From 0179666a8980108dbd532b32c42c9d461f1cc9c4 Mon Sep 17 00:00:00 2001
From: Johan Appelgren <johan.appelgren@gmail.com>
Date: Wed, 6 Mar 2024 20:09:03 +0100
Subject: [PATCH] Fix parsing type cast of attached property. (#14838)

---
 .../Parsers/BindingExpressionGrammar.cs       |  4 +++-
 ...onObserverBuilderTests_AttachedProperty.cs | 21 +++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/Markup/Avalonia.Markup/Markup/Parsers/BindingExpressionGrammar.cs b/src/Markup/Avalonia.Markup/Markup/Parsers/BindingExpressionGrammar.cs
index 5a4a56b746..179ba009c0 100644
--- a/src/Markup/Avalonia.Markup/Markup/Parsers/BindingExpressionGrammar.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/BindingExpressionGrammar.cs
@@ -257,8 +257,10 @@ namespace Avalonia.Markup.Parsers
                 }
 
                 result = ParseBeforeMember(ref r, nodes);
+                if (result == State.AttachedProperty)
+                    result = ParseAttachedProperty(ref r, nodes);
 
-                if(r.Peek == '[')
+                if (r.Peek == '[')
                 {
                     result = ParseIndexer(ref r, nodes);
                 }
diff --git a/tests/Avalonia.Markup.UnitTests/Parsers/ExpressionObserverBuilderTests_AttachedProperty.cs b/tests/Avalonia.Markup.UnitTests/Parsers/ExpressionObserverBuilderTests_AttachedProperty.cs
index 4c9333c42b..cc2dc35f0b 100644
--- a/tests/Avalonia.Markup.UnitTests/Parsers/ExpressionObserverBuilderTests_AttachedProperty.cs
+++ b/tests/Avalonia.Markup.UnitTests/Parsers/ExpressionObserverBuilderTests_AttachedProperty.cs
@@ -65,6 +65,22 @@ namespace Avalonia.Markup.UnitTests.Parsers
             Assert.Null(((IAvaloniaObjectDebug)data).GetPropertyChangedSubscribers());
         }
 
+        [Fact]
+        public async Task Should_Get_Chained_Attached_Property_Value_With_TypeCast()
+        {
+            var expected = new Class1();
+
+            var data = new Class1();
+            data.SetValue(Owner.SomethingProperty, new Class1() { Next = expected });
+
+            var target = Build(data, "((Class1)(Owner.Something)).Next", typeResolver: (ns, name) => name == "Class1" ? typeof(Class1) : _typeResolver(ns, name));
+            var result = await target.Take(1);
+
+            Assert.Equal(expected, result);
+
+            Assert.Null(((IAvaloniaObjectDebug)data).GetPropertyChangedSubscribers());
+        }
+
         [Fact]
         public void Should_Track_Simple_Attached_Value()
         {
@@ -159,6 +175,11 @@ namespace Avalonia.Markup.UnitTests.Parsers
                     "Foo",
                     typeof(Owner),
                     defaultValue: "foo");
+
+            public static readonly AttachedProperty<AvaloniaObject> SomethingProperty =
+                AvaloniaProperty.RegisterAttached<Class1, AvaloniaObject>(
+                    "Something",
+                    typeof(Owner));
         }
 
         private class Class1 : AvaloniaObject