Fix error when trying to unobserve detached targets in IntersectionOb…

…server

Summary:
Yet another problem caused by React being too aggressive cleaning up detached fibers. This fixes a problem in `IntersectionObserver` when trying to `unobserve` detached targets. In that case we didn't have access to its shadow node anymore, so we didn't have a way to unobserve in native. This keeps an additional mapping in JS to do the conversion even after detached.

Changelog: [internal]

Differential Revision: D51257960

packages/react-native/Libraries/IntersectionObserver/IntersectionObserverManager.js

@@ -70,6 +70,13 @@ function unsetTargetForInstanceHandle(instanceHandle: mixed): void {
   instanceHandleToTargetMap.delete(key);
 }
 
+// The mapping between ReactNativeElement and their corresponding shadow nodes
+// also needs to be kept here because React removes the link when unmounting.
+const targetToShadowNodeMap: WeakMap<
+  ReactNativeElement,
+  ReturnType<typeof getShadowNode>,
+> = new WeakMap();
+
 /**
  * Registers the given intersection observer and returns a unique ID for it,
  * which is required to start observing targets.
@@ -151,6 +158,9 @@ export function observe({
   // access it even after the instance handle has been unmounted.
   setTargetForInstanceHandle(instanceHandle, target);
 
+  // Same for the mapping between the target and its shadow node.
+  targetToShadowNodeMap.set(target, targetShadowNode);
+
   if (!isConnected) {
     NativeIntersectionObserver.connect(notifyIntersectionObservers);
     isConnected = true;
@@ -182,7 +192,7 @@ export function unobserve(
     return;
   }
 
-  const targetShadowNode = getShadowNode(target);
+  const targetShadowNode = targetToShadowNodeMap.get(target);
   if (targetShadowNode == null) {
     console.error(
       'IntersectionObserverManager: could not find reference to host node from target',
@@ -204,8 +214,9 @@ export function unobserve(
   );
 
   // We can guarantee we won't receive any more entries for this target,
-  // so we don't need to keep the mapping anymore.
+  // so we don't need to keep the mappings anymore.
   unsetTargetForInstanceHandle(instanceHandle);
+  targetToShadowNodeMap.delete(target);
 }
 
 /**