Add unmount method in UIManagerMountHook and use it to notify not int…

…ersecting state in IntersectionObserver (#45186)

Summary:
Pull Request resolved: #45186

Changelog: [internal]

(this is an internal change because `IntersectionObserver` hasn't been released yet).

When testing IntersectionObserver, I realized that it wasn't triggering notifications for elements not intersecting when the surface that contained them was completely deallocated.

This is unexpected because IntersectionObserver notifications are delivered when the element is removed from the root, but not when the root itself is removed.

This fixes that behavior by:
1. Adding a method in `UIManagerMountHooks` to get a notification about the surface being unmounted. This is necessary to keep the API backwards compatible.
2. Using that method in `IntersectionObserverManager` to notify all observers (and report a change if necessary).

Differential Revision: D59061136

packages/react-native/ReactCommon/react/renderer/observers/intersection/IntersectionObserver.cpp

@@ -90,7 +90,7 @@ static Rect computeIntersection(
 std::optional<IntersectionObserverEntry>
 IntersectionObserver::updateIntersectionObservation(
     const RootShadowNode& rootShadowNode,
-    double mountTime) {
+    double time) {
   const auto layoutableRootShadowNode =
       dynamic_cast<const LayoutableShadowNode*>(&rootShadowNode);
 
@@ -121,22 +121,26 @@ IntersectionObserver::updateIntersectionObservation(
       : intersectionRectArea / targetBoundingRectArea;
 
   if (intersectionRatio == 0) {
-    return setNotIntersectingState(
-        rootBoundingRect, targetBoundingRect, mountTime);
+    return setNotIntersectingState(rootBoundingRect, targetBoundingRect, time);
   }
 
   auto highestThresholdCrossed = getHighestThresholdCrossed(intersectionRatio);
   if (highestThresholdCrossed == -1) {
-    return setNotIntersectingState(
-        rootBoundingRect, targetBoundingRect, mountTime);
+    return setNotIntersectingState(rootBoundingRect, targetBoundingRect, time);
   }
 
   return setIntersectingState(
       rootBoundingRect,
       targetBoundingRect,
       intersectionRect,
       highestThresholdCrossed,
-      mountTime);
+      time);
+}
+
+std::optional<IntersectionObserverEntry>
+IntersectionObserver::updateIntersectionObservationForSurfaceUnmount(
+    double time) {
+  return setNotIntersectingState(Rect{}, Rect{}, time);
 }
 
 Float IntersectionObserver::getHighestThresholdCrossed(
@@ -156,7 +160,7 @@ IntersectionObserver::setIntersectingState(
     const Rect& targetBoundingRect,
     const Rect& intersectionRect,
     Float threshold,
-    double mountTime) {
+    double time) {
   auto newState = IntersectionObserverState::Intersecting(threshold);
 
   if (state_ != newState) {
@@ -168,7 +172,7 @@ IntersectionObserver::setIntersectingState(
         rootBoundingRect,
         intersectionRect,
         true,
-        mountTime,
+        time,
     };
     return std::optional<IntersectionObserverEntry>{std::move(entry)};
   }
@@ -180,7 +184,7 @@ std::optional<IntersectionObserverEntry>
 IntersectionObserver::setNotIntersectingState(
     const Rect& rootBoundingRect,
     const Rect& targetBoundingRect,
-    double mountTime) {
+    double time) {
   if (state_ != IntersectionObserverState::NotIntersecting()) {
     state_ = IntersectionObserverState::NotIntersecting();
     IntersectionObserverEntry entry{
@@ -190,7 +194,7 @@ IntersectionObserver::setNotIntersectingState(
         rootBoundingRect,
         std::nullopt,
         false,
-        mountTime,
+        time,
     };
     return std::optional<IntersectionObserverEntry>(std::move(entry));
   }

packages/react-native/ReactCommon/react/renderer/observers/intersection/IntersectionObserver.h

@@ -41,7 +41,10 @@ class IntersectionObserver {
   // https://w3c.github.io/IntersectionObserver/#update-intersection-observations-algo
   std::optional<IntersectionObserverEntry> updateIntersectionObservation(
       const RootShadowNode& rootShadowNode,
-      double mountTime);
+      double time);
+
+  std::optional<IntersectionObserverEntry>
+  updateIntersectionObservationForSurfaceUnmount(double time);
 
   IntersectionObserverObserverId getIntersectionObserverId() const {
     return intersectionObserverId_;
@@ -63,12 +66,12 @@ class IntersectionObserver {
       const Rect& targetBoundingRect,
       const Rect& intersectionRect,
       Float threshold,
-      double mountTime);
+      double time);
 
   std::optional<IntersectionObserverEntry> setNotIntersectingState(
       const Rect& rootBoundingRect,
       const Rect& targetBoundingRect,
-      double mountTime);
+      double time);
 
   IntersectionObserverObserverId intersectionObserverId_;
   ShadowNode::Shared targetShadowNode_;

packages/react-native/ReactCommon/react/renderer/observers/intersection/IntersectionObserverManager.cpp

@@ -160,15 +160,27 @@ IntersectionObserverManager::takeRecords() {
   return entries;
 }
 
+#pragma mark - UIManagerMountHook
+
 void IntersectionObserverManager::shadowTreeDidMount(
     const RootShadowNode::Shared& rootShadowNode,
-    double mountTime) noexcept {
-  updateIntersectionObservations(*rootShadowNode, mountTime);
+    double time) noexcept {
+  updateIntersectionObservations(
+      rootShadowNode->getSurfaceId(), rootShadowNode, time);
+}
+
+void IntersectionObserverManager::shadowTreeDidUnmount(
+    SurfaceId surfaceId,
+    double time) noexcept {
+  updateIntersectionObservations(surfaceId, nullptr, time);
 }
 
+#pragma mark - Private methods
+
 void IntersectionObserverManager::updateIntersectionObservations(
-    const RootShadowNode& rootShadowNode,
-    double mountTime) {
+    SurfaceId surfaceId,
+    const RootShadowNode::Shared& rootShadowNode,
+    double time) {
   SystraceSection s(
       "IntersectionObserverManager::updateIntersectionObservations");
 
@@ -178,17 +190,21 @@ void IntersectionObserverManager::updateIntersectionObservations(
   {
     std::shared_lock lock(observersMutex_);
 
-    auto surfaceId = rootShadowNode.getSurfaceId();
-
     auto observersIt = observersBySurfaceId_.find(surfaceId);
     if (observersIt == observersBySurfaceId_.end()) {
       return;
     }
 
     auto& observers = observersIt->second;
     for (auto& observer : observers) {
-      auto entry =
-          observer.updateIntersectionObservation(rootShadowNode, mountTime);
+      std::optional<IntersectionObserverEntry> entry;
+
+      if (rootShadowNode != nullptr) {
+        entry = observer.updateIntersectionObservation(*rootShadowNode, time);
+      } else {
+        entry = observer.updateIntersectionObservationForSurfaceUnmount(time);
+      }
+
       if (entry) {
         entries.push_back(std::move(entry).value());
       }

packages/react-native/ReactCommon/react/renderer/observers/intersection/IntersectionObserverManager.h

@@ -42,7 +42,9 @@ class IntersectionObserverManager final : public UIManagerMountHook {
 
   void shadowTreeDidMount(
       const RootShadowNode::Shared& rootShadowNode,
-      double mountTime) noexcept override;
+      double time) noexcept override;
+
+  void shadowTreeDidUnmount(SurfaceId surfaceId, double time) noexcept override;
 
  private:
   mutable std::unordered_map<SurfaceId, std::vector<IntersectionObserver>>
@@ -63,8 +65,9 @@ class IntersectionObserverManager final : public UIManagerMountHook {
   // Equivalent to
   // https://w3c.github.io/IntersectionObserver/#update-intersection-observations-algo
   void updateIntersectionObservations(
-      const RootShadowNode& rootShadowNode,
-      double mountTime);
+      SurfaceId surfaceId,
+      const RootShadowNode::Shared& rootShadowNode,
+      double time);
 
   const IntersectionObserver& getRegisteredIntersectionObserver(
       SurfaceId surfaceId,

packages/react-native/ReactCommon/react/renderer/uimanager/UIManager.cpp

@@ -636,15 +636,15 @@ void UIManager::reportMount(SurfaceId surfaceId) const {
         shadowTree.getMountingCoordinator()->getBaseRevision().rootShadowNode;
   });
 
-  if (!rootShadowNode) {
-    return;
-  }
-
   {
     std::shared_lock lock(mountHookMutex_);
 
     for (auto* mountHook : mountHooks_) {
-      mountHook->shadowTreeDidMount(rootShadowNode, time);
+      if (rootShadowNode) {
+        mountHook->shadowTreeDidMount(rootShadowNode, time);
+      } else {
+        mountHook->shadowTreeDidUnmount(surfaceId, time);
+      }
     }
   }
 }

packages/react-native/ReactCommon/react/renderer/uimanager/UIManagerMountHook.h

@@ -28,6 +28,12 @@ class UIManagerMountHook {
       const RootShadowNode::Shared& rootShadowNode,
       double mountTime) noexcept = 0;
 
+  virtual void shadowTreeDidUnmount(
+      SurfaceId /*surfaceId*/,
+      double /*unmountTime*/) noexcept {
+    // Default no-op implementation for backwards compatibility.
+  }
+
   virtual ~UIManagerMountHook() noexcept = default;
 };