From 46eb3ec474ac3746d650adc817146d1d5373911d Mon Sep 17 00:00:00 2001
From: Joshua Gross <joshuagross@fb.com>
Date: Sat, 24 Oct 2020 07:19:50 -0700
Subject: [PATCH] Disable `childrenDrawingOrder` of ReactViewGroup in Fabric

Summary:
Fabric should be inserting Views into the hierarchy in the correct order based on z-index already, so there should be no reason to enable this mechanism.

At best it's a perf pessimisation and at worst it could be causing consistency issues or crashing (TBD). Most likely this is a noop.

Changelog: [Internal]

Reviewed By: ejanzer

Differential Revision: D24512203

fbshipit-source-id: b9336240ef8506742bcbd8d08fc8b830f82cdfe2
---
 .../react/config/ReactFeatureFlags.java       |  3 ++
 .../react/views/view/ReactViewGroup.java      | 42 ++++++++++++++++---
 2 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java b/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java
index b83c4c821d9..358bc8a0861 100644
--- a/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java
+++ b/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java
@@ -71,4 +71,7 @@ public class ReactFeatureFlags {
 
   /** Enable caching of Spannable objects using equality of ReadableNativeMaps */
   public static boolean enableSpannableCacheByReadableNativeMapEquality = true;
+
+  /** Disable customDrawOrder in ReactViewGroup under Fabric only. */
+  public static boolean disableCustomDrawOrderFabric = false;
 }
diff --git a/ReactAndroid/src/main/java/com/facebook/react/views/view/ReactViewGroup.java b/ReactAndroid/src/main/java/com/facebook/react/views/view/ReactViewGroup.java
index 20e916290cf..659a8afb341 100644
--- a/ReactAndroid/src/main/java/com/facebook/react/views/view/ReactViewGroup.java
+++ b/ReactAndroid/src/main/java/com/facebook/react/views/view/ReactViewGroup.java
@@ -48,6 +48,8 @@ import com.facebook.react.uimanager.RootView;
 import com.facebook.react.uimanager.RootViewUtil;
 import com.facebook.react.uimanager.ViewGroupDrawingOrderHelper;
 import com.facebook.react.uimanager.ViewProps;
+import com.facebook.react.uimanager.common.UIManagerType;
+import com.facebook.react.uimanager.common.ViewUtil;
 import com.facebook.yoga.YogaConstants;
 
 /**
@@ -433,12 +435,28 @@ public class ReactViewGroup extends ViewGroup
     }
   }
 
+  private boolean customDrawOrderDisabled() {
+    if (getId() == NO_ID) {
+      return false;
+    }
+    if (ViewUtil.getUIManagerType(getId()) != UIManagerType.FABRIC) {
+      return false;
+    }
+
+    return ReactFeatureFlags.disableCustomDrawOrderFabric;
+  }
+
   @Override
   public void addView(View child, int index, ViewGroup.LayoutParams params) {
     // This will get called for every overload of addView so there is not need to override every
     // method.
-    mDrawingOrderHelper.handleAddView(child);
-    setChildrenDrawingOrderEnabled(mDrawingOrderHelper.shouldEnableCustomDrawingOrder());
+
+    if (!customDrawOrderDisabled()) {
+      mDrawingOrderHelper.handleAddView(child);
+      setChildrenDrawingOrderEnabled(mDrawingOrderHelper.shouldEnableCustomDrawingOrder());
+    } else {
+      setChildrenDrawingOrderEnabled(false);
+    }
 
     super.addView(child, index, params);
   }
@@ -447,8 +465,12 @@ public class ReactViewGroup extends ViewGroup
   public void removeView(View view) {
     UiThreadUtil.assertOnUiThread();
 
-    mDrawingOrderHelper.handleRemoveView(view);
-    setChildrenDrawingOrderEnabled(mDrawingOrderHelper.shouldEnableCustomDrawingOrder());
+    if (!customDrawOrderDisabled()) {
+      mDrawingOrderHelper.handleRemoveView(view);
+      setChildrenDrawingOrderEnabled(mDrawingOrderHelper.shouldEnableCustomDrawingOrder());
+    } else {
+      setChildrenDrawingOrderEnabled(false);
+    }
 
     super.removeView(view);
   }
@@ -457,8 +479,12 @@ public class ReactViewGroup extends ViewGroup
   public void removeViewAt(int index) {
     UiThreadUtil.assertOnUiThread();
 
-    mDrawingOrderHelper.handleRemoveView(getChildAt(index));
-    setChildrenDrawingOrderEnabled(mDrawingOrderHelper.shouldEnableCustomDrawingOrder());
+    if (!customDrawOrderDisabled()) {
+      mDrawingOrderHelper.handleRemoveView(getChildAt(index));
+      setChildrenDrawingOrderEnabled(mDrawingOrderHelper.shouldEnableCustomDrawingOrder());
+    } else {
+      setChildrenDrawingOrderEnabled(false);
+    }
 
     super.removeViewAt(index);
   }
@@ -479,6 +505,10 @@ public class ReactViewGroup extends ViewGroup
 
   @Override
   public void updateDrawingOrder() {
+    if (customDrawOrderDisabled()) {
+      return;
+    }
+
     mDrawingOrderHelper.update();
     setChildrenDrawingOrderEnabled(mDrawingOrderHelper.shouldEnableCustomDrawingOrder());
     invalidate();