WIP

samples/ControlCatalog/App.xaml

@@ -1,6 +1,7 @@
 <Application xmlns="https://github.com/avaloniaui"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-             x:Class="ControlCatalog.App">
+             x:Class="ControlCatalog.App"
+             DataContext="1">
   <Application.Styles>
     <StyleInclude Source="avares://Avalonia.Themes.Default/DefaultTheme.xaml"/>
     <StyleInclude Source="avares://Avalonia.Themes.Default/Accents/BaseLight.xaml"/>

samples/ControlCatalog/CustomControl.cs

@@ -0,0 +1,21 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Avalonia;
+using Avalonia.Controls.Primitives;
+using Avalonia.Media;
+
+namespace ControlCatalog
+{
+    public class CustomControl : TemplatedControl
+    {
+        public static readonly StyledProperty<IBrush> StrokeProperty =
+            AvaloniaProperty.Register<CustomControl, IBrush>(nameof(Stroke));
+
+        public IBrush Stroke
+        {
+            get => GetValue(StrokeProperty);
+            set => SetValue(StrokeProperty, value);
+        }
+    }
+}

samples/ControlCatalog/CustomControl.xaml

@@ -0,0 +1,12 @@
+<ControlTheme xmlns="https://github.com/avaloniaui"
+              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+              xmlns:local="clr-namespace:ControlCatalog"
+              x:DefaultControlThemeFor="{x:Type local:CustomControl}">
+  <Setter Property="Template">
+    <ControlTemplate TargetType="{x:Type local:CustomControl}">
+      <Border Background="Yellow" BorderBrush="{TemplateBinding Stroke}" BorderThickness="1">
+        <TextBlock>Custom Control</TextBlock>
+      </Border>
+    </ControlTemplate>
+  </Setter>
+</ControlTheme>

samples/ControlCatalog/MainWindow.xaml

@@ -71,6 +71,6 @@
         <MenuItem Header="About" Command="{Binding AboutCommand}" />
       </MenuItem>
     </Menu>
-    <local:MainView />
+    <local:CustomControl />
   </DockPanel>
 </Window>

src/Avalonia.Build.Tasks/Properties/launchSettings.json

@@ -0,0 +1,9 @@
+{
+  "profiles": {
+    "Avalonia.Build.Tasks": {
+      "commandName": "Executable",
+      "executablePath": "dotnet",
+      "commandLineArgs": "D:\\projects\\AvaloniaUI\\Avalonia\\src\\Avalonia.Build.Tasks\\bin\\Debug\\netcoreapp2.0\\Avalonia.Build.Tasks.dll D:\\projects\\AvaloniaUI\\Avalonia\\samples\\ControlCatalog\\obj\\Debug\\netstandard2.0\\Avalonia\\"
+    }
+  }
+}

src/Avalonia.Build.Tasks/XamlCompilerTaskExecutor.cs

@@ -156,8 +156,10 @@ namespace Avalonia.Build.Tasks
                                 new XamlIlAstClrTypeReference(classDirective, classType, false));
                             initialRoot.Children.Remove(classDirective);
                         }
-                        
-                        
+
+                        var controlThemeForDirective = initialRoot.Children.OfType<XamlIlAstXmlDirective>()
+                            .FirstOrDefault(d => d.Namespace == XamlNamespaces.Xaml2006 && d.Name == "DefaultControlThemeFor");
+
                         compiler.Transform(parsed);
                         var populateName = classType == null ? "Populate:" + res.Name : "!XamlIlPopulate";
                         var buildName = classType == null ? "Build:" + res.Name : null; 
@@ -165,7 +167,6 @@ namespace Avalonia.Build.Tasks
                         var classTypeDefinition =
                             classType == null ? null : typeSystem.GetTypeReference(classType).Resolve();
 
-
                         var populateBuilder = classTypeDefinition == null ?
                             builder :
                             typeSystem.CreateTypeBuilder(classTypeDefinition);
@@ -286,6 +287,24 @@ namespace Avalonia.Build.Tasks
 
                         }
 
+                        if (controlThemeForDirective != null)
+                        {
+                            var controlType = ((XamlIlTypeExtensionNode)controlThemeForDirective.Values[0]).Value.GetClrType();
+
+                            if (controlType.Methods.Any(x => x.Name == "GetDefaultControlTheme" && x.Parameters.Count == 0))
+                            {
+                                throw new XamlIlParseException($"Default control theme provided for '{controlType.FullName}' " +
+                                    "but the class already overrides GetDefaultControlTheme.", classDirective);
+                            }
+
+                            var controlTypeDefinition = typeSystem.GetTypeReference(controlType).Resolve();
+                            var themeBuilder = typeSystem.CreateTypeBuilder(controlTypeDefinition);
+                            var method = themeBuilder.DefineMethod(typeSystem.FindType("Avalonia.Styling.IStyle"),
+                                new IXamlIlType[0], "GetDefaultControlTheme", false, false, false,
+                                typeSystem.FindType("Avalonia.Controls.Primitives.TemplatedControl")
+                                .FindMethod(x => x.Name == "GetDefaultControlTheme" && x.Parameters.Count == 0));
+                        }
+
                         if (buildName != null || classTypeDefinition != null)
                         {
                             var compiledBuildMethod = buildName == null ?

src/Avalonia.Controls/ControlTheme.cs

@@ -18,6 +18,11 @@ namespace Avalonia.Controls
         /// </summary>
         public Styles Styles => _styles ??= new Styles(Owner);
 
+        /// <summary>
+        /// Gets or sets the control type that the theme applies to.
+        /// </summary>
+        public Type? TargetType { get; set; }
+
         protected override IReadOnlyList<IStyle> GetChildrenCore()
         {
             return (IReadOnlyList<IStyle>?)_styles ?? Array.Empty<IStyle>();

src/Markup/Avalonia.Markup.Xaml/Avalonia.Markup.Xaml.csproj

@@ -39,6 +39,7 @@
         <Compile Include="XamlIl\CompilerExtensions\Transformers\AvaloniaBindingExtensionHackTransformer.cs" />
         <Compile Include="XamlIl\CompilerExtensions\Transformers\AvaloniaXamlIlAvaloniaPropertyResolver.cs" />
         <Compile Include="XamlIl\CompilerExtensions\Transformers\AvaloniaXamlIlConstructorServiceProviderTransformer.cs" />
+        <Compile Include="XamlIl\CompilerExtensions\Transformers\AvaloniaXamlIlControlThemeMetadataTransformer.cs" />
         <Compile Include="XamlIl\CompilerExtensions\Transformers\AvaloniaXamlIlControlTemplateTargetTypeMetadataTransformer.cs" />
         <Compile Include="XamlIl\CompilerExtensions\Transformers\AvaloniaXamlIlDesignPropertiesTransformer.cs" />
         <Compile Include="XamlIl\CompilerExtensions\Transformers\AvaloniaXamlIlMetadataRemover.cs" />

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

@@ -45,6 +45,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             InsertBefore<XamlIlContentConvertTransformer>(
                 new AvaloniaXamlIlSelectorTransformer(),
                 new AvaloniaXamlIlSetterTransformer(),
+                new AvaloniaXamlIlControlThemeMetadataTransformer(),
                 new AvaloniaXamlIlControlTemplateTargetTypeMetadataTransformer(),
                 new AvaloniaXamlIlConstructorServiceProviderTransformer(),
                 new AvaloniaXamlIlTransitionsTypeMetadataTransformer()

src/Markup/Avalonia.Markup.Xaml/XamlIl/CompilerExtensions/Transformers/AvaloniaXamlIlControlThemeMetadataTransformer.cs

@@ -0,0 +1,36 @@
+using System.Linq;
+using XamlIl;
+using XamlIl.Ast;
+using XamlIl.Transform;
+using XamlIl.TypeSystem;
+
+namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
+{
+    class AvaloniaXamlIlControlThemeMetadataTransformer : IXamlIlAstTransformer
+    {
+        public IXamlIlAstNode Transform(XamlIlAstTransformationContext context, IXamlIlAstNode node)
+        {
+            if (!(node is XamlIlAstObjectNode on
+                  && on.Type.GetClrType().FullName == "Avalonia.Controls.ControlTheme"))
+                return node;
+
+            if (context.ParentNodes().FirstOrDefault() is AvaloniaXamlIlTargetTypeMetadataNode)
+                // Deja vu. I've just been in this place before
+                return node;
+
+            var themeFor = on.Children.OfType<XamlIlAstXmlDirective>().FirstOrDefault(ch =>
+                                              ch.Name == "DefaultControlThemeFor");
+
+            if (themeFor?.Values.FirstOrDefault() is XamlIlTypeExtensionNode tn)
+            {
+                on.Children.Remove(themeFor);
+                return new AvaloniaXamlIlTargetTypeMetadataNode(on, tn.Value,
+                    AvaloniaXamlIlTargetTypeMetadataNode.ScopeTypes.Style);
+            }
+            else
+            {
+                throw new XamlIlParseException("ControlTheme does not have a x:DefaultControlThemeFor attribute", node);
+            }
+        }
+    }
+}

src/Markup/Avalonia.Markup.Xaml/XamlIl/CompilerExtensions/Transformers/AvaloniaXamlIlSetterTransformer.cs

@@ -17,23 +17,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                   && on.Type.GetClrType().FullName == "Avalonia.Styling.Setter"))
                 return node;
 
-            var parent = context.ParentNodes().OfType<XamlIlAstObjectNode>()
-                .FirstOrDefault(p => p.Type.GetClrType().FullName == "Avalonia.Styling.Style");
-            
-            if (parent == null)
-                throw new XamlIlParseException(
-                    "Avalonia.Styling.Setter is only valid inside Avalonia.Styling.Style", node);
-            var selectorProperty = parent.Children.OfType<XamlIlAstXamlPropertyValueNode>()
-                .FirstOrDefault(p => p.Property.GetClrProperty().Name == "Selector");
-            if (selectorProperty == null)
-                throw new XamlIlParseException(
-                    "Can not find parent Style Selector", node);
-            var selector = selectorProperty.Values.FirstOrDefault() as XamlIlSelectorNode;
-            if (selector?.TargetType == null)
-                throw new XamlIlParseException(
-                    "Can not resolve parent Style Selector type", node);
-
-
+            var targetType = GetTargetType(context, on);
             var property = @on.Children.OfType<XamlIlAstXamlPropertyValueNode>()
                 .FirstOrDefault(x => x.Property.GetClrProperty().Name == "Property");
             if (property == null)
@@ -43,9 +27,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             if (propertyName == null)
                 throw new XamlIlParseException("Setter.Property must be a string", node);
 
-
             var avaloniaPropertyNode = XamlIlAvaloniaPropertyHelper.CreateNode(context, propertyName,
-                new XamlIlAstClrTypeReference(selector, selector.TargetType, false), property.Values[0]);
+                new XamlIlAstClrTypeReference(on, targetType, false), property.Values[0]);
             property.Values = new List<IXamlIlAstValueNode>
             {
                 avaloniaPropertyNode
@@ -69,6 +52,43 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             return node;
         }
 
+        IXamlIlType GetTargetType(XamlIlAstTransformationContext context, XamlIlAstObjectNode node)
+        {
+            var parent = context.ParentNodes().OfType<XamlIlAstObjectNode>()
+                .FirstOrDefault(p =>
+                    p.Type.GetClrType().FullName == "Avalonia.Styling.Style" ||
+                    p.Type.GetClrType().FullName == "Avalonia.Controls.ControlTheme");
+
+            if (parent == null)
+                throw new XamlIlParseException(
+                    "Avalonia.Styling.Setter is only valid inside Avalonia.Styling.Style or Avalonia.Controls.ControlTheme", node);
+
+            if (parent.Type.GetClrType().FullName == "Avalonia.Styling.Style")
+            {
+                var selectorProperty = parent.Children.OfType<XamlIlAstXamlPropertyValueNode>()
+                    .FirstOrDefault(p => p.Property.GetClrProperty().Name == "Selector");
+                if (selectorProperty == null)
+                    throw new XamlIlParseException(
+                        "Can not find parent Style Selector", node);
+                var selector = selectorProperty.Values.FirstOrDefault() as XamlIlSelectorNode;
+                if (selector?.TargetType == null)
+                    throw new XamlIlParseException(
+                        "Can not resolve parent Style Selector type", node);
+                return selector.TargetType;
+            }
+            else
+            {
+                var themeFor = parent.Children.OfType<XamlIlAstXmlDirective>()
+                    .FirstOrDefault(ch => ch.Name == "DefaultControlThemeFor");
+
+                if (themeFor?.Values.FirstOrDefault() is XamlIlTypeExtensionNode tn)
+                    return tn.Value.GetClrType();
+                else
+                    throw new XamlIlParseException(
+                        "ControlTheme must have a x:DefaultControlThemeFor directive.", node);
+            }
+        }
+
         class SetterValueProperty : XamlIlAstClrProperty
         {
             public SetterValueProperty(IXamlIlLineInfo line, IXamlIlType setterType, IXamlIlType targetType,

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

@@ -1,3 +1,4 @@
+using System.Linq;
 using XamlIl.Transform;
 using XamlIl.TypeSystem;
 
@@ -26,6 +27,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         public IXamlIlType INameScope { get; }
         public IXamlIlMethod INameScopeRegister { get; }
         public IXamlIlMethod INameScopeComplete { get; }
+        public IXamlIlType ControlTheme { get; }
+        public IXamlIlProperty ControlThemeTargetType { get; }
         
         public AvaloniaXamlIlWellKnownTypes(XamlIlAstTransformationContext ctx)
         {
@@ -61,6 +64,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             NameScope = ctx.Configuration.TypeSystem.GetType("Avalonia.Controls.NameScope");
             NameScopeSetNameScope = NameScope.GetMethod(new FindMethodMethodSignature("SetNameScope",
                 XamlIlTypes.Void, StyledElement, INameScope) {IsStatic = true});
+            ControlTheme = ctx.Configuration.TypeSystem.GetType("Avalonia.Controls.ControlTheme");
+            ControlThemeTargetType = ControlTheme.GetAllProperties().Single(x => x.Name == "TargetType");
 
             AvaloniaObjectSetValueMethod = AvaloniaObject.FindMethod("SetValue", XamlIlTypes.Void,
                 false, AvaloniaProperty, XamlIlTypes.Object, BindingPriority);