Fix a11y for popup windows.

- Don't show when creating a popup window with a11y enabled
- Raise focus changed notification on element that got focus instead of the window

native/Avalonia.Native/src/OSX/window.mm

@@ -520,7 +520,12 @@ public:
     
     virtual void FocusChanged(IAvnAutomationPeer* peer) override
     {
-        NSAccessibilityPostNotification(Window, NSAccessibilityFocusedUIElementChangedNotification);
+        auto element = GetAccessibilityElement(peer);
+        
+        if (element != nullptr)
+        {
+            NSAccessibilityPostNotification(element, NSAccessibilityFocusedUIElementChangedNotification);
+        }
     }
     
 protected:
@@ -2318,7 +2323,7 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
     return [super accessibilityFocusedUIElement];
 }
 
-- (IAvnAutomationPeer* _Nonnull) getAutomationPeer
+- (IAvnAutomationPeer*) getAutomationPeer
 {
     if (_automationPeer == nullptr)
         _automationPeer = _parent->BaseEvents->AutomationStarted(_parent);

src/Avalonia.Native/WindowImplBase.cs

@@ -63,6 +63,9 @@ namespace Avalonia.Native
         private GlPlatformSurface _glSurface;
         private NativeControlHostImpl _nativeControlHost;
         private IGlContext _glContext;
+        private IAutomationNode _automationNode;
+        private AvnAutomationPeer _automationPeer;
+        private Func<IAutomationNode, AutomationPeer> _automationStarted;
 
         internal WindowBaseImpl(IAvaloniaNativeFactory factory, AvaloniaNativePlatformOptions opts,
             AvaloniaNativePlatformOpenGlInterface glFeature)
@@ -209,7 +212,6 @@ namespace Avalonia.Native
                 return _parent.RawTextInputEvent(timeStamp, text).AsComBool();
             }
 
-
             void IAvnWindowBaseEvents.ScalingChanged(double scaling)
             {
                 _parent._savedScaling = scaling;
@@ -250,11 +252,7 @@ namespace Avalonia.Native
                 }
             }
 
-            public IAvnAutomationPeer AutomationStarted(IAvnAutomationNode node)
-            {
-                var factory = AutomationNodeFactory.GetInstance(_parent._factory);
-                return new AvnAutomationPeer(_parent.AutomationStarted(new AutomationNode(factory, node)));
-            }
+            public IAvnAutomationPeer AutomationStarted(IAvnAutomationNode node) => _parent.HandleAutomationStarted(node);
         }
        
         public void Activate()
@@ -477,6 +475,38 @@ namespace Avalonia.Native
         public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; } = new AcrylicPlatformCompensationLevels(1, 0, 0);
 
         public IPlatformHandle Handle { get; private set; }
-        public Func<IAutomationNode, AutomationPeer> AutomationStarted { get; set; }
+
+        public Func<IAutomationNode, AutomationPeer> AutomationStarted
+        {
+            get => _automationStarted;
+            set
+            {
+                _automationStarted = value;
+                
+                // We've already received an AutomationStarted event, but the Window/PopupRoot wasn't initialized.
+                // Now it is, so notify it and store the automation peer for the next time the OS invokes an a11y
+                // query.
+                if (value is object && _automationNode is object) 
+                    _automationPeer = new AvnAutomationPeer(_automationStarted.Invoke(_automationNode));
+            }
+        }
+
+        private AvnAutomationPeer HandleAutomationStarted(IAvnAutomationNode node)
+        {
+            if (_automationPeer is object)
+                return _automationPeer;
+            
+            var factory = AutomationNodeFactory.GetInstance(_factory);
+            _automationNode = new AutomationNode(factory, node);
+
+            // If automation is started during platform window creation we don't yet have a Window/PopupRoot
+            // control to notify. In this case we'll notify them when AutomationStarted gets set. We can safely
+            // return null here because the peer isn't actually needed at this point and will be re-queried the next
+            // time it's needed. 
+            if (AutomationStarted is null)
+                return null;
+                
+            return _automationPeer = new AvnAutomationPeer(AutomationStarted(_automationNode));
+        }
     }
 }