accessibleElements impl on iOS (facebook#49582)

Summary:
Pull Request resolved: facebook#49582

TSIA, this is a fairly straightforward implementation since iOS likes the shape the data is already in. Note I form a stacking context since I need the native view that has `accessibilityElements` to actually be an ancestor of everything under it

Note I am not exposing anything yet on the JS side, since we need to do Android also

Changelog: [Internal]

Reviewed By: NickGerleman

Differential Revision: D69625269

Author: joevilches

packages/react-native/React/Fabric/Mounting/ComponentViews/View/RCTViewComponentView.mm

@@ -18,6 +18,7 @@
 #import <React/RCTConversions.h>
 #import <React/RCTLinearGradient.h>
 #import <React/RCTLocalizedString.h>
+#import <React/RCTViewFinder.h>
 #import <react/featureflags/ReactNativeFeatureFlags.h>
 #import <react/renderer/components/view/ViewComponentDescriptor.h>
 #import <react/renderer/components/view/ViewEventEmitter.h>
@@ -48,6 +49,7 @@ @implementation RCTViewComponentView {
   NSSet<NSString *> *_Nullable _propKeysManagedByAnimated_DO_NOT_USE_THIS_IS_BROKEN;
   UIView *_containerView;
   BOOL _useCustomContainerView;
+  NSMutableArray<NSString *> *_accessibleElementsNativeIds;
 }
 
 #ifdef RCT_DYNAMIC_FRAMEWORKS
@@ -389,6 +391,13 @@ - (void)updateProps:(const Props::Shared &)props oldProps:(const Props::Shared &
     }
   }
 
+  if (oldViewProps.accessibilityElements != newViewProps.accessibilityElements) {
+    _accessibleElementsNativeIds = [NSMutableArray new];
+    for (const std::string &childId : newViewProps.accessibilityElements) {
+      [_accessibleElementsNativeIds addObject:RCTNSStringFromString(childId)];
+    }
+  }
+
   // `accessibilityTraits`
   if (oldViewProps.accessibilityTraits != newViewProps.accessibilityTraits) {
     self.accessibilityElement.accessibilityTraits =
@@ -595,6 +604,23 @@ - (void)prepareForRecycle
   _reactSubviews = [NSMutableArray new];
 }
 
+- (NSArray<NSObject *> *)accessibilityElements
+{
+  if ([_accessibleElementsNativeIds count] <= 0) {
+    return super.accessibilityElements;
+  }
+
+  NSMutableArray<UIView *> *elements = [NSMutableArray new];
+  for (NSString *childId : _accessibleElementsNativeIds) {
+    UIView *viewWithMatchingNativeId = [RCTViewFinder findView:self withNativeId:childId];
+    if (viewWithMatchingNativeId) {
+      [elements addObject:viewWithMatchingNativeId];
+    }
+  }
+
+  return elements;
+}
+
 - (void)setPropKeysManagedByAnimated_DO_NOT_USE_THIS_IS_BROKEN:(NSSet<NSString *> *_Nullable)props
 {
   _propKeysManagedByAnimated_DO_NOT_USE_THIS_IS_BROKEN = props;

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

@@ -46,6 +46,15 @@ AccessibilityProps::AccessibilityProps(
                     "accessibilityLabel",
                     sourceProps.accessibilityLabel,
                     "")),
+      accessibilityElements(
+          ReactNativeFeatureFlags::enableCppPropsIteratorSetter()
+              ? sourceProps.accessibilityElements
+              : convertRawProp(
+                    context,
+                    rawProps,
+                    "accessibilityElements",
+                    sourceProps.accessibilityElements,
+                    {})),
       accessibilityLabelledBy(
           ReactNativeFeatureFlags::enableCppPropsIteratorSetter()
               ? sourceProps.accessibilityLabelledBy
@@ -246,6 +255,7 @@ void AccessibilityProps::setProp(
     RAW_SET_PROP_SWITCH_CASE_BASIC(accessible);
     RAW_SET_PROP_SWITCH_CASE_BASIC(accessibilityState);
     RAW_SET_PROP_SWITCH_CASE_BASIC(accessibilityLabel);
+    RAW_SET_PROP_SWITCH_CASE_BASIC(accessibilityElements);
     RAW_SET_PROP_SWITCH_CASE_BASIC(accessibilityLabelledBy);
     RAW_SET_PROP_SWITCH_CASE_BASIC(accessibilityHint);
     RAW_SET_PROP_SWITCH_CASE_BASIC(accessibilityLanguage);

packages/react-native/ReactCommon/react/renderer/components/view/AccessibilityProps.h

@@ -34,6 +34,7 @@ class AccessibilityProps {
   bool accessible{false};
   std::optional<AccessibilityState> accessibilityState{std::nullopt};
   std::string accessibilityLabel{""};
+  std::vector<std::string> accessibilityElements{};
   AccessibilityLabelledBy accessibilityLabelledBy{};
   AccessibilityLiveRegion accessibilityLiveRegion{
       AccessibilityLiveRegion::None};

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

@@ -62,7 +62,8 @@ void ViewShadowNode::initialize() noexcept {
       !viewProps.filter.empty() ||
       viewProps.mixBlendMode != BlendMode::Normal ||
       viewProps.isolation == Isolation::Isolate ||
-      HostPlatformViewTraitsInitializer::formsStackingContext(viewProps);
+      HostPlatformViewTraitsInitializer::formsStackingContext(viewProps) ||
+      !viewProps.accessibilityElements.empty();
 
   bool formsView = formsStackingContext ||
       isColorMeaningful(viewProps.backgroundColor) || hasBorder() ||