Fix WKWebView Accessibility (#1955)

* Return nil instead of empty array when no accessibility elements are found. Fixes #1954.

* Use nullability annotations to fix static analyzer warnings.

* Add UI test target.

* Add UI test to make sure web view stays accessible.

* Revert "Add UI test to make sure web view stays accessible."

This reverts commit 00253f4.

* Revert "Add UI test target."

This reverts commit 288b5e0.

* Add unit test to make sure accessibility elements are correct when a WKWebView is wrapped in an ASDisplayNode.

AsyncDisplayKit.xcodeproj/project.pbxproj

@@ -453,6 +453,7 @@
 		CCEDDDD9200C518800FFCD0A /* ASConfigurationTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = CCEDDDD8200C518800FFCD0A /* ASConfigurationTests.mm */; };
 		CCF18FF41D2575E300DF5895 /* NSIndexSet+ASHelpers.h in Headers */ = {isa = PBXBuildFile; fileRef = CC4981BA1D1C7F65004E13CC /* NSIndexSet+ASHelpers.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		CCF1FF5E20C4785000AAD8FC /* ASLocking.h in Headers */ = {isa = PBXBuildFile; fileRef = CCF1FF5D20C4785000AAD8FC /* ASLocking.h */; settings = {ATTRIBUTES = (Public, ); }; };
+		CD0F261C25CA03BB00735A79 /* WebKit.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = CD0F261B25CA03BB00735A79 /* WebKit.framework */; };
 		D933F041224AD17F00FF495E /* ASTransactionTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = D933F040224AD17F00FF495E /* ASTransactionTests.mm */; };
 		D99F9158232990F30083CC8E /* ASImageNodeTests.m in Sources */ = {isa = PBXBuildFile; fileRef = D99F9157232990F30083CC8E /* ASImageNodeTests.m */; };
 		DB55C2671C641AE4004EDCF5 /* ASContextTransitioning.h in Headers */ = {isa = PBXBuildFile; fileRef = DB55C2651C641AE4004EDCF5 /* ASContextTransitioning.h */; settings = {ATTRIBUTES = (Public, ); }; };
@@ -994,6 +995,7 @@
 		CCEDDDD0200C488000FFCD0A /* ASConfiguration.mm */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.objcpp; path = ASConfiguration.mm; sourceTree = "<group>"; };
 		CCEDDDD8200C518800FFCD0A /* ASConfigurationTests.mm */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.objcpp; path = ASConfigurationTests.mm; sourceTree = "<group>"; };
 		CCF1FF5D20C4785000AAD8FC /* ASLocking.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = ASLocking.h; sourceTree = "<group>"; };
+		CD0F261B25CA03BB00735A79 /* WebKit.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = WebKit.framework; path = Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/System/Library/Frameworks/WebKit.framework; sourceTree = DEVELOPER_DIR; };
 		D3779BCFF841AD3EB56537ED /* Pods-AsyncDisplayKitTests.release.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-AsyncDisplayKitTests.release.xcconfig"; path = "Pods/Target Support Files/Pods-AsyncDisplayKitTests/Pods-AsyncDisplayKitTests.release.xcconfig"; sourceTree = "<group>"; };
 		D785F6601A74327E00291744 /* ASScrollNode.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ASScrollNode.h; sourceTree = "<group>"; };
 		D785F6611A74327E00291744 /* ASScrollNode.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = ASScrollNode.mm; sourceTree = "<group>"; };
@@ -1075,6 +1077,7 @@
 			isa = PBXFrameworksBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				CD0F261C25CA03BB00735A79 /* WebKit.framework in Frameworks */,
 				CC36C19F218B894800232F23 /* CoreMedia.framework in Frameworks */,
 				CC36C19E218B894400232F23 /* AVFoundation.framework in Frameworks */,
 				CC90E1F41E383C0400FED591 /* AsyncDisplayKit.framework in Frameworks */,
@@ -1155,6 +1158,7 @@
 		058D09AE195D04C000B7D73C /* Frameworks */ = {
 			isa = PBXGroup;
 			children = (
+				CD0F261B25CA03BB00735A79 /* WebKit.framework */,
 				CC36C19B218B847400232F23 /* CoreMedia.framework */,
 				CC36C199218B846F00232F23 /* CoreLocation.framework */,
 				CC36C197218B846300232F23 /* QuartzCore.framework */,

Source/Details/_ASDisplayViewAccessiblity.mm

@@ -315,14 +315,14 @@ @implementation _ASDisplayView (UIAccessibilityContainer)
 
 #pragma mark - UIAccessibility
 
-- (void)setAccessibilityElements:(NSArray *)accessibilityElements
+- (void)setAccessibilityElements:(nullable NSArray *)accessibilityElements
 {
   // this is a no-op. You should not be setting accessibilityElements directly on _ASDisplayView.
   // if you wish to set accessibilityElements, do so in your node. UIKit will call _ASDisplayView's
   // accessibilityElements which will in turn ask its node for its elements.
 }
 
-- (NSArray *)accessibilityElements
+- (nullable NSArray *)accessibilityElements
 {
   ASDisplayNodeAssertMainThread();
 
@@ -343,7 +343,7 @@ - (NSArray *)accessibilityElements
 
 @implementation ASDisplayNode (AccessibilityInternal)
 
-- (NSArray *)accessibilityElements
+- (nullable NSArray *)accessibilityElements
 {
   // NSObject implements the informal accessibility protocol. This means that all ASDisplayNodes already have an accessibilityElements
   // property. If an ASDisplayNode subclass has explicitly set the property, let's use that instead of traversing the node tree to try
@@ -355,12 +355,14 @@ - (NSArray *)accessibilityElements
 
   if (!self.isNodeLoaded) {
     ASDisplayNodeFailAssert(@"Cannot access accessibilityElements since node is not loaded");
-    return @[];
+    return nil;
   }
   NSMutableArray *accessibilityElements = [[NSMutableArray alloc] init];
   CollectAccessibilityElements(self, accessibilityElements);
   SortAccessibilityElements(accessibilityElements);
-  return accessibilityElements;
+  // If we did not find any accessibility elements, return nil instead of empty array. This allows a WKWebView within the node
+  // to participate in accessibility.
+  return accessibilityElements.count == 0 ? nil : accessibilityElements;
 }
 
 @end

Source/Private/ASDisplayNode+FrameworkPrivate.h

@@ -321,7 +321,7 @@ NS_INLINE UIAccessibilityTraits ASInteractiveAccessibilityTraitsMask() {
 }
 
 @interface ASDisplayNode (AccessibilityInternal)
-- (NSArray *)accessibilityElements;
+- (nullable NSArray *)accessibilityElements;
 @end;
 
 @interface UIView (ASDisplayNodeInternal)

Tests/ASDisplayViewAccessibilityTests.mm

@@ -24,6 +24,7 @@
 #import <AsyncDisplayKit/ASDKViewController.h>
 #import <OCMock/OCMock.h>
 #import "ASDisplayNodeTestsHelper.h"
+#import <WebKit/WebKit.h>
 
 extern void SortAccessibilityElements(NSMutableArray *elements);
 
@@ -187,6 +188,34 @@ - (void)testAccessibilityNonLayerbackedNodesOperationInNonContainer
   XCTAssertTrue([[updatedElements2.lastObject accessibilityLabel] isEqualToString:@"world"]);
 }
 
+- (void)testAccessibilityElementsAreNilForWrappedWKWebView {
+  ASDisplayNode *container = [[ASDisplayNode alloc] init];
+  UIWindow *window = [[UIWindow alloc] initWithFrame:CGRectMake(0, 0, 320, 560)];
+  [window addSubnode:container];
+  [window makeKeyAndVisible];
+
+  container.frame = CGRectMake(50, 50, 200, 600);  
+  WKWebView *webView = [[WKWebView alloc] initWithFrame:CGRectMake(0, 0, 200, 400)];
+  [container.view addSubview:webView];
+
+  NSString *htmlString =
+  @"<html>"
+  @"    <head>"
+  @"      <meta name='viewport' content='width=device-width' />"
+  @"    </head>"
+  @"    <body>"
+  @"      <h1>Texture is Awesome!</h1>"
+  @"      <p>Especially when web views inside nodes are accessible.</p>"
+  @"    </body>"
+  @"  </html>";
+  [webView loadHTMLString:htmlString baseURL:nil];
+
+  // Accessibility elements should be nil in this case, because
+  // WKWebView handles accessibility out of process.
+  NSArray *accessibilityElements = container.accessibilityElements;
+  XCTAssertNil(accessibilityElements);
+}
+
 #pragma mark -
 #pragma mark UIAccessibilityAction Forwarding