Do not resolve markup extensions when resolving selector types (#20903)

* Do not resolve markup extensions when resolving selector types

* Added commen

* Added unit test

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlSelectorTransformer.cs

@@ -209,8 +209,10 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 throw new XamlSelectorsTransformException("Unable to parse selector: " + e.Message, node, e);
             }
 
+            // Selectors should resolve control types only.
+            // isMarkupExtension = false to prevent resolving selector types to XExtension.
             var selector = Create(parsed, (p, n) 
-                => TypeReferenceResolver.ResolveType(context, $"{p}:{n}", true, node, true));
+                => TypeReferenceResolver.ResolveType(context, $"{p}:{n}", false, node, true));
             pn.Values[0] = selector;
 
             var templateType = GetLastTemplateTypeFromSelector(selector);

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/StyleTests.cs

@@ -788,5 +788,25 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
 
             Assert.Equal("Cannot add a Style without selector to a ControlTheme. Line 5, position 14.", exception.Message);
         }
+
+        [Fact]
+        public void Selector_Should_Not_Resolve_To_MarkupExtension_Type()
+        {
+            using var _ = UnitTestApplication.Start(TestServices.StyledWindow);
+
+            var style = (Style)AvaloniaRuntimeXamlLoader.Load(
+                $"""
+                <Style xmlns='https://github.com/avaloniaui'
+                        xmlns:u='using:Avalonia.Markup.Xaml.UnitTests.Xaml'
+                        Selector='u|TestSelectorControl'>
+                </Style>
+                """);
+
+            Assert.NotNull(style.Selector);
+
+            var targetType = style.Selector.TargetType;
+
+            Assert.NotEqual(typeof(TestSelectorControlExtension), targetType);
+        }
     }
 }

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/TestSelectorControl.cs

@@ -0,0 +1,5 @@
+namespace Avalonia.Markup.Xaml.UnitTests.Xaml;
+
+public class TestSelectorControl;
+
+public class TestSelectorControlExtension;