Create option for out-of-tree platforms to customize View traits (#38580

)

Summary:
Pull Request resolved: #38580

We already have a differential between Android and iOS View props that force view flattening (or unflattening) behaviors. Other out-of-tree platforms may have a need to customize view flattening behaviors.

This change adds a ViewTraitsInitializer header that out of tree platforms can inject to include platform-specific ViewProps fields when considering view flattening behaviors.

## Changelog:
[General] [Added] - Support customization of View traits for flattening in out of tree platform Fabric implementations

Reviewed By: christophpurrer

Differential Revision: D47721377

fbshipit-source-id: 1eeab5f847fb1813172d0ff0fad4182fcdd2cf21

packages/react-native/ReactCommon/react/renderer/components/view/ViewShadowNode.cpp

@@ -7,6 +7,7 @@
 
 #include "ViewShadowNode.h"
 #include <react/config/ReactNativeConfig.h>
+#include <react/renderer/components/view/ViewTraitsInitializer.h>
 #include <react/renderer/components/view/primitives.h>
 #include <react/utils/CoreFeatures.h>
 
@@ -54,24 +55,13 @@ void ViewShadowNode::initialize() noexcept {
       viewProps.accessibilityElementsHidden ||
       viewProps.accessibilityViewIsModal ||
       viewProps.importantForAccessibility != ImportantForAccessibility::Auto ||
-      viewProps.removeClippedSubviews;
-
-#ifdef ANDROID
-  formsStackingContext = formsStackingContext || viewProps.elevation != 0;
-#endif
+      viewProps.removeClippedSubviews ||
+      ViewTraitsInitializer::formsStackingContext(viewProps);
 
   bool formsView = formsStackingContext ||
       isColorMeaningful(viewProps.backgroundColor) ||
       !(viewProps.yogaStyle.border() == YGStyle::Edges{}) ||
-      !viewProps.testId.empty();
-
-#ifdef ANDROID
-  formsView = formsView || viewProps.nativeBackground.has_value() ||
-      viewProps.nativeForeground.has_value() || viewProps.focusable ||
-      viewProps.hasTVPreferredFocus ||
-      viewProps.needsOffscreenAlphaCompositing ||
-      viewProps.renderToHardwareTextureAndroid;
-#endif
+      !viewProps.testId.empty() || ViewTraitsInitializer::formsView(viewProps);
 
   if (formsView) {
     traits_.set(ShadowNodeTraits::Trait::FormsView);
@@ -85,9 +75,7 @@ void ViewShadowNode::initialize() noexcept {
     traits_.unset(ShadowNodeTraits::Trait::FormsStackingContext);
   }
 
-#ifdef ANDROID
-  traits_.set(ShadowNodeTraits::Trait::AndroidMapBufferPropsSupported);
-#endif
+  traits_.set(ViewTraitsInitializer::extraTraits());
 }
 
 } // namespace facebook::react

packages/react-native/ReactCommon/react/renderer/components/view/platform/android/react/renderer/components/view/ViewTraitsInitializer.h

@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <react/renderer/components/view/ViewProps.h>
+#include <react/renderer/core/ShadowNodeTraits.h>
+
+namespace facebook::react::ViewTraitsInitializer {
+
+static bool formsStackingContext(ViewProps const &viewProps) {
+  return viewProps.elevation != 0;
+}
+
+static bool formsView(ViewProps const &viewProps) {
+  return viewProps.nativeBackground.has_value() ||
+      viewProps.nativeForeground.has_value() || viewProps.focusable ||
+      viewProps.hasTVPreferredFocus ||
+      viewProps.needsOffscreenAlphaCompositing ||
+      viewProps.renderToHardwareTextureAndroid;
+}
+
+static ShadowNodeTraits::Trait extraTraits() {
+  return ShadowNodeTraits::Trait::AndroidMapBufferPropsSupported;
+}
+
+} // namespace facebook::react::ViewTraitsInitializer

packages/react-native/ReactCommon/react/renderer/components/view/platform/common/react/renderer/components/view/ViewTraitsInitializer.h

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <react/renderer/components/view/ViewProps.h>
+#include <react/renderer/core/ShadowNodeTraits.h>
+
+namespace facebook::react::ViewTraitsInitializer {
+
+static bool formsStackingContext(ViewProps const &props) {
+  return false;
+}
+
+static bool formsView(ViewProps const &props) {
+  return false;
+}
+
+static ShadowNodeTraits::Trait extraTraits() {
+  return ShadowNodeTraits::Trait::None;
+}
+
+} // namespace facebook::react::ViewTraitsInitializer