Initial support for deferred resources in XAML compiler.

src/Avalonia.Base/Controls/ResourceDictionary.cs

@@ -192,6 +192,11 @@ namespace Avalonia.Controls
             return false;
         }
 
+        public IEnumerator<KeyValuePair<object, object?>> GetEnumerator()
+        {
+            return _inner?.GetEnumerator() ?? Enumerable.Empty<KeyValuePair<object, object?>>().GetEnumerator();
+        }
+
         void ICollection<KeyValuePair<object, object?>>.Add(KeyValuePair<object, object?> item)
         {
             Add(item.Key, item.Value);
@@ -218,12 +223,17 @@ namespace Avalonia.Controls
             return false;
         }
 
-        public IEnumerator<KeyValuePair<object, object?>> GetEnumerator()
+        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+
+        internal bool ContainsDeferredKey(object key)
         {
-            return _inner?.GetEnumerator() ?? Enumerable.Empty<KeyValuePair<object, object?>>().GetEnumerator();
-        }
+            if (_inner is not null && _inner.TryGetValue(key, out var result))
+            {
+                return result is DeferredItem;
+            }
 
-        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+            return false;
+        }
 
         void IResourceProvider.AddOwner(IResourceHost owner)
         {

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

@@ -59,6 +59,10 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             InsertAfter<TypeReferenceResolver>(
                 new XDataTypeTransformer());
 
+            InsertBefore<DeferredContentTransformer>(
+                new AvaloniaXamlIlDeferredResourceTransformer()
+            );
+
             // After everything else
             InsertBefore<NewObjectTransformer>(
                 new AddNameScopeRegistration(),

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

@@ -0,0 +1,80 @@
+using System.Collections.Generic;
+using System.Linq;
+using XamlX.Ast;
+using XamlX.Emit;
+using XamlX.IL;
+using XamlX.Transform;
+using XamlX.TypeSystem;
+
+namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
+{
+    internal class AvaloniaXamlIlDeferredResourceTransformer : IXamlAstTransformer
+    {
+        public IXamlAstNode Transform(AstTransformationContext context, IXamlAstNode node)
+        {
+            if (!(node is XamlPropertyAssignmentNode pa) || pa.Values.Count != 2)
+                return node;
+
+            var types = context.GetAvaloniaTypes();
+
+            if (pa.Property.DeclaringType == types.ResourceDictionary && pa.Property.Name == "Content")
+            {
+                pa.Values[1] = new XamlDeferredContentNode(pa.Values[1], types.XamlIlTypes.Object, context.Configuration);
+                pa.PossibleSetters = new List<IXamlPropertySetter>
+                {
+                    new XamlDirectCallPropertySetter(types.ResourceDictionaryDeferredAdd),
+                };
+            }
+            else if (pa.Property.Name == "Resources" && pa.Property.Getter.ReturnType.Equals(types.IResourceDictionary))
+            {
+                pa.Values[1] = new XamlDeferredContentNode(pa.Values[1], types.XamlIlTypes.Object, context.Configuration);
+                pa.PossibleSetters = new List<IXamlPropertySetter>
+                {
+                    new AdderSetter(pa.Property.Getter, types.ResourceDictionaryDeferredAdd),
+                };
+            }
+
+            return node;
+        }
+
+        class AdderSetter : IXamlPropertySetter, IXamlEmitablePropertySetter<IXamlILEmitter>
+        {
+            private readonly IXamlMethod _getter;
+            private readonly IXamlMethod _adder;
+
+            public AdderSetter(IXamlMethod getter, IXamlMethod adder)
+            {
+                _getter = getter;
+                _adder = adder;
+                TargetType = getter.DeclaringType;
+                Parameters = adder.ParametersWithThis().Skip(1).ToList();
+            }
+
+            public IXamlType TargetType { get; }
+
+            public PropertySetterBinderParameters BinderParameters { get; } = new PropertySetterBinderParameters
+            {
+                AllowMultiple = true
+            };
+
+            public IReadOnlyList<IXamlType> Parameters { get; }
+            public void Emit(IXamlILEmitter emitter)
+            {
+                var locals = new Stack<XamlLocalsPool.PooledLocal>();
+                // Save all "setter" parameters
+                for (var c = Parameters.Count - 1; c >= 0; c--)
+                {
+                    var loc = emitter.LocalsPool.GetLocal(Parameters[c]);
+                    locals.Push(loc);
+                    emitter.Stloc(loc.Local);
+                }
+
+                emitter.EmitCall(_getter);
+                while (locals.Count > 0)
+                    using (var loc = locals.Pop())
+                        emitter.Ldloc(loc.Local);
+                emitter.EmitCall(_adder, true);
+            }
+        }
+    }
+}

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

@@ -96,6 +96,9 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         public IXamlType TextDecorations { get; }
         public IXamlType TextTrimming { get; }
         public IXamlType ISetter { get; }
+        public IXamlType IResourceDictionary { get; }
+        public IXamlType ResourceDictionary { get; }
+        public IXamlMethod ResourceDictionaryDeferredAdd { get; }
 
         public AvaloniaXamlIlWellKnownTypes(TransformerConfiguration cfg)
         {
@@ -210,6 +213,12 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             TextDecorations = cfg.TypeSystem.GetType("Avalonia.Media.TextDecorations");
             TextTrimming = cfg.TypeSystem.GetType("Avalonia.Media.TextTrimming");
             ISetter = cfg.TypeSystem.GetType("Avalonia.Styling.ISetter");
+            IResourceDictionary = cfg.TypeSystem.GetType("Avalonia.Controls.IResourceDictionary");
+            ResourceDictionary = cfg.TypeSystem.GetType("Avalonia.Controls.ResourceDictionary");
+            ResourceDictionaryDeferredAdd = ResourceDictionary.FindMethod("AddDeferred", XamlIlTypes.Void, true, XamlIlTypes.Object,
+                cfg.TypeSystem.GetType("System.Func`2").MakeGenericType(
+                    cfg.TypeSystem.GetType("System.IServiceProvider"),
+                    XamlIlTypes.Object));
         }
     }
 

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

@@ -66,6 +66,104 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
             }
         }
 
+        [Fact]
+        public void Item_Is_Added_To_ResourceDictionary_As_Deferred()
+        {
+            using (StyledWindow())
+            {
+                var xaml = @"
+<ResourceDictionary xmlns='https://github.com/avaloniaui'
+                    xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
+  <Color x:Key='Red'>Red</Color>
+</ResourceDictionary>";
+                var resources = (ResourceDictionary)AvaloniaRuntimeXamlLoader.Load(xaml);
+
+                Assert.True(resources.ContainsDeferredKey("Red"));
+            }
+        }
+
+        [Fact]
+        public void Item_Is_Added_To_Window_Resources_As_Deferred()
+        {
+            using (StyledWindow())
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
+    <Window.Resources>
+        <Color x:Key='Red'>Red</Color>
+    </Window.Resources>
+</Window>";
+                var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var resources = (ResourceDictionary)window.Resources;
+
+                Assert.True(resources.ContainsDeferredKey("Red"));
+            }
+        }
+
+        [Fact]
+        public void Item_Is_Added_To_Window_MergedDictionaries_As_Deferred()
+        {
+            using (StyledWindow())
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
+    <Window.Resources>
+        <ResourceDictionary>
+            <ResourceDictionary.MergedDictionaries>
+                <ResourceDictionary>
+                    <Color x:Key='Red'>Red</Color>
+                </ResourceDictionary>
+            </ResourceDictionary.MergedDictionaries>
+        </ResourceDictionary>
+    </Window.Resources>
+</Window>";
+                var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var resources = (ResourceDictionary)window.Resources.MergedDictionaries[0];
+
+                Assert.True(resources.ContainsDeferredKey("Red"));
+            }
+        }
+
+        [Fact]
+        public void Item_Is_Added_To_Style_Resources_As_Deferred()
+        {
+            using (StyledWindow())
+            {
+                var xaml = @"
+<Style xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
+    <Style.Resources>
+        <Color x:Key='Red'>Red</Color>
+    </Style.Resources>
+</Style>";
+                var style = (Style)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var resources = (ResourceDictionary)style.Resources;
+
+                Assert.True(resources.ContainsDeferredKey("Red"));
+            }
+        }
+
+        [Fact]
+        public void Item_Is_Added_To_Styles_Resources_As_Deferred()
+        {
+            using (StyledWindow())
+            {
+                var xaml = @"
+<Styles xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
+    <Styles.Resources>
+        <Color x:Key='Red'>Red</Color>
+    </Styles.Resources>
+</Styles>";
+                var style = (Styles)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var resources = (ResourceDictionary)style.Resources;
+
+                Assert.True(resources.ContainsDeferredKey("Red"));
+            }
+        }
+
         private IDisposable StyledWindow(params (string, string)[] assets)
         {
             var services = TestServices.StyledWindow.With(