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

using System;
using System.Linq;
using XamlX;
using XamlX.Ast;
using XamlX.Transform;
using XamlX.TypeSystem;
using XamlX.Emit;
using XamlX.IL;

namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
{
    class AddNameScopeRegistration : IXamlAstTransformer
    {
        public IXamlAstNode Transform(AstTransformationContext context, IXamlAstNode node)
        {
            if (node is XamlPropertyAssignmentNode pa)
            {
                if (pa.Property.Name == "Name"
                    && pa.Property.DeclaringType.FullName == "Avalonia.StyledElement")
                {
                    if (context.ParentNodes().FirstOrDefault() is XamlManipulationGroupNode mg
                        && mg.Children.OfType<AvaloniaNameScopeRegistrationXamlIlNode>().Any())
                        return node;

                    IXamlAstValueNode value = null;
                    for (var c = 0; c < pa.Values.Count; c++)
                        if (pa.Values[c].Type.GetClrType().Equals(context.Configuration.WellKnownTypes.String))
                        {
                            value = pa.Values[c];
                            if (!(value is XamlAstTextNode))
                            {
                                var local = new XamlAstCompilerLocalNode(value);
                                // Wrap original in local initialization
                                pa.Values[c] = new XamlAstLocalInitializationNodeEmitter(value, value, local);
                                // Use local
                                value = local;
                            }

                            break;
                        }

                    if (value != null)
                    {
                        var objectType = context.ParentNodes().OfType<XamlAstConstructableObjectNode>().FirstOrDefault()?.Type.GetClrType();
                        return new XamlManipulationGroupNode(pa)
                        {
                            Children =
                            {
                                pa,
                                new AvaloniaNameScopeRegistrationXamlIlNode(value, objectType)
                            }
                        };
                    }
                }
                else if (pa.Property.CustomAttributes.Select(attr => attr.Type).Intersect(context.Configuration.TypeMappings.DeferredContentPropertyAttributes).Any())
                {
                    pa.Values[pa.Values.Count - 1] =
                        new NestedScopeMetadataNode(pa.Values[pa.Values.Count - 1]);
                }
            }

            return node;
        }
    }

    class NestedScopeMetadataNode : XamlValueWithSideEffectNodeBase
    {
        public NestedScopeMetadataNode(IXamlAstValueNode value) : base(value, value)
        {
        }
    }

    class AvaloniaNameScopeRegistrationXamlIlNode : XamlAstNode, IXamlAstManipulationNode
    {
        public IXamlAstValueNode Name { get; set; }
        public IXamlType TargetType { get; }

        public AvaloniaNameScopeRegistrationXamlIlNode(IXamlAstValueNode name, IXamlType targetType) : base(name)
        {
            TargetType = targetType;
            Name = name;
        }

        public override void VisitChildren(IXamlAstVisitor visitor)
            => Name = (IXamlAstValueNode)Name.Visit(visitor);
    }

    class AvaloniaNameScopeRegistrationXamlIlNodeEmitter : IXamlAstLocalsNodeEmitter<IXamlILEmitter, XamlILNodeEmitResult>
    {
        public XamlILNodeEmitResult Emit(IXamlAstNode node, XamlEmitContextWithLocals<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen)
        {
            if (node is AvaloniaNameScopeRegistrationXamlIlNode registration)
            {

                var scopeField = context.RuntimeContext.ContextType.Fields.First(f =>
                    f.Name == AvaloniaXamlIlLanguage.ContextNameScopeFieldName);

                using (var targetLoc = context.GetLocalOfType(context.Configuration.WellKnownTypes.Object))
                {

                    codeGen
                        // var target = {pop}
                        .Stloc(targetLoc.Local)
                        // _context.NameScope.Register(Name, target)
                        .Ldloc(context.ContextLocal)
                        .Ldfld(scopeField);

                    context.Emit(registration.Name, codeGen, registration.Name.Type.GetClrType());

                    codeGen
                        .Ldloc(targetLoc.Local)
                        .EmitCall(context.GetAvaloniaTypes().INameScopeRegister, true);
                }

                return XamlILNodeEmitResult.Void(1);
            }
            return default;
        }
    }
}