Fix DataType set on Binding extension + add tests

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

@@ -105,6 +105,11 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 {
                     startType = TypeReferenceResolver.ResolveType(context, text.Text, isMarkupExtension: false, text, strict: true).Type;
                 }
+                
+                if (dataTypeProperty?.Values.Count is 1 && dataTypeProperty.Values[0] is XamlTypeExtensionNode typeNode)
+                {
+                    startType = typeNode.Value.GetClrType();
+                }
 
                 Func<IXamlType> startTypeResolver = startType is not null ? () => startType : () =>
                 {

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/CompiledBindingPath.cs

@@ -74,6 +74,8 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
             return pathRoot ?? new EmptyExpressionNode();
         }
 
+        internal IEnumerable<ICompiledBindingPathElement> Elements => _elements;
+        
         internal SourceMode SourceMode => _elements.Count > 0 && _elements[0] is IControlSourceBindingPathElement ? SourceMode.Control : SourceMode.Data;
 
         internal object RawSource { get; }

tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/CompiledBindingExtensionTests.cs

@@ -9,10 +9,13 @@ using System.Threading.Tasks;
 using Avalonia.Controls;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Templates;
+using Avalonia.Data;
 using Avalonia.Data.Converters;
 using Avalonia.Data.Core;
 using Avalonia.Input;
 using Avalonia.Markup.Data;
+using Avalonia.Markup.Xaml.MarkupExtensions;
+using Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings;
 using Avalonia.Markup.Xaml.Templates;
 using Avalonia.Media;
 using Avalonia.Metadata;
@@ -135,6 +138,56 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
                 Assert.Equal(dataContext.ListProperty, textBlock.Items);
             }
         }
+        
+        [Fact]
+        public void ResolvesDataTypeFromBindingProperty()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
+        xmlns:local='clr-namespace:Avalonia.Markup.Xaml.UnitTests.MarkupExtensions;assembly=Avalonia.Markup.Xaml.UnitTests'>
+    <TextBlock Text='{CompiledBinding StringProperty, DataType=local:TestDataContext}' Name='textBlock' />
+</Window>";
+                var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var textBlock = window.FindControl<TextBlock>("textBlock");
+
+                var dataContext = new TestDataContext
+                {
+                    StringProperty = "foobar"
+                };
+
+                window.DataContext = dataContext;
+
+                Assert.Equal(dataContext.StringProperty, textBlock.Text);
+            }
+        }
+        
+        [Fact]
+        public void ResolvesDataTypeFromBindingProperty_TypeExtension()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
+        xmlns:local='clr-namespace:Avalonia.Markup.Xaml.UnitTests.MarkupExtensions;assembly=Avalonia.Markup.Xaml.UnitTests'>
+    <TextBlock Text='{CompiledBinding StringProperty, DataType={x:Type local:TestDataContext}}' Name='textBlock' />
+</Window>";
+                var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var textBlock = window.FindControl<TextBlock>("textBlock");
+
+                var dataContext = new TestDataContext
+                {
+                    StringProperty = "foobar"
+                };
+
+                window.DataContext = dataContext;
+
+                Assert.Equal(dataContext.StringProperty, textBlock.Text);
+            }
+        }
 
         [Fact]
         public void ResolvesStreamTaskBindingCorrectly()
@@ -1479,6 +1532,43 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
             }
         }
 
+        [Fact]
+        public void ResolvesDataTypeForAssignBinding()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var xaml = @"
+<local:AssignBindingControl xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
+        xmlns:local='clr-namespace:Avalonia.Markup.Xaml.UnitTests.MarkupExtensions;assembly=Avalonia.Markup.Xaml.UnitTests'
+        x:DataType='local:TestDataContext'
+        X='{CompiledBinding StringProperty}' />";
+                var control = (AssignBindingControl)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var compiledPath = ((CompiledBindingExtension)control.X).Path;
+
+                var node = Assert.IsType<PropertyElement>(Assert.Single(compiledPath.Elements));
+                Assert.Equal(typeof(string), node.Property.PropertyType);
+            }
+        }
+        
+        [Fact]
+        public void ResolvesDataTypeForAssignBinding_FromBindingProperty()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var xaml = @"
+<local:AssignBindingControl xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
+        xmlns:local='clr-namespace:Avalonia.Markup.Xaml.UnitTests.MarkupExtensions;assembly=Avalonia.Markup.Xaml.UnitTests'
+        X='{CompiledBinding StringProperty, DataType=local:TestDataContext}' />";
+                var control = (AssignBindingControl)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var compiledPath = ((CompiledBindingExtension)control.X).Path;
+
+                var node = Assert.IsType<PropertyElement>(Assert.Single(compiledPath.Elements));
+                Assert.Equal(typeof(string), node.Property.PropertyType);
+            }
+        }
+        
         void Throws(string type, Action cb)
         {
             try
@@ -1656,4 +1746,9 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
     }
     
     public class CustomDataTemplateInherit : CustomDataTemplate { }
+
+    public class AssignBindingControl : Control
+    {
+        [AssignBinding] public IBinding X { get; set; }
+    }
 }