From 95e7a74a50764920da95a531d3bf1641f7acea2f Mon Sep 17 00:00:00 2001
From: Samuel Susla <samuelsusla@meta.com>
Date: Wed, 2 Aug 2023 05:56:31 -0700
Subject: [PATCH] Do not swapLeftAnd right if not in RTL (#38748)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/38748

changelog: [internal]

Android was setting flag `swapLeftAndRightInRTL` to true regardless if the context was RTL or LTR. This causes unnecessary tree traversal + invalidation of all yoga nodes. This is a completely unnecessary work when layout direction is left to right.

To fix this, I made sure Android not longer sets `swapLeftAndRightInRTL` to true and in Fabric we only check the flag for RTL context.

Reviewed By: NickGerleman

Differential Revision: D47913605

fbshipit-source-id: 1d938b0dc9ba16a73b076f626055055162e3495f
---
 .../com/facebook/react/config/ReactFeatureFlags.java |  3 +++
 .../src/main/jni/react/fabric/Binding.cpp            |  2 ++
 .../components/view/YogaLayoutableShadowNode.cpp     | 12 ++++++++++--
 .../ReactCommon/react/utils/CoreFeatures.cpp         |  1 +
 .../ReactCommon/react/utils/CoreFeatures.h           |  3 +++
 5 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java
index 48771fd5cb6..82b05cec891 100644
--- a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java
+++ b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java
@@ -154,4 +154,7 @@ public class ReactFeatureFlags {
 
   /** Use native view configs in bridgeless mode. */
   public static boolean useNativeViewConfigsInBridgelessMode = false;
+
+  /** Only swap left and right on Android in RTL scripts. */
+  public static boolean doNotSwapLeftAndRightOnAndroidInLTR = false;
 }
diff --git a/packages/react-native/ReactAndroid/src/main/jni/react/fabric/Binding.cpp b/packages/react-native/ReactAndroid/src/main/jni/react/fabric/Binding.cpp
index c23648f0ea0..65d6db392f8 100644
--- a/packages/react-native/ReactAndroid/src/main/jni/react/fabric/Binding.cpp
+++ b/packages/react-native/ReactAndroid/src/main/jni/react/fabric/Binding.cpp
@@ -431,6 +431,8 @@ void Binding::installFabricUIManager(
       getFeatureFlagValue("enableCppPropsIteratorSetter");
   CoreFeatures::useNativeState = getFeatureFlagValue("useNativeState");
   CoreFeatures::enableMapBuffer = getFeatureFlagValue("useMapBufferProps");
+  CoreFeatures::doNotSwapLeftAndRightOnAndroidInLTR =
+      getFeatureFlagValue("doNotSwapLeftAndRightOnAndroidInLTR");
 
   // RemoveDelete mega-op
   ShadowViewMutation::PlatformSupportsRemoveDeleteTreeInstruction =
diff --git a/packages/react-native/ReactCommon/react/renderer/components/view/YogaLayoutableShadowNode.cpp b/packages/react-native/ReactCommon/react/renderer/components/view/YogaLayoutableShadowNode.cpp
index fb4e57deaff..08f15ec203c 100644
--- a/packages/react-native/ReactCommon/react/renderer/components/view/YogaLayoutableShadowNode.cpp
+++ b/packages/react-native/ReactCommon/react/renderer/components/view/YogaLayoutableShadowNode.cpp
@@ -17,6 +17,7 @@
 #include <react/renderer/core/TraitCast.h>
 #include <react/renderer/debug/DebugStringConvertibleItem.h>
 #include <react/renderer/debug/SystraceSection.h>
+#include <react/utils/CoreFeatures.h>
 #include <yoga/Yoga.h>
 #include <algorithm>
 #include <limits>
@@ -550,8 +551,15 @@ void YogaLayoutableShadowNode::layoutTree(
 
   threadLocalLayoutContext = layoutContext;
 
-  if (layoutContext.swapLeftAndRightInRTL) {
-    swapLeftAndRightInTree(*this);
+  if (CoreFeatures::doNotSwapLeftAndRightOnAndroidInLTR) {
+    if (layoutConstraints.layoutDirection == LayoutDirection::RightToLeft &&
+        layoutContext.swapLeftAndRightInRTL) {
+      swapLeftAndRightInTree(*this);
+    }
+  } else {
+    if (layoutContext.swapLeftAndRightInRTL) {
+      swapLeftAndRightInTree(*this);
+    }
   }
 
   {
diff --git a/packages/react-native/ReactCommon/react/utils/CoreFeatures.cpp b/packages/react-native/ReactCommon/react/utils/CoreFeatures.cpp
index b23cdfbb125..2c3ce14e5ba 100644
--- a/packages/react-native/ReactCommon/react/utils/CoreFeatures.cpp
+++ b/packages/react-native/ReactCommon/react/utils/CoreFeatures.cpp
@@ -17,5 +17,6 @@ bool CoreFeatures::cacheLastTextMeasurement = false;
 bool CoreFeatures::cancelImageDownloadsOnRecycle = false;
 bool CoreFeatures::enableGranularScrollViewStateUpdatesIOS = false;
 bool CoreFeatures::enableMountHooks = false;
+bool CoreFeatures::doNotSwapLeftAndRightOnAndroidInLTR = false;
 
 } // namespace facebook::react
diff --git a/packages/react-native/ReactCommon/react/utils/CoreFeatures.h b/packages/react-native/ReactCommon/react/utils/CoreFeatures.h
index 84612fcfc97..8070cb4006f 100644
--- a/packages/react-native/ReactCommon/react/utils/CoreFeatures.h
+++ b/packages/react-native/ReactCommon/react/utils/CoreFeatures.h
@@ -50,6 +50,9 @@ class CoreFeatures {
 
   // Report mount operations from the host platform to notify mount hooks.
   static bool enableMountHooks;
+
+  // Only swap left and right on Android in RTL scripts.
+  static bool doNotSwapLeftAndRightOnAndroidInLTR;
 };
 
 } // namespace facebook::react