
+            }
+          }}>
+          <Text text={label} />
+        </span>
+      );
+    }
+
+    function ChildB({label}) {
+      return (
+        <span
+          ref={node => {
+            if (node) {
+              Scheduler.unstable_yieldValue('Ref mount: ' + label);
+            } else {
+              Scheduler.unstable_yieldValue('Ref unmount: ' + label);
+            }
+          }}>
+          <Text text={label} />
+        </span>
+      );
+    }
+
+    const LazyChildA = React.lazy(() => fakeImport(ChildA));
+    const LazyChildB = React.lazy(() => fakeImport(ChildB));
+
+    function Parent({swap}) {
+      return (
+        <React.Suspense fallback={<Text text="Loading..." />}>
+          {swap ? <LazyChildB label="B" /> : <LazyChildA label="A" />}
+        </React.Suspense>
+      );
+    }
+
+    const root = ReactDOMClient.createRoot(container);
+    act(() => {
+      root.render(<Parent swap={false} />);
+    });
+    expect(Scheduler).toHaveYielded(['Loading...']);
+
+    await LazyChildA;
+    expect(Scheduler).toFlushAndYield(['A', 'Ref mount: A']);
+    expect(container.innerHTML).toBe('<span>A</span>');
+
+    // Swap the position of A and B
+    ReactDOM.flushSync(() => {
+      root.render(<Parent swap={true} />);
+    });
+    expect(Scheduler).toHaveYielded(['Loading...', 'Ref unmount: A']);
+    expect(container.innerHTML).toBe(
+      '<span style="display: none;">A</span>Loading...',
+    );
+
+    // Destroy the whole tree, including the hidden A
+    ReactDOM.flushSync(() => {
+      root.render(<h1>Hello</h1>);
+    });
+    expect(Scheduler).toFlushAndYield([]);
+    expect(container.innerHTML).toBe('<h1>Hello</h1>');
+  });
+
+  it('does not call componentWillUnmount twice when parent suspense is removed', async () => {
+    class ChildA extends React.Component {
+      componentDidMount() {
+        Scheduler.unstable_yieldValue('Did mount: ' + this.props.label);
+      }
+      componentWillUnmount() {
+        Scheduler.unstable_yieldValue('Will unmount: ' + this.props.label);
+      }
+      render() {
+        return <Text text={this.props.label} />;
+      }
+    }
+
+    class ChildB extends React.Component {
+      componentDidMount() {
+        Scheduler.unstable_yieldValue('Did mount: ' + this.props.label);
+      }
+      componentWillUnmount() {
+        Scheduler.unstable_yieldValue('Will unmount: ' + this.props.label);
+      }
+      render() {
+        return <Text text={this.props.label} />;
+      }
+    }
+
+    const LazyChildA = React.lazy(() => fakeImport(ChildA));
+    const LazyChildB = React.lazy(() => fakeImport(ChildB));
+
+    function Parent({swap}) {
+      return (
+        <React.Suspense fallback={<Text text="Loading..." />}>
+          {swap ? <LazyChildB label="B" /> : <LazyChildA label="A" />}
+        </React.Suspense>
+      );
+    }
+
+    const root = ReactDOMClient.createRoot(container);
+    act(() => {
+      root.render(<Parent swap={false} />);
+    });
+    expect(Scheduler).toHaveYielded(['Loading...']);
+
+    await LazyChildA;
+    expect(Scheduler).toFlushAndYield(['A', 'Did mount: A']);
+    expect(container.innerHTML).toBe('A');
+
+    // Swap the position of A and B
+    ReactDOM.flushSync(() => {
+      root.render(<Parent swap={true} />);
+    });
+    expect(Scheduler).toHaveYielded(['Loading...', 'Will unmount: A']);
+    expect(container.innerHTML).toBe('Loading...');
+
+    // Destroy the whole tree, including the hidden A
+    ReactDOM.flushSync(() => {
+      root.render(<h1>Hello</h1>);
+    });
+    expect(Scheduler).toFlushAndYield([]);
+    expect(container.innerHTML).toBe('<h1>Hello</h1>');
+  });
 });