Fix style without selector not finding target type (#18026)

* Add failing style test without selector

* Fix XAML target type of style without selector

* Address review

* Throw for style without selector in ControlTheme

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

@@ -32,8 +32,26 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             var pn = on.Children.OfType<XamlAstXamlPropertyValueNode>()
                 .FirstOrDefault(p => p.Property.GetClrProperty().Name == "Selector");
 
+            // Missing selector, use the object's target type if available
             if (pn == null)
+            {
+                // We already went through this node
+                if (context.ParentNodes().FirstOrDefault() is AvaloniaXamlIlTargetTypeMetadataNode metadataNode
+                    && metadataNode.Value == on)
+                {
+                    return node;
+                }
+
+                if (FindStyleParentObject(on, context) is { } parentObjectNode)
+                {
+                    return new AvaloniaXamlIlTargetTypeMetadataNode(
+                        on,
+                        new XamlAstClrTypeReference(node, parentObjectNode.Type.GetClrType(), false),
+                        AvaloniaXamlIlTargetTypeMetadataNode.ScopeTypes.Style);
+                }
+
                 return node;
+            }
 
             if (pn.Values.Count != 1)
                 throw new XamlSelectorsTransformException("Selector property should have exactly one value",
@@ -195,6 +213,20 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             pn.Values[0] = selector;
 
             var templateType = GetLastTemplateTypeFromSelector(selector);
+
+            // Empty selector, use the object's target type if available
+            if (selector == initialNode)
+            {
+                if (FindStyleParentObject(on, context) is { } parentObjectNode)
+                {
+                    return new AvaloniaXamlIlTargetTypeMetadataNode(
+                        on,
+                        new XamlAstClrTypeReference(node, parentObjectNode.Type.GetClrType(), false),
+                        AvaloniaXamlIlTargetTypeMetadataNode.ScopeTypes.Style);
+                }
+
+                return node;
+            }
             
             var styleNode = new AvaloniaXamlIlTargetTypeMetadataNode(on,
                 new XamlAstClrTypeReference(selector, selector.TargetType!, false),
@@ -209,6 +241,29 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             };
         }
 
+        private static XamlAstObjectNode? FindStyleParentObject(XamlAstNode styleNode, AstTransformationContext context)
+        {
+            var avaloniaTypes = context.GetAvaloniaTypes();
+
+            var parentNode = context
+                .ParentNodes()
+                .OfType<XamlAstObjectNode>()
+                .FirstOrDefault(n => !avaloniaTypes.Styles.IsAssignableFrom(n.Type.GetClrType()));
+
+            if (parentNode is not null)
+            {
+                var parentType = parentNode.Type.GetClrType();
+
+                if (avaloniaTypes.StyledElement.IsAssignableFrom(parentType))
+                    return parentNode;
+
+                if (avaloniaTypes.ControlTheme.IsAssignableFrom(parentType))
+                    throw new XamlTransformException("Cannot add a Style without selector to a ControlTheme.", styleNode);
+            }
+
+            return null;
+        }
+
         private static IXamlType? GetLastTemplateTypeFromSelector(XamlIlSelectorNode? node)
         {
             while (node is not null)

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

@@ -126,6 +126,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         public IXamlType UriKind { get; }
         public IXamlConstructor UriConstructor { get; }
         public IXamlType Style { get; }
+        public IXamlType Styles { get; }
         public IXamlType ControlTheme { get; }
         public IXamlType WindowTransparencyLevel { get; }
         public IXamlType IReadOnlyListOfT { get; }
@@ -325,6 +326,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             UriKind = cfg.TypeSystem.GetType("System.UriKind");
             UriConstructor = Uri.GetConstructor(new List<IXamlType>() { cfg.WellKnownTypes.String, UriKind });
             Style = cfg.TypeSystem.GetType("Avalonia.Styling.Style");
+            Styles = cfg.TypeSystem.GetType("Avalonia.Styling.Styles");
             ControlTheme = cfg.TypeSystem.GetType("Avalonia.Styling.ControlTheme");
             ControlTemplate = cfg.TypeSystem.GetType("Avalonia.Markup.Xaml.Templates.ControlTemplate");
             IReadOnlyListOfT = cfg.TypeSystem.GetType("System.Collections.Generic.IReadOnlyList`1");

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

@@ -15,6 +15,7 @@ using Xunit;
 
 namespace Avalonia.Markup.Xaml.UnitTests.Xaml
 {
+    [InvariantCulture]
     public class StyleTests : XamlTestBase
     {
         [Fact]
@@ -713,9 +714,6 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
         [Fact]
         public void Fails_Use_Classes_In_Setter_When_Selector_Is_Complex()
         {
-            // XmlException contains culture specific position message
-            Thread.CurrentThread.CurrentUICulture = CultureInfo.InvariantCulture;
-            
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
                 var xaml = $"""
@@ -739,5 +737,53 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
                 Assert.Equal ("Cannot set Classes Binding property '(Classes.Banned)' because the style has an activator. Line 6, position 14.", exception.Message);
             }
         }
+
+        [Theory]
+        [InlineData("<Style>", "</Style>")]
+        [InlineData("<Style Selector=''>", "</Style>")]
+        [InlineData("<Styles><Style>", "</Style></Styles>")]
+        [InlineData("<Styles><Style Selector=''>", "</Style></Styles>")]
+        public void No_Selector_Should_Target_Parent_Type(string styleStart, string styleEnd)
+        {
+            using var app = UnitTestApplication.Start(TestServices.StyledWindow);
+
+            var window = (Window)AvaloniaRuntimeXamlLoader.Load(
+                $"""
+                <Window xmlns="https://github.com/avaloniaui">
+                    <Window.Styles>
+                        {styleStart}
+                            <Setter Property="Title" Value="title set via style!" />
+                        {styleEnd}
+                    </Window.Styles>
+                </Window>
+                """);
+
+            Assert.Equal("title set via style!", window.Title);
+        }
+
+
+        [Theory]
+        [InlineData("<Style>", "</Style>")]
+        [InlineData("<Style Selector=''>", "</Style>")]
+        public void No_Selector_Should_Fail_In_Control_Theme(string styleStart, string styleEnd)
+        {
+            using var app = UnitTestApplication.Start(TestServices.StyledWindow);
+
+            var exception = Assert.ThrowsAny<XmlException>(() => (Window)AvaloniaRuntimeXamlLoader.Load(
+                $$"""
+                  <Window xmlns="https://github.com/avaloniaui"
+                          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                     <Window.Resources>
+                          <ControlTheme x:Key="{x:Type Window}" TargetType="Window">
+                              {{styleStart}}
+                                  <Setter Property="Title" Value="title set via style!" />
+                              {{styleEnd}}
+                          </ControlTheme>
+                      </Window.Resources>
+                  </Window>
+                  """));
+
+            Assert.Equal("Cannot add a Style without selector to a ControlTheme. Line 5, position 14.", exception.Message);
+        }
     }
 }