Fix LayoutAnimation crash from mutation sort ordering

Summary:
`LayoutAnimationDriver::animationMutationsForFrame` was sorting animation-frame Update mutations together with structural mutations (Remove/Insert/Delete) from completed animations. Animation-frame Updates reference views by their pre-structural-change parentTag. When `std::stable_sort` reordered these Updates after Remove/Insert pairs that reparented a view, `StubViewTree::mutate` hit a parentTag mismatch assertion (`react_native_assert(oldStubView->parentTag == mutation.parentTag)`) and crashed with SIGABRT.

The fix records the boundary between animation-frame Updates and final structural mutations, then only sorts the structural portion. This preserves the invariant that animation-frame Updates execute before any structural changes.

Additionally, the mutation comparator in `utils.h` was missing an explicit `Update < Insert` ordering rule, which could cause nondeterministic sort results between Update and Insert mutations of different types. This is now handled.

The test fixture is converted to `TEST_F` with a `LayoutAnimationTest` class that enables the `fixDifferentiatorParentTagForUnflattenCase` feature flag, ensuring consistent parentTag assignment across platforms.

Changelog: [Internal]

Differential Revision: D102696875

Author: fkgozali

packages/react-native/ReactCommon/react/renderer/animations/LayoutAnimationDriver.cpp

@@ -74,6 +74,10 @@ void LayoutAnimationDriver::animationMutationsForFrame(
     }
   }
 
+  // Record boundary: animation-frame Updates above this point carry
+  // parentTag from before any structural changes and must execute first.
+  auto animationUpdatesEnd = mutationsList.size();
+
   // Clear out finished animations
   for (auto it = inflightAnimations_.begin();
        it != inflightAnimations_.end();) {
@@ -99,10 +103,11 @@ void LayoutAnimationDriver::animationMutationsForFrame(
     }
   }
 
-  // Final step: make sure that all operations execute in the proper order.
-  // REMOVE operations with highest indices must operate first.
+  // Sort only the final mutations from completed animations.
+  // Animation-frame Updates must stay before structural mutations because
+  // they reference views by their pre-structural-change parentTag.
   std::stable_sort(
-      mutationsList.begin(),
+      mutationsList.begin() + static_cast<ptrdiff_t>(animationUpdatesEnd),
       mutationsList.end(),
       &shouldFirstComeBeforeSecondMutation);
 }

packages/react-native/ReactCommon/react/renderer/animations/tests/LayoutAnimationTest.cpp

@@ -26,6 +26,9 @@
 #include <react/test_utils/MockClock.h>
 #include <react/test_utils/shadowTreeGeneration.h>
 
+#include <react/featureflags/ReactNativeFeatureFlags.h>
+#include <react/featureflags/ReactNativeFeatureFlagsDefaults.h>
+
 // Uncomment when random test blocks are uncommented below.
 // #include <algorithm>
 // #include <random>
@@ -34,6 +37,17 @@ MockClock::time_point MockClock::time_ = {};
 
 namespace facebook::react {
 
+namespace {
+
+class TestFeatureFlags : public ReactNativeFeatureFlagsDefaults {
+ public:
+  bool fixDifferentiatorParentTagForUnflattenCase() override {
+    return true;
+  }
+};
+
+} // namespace
+
 static void testShadowNodeTreeLifeCycleLayoutAnimations(
     uint_fast32_t seed,
     int treeSize,
@@ -326,7 +340,18 @@ static void testShadowNodeTreeLifeCycleLayoutAnimations(
 
 using namespace facebook::react;
 
-TEST(
+class LayoutAnimationTest : public ::testing::Test {
+ protected:
+  void SetUp() override {
+    ReactNativeFeatureFlags::override(std::make_unique<TestFeatureFlags>());
+  }
+
+  void TearDown() override {
+    ReactNativeFeatureFlags::dangerouslyReset();
+  }
+};
+
+TEST_F(
     LayoutAnimationTest,
     stableSmallerTreeFewRepeatsFewStages_NonOverlapping_2029343357) {
   testShadowNodeTreeLifeCycleLayoutAnimations(
@@ -341,7 +366,7 @@ TEST(
       /* delay_ms_between_repeats */ 2000);
 }
 
-TEST(
+TEST_F(
     LayoutAnimationTest,
     stableSmallerTreeFewRepeatsFewStages_NonOverlapping_3619914559) {
   testShadowNodeTreeLifeCycleLayoutAnimations(
@@ -356,7 +381,7 @@ TEST(
       /* delay_ms_between_repeats */ 2000);
 }
 
-TEST(
+TEST_F(
     LayoutAnimationTest,
     stableSmallerTreeFewRepeatsFewStages_NonOverlapping_597132284) {
   testShadowNodeTreeLifeCycleLayoutAnimations(
@@ -371,7 +396,7 @@ TEST(
       /* delay_ms_between_repeats */ 2000);
 }
 
-TEST(
+TEST_F(
     LayoutAnimationTest,
     stableSmallerTreeFewRepeatsFewStages_NonOverlapping_774986518) {
   testShadowNodeTreeLifeCycleLayoutAnimations(
@@ -386,7 +411,7 @@ TEST(
       /* delay_ms_between_repeats */ 2000);
 }
 
-TEST(
+TEST_F(
     LayoutAnimationTest,
     stableSmallerTreeFewRepeatsFewStages_NonOverlapping_1450614414) {
   testShadowNodeTreeLifeCycleLayoutAnimations(
@@ -401,7 +426,9 @@ TEST(
       /* delay_ms_between_repeats */ 2000);
 }
 
-TEST(LayoutAnimationTest, stableBiggerTreeFewRepeatsFewStages_NonOverlapping) {
+TEST_F(
+    LayoutAnimationTest,
+    stableBiggerTreeFewRepeatsFewStages_NonOverlapping) {
   testShadowNodeTreeLifeCycleLayoutAnimations(
       /* seed */ 2029343357,
       /* size */ 512,
@@ -414,7 +441,9 @@ TEST(LayoutAnimationTest, stableBiggerTreeFewRepeatsFewStages_NonOverlapping) {
       /* delay_ms_between_repeats */ 2000);
 }
 
-TEST(LayoutAnimationTest, stableBiggerTreeFewRepeatsManyStages_NonOverlapping) {
+TEST_F(
+    LayoutAnimationTest,
+    stableBiggerTreeFewRepeatsManyStages_NonOverlapping) {
   testShadowNodeTreeLifeCycleLayoutAnimations(
       /* seed */ 2029343357,
       /* size */ 512,
@@ -454,7 +483,7 @@ TEST(LayoutAnimationTest, stableBiggerTreeFewRepeatsManyStages_NonOverlapping) {
 // before the previous animation completes.
 //
 
-TEST(
+TEST_F(
     LayoutAnimationTest,
     stableSmallerTreeFewRepeatsFewStages_Overlapping_2029343357) {
   testShadowNodeTreeLifeCycleLayoutAnimations(
@@ -472,7 +501,7 @@ TEST(
       /* final_animation_delay */ 10000 + 1);
 }
 
-TEST(
+TEST_F(
     LayoutAnimationTest,
     stableSmallerTreeFewRepeatsFewStages_Overlapping_597132284) {
   testShadowNodeTreeLifeCycleLayoutAnimations(
@@ -490,7 +519,7 @@ TEST(
       /* final_animation_delay */ 10000 + 1);
 }
 
-TEST(
+TEST_F(
     LayoutAnimationTest,
     stableSmallerTreeFewRepeatsFewStages_Overlapping_ManyConflicts_597132284) {
   GTEST_SKIP();
@@ -511,7 +540,7 @@ TEST(
       /* final_animation_delay */ 50000 + 1);
 }
 
-TEST(
+TEST_F(
     LayoutAnimationTest,
     stableBiggerTreeFewRepeatsManyStages_Overlapping_ManyConflicts_2029343357) {
   GTEST_SKIP();

packages/react-native/ReactCommon/react/renderer/animations/tests/MutationComparatorTest.cpp

@@ -117,6 +117,10 @@ TEST(MutationComparatorTest, TypeOrdering) {
   EXPECT_TRUE(shouldFirstComeBeforeSecondMutation(create, insert));
   EXPECT_FALSE(shouldFirstComeBeforeSecondMutation(insert, create));
 
+  // Update comes before Insert
+  EXPECT_TRUE(shouldFirstComeBeforeSecondMutation(update, insert));
+  EXPECT_FALSE(shouldFirstComeBeforeSecondMutation(insert, update));
+
   // Remove comes before Update
   EXPECT_TRUE(shouldFirstComeBeforeSecondMutation(remove, update));
   EXPECT_FALSE(shouldFirstComeBeforeSecondMutation(update, remove));

packages/react-native/ReactCommon/react/renderer/animations/utils.h

@@ -88,6 +88,14 @@ static inline bool shouldFirstComeBeforeSecondMutation(
       return false;
     }
 
+    // Update comes before Insert
+    if (lhs.type == ShadowViewMutation::Type::Update && rhs.type == ShadowViewMutation::Type::Insert) {
+      return true;
+    }
+    if (rhs.type == ShadowViewMutation::Type::Update && lhs.type == ShadowViewMutation::Type::Insert) {
+      return false;
+    }
+
   } else {
     // Make sure that removes on the same level are sorted - highest indices
     // must come first.