fix: Memory leak when unmounting views mid-animation

packages/react-native-reanimated/Common/cpp/reanimated/Fabric/ReanimatedMountHook.cpp

@@ -30,12 +30,12 @@ void ReanimatedMountHook::shadowTreeDidMount(
   auto reaShadowNode = std::reinterpret_pointer_cast<ReanimatedCommitShadowNode>(
       std::const_pointer_cast<RootShadowNode>(rootShadowNode));
 
+  // We mark reanimated commits with ReanimatedMountTrait. We don't want other
+  // shadow nodes to use this trait, but since this rootShadowNode is Shared,
+  // we don't have that guarantee. That's why we also unset this trait in the
+  // commit hook. We remove it here mainly for the sake of cleanliness.
   const bool isReanimatedMount = reaShadowNode->hasReanimatedMountTrait();
   if (isReanimatedMount) {
-    // We mark reanimated commits with ReanimatedMountTrait. We don't want other
-    // shadow nodes to use this trait, but since this rootShadowNode is Shared,
-    // we don't have that guarantee. That's why we also unset this trait in the
-    // commit hook. We remove it here mainly for the sake of cleanliness.
     reaShadowNode->unsetReanimatedMountTrait();
   }
 
@@ -44,17 +44,19 @@ void ReanimatedMountHook::shadowTreeDidMount(
     // Record the mounted tree for relative-length resolution.
     viewStylesRepository_->setLastMountedRoot(rootShadowNode);
 
-    if (isReanimatedMount) {
-      return;
-    }
-
+    // Always drain removable nodes, even on Reanimated's own commits. While CSS
+    // animations run every mount carries the mount trait, so returning early here
+    // would skip removals for the whole animation and leak unmounted nodes if the
+    // tree is torn down mid-animation.
     updatesRegistryManager_->handleNodeRemovals(*rootShadowNode);
 
-    // When commit from React Native has finished, we reset the skip commit flag
-    // in order to allow Reanimated to commit its tree
-    updatesRegistryManager_->unpauseReanimatedCommits();
-    if (updatesRegistryManager_->shouldCommitAfterPause()) {
-      requestFlush_();
+    if (!isReanimatedMount) {
+      // When a commit from React Native has finished, we reset the skip commit
+      // flag in order to allow Reanimated to commit its tree.
+      updatesRegistryManager_->unpauseReanimatedCommits();
+      if (updatesRegistryManager_->shouldCommitAfterPause()) {
+        requestFlush_();
+      }
     }
   }
 }