C++ LayoutAnimations: solve crash when "animating" virtual views

Summary:
Index adjustment doesn't work if virtual views are inserted, because those don't actually result in the view hierarchy being mutated, as such.

Add an Android-specific check to solve the crash.

I don't love adding platform-specific checks here, so I'm considering wrapping this logic in a platform-specific class, so that logic lives outside of the core of LayoutAnimations and entirely in platform code.

Changelog: [Internal]

Reviewed By: mdvacca

Differential Revision: D21727805

fbshipit-source-id: 5af2cf479beaa4d0e9d94ea16ac989c4268920f8

ReactCommon/fabric/animations/LayoutAnimationKeyFrameManager.cpp

@@ -311,6 +311,10 @@ void LayoutAnimationKeyFrameManager::adjustDelayedMutationIndicesForMutation(
   bool isInsertMutation = mutation.type == ShadowViewMutation::Type::Insert;
   assert(isRemoveMutation || isInsertMutation);
 
+  if (mutatedViewIsVirtual(mutation)) {
+    return;
+  }
+
   for (auto &inflightAnimation : inflightAnimations_) {
     if (inflightAnimation.surfaceId != surfaceId) {
       continue;
@@ -691,7 +695,8 @@ LayoutAnimationKeyFrameManager::pullTransaction(
               for (const auto &otherMutation : mutations) {
                 if (otherMutation.type == ShadowViewMutation::Type::Insert &&
                     otherMutation.parentShadowView.tag == parentTag) {
-                  if (otherMutation.index <= adjustedIndex) {
+                  if (otherMutation.index <= adjustedIndex &&
+                      !mutatedViewIsVirtual(otherMutation)) {
                     adjustedIndex++;
                   }
                 }
@@ -861,6 +866,22 @@ LayoutAnimationKeyFrameManager::pullTransaction(
       surfaceId, transactionNumber, std::move(mutations), {}};
 }
 
+bool LayoutAnimationKeyFrameManager::mutatedViewIsVirtual(
+    ShadowViewMutation const &mutation) const {
+  bool viewIsVirtual = false;
+
+  // TODO: extract this into an Android platform-specific class
+  // Explanation: for "Insert" mutations, oldChildShadowView is always empty.
+  //              for "Remove" mutations, newChildShadowView is always empty.
+#ifdef ANDROID
+  viewIsVirtual =
+      mutation.newChildShadowView.layoutMetrics == EmptyLayoutMetrics &&
+      mutation.oldChildShadowView.layoutMetrics == EmptyLayoutMetrics;
+#endif
+
+  return viewIsVirtual;
+}
+
 ComponentDescriptor const &
 LayoutAnimationKeyFrameManager::getComponentDescriptorForShadowView(
     ShadowView const &shadowView) const {

ReactCommon/fabric/animations/LayoutAnimationKeyFrameManager.h

@@ -144,6 +144,8 @@ class LayoutAnimationKeyFrameManager : public UIManagerAnimationDelegate,
       ShadowViewMutation const &mutation) const;
 
  protected:
+  bool mutatedViewIsVirtual(ShadowViewMutation const &mutation) const;
+
   ComponentDescriptor const &getComponentDescriptorForShadowView(
       ShadowView const &shadowView) const;
   std::pair<double, double> calculateAnimationProgress(