Update target and declaring types for properties of the root object with x:Class, fixes #2520

src/Avalonia.Build.Tasks/XamlCompilerTaskExecutor.cs

@@ -150,7 +150,8 @@ namespace Avalonia.Build.Tasks
                             classType = typeSystem.TargetAssembly.FindType(tn.Text);
                             if (classType == null)
                                 throw new XamlIlParseException($"Unable to find type `{tn.Text}`", classDirective);
-                            initialRoot.Type = new XamlIlAstClrTypeReference(classDirective, classType, false);
+                            compiler.OverrideRootType(parsed,
+                                new XamlIlAstClrTypeReference(classDirective, classType, false));
                             initialRoot.Children.Remove(classDirective);
                         }
                         

src/Markup/Avalonia.Markup.Xaml/XamlIl/CompilerExtensions/AvaloniaXamlIlCompiler.cs

@@ -112,13 +112,31 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 rootType = new XamlIlAstClrTypeReference(rootObject, overrideRootType, false);
             }
 
-            rootObject.Type = rootType;
+            OverrideRootType(parsed, rootType);
 
             Transform(parsed);
             Compile(parsed, tb, _contextType, PopulateName, BuildName, "__AvaloniaXamlIlNsInfo", baseUri, fileSource);
             
         }
-        
-        
+
+        public void OverrideRootType(XamlIlDocument doc, IXamlIlAstTypeReference newType)
+        {
+            var root = (XamlIlAstObjectNode)doc.Root;
+            var oldType = root.Type;
+            if (oldType.Equals(newType))
+                return;
+
+            root.Type = newType;
+            foreach (var child in root.Children.OfType<XamlIlAstXamlPropertyValueNode>())
+            {
+                if (child.Property is XamlIlAstNamePropertyReference prop)
+                {
+                    if (prop.DeclaringType.Equals(oldType))
+                        prop.DeclaringType = newType;
+                    if (prop.TargetType.Equals(oldType))
+                        prop.TargetType = newType;
+                }
+            }
+        }
     }
 }

src/Markup/Avalonia.Markup.Xaml/XamlIl/xamlil.github

@@ -1 +1 @@
-Subproject commit 50920ece52647b19760f65b417940da125101365
+Subproject commit 1e3ffc315401f0b2eb96a0e79b25c2fc19a80d78

tests/Avalonia.Markup.Xaml.UnitTests/Avalonia.Markup.Xaml.UnitTests.csproj

@@ -32,7 +32,8 @@
     <EmbeddedResource Include="Xaml\Style2.xaml">
       <SubType>Designer</SubType>
     </EmbeddedResource>
-    <AvaloniaResource Include="Xaml\XamlIlClassWithPrecompiledXaml.xaml"/>
+    <AvaloniaResource Include="Xaml\XamlIlClassWithPrecompiledXaml.xaml" />
+    <AvaloniaResource Include="Xaml\XamlIlClassWithCustomProperty.xaml" />
   </ItemGroup>
   <Import Project="..\..\build\BuildTargets.targets" />
 </Project>

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/XamlIlClassWithCustomProperty.xaml

@@ -0,0 +1,6 @@
+<UserControl xmlns='https://github.com/avaloniaui'
+             xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
+             x:Class='Avalonia.Markup.Xaml.UnitTests.XamlIlClassWithCustomProperty'
+             Test="123">
+
+</UserControl>

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

@@ -141,6 +141,22 @@ namespace Avalonia.Markup.Xaml.UnitTests
                 Assert.Equal(20, w.Args.ClickCount);
             }
         }
+        
+        [Fact]
+        public void Custom_Properties_Should_Work_With_XClass()
+        {
+            var precompiled = new XamlIlClassWithCustomProperty();
+            Assert.Equal("123", precompiled.Test);
+            var loaded = (XamlIlClassWithCustomProperty)AvaloniaXamlLoader.Parse(@"
+<UserControl xmlns='https://github.com/avaloniaui'
+             xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
+             x:Class='Avalonia.Markup.Xaml.UnitTests.XamlIlClassWithCustomProperty'
+             Test='321'>
+
+</UserControl>");
+            Assert.Equal("321", loaded.Test);
+            
+        }
     }
     
     public class XamlIlBugTestsEventHandlerCodeBehind : Window
@@ -172,6 +188,16 @@ namespace Avalonia.Markup.Xaml.UnitTests
         }
     }
 
+    public class XamlIlClassWithCustomProperty : UserControl
+    {
+        public string Test { get; set; }
+
+        public XamlIlClassWithCustomProperty()
+        {
+            AvaloniaXamlLoader.Load(this);
+        }
+    }
+
     public class XamlIlBugTestsBrushToColorConverter : IMultiValueConverter
     {
         public object Convert(IList<object> values, Type targetType, object parameter, CultureInfo culture)