From ff79b8fe5b40f6d239564a0a15c5285faba4eb74 Mon Sep 17 00:00:00 2001
From: Samuel Susla <samuel.susla@gmail.com>
Date: Thu, 10 Nov 2022 13:34:15 +0000
Subject: [PATCH 1/2] Don't disappear layout effects unnecessarily

Nested Offscreens can run into a case where anscestor Offscreen
is revealed while inner one is hidden. This is an edge case that
was previously missed. We need to prevent call to disappear layout
effects. Check unit tests for an example of this.
---
 .../src/ReactFiberCommitWork.new.js           |  7 +-
 .../src/ReactFiberCommitWork.old.js           |  7 +-
 .../src/__tests__/ReactOffscreen-test.js      | 92 ++++++++++++++-----
 3 files changed, 75 insertions(+), 31 deletions(-)

diff --git a/packages/react-reconciler/src/ReactFiberCommitWork.new.js b/packages/react-reconciler/src/ReactFiberCommitWork.new.js
index 0b885bf13488b..1a9b72c8aeb0b 100644
--- a/packages/react-reconciler/src/ReactFiberCommitWork.new.js
+++ b/packages/react-reconciler/src/ReactFiberCommitWork.new.js
@@ -2880,12 +2880,13 @@ function commitMutationEffectsOnFiber(
 
         if (isHidden) {
           const isUpdate = current !== null;
-          const isAncestorOffscreenHidden = offscreenSubtreeIsHidden;
+          const wasHiddenByAncestorOffscreen =
+            offscreenSubtreeIsHidden || offscreenSubtreeWasHidden;
           // Only trigger disapper layout effects if:
           //   - This is an update, not first mount.
           //   - This Offscreen was not hidden before.
-          //   - No ancestor Offscreen is hidden.
-          if (isUpdate && !wasHidden && !isAncestorOffscreenHidden) {
+          //   - Ancestor Offscreen was not hidden in previous commit.
+          if (isUpdate && !wasHidden && !wasHiddenByAncestorOffscreen) {
             if ((finishedWork.mode & ConcurrentMode) !== NoMode) {
               // Disappear the layout effects of all the children
               recursivelyTraverseDisappearLayoutEffects(finishedWork);
diff --git a/packages/react-reconciler/src/ReactFiberCommitWork.old.js b/packages/react-reconciler/src/ReactFiberCommitWork.old.js
index cbbca982127f0..c1824d903453e 100644
--- a/packages/react-reconciler/src/ReactFiberCommitWork.old.js
+++ b/packages/react-reconciler/src/ReactFiberCommitWork.old.js
@@ -2880,12 +2880,13 @@ function commitMutationEffectsOnFiber(
 
         if (isHidden) {
           const isUpdate = current !== null;
-          const isAncestorOffscreenHidden = offscreenSubtreeIsHidden;
+          const wasHiddenByAncestorOffscreen =
+            offscreenSubtreeIsHidden || offscreenSubtreeWasHidden;
           // Only trigger disapper layout effects if:
           //   - This is an update, not first mount.
           //   - This Offscreen was not hidden before.
-          //   - No ancestor Offscreen is hidden.
-          if (isUpdate && !wasHidden && !isAncestorOffscreenHidden) {
+          //   - Ancestor Offscreen was not hidden for previous pass.
+          if (isUpdate && !wasHidden && !wasHiddenByAncestorOffscreen) {
             if ((finishedWork.mode & ConcurrentMode) !== NoMode) {
               // Disappear the layout effects of all the children
               recursivelyTraverseDisappearLayoutEffects(finishedWork);
diff --git a/packages/react-reconciler/src/__tests__/ReactOffscreen-test.js b/packages/react-reconciler/src/__tests__/ReactOffscreen-test.js
index 417f851ad45b7..d830265610823 100644
--- a/packages/react-reconciler/src/__tests__/ReactOffscreen-test.js
+++ b/packages/react-reconciler/src/__tests__/ReactOffscreen-test.js
@@ -275,7 +275,7 @@ describe('ReactOffscreen', () => {
     // goes from visible to hidden in synchronous update.
     class ClassComponent extends React.Component {
       render() {
-        return <Text text="Child" />;
+        return <Text text="child" />;
       }
 
       componentWillUnmount() {
@@ -287,47 +287,89 @@ describe('ReactOffscreen', () => {
       }
     }
 
-    let _setIsVisible;
-    let isFirstRender = true;
+    const root = ReactNoop.createRoot();
+    await act(async () => {
+      // Outer and inner offscreen are hidden.
+      root.render(
+        <Offscreen mode={'hidden'}>
+          <Offscreen mode={'hidden'}>
+            <ClassComponent />
+          </Offscreen>
+        </Offscreen>,
+      );
+    });
 
-    function App() {
-      const [isVisible, setIsVisible] = React.useState(true);
-      _setIsVisible = setIsVisible;
-      if (isFirstRender === true) {
-        setIsVisible(false);
-        isFirstRender = false;
-      }
+    expect(Scheduler).toHaveYielded(['child']);
+    expect(root).toMatchRenderedOutput(<span hidden={true} prop="child" />);
 
-      return (
-        <Offscreen mode="hidden">
-          <Offscreen mode={isVisible ? 'visible' : 'hidden'}>
+    await act(async () => {
+      // Inner offscreen is visible.
+      root.render(
+        <Offscreen mode={'hidden'}>
+          <Offscreen mode={'visible'}>
             <ClassComponent />
           </Offscreen>
-        </Offscreen>
+        </Offscreen>,
       );
-    }
+    });
+
+    expect(Scheduler).toHaveYielded(['child']);
+    expect(root).toMatchRenderedOutput(<span hidden={true} prop="child" />);
 
-    const root = ReactNoop.createRoot();
     await act(async () => {
-      root.render(<App />);
+      // Inner offscreen is hidden.
+      root.render(
+        <Offscreen mode={'hidden'}>
+          <Offscreen mode={'hidden'}>
+            <ClassComponent />
+          </Offscreen>
+        </Offscreen>,
+      );
     });
 
-    expect(Scheduler).toHaveYielded(['Child']);
-    expect(root).toMatchRenderedOutput(<span hidden={true} prop="Child" />);
+    expect(Scheduler).toHaveYielded(['child']);
+    expect(root).toMatchRenderedOutput(<span hidden={true} prop="child" />);
 
     await act(async () => {
-      _setIsVisible(true);
+      // Inner offscreen is visible.
+      root.render(
+        <Offscreen mode={'hidden'}>
+          <Offscreen mode={'visible'}>
+            <ClassComponent />
+          </Offscreen>
+        </Offscreen>,
+      );
     });
 
-    expect(Scheduler).toHaveYielded(['Child']);
-    expect(root).toMatchRenderedOutput(<span hidden={true} prop="Child" />);
+    Scheduler.unstable_clearYields();
+
+    await act(async () => {
+      // Outer offscreen is visible.
+      // Inner offscreen is hidden.
+      root.render(
+        <Offscreen mode={'visible'}>
+          <Offscreen mode={'hidden'}>
+            <ClassComponent />
+          </Offscreen>
+        </Offscreen>,
+      );
+    });
+
+    expect(Scheduler).toHaveYielded(['child']);
 
     await act(async () => {
-      _setIsVisible(false);
+      // Outer offscreen is hidden.
+      // Inner offscreen is visible.
+      root.render(
+        <Offscreen mode={'hidden'}>
+          <Offscreen mode={'visible'}>
+            <ClassComponent />
+          </Offscreen>
+        </Offscreen>,
+      );
     });
 
-    expect(Scheduler).toHaveYielded(['Child']);
-    expect(root).toMatchRenderedOutput(<span hidden={true} prop="Child" />);
+    expect(Scheduler).toHaveYielded(['child']);
   });
 
   // @gate enableOffscreen

From d5adfe0137c4665982bd9cf315894dd3e8a920b5 Mon Sep 17 00:00:00 2001
From: Samuel Susla <samuel.susla@gmail.com>
Date: Thu, 10 Nov 2022 13:49:14 +0000
Subject: [PATCH 2/2] yarn replace-fork

---
 packages/react-reconciler/src/ReactFiberCommitWork.old.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/react-reconciler/src/ReactFiberCommitWork.old.js b/packages/react-reconciler/src/ReactFiberCommitWork.old.js
index c1824d903453e..a873d23c3d729 100644
--- a/packages/react-reconciler/src/ReactFiberCommitWork.old.js
+++ b/packages/react-reconciler/src/ReactFiberCommitWork.old.js
@@ -2885,7 +2885,7 @@ function commitMutationEffectsOnFiber(
           // Only trigger disapper layout effects if:
           //   - This is an update, not first mount.
           //   - This Offscreen was not hidden before.
-          //   - Ancestor Offscreen was not hidden for previous pass.
+          //   - Ancestor Offscreen was not hidden in previous commit.
           if (isUpdate && !wasHidden && !wasHiddenByAncestorOffscreen) {
             if ((finishedWork.mode & ConcurrentMode) !== NoMode) {
               // Disappear the layout effects of all the children