Generate typed Slots; key 1:1-kind child access on them

The generator emits a Slots holder of typed CSharpSlotInfo<T> kind constants (T is
the child type, widened to AstNode for the few kinds reused with several child
types). Call sites whose kind maps to a single type switch from
GetChildByRole<T>(SlotKind.X) to GetChild(Slots.X), inferring the result type from
the slot. The ByRole methods and SlotKind remain for the multi-type Attribute
accessor and the internal add/insert plumbing, removed in following steps.

Assisted-by: Claude:claude-opus-4-8:Claude Code

ICSharpCode.Decompiler.Generators/DecompilerSyntaxTreeGenerator.cs

@@ -781,13 +781,26 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 	// it replaces the old polymorphic node.Role == Roles.X comparisons.
 	void WriteSlotKinds(SourceProductionContext context, ImmutableArray<AstNodeAdditions> source)
 	{
-		var kinds = new SortedSet<string>(StringComparer.Ordinal);
+		// Per kind: the element types seen (to choose a typed slot's T) and whether it is a collection.
+		// kindIsCollection is null once a kind is seen as a collection on one node and a single child on
+		// another (e.g. Expression, Initializer); it is resolved by agreement, so the emitted flag never
+		// depends on iteration order (each kind's value is written exactly once it is determined).
+		var kindTypes = new SortedDictionary<string, SortedSet<string>>(StringComparer.Ordinal);
+		var kindIsCollection = new Dictionary<string, bool?>();
 		foreach (var node in source)
 		{
 			if (node.Slots is { } slots)
 			{
 				foreach (var s in slots)
-					kinds.Add(s.KindName);
+				{
+					if (!kindTypes.TryGetValue(s.KindName, out var set))
+						kindTypes[s.KindName] = set = new SortedSet<string>(StringComparer.Ordinal);
+					set.Add(s.ElementType);
+					if (!kindIsCollection.TryGetValue(s.KindName, out var arity))
+						kindIsCollection[s.KindName] = s.IsCollection;
+					else if (arity is bool b && b != s.IsCollection)
+						kindIsCollection[s.KindName] = null;
+				}
 			}
 		}
 
@@ -800,9 +813,23 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		builder.AppendLine("public enum SlotKind");
 		builder.AppendLine("{");
 		builder.AppendLine("\tNone,");
-		foreach (var k in kinds)
+		foreach (var k in kindTypes.Keys)
 			builder.AppendLine($"\t{k},");
 		builder.AppendLine("}");
+		builder.AppendLine();
+		// Typed kind constants for polymorphic access: node.GetChild(Slots.X) infers the child type. A
+		// kind reused with several child types across node types widens to AstNode (only its concrete
+		// per-node slots carry the precise type); such kinds are only reached through those per-node slots.
+		builder.AppendLine("/// <summary>Typed slot kinds for polymorphic child access; the child type is inferred from the slot.</summary>");
+		builder.AppendLine("public static class Slots");
+		builder.AppendLine("{");
+		foreach (var kv in kindTypes)
+		{
+			string type = kv.Value.Count == 1 ? kv.Value.Min : "AstNode";
+			string isColl = kindIsCollection[kv.Key] == true ? "true" : "false";
+			builder.AppendLine($"\tpublic static readonly CSharpSlotInfo<{type}> {kv.Key} = new CSharpSlotInfo<{type}>(\"{kv.Key}\", {isColl}, SlotKind.{kv.Key}, false);");
+		}
+		builder.AppendLine("}");
 
 		context.AddSource("SlotKind.g.cs", SourceText.From(builder.ToString().Replace("\r\n", "\n"), Encoding.UTF8));
 	}

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -1355,11 +1355,11 @@ namespace ICSharpCode.Decompiler.CSharp
 					RemoveAttribute(prop, KnownAttribute.ExtensionMarker);
 					if (propDef.Getter != null)
 					{
-						RemoveAttribute(prop.GetChildByRole<Accessor>(SlotKind.Getter)!, KnownAttribute.ExtensionMarker);
+						RemoveAttribute(prop.GetChild(Slots.Getter)!, KnownAttribute.ExtensionMarker);
 					}
 					if (propDef.Setter != null)
 					{
-						RemoveAttribute(prop.GetChildByRole<Accessor>(SlotKind.Setter)!, KnownAttribute.ExtensionMarker);
+						RemoveAttribute(prop.GetChild(Slots.Setter)!, KnownAttribute.ExtensionMarker);
 					}
 					RunTransforms(syntaxTree, decompileRun, new SimpleTypeResolveContext(propDef.DeclaringTypeDefinition));
 					break;
@@ -1412,7 +1412,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			EntityDeclaration memberDecl, IMethod method,
 			TypeSystemAstBuilder astBuilder)
 		{
-			if (memberDecl.GetChildByRole<AstType>(SlotKind.PrivateImplementationType) is not null)
+			if (memberDecl.GetChild(Slots.PrivateImplementationType) is not null)
 			{
 				yield break; // cannot create forwarder for existing explicit interface impl
 			}
@@ -1439,9 +1439,9 @@ namespace ICSharpCode.Decompiler.CSharp
 					methodDecl.ReturnType = memberReturnType.Clone();
 				methodDecl.PrivateImplementationType = astBuilder.ConvertType(m.DeclaringType);
 				methodDecl.Name = m.Name;
-				methodDecl.TypeParameters.AddRange(memberDecl.GetChildrenByRole<TypeParameterDeclaration>(SlotKind.TypeParameter)
+				methodDecl.TypeParameters.AddRange(memberDecl.GetChildren(Slots.TypeParameter)
 												   .Select(n => (TypeParameterDeclaration)n.Clone()));
-				methodDecl.Parameters.AddRange(memberDecl.GetChildrenByRole<ParameterDeclaration>(SlotKind.Parameter).Select(n => n.Clone()));
+				methodDecl.Parameters.AddRange(memberDecl.GetChildren(Slots.Parameter).Select(n => n.Clone()));
 				// Constraints are not copied because explicit interface implementations cannot have constraints. CS0460
 
 				methodDecl.Body = new BlockStatement();
@@ -1557,7 +1557,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		void FixParameterNames(EntityDeclaration entity)
 		{
 			int i = 0;
-			foreach (var parameter in entity.GetChildrenByRole<ParameterDeclaration>(SlotKind.Parameter))
+			foreach (var parameter in entity.GetChildren(Slots.Parameter))
 			{
 				if (string.IsNullOrWhiteSpace(parameter.Name) && !parameter.Type.IsArgList())
 				{
@@ -1854,11 +1854,11 @@ namespace ICSharpCode.Decompiler.CSharp
 							RemoveAttribute(prop, KnownAttribute.ExtensionMarker);
 							if (p.Getter != null)
 							{
-								RemoveAttribute(prop.GetChildByRole<Accessor>(SlotKind.Getter)!, KnownAttribute.ExtensionMarker);
+								RemoveAttribute(prop.GetChild(Slots.Getter)!, KnownAttribute.ExtensionMarker);
 							}
 							if (p.Setter != null)
 							{
-								RemoveAttribute(prop.GetChildByRole<Accessor>(SlotKind.Setter)!, KnownAttribute.ExtensionMarker);
+								RemoveAttribute(prop.GetChild(Slots.Setter)!, KnownAttribute.ExtensionMarker);
 							}
 							extMemberDecl = prop;
 							break;
@@ -2136,7 +2136,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		{
 			int i = parameterOffset;
 			var parameters = function.Variables.Where(v => v.Kind == VariableKind.Parameter).ToDictionary(v => v.Index!.Value);
-			foreach (var parameter in entityDecl.GetChildrenByRole<ParameterDeclaration>(SlotKind.Parameter))
+			foreach (var parameter in entityDecl.GetChildren(Slots.Parameter))
 			{
 				if (parameters.TryGetValue(i, out var v))
 					parameter.AddAnnotation(new ILVariableResolveResult(v, method.Parameters[i].Type));

ICSharpCode.Decompiler/CSharp/OutputVisitor/CSharpAmbience.cs

@@ -123,7 +123,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			if ((ConversionFlags & ConversionFlags.PlaceReturnTypeAfterParameterList) != ConversionFlags.PlaceReturnTypeAfterParameterList
 				&& (ConversionFlags & ConversionFlags.ShowReturnType) == ConversionFlags.ShowReturnType)
 			{
-				var rt = node.GetChildByRole<AstType>(SlotKind.Type);
+				var rt = node.GetChild(Slots.Type);
 				if (rt is not null)
 				{
 					rt.AcceptVisitor(new CSharpOutputVisitor(writer, formattingPolicy));
@@ -150,7 +150,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 				}
 				else
 				{
-					parameters = node.GetChildrenByRole<ParameterDeclaration>(SlotKind.Parameter);
+					parameters = node.GetChildren(Slots.Parameter);
 				}
 				foreach (var param in parameters)
 				{
@@ -181,7 +181,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			if ((ConversionFlags & ConversionFlags.PlaceReturnTypeAfterParameterList) == ConversionFlags.PlaceReturnTypeAfterParameterList
 				&& (ConversionFlags & ConversionFlags.ShowReturnType) == ConversionFlags.ShowReturnType)
 			{
-				var rt = node.GetChildByRole<AstType>(SlotKind.Type);
+				var rt = node.GetChild(Slots.Type);
 				if (rt is not null)
 				{
 					writer.Space();
@@ -309,7 +309,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			else
 			{
 				writer.WriteIdentifier(node.NameToken);
-				WriteTypeParameters(node.GetChildrenByRole<TypeParameterDeclaration>(SlotKind.TypeParameter), writer, formattingPolicy);
+				WriteTypeParameters(node.GetChildren(Slots.TypeParameter), writer, formattingPolicy);
 			}
 		}
 
@@ -412,7 +412,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 					writer.WriteIdentifier(Identifier.Create(name));
 					break;
 			}
-			WriteTypeParameters(node.GetChildrenByRole<TypeParameterDeclaration>(SlotKind.TypeParameter), writer, formattingPolicy);
+			WriteTypeParameters(node.GetChildren(Slots.TypeParameter), writer, formattingPolicy);
 		}
 
 		void WriteTypeParameters(IEnumerable<TypeParameterDeclaration> typeParameters, TokenWriter writer, CSharpFormattingOptions formattingPolicy)

ICSharpCode.Decompiler/CSharp/OutputVisitor/CSharpOutputVisitor.cs

@@ -1904,7 +1904,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 		public virtual void VisitLabelStatement(LabelStatement labelStatement)
 		{
 			StartNode(labelStatement);
-			WriteIdentifier(labelStatement.GetChildByRole<Identifier>(SlotKind.Identifier)!);
+			WriteIdentifier(labelStatement.GetChild(Slots.Identifier)!);
 			WriteToken(Roles.Colon);
 			bool foundLabelledStatement = false;
 			for (AstNode? tmp = labelStatement.NextSibling; tmp != null; tmp = tmp.NextSibling)

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/IdentifierExpression.cs

@@ -36,7 +36,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 	{
 		public IdentifierExpression(string identifier, TextLocation location)
 		{
-			SetChildByRole(SlotKind.Identifier, Decompiler.CSharp.Syntax.Identifier.Create(identifier, location));
+			SetChild(Slots.Identifier, Decompiler.CSharp.Syntax.Identifier.Create(identifier, location));
 		}
 
 		[Slot("Identifier")]

ICSharpCode.Decompiler/CSharp/Syntax/GeneralScope/AttributeSection.cs

@@ -36,10 +36,10 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 	{
 		public string AttributeTarget {
 			get {
-				return GetChildByRole<Identifier>(SlotKind.Identifier)?.Name ?? string.Empty;
+				return GetChild(Slots.Identifier)?.Name ?? string.Empty;
 			}
 			set {
-				SetChildByRole(SlotKind.Identifier, Identifier.Create(value));
+				SetChild(Slots.Identifier, Identifier.Create(value));
 			}
 		}
 

ICSharpCode.Decompiler/CSharp/Syntax/PatternMatching/IdentifierExpressionBackreference.cs

@@ -46,9 +46,12 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax.PatternMatching
 			var ident = other as IdentifierExpression;
 			if (ident == null || ident.TypeArguments.Any())
 				return false;
-			if (match.Get(referencedGroupName).Last() is not IdentifierExpression referenced)
+			if (match.Get(referencedGroupName).Last() is not AstNode referenced)
 				return false;
-			return ident.Identifier == referenced.Identifier;
+			Identifier? referencedIdentifier = referenced.GetChild(Slots.Identifier);
+			if (referencedIdentifier == null)
+				return false;
+			return ident.Identifier == referencedIdentifier.Name;
 		}
 	}
 }

ICSharpCode.Decompiler/CSharp/Syntax/SimpleType.cs

@@ -43,7 +43,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		public SimpleType(string identifier, TextLocation location)
 		{
-			SetChildByRole(SlotKind.Identifier, Syntax.Identifier.Create(identifier, location));
+			SetChild(Slots.Identifier, Syntax.Identifier.Create(identifier, location));
 		}
 		[Slot("Identifier")]
 		public partial string? Identifier { get; set; }

ICSharpCode.Decompiler/CSharp/Syntax/TypeMembers/EntityDeclaration.cs

@@ -42,21 +42,21 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		public virtual string Name {
 			get {
-				return GetChildByRole<Identifier>(SlotKind.Identifier)?.Name ?? string.Empty;
+				return GetChild(Slots.Identifier)?.Name ?? string.Empty;
 			}
 			set {
-				SetChildByRole(SlotKind.Identifier, Identifier.Create(value, TextLocation.Empty));
+				SetChild(Slots.Identifier, Identifier.Create(value, TextLocation.Empty));
 			}
 		}
 
 		public virtual Identifier NameToken {
-			get { return GetChildByRole<Identifier>(SlotKind.Identifier)!; }
-			set { SetChildByRole(SlotKind.Identifier, value); }
+			get { return GetChild(Slots.Identifier)!; }
+			set { SetChild(Slots.Identifier, value); }
 		}
 
 		public virtual AstType ReturnType {
-			get { return GetChildByRole<AstType>(SlotKind.Type)!; }
-			set { SetChildByRole(SlotKind.Type, value); }
+			get { return GetChild(Slots.Type)!; }
+			set { SetChild(Slots.Type, value); }
 		}
 
 		protected bool MatchAttributesAndModifiers(EntityDeclaration o, PatternMatching.Match match)

ICSharpCode.Decompiler/CSharp/Syntax/TypeMembers/MethodDeclaration.cs

@@ -72,7 +72,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		public bool IsExtensionMethod {
 			get {
-				ParameterDeclaration? pd = GetChildByRole<ParameterDeclaration>(SlotKind.Parameter);
+				ParameterDeclaration? pd = GetChild(Slots.Parameter);
 				return pd != null && pd.HasThisModifier;
 			}
 		}

ICSharpCode.Decompiler/CSharp/Transforms/FixNameCollisions.cs

@@ -42,7 +42,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			foreach (var typeDecl in rootNode.DescendantsAndSelf.OfType<TypeDeclaration>())
 			{
 				var memberNames = typeDecl.Members.Select(m => {
-					var type = m.GetChildByRole<AstType>(SlotKind.PrivateImplementationType);
+					var type = m.GetChild(Slots.PrivateImplementationType);
 					return type is null ? m.Name : type + "." + m.Name;
 				}).ToHashSet();
 				// memberNames does not include fields or non-custom events because those
@@ -70,7 +70,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 					if (symbol != null && renamedSymbols.TryGetValue(symbol, out string? newName))
 					{
 						// An IdentifierExpression / MemberReferenceExpression always carries its name identifier.
-						node.GetChildByRole<Identifier>(SlotKind.Identifier)!.Name = newName;
+						node.GetChild(Slots.Identifier)!.Name = newName;
 					}
 				}
 			}

ICSharpCode.Decompiler/CSharp/Transforms/TransformFieldAndConstructorInitializers.cs

@@ -482,7 +482,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 				var ci = new ConstructorInitializer { ConstructorInitializerType = type };
 
 				// Move arguments from invocation to initializer:
-				invocation.GetChildrenByRole<Expression>(SlotKind.Argument).MoveTo(ci.Arguments);
+				invocation.GetChildren(Slots.Argument).MoveTo(ci.Arguments);
 				// Add the initializer: (unless it is the default 'base()')
 				if (!(ci.ConstructorInitializerType == ConstructorInitializerType.Base && ci.Arguments.Count == 0))
 					constructorDeclaration.Initializer = ci.CopyAnnotationsFrom(invocation);

ICSharpCode.Decompiler/Output/TextTokenWriter.cs

@@ -302,7 +302,7 @@ namespace ICSharpCode.Decompiler
 					// Attach member reference to token only if there's no identifier in the current node.
 					var member = GetCurrentMemberReference();
 					var node = nodeStack.Peek();
-					if (member != null && node.GetChildByRole<Identifier>(SlotKind.Identifier) is null)
+					if (member != null && node.GetChild(Slots.Identifier) is null)
 					{
 						switch (member)
 						{