[ios] Link PlatformView back to semantics tree (flutter#46471)

The PlatformView does not have a semantics container when added to semantics tree, this PR gives it a semantics container to ensure accessibility traversal works.

This fixes flutter/flutter#135504, which is a regression of flutter@b8332e3

Before flutter@b8332e3, the traversal works because the PlatformView is added to the accessibilityElements of the FlutterPlatFormViewSemanticsContainer, which implicitly made the FlutterPlatFormViewSemanticsContainer as the PlatformVIew's AccessibilityContainer.

Now we use the PlatformVIew as the nativeAccessibility of the  FlutterPlatFormViewSemanticsContainer, we need to expilicitly set the container.

This needs to be cherry-picked since the commit caused the regression was cherry-picked in flutter@b8332e3

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: Chris Yang

ci/licenses_golden/licenses_flutter

@@ -2633,6 +2633,7 @@ ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextI
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelay.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelay.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelayTest.mm + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTouchInterceptingView_Test.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterUIPressProxy.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterUIPressProxy.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterUmbrellaImport.m + ../../../flutter/LICENSE
@@ -2654,6 +2655,14 @@ ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/KeyCodeMap_I
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/SemanticsObject.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/SemanticsObject.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/SemanticsObjectTest.mm + ../../../flutter/LICENSE
+<<<<<<< HEAD
+=======
+ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/SemanticsObjectTestMocks.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/SemanticsObjectTest_mrc.mm + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/UIViewController+FlutterScreenAndSceneIfLoaded.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/UIViewController+FlutterScreenAndSceneIfLoaded.mm + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/UIViewController_FlutterScreenAndSceneIfLoadedTest.mm + ../../../flutter/LICENSE
+>>>>>>> 250daadbca ([ios] Link PlatformView back to semantics tree (#46471))
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/VsyncWaiterIosTest.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/accessibility_bridge.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/accessibility_bridge.mm + ../../../flutter/LICENSE
@@ -5328,6 +5337,7 @@ FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInp
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelay.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelay.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelayTest.mm
+FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTouchInterceptingView_Test.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterUIPressProxy.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterUIPressProxy.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterUmbrellaImport.m
@@ -5349,6 +5359,8 @@ FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/KeyCodeMap_Int
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/SemanticsObject.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/SemanticsObject.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/SemanticsObjectTest.mm
+FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/SemanticsObjectTestMocks.h
+FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/SemanticsObjectTest_mrc.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/VsyncWaiterIosTest.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/accessibility_bridge.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/accessibility_bridge.mm

shell/platform/darwin/ios/BUILD.gn

@@ -225,8 +225,11 @@ source_set("ios_test_flutter_mrc") {
     "framework/Source/FlutterEngineTest_mrc.mm",
     "framework/Source/FlutterPlatformPluginTest.mm",
     "framework/Source/FlutterPlatformViewsTest.mm",
+    "framework/Source/FlutterTouchInterceptingView_Test.h",
     "framework/Source/FlutterViewControllerTest_mrc.mm",
     "framework/Source/FlutterViewTest.mm",
+    "framework/Source/SemanticsObjectTestMocks.h",
+    "framework/Source/SemanticsObjectTest_mrc.mm",
     "framework/Source/VsyncWaiterIosTest.mm",
     "framework/Source/accessibility_bridge_test.mm",
     "platform_message_handler_ios_test.mm",

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews.mm

@@ -407,10 +407,15 @@ static bool ClipRRectContainsPlatformViewBoundingRect(const SkRRect& clip_rrect,
 }
 
 UIView* FlutterPlatformViewsController::GetPlatformViewByID(int64_t view_id) {
+  return [GetFlutterTouchInterceptingViewByID(view_id) embeddedView];
+}
+
+FlutterTouchInterceptingView* FlutterPlatformViewsController::GetFlutterTouchInterceptingViewByID(
+    int64_t view_id) {
   if (views_.empty()) {
     return nil;
   }
-  return [touch_interceptors_[view_id].get() embeddedView];
+  return touch_interceptors_[view_id].get();
 }
 
 long FlutterPlatformViewsController::FindFirstResponderPlatformViewId() {
@@ -958,6 +963,10 @@ @implementation FlutterTouchInterceptingView {
   fml::scoped_nsobject<DelayingGestureRecognizer> _delayingRecognizer;
   FlutterPlatformViewGestureRecognizersBlockingPolicy _blockingPolicy;
   UIView* _embeddedView;
+  // The used as the accessiblityContainer.
+  // The `accessiblityContainer` is used in UIKit to determine the parent of this accessibility
+  // node.
+  NSObject* _flutterAccessibilityContainer;
 }
 - (instancetype)initWithEmbeddedView:(UIView*)embeddedView
              platformViewsController:
@@ -1036,6 +1045,14 @@ - (void)touchesCancelled:(NSSet<UITouch*>*)touches withEvent:(UIEvent*)event {
 - (void)touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event {
 }
 
+- (void)setFlutterAccessibilityContainer:(NSObject*)flutterAccessibilityContainer {
+  _flutterAccessibilityContainer = flutterAccessibilityContainer;
+}
+
+- (id)accessibilityContainer {
+  return _flutterAccessibilityContainer;
+}
+
 @end
 
 @implementation DelayingGestureRecognizer {

shell/platform/darwin/ios/framework/Source/FlutterPlatformViewsTest.mm

@@ -11,6 +11,7 @@
 #import "flutter/shell/platform/darwin/ios/framework/Headers/FlutterPlatformViews.h"
 #import "flutter/shell/platform/darwin/ios/framework/Headers/FlutterViewController.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h"
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterTouchInterceptingView_Test.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterViewController_Internal.h"
 #import "flutter/shell/platform/darwin/ios/platform_view_ios.h"
 
@@ -3098,4 +3099,12 @@ - (void)testOnlyPlatformViewsAreRemovedWhenReset {
   XCTAssertEqual(mockFlutterView.subviews.firstObject, someView);
 }
 
+- (void)testFlutterTouchInterceptingViewLinksToAccessibilityContainer {
+  FlutterTouchInterceptingView* touchInteceptorView =
+      [[[FlutterTouchInterceptingView alloc] init] autorelease];
+  NSObject* container = [[[NSObject alloc] init] autorelease];
+  [touchInteceptorView setFlutterAccessibilityContainer:container];
+  XCTAssertEqualObjects([touchInteceptorView accessibilityContainer], container);
+}
+
 @end

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h

@@ -13,6 +13,7 @@
 #import "flutter/shell/platform/darwin/common/framework/Headers/FlutterChannels.h"
 #import "flutter/shell/platform/darwin/ios/framework/Headers/FlutterPlatformViews.h"
 #import "flutter/shell/platform/darwin/ios/framework/Headers/FlutterPlugin.h"
+#import "flutter/shell/platform/darwin/ios/framework/Source/SemanticsObject.h"
 #import "flutter/shell/platform/darwin/ios/ios_context.h"
 #include "third_party/skia/include/core/SkPictureRecorder.h"
 
@@ -232,10 +233,17 @@ class FlutterPlatformViewsController {
   // Returns the `FlutterPlatformView`'s `view` object associated with the view_id.
   //
   // If the `FlutterPlatformViewsController` does not contain any `FlutterPlatformView` object or
-  // a `FlutterPlatformView` object asscociated with the view_id cannot be found, the method
+  // a `FlutterPlatformView` object associated with the view_id cannot be found, the method
   // returns nil.
   UIView* GetPlatformViewByID(int64_t view_id);
 
+  // Returns the `FlutterTouchInterceptingView` with the view_id.
+  //
+  // If the `FlutterPlatformViewsController` does not contain any `FlutterPlatformView` object or
+  // a `FlutterPlatformView` object associated with the view_id cannot be found, the method
+  // returns nil.
+  FlutterTouchInterceptingView* GetFlutterTouchInterceptingViewByID(int64_t view_id);
+
   PostPrerollResult PostPrerollAction(
       const fml::RefPtr<fml::RasterThreadMerger>& raster_thread_merger);
 
@@ -426,6 +434,9 @@ class FlutterPlatformViewsController {
 
 // Get embedded view
 - (UIView*)embeddedView;
+
+// Sets flutterAccessibilityContainer as this view's accessibilityContainer.
+- (void)setFlutterAccessibilityContainer:(NSObject*)flutterAccessibilityContainer;
 @end
 
 @interface UIView (FirstResponder)

shell/platform/darwin/ios/framework/Source/FlutterTouchInterceptingView_Test.h

@@ -0,0 +1,14 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h"
+
+#ifndef SHELL_PLATFORM_IOS_FRAMEWORK_SOURCE_FLUTTER_TOUCH_INTERCEPTING_VIEW_TEST_H_
+#define SHELL_PLATFORM_IOS_FRAMEWORK_SOURCE_FLUTTER_TOUCH_INTERCEPTING_VIEW_TEST_H_
+
+@interface FlutterTouchInterceptingView (Tests)
+- (id)accessibilityContainer;
+@end
+
+#endif  // SHELL_PLATFORM_IOS_FRAMEWORK_SOURCE_FLUTTER_TOUCH_INTERCEPTING_VIEW_TESTS_H_

shell/platform/darwin/ios/framework/Source/SemanticsObject.h

@@ -18,6 +18,7 @@ constexpr float kScrollExtentMaxForInf = 1000;
 
 @class FlutterCustomAccessibilityAction;
 @class FlutterPlatformViewSemanticsContainer;
+@class FlutterTouchInterceptingView;
 
 /**
  * A node in the iOS semantics tree. This object is a wrapper over a native accessibiliy
@@ -171,7 +172,8 @@ constexpr float kScrollExtentMaxForInf = 1000;
 
 - (instancetype)initWithBridge:(fml::WeakPtr<flutter::AccessibilityBridgeIos>)bridge
                            uid:(int32_t)uid
-                  platformView:(UIView*)platformView NS_DESIGNATED_INITIALIZER;
+                  platformView:(FlutterTouchInterceptingView*)platformView
+    NS_DESIGNATED_INITIALIZER;
 
 @end
 

shell/platform/darwin/ios/framework/Source/SemanticsObject.mm

@@ -157,9 +157,7 @@ @interface FlutterScrollableSemanticsObject ()
 @property(nonatomic, retain) FlutterSemanticsScrollView* scrollView;
 @end
 
-@implementation FlutterScrollableSemanticsObject {
-  fml::scoped_nsobject<SemanticsObjectContainer> _container;
-}
+@implementation FlutterScrollableSemanticsObject
 
 - (instancetype)initWithBridge:(fml::WeakPtr<flutter::AccessibilityBridgeIos>)bridge
                            uid:(int32_t)uid {
@@ -865,9 +863,10 @@ @implementation FlutterPlatformViewSemanticsContainer
 
 - (instancetype)initWithBridge:(fml::WeakPtr<flutter::AccessibilityBridgeIos>)bridge
                            uid:(int32_t)uid
-                  platformView:(nonnull UIView*)platformView {
+                  platformView:(nonnull FlutterTouchInterceptingView*)platformView {
   if (self = [super initWithBridge:bridge uid:uid]) {
     _platformView = [platformView retain];
+    [platformView setFlutterAccessibilityContainer:self];
   }
   return self;
 }
@@ -882,12 +881,6 @@ - (id)nativeAccessibility {
   return _platformView;
 }
 
-#pragma mark - UIAccessibilityContainer overrides
-
-- (NSArray*)accessibilityElements {
-  return @[ _platformView ];
-}
-
 @end
 
 @implementation SemanticsObjectContainer {