Convert IAvaloniaXamlIlParentStackProvider to eager one if needed

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

@@ -76,7 +76,7 @@ public static (XamlLanguageTypeMappings language, XamlLanguageEmitMappings<IXaml
                 ContextTypeBuilderCallback = definition =>
                 {
                     EmitNameScopeField(rv, typeSystem, definition);
-                    EmitEagerParentStackProvider(rv, typeSystem, definition);
+                    EmitEagerParentStackProvider(rv, typeSystem, definition, runtimeHelpers);
                 }
             };
             return (rv, emit);
@@ -104,7 +104,8 @@ private static void EmitNameScopeField(
         private static void EmitEagerParentStackProvider(
             XamlLanguageTypeMappings mappings,
             IXamlTypeSystem typeSystem,
-            IXamlILContextDefinition<IXamlILEmitter> definition)
+            IXamlILContextDefinition<IXamlILEmitter> definition,
+            IXamlType runtimeHelpers)
         {
             var interfaceType = typeSystem.FindType("Avalonia.Markup.Xaml.XamlIl.Runtime.IAvaloniaXamlIlEagerParentStackProvider");
 
@@ -122,14 +123,22 @@ private static void EmitEagerParentStackProvider(
                 typeSystem.FindType("System.Object"),
                 typeSystem.FindType("System.Type")));
 
+            var asEagerParentStackProviderMethod = runtimeHelpers.GetMethod(new FindMethodMethodSignature(
+                "AsEagerParentStackProvider",
+                interfaceType,
+                mappings.ParentStackProvider)
+            {
+                IsStatic = true
+            });
+
             // IAvaloniaXamlIlEagerParentStackProvider? ParentProvider
-            // => (IAvaloniaXamlIlEagerParentStackProvider)_serviceProvider.GetService(typeof(IAvaloniaXamlIlParentStackProvider))
+            // => XamlIlRuntimeHelpers.AsEagerParentStackProvider(_serviceProvider.GetService(typeof(IAvaloniaXamlIlParentStackProvider)));
             var parentProviderGetter = ImplementInterfacePropertyGetter("ParentProvider");
             parentProviderGetter.Generator
                 .LdThisFld(definition.ParentServiceProviderField)
                 .Ldtype(mappings.ParentStackProvider)
                 .EmitCall(serviceProviderGetServiceMethod)
-                .Castclass(interfaceType)
+                .EmitCall(asEagerParentStackProviderMethod)
                 .Ret();
 
             IXamlMethodBuilder<IXamlILEmitter> ImplementInterfacePropertyGetter(string propertyName)

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

@@ -52,6 +52,7 @@
     <Compile Include="XamlIl\Runtime\IAvaloniaXamlIlControlTemplateProvider.cs" />
     <Compile Include="XamlIl\Runtime\IAvaloniaXamlIlParentStackProvider.cs" />
     <Compile Include="XamlIl\Runtime\IAvaloniaXamlIlXmlNamespaceInfoProviderV1.cs" />
+    <Compile Include="XamlIl\Runtime\XamlIlParentStackProviderWrapper.cs" />
     <Compile Include="XamlIl\Runtime\XamlIlRuntimeHelpers.cs" />
     <Compile Include="XamlLoadException.cs" />
     <Compile Include="XamlTypes.cs" />

src/Markup/Avalonia.Markup.Xaml/XamlIl/Runtime/XamlIlParentStackProviderWrapper.cs

@@ -0,0 +1,27 @@
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Avalonia.Markup.Xaml.XamlIl.Runtime;
+
+/// <summary>
+/// Wraps a <see cref="IAvaloniaXamlIlParentStackProvider"/> into a <see cref="IAvaloniaXamlIlEagerParentStackProvider"/>,
+/// for backwards compatibility.
+/// </summary>
+internal sealed class XamlIlParentStackProviderWrapper : IAvaloniaXamlIlEagerParentStackProvider
+{
+    private readonly IAvaloniaXamlIlParentStackProvider _provider;
+
+    private IReadOnlyList<object>? _directParentsStack;
+
+    public XamlIlParentStackProviderWrapper(IAvaloniaXamlIlParentStackProvider provider)
+        => _provider = provider;
+
+    public IEnumerable<object> Parents
+        => _provider.Parents;
+
+    public IReadOnlyList<object> DirectParentsStack
+        => _directParentsStack ??= _provider.Parents.Reverse().ToArray();
+
+    public IAvaloniaXamlIlEagerParentStackProvider? ParentProvider
+        => null;
+}

src/Markup/Avalonia.Markup.Xaml/XamlIl/Runtime/XamlIlRuntimeHelpers.cs

@@ -95,6 +95,14 @@ private static IResourceNode[] AsResourceNodesStack(IAvaloniaXamlIlParentStackPr
             return resourceNodes;
         }
 
+        /// <summary>
+        /// Converts a <see cref="IAvaloniaXamlIlParentStackProvider"/> into a
+        /// <see cref="IAvaloniaXamlIlEagerParentStackProvider"/>.
+        /// </summary>
+        public static IAvaloniaXamlIlEagerParentStackProvider AsEagerParentStackProvider(
+            this IAvaloniaXamlIlParentStackProvider provider)
+            => provider as IAvaloniaXamlIlEagerParentStackProvider ?? new XamlIlParentStackProviderWrapper(provider);
+
         // Parent resource nodes are often the same (e.g. most values in a ResourceDictionary), cache the last ones.
         private sealed class LastParentStack
         {