Format generated AST source like hand-written code

The per-node .g.cs files are read during debugging and review, so the emitter
now shapes them the way a person would: fixed-slot nodes dispatch child access
through a switch, collection nodes through a readable running-index walk (no dead
trailing decrement), GetChildCount folds its constant terms, and the fully
qualified System.Collections.Generic names collapse behind a using. The visitor
interface and SlotKind enum gain the auto-generated header and #nullable, and all
three writers normalize newlines to LF.

No behavior change: the dispatch logic is identical; only formatting and the
unreachable final decrement differ.

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

ICSharpCode.Decompiler.Generators/DecompilerSyntaxTreeGenerator.cs

@@ -188,17 +188,18 @@ internal class DecompilerSyntaxTreeGenerator : IIncrementalGenerator
 		var builder = new StringBuilder();
 
 		builder.AppendLine("// <auto-generated/>");
-		builder.AppendLine("namespace ICSharpCode.Decompiler.CSharp.Syntax;");
+		builder.AppendLine("#nullable enable");
 		builder.AppendLine();
 
+		bool hasSlots = source.Slots is not null;
+		if (hasSlots)
+			builder.AppendLine("using System.Collections.Generic;");
 		if (source.NeedsPatternPlaceholder)
-		{
 			builder.AppendLine("using ICSharpCode.Decompiler.CSharp.Syntax.PatternMatching;");
-		}
+		if (hasSlots || source.NeedsPatternPlaceholder)
-
 			builder.AppendLine();
 
-		builder.AppendLine("#nullable enable");
+		builder.AppendLine("namespace ICSharpCode.Decompiler.CSharp.Syntax;");
 		builder.AppendLine();
 
 		builder.AppendLine($"partial class {source.NodeName}");
@@ -387,7 +388,7 @@ internal class DecompilerSyntaxTreeGenerator : IIncrementalGenerator
 					return SyntaxFacts.GetKeywordKind(p) != SyntaxKind.None ? "@" + p : p;
 				}
 				string ParamType(int i) => cp[i].IsCollection
-					? $"global::System.Collections.Generic.IEnumerable<{cp[i].ElementType}>"
+					? $"IEnumerable<{cp[i].ElementType}>"
 					: cp[i].ParamType;
 
 				builder.AppendLine($"\tpublic {source.NodeName}()");
@@ -421,7 +422,7 @@ internal class DecompilerSyntaxTreeGenerator : IIncrementalGenerator
 						var args = new List<string>();
 						for (int i = 0; i < len; i++)
 							args.Add(i == len - 1
-								? $"(global::System.Collections.Generic.IEnumerable<{cp[i].ElementType}>){ParamName(cp[i].PropertyName)}"
+								? $"(IEnumerable<{cp[i].ElementType}>){ParamName(cp[i].PropertyName)}"
 								: ParamName(cp[i].PropertyName));
 						builder.AppendLine($"\t\t: this({string.Join(", ", args)})");
 						builder.AppendLine("\t{");
@@ -465,46 +466,119 @@ internal class DecompilerSyntaxTreeGenerator : IIncrementalGenerator
 
 			// Flattened child-index space: slots in declaration order, a single slot occupying one index
 			// (even when empty), a collection slot a contiguous run of its current length.
-			builder.Append("\tinternal override int GetChildCount() => ");
+			var countTerms = new List<string>();
-			builder.Append(string.Join(" + ", slots.Select(s => s.IsCollection ? $"({FieldName(s.PropertyName)}?.Count ?? 0)" : "1")));
+			int singleSlotCount = slots.Count(s => !s.IsCollection);
-			builder.AppendLine(";");
+			if (singleSlotCount > 0)
+				countTerms.Add(singleSlotCount.ToString());
+			foreach (var s in slots.Where(s => s.IsCollection))
+				countTerms.Add($"({FieldName(s.PropertyName)}?.Count ?? 0)");
+			builder.AppendLine($"\tinternal override int GetChildCount() => {string.Join(" + ", countTerms)};");
 			builder.AppendLine();
 
-			builder.AppendLine("\tinternal override AstNode? GetChild(int index)");
+			bool anyCollection = slots.Any(s => s.IsCollection);
-			builder.AppendLine("\t{");
+
+			// Emits a method body that maps a flat child index to a slot and returns an expression for it.
+			// With only single slots the index is a constant offset, so a switch reads best; once a
+			// collection slot is present the widths are dynamic, so walk the slots subtracting each one's
+			// length from a running index.
+			void EmitReturnDispatch(Func<int, string> singleExpr, Func<int, string> collectionExpr)
+			{
+				if (!anyCollection)
+				{
+					builder.AppendLine("\t\tswitch (index)");
+					builder.AppendLine("\t\t{");
+					for (int k = 0; k < slots.Count; k++)
+					{
+						builder.AppendLine($"\t\t\tcase {k}:");
+						builder.AppendLine($"\t\t\t\treturn {singleExpr(k)};");
+					}
+					builder.AppendLine("\t\t\tdefault:");
+					builder.AppendLine("\t\t\t\tthrow new System.ArgumentOutOfRangeException(nameof(index));");
+					builder.AppendLine("\t\t}");
+					return;
+				}
 				builder.AppendLine("\t\tint i = index;");
-			foreach (var s in slots)
+				for (int k = 0; k < slots.Count; k++)
 				{
-				if (s.IsCollection)
+					bool last = k == slots.Count - 1;
+					if (slots[k].IsCollection)
 					{
-					string field = FieldName(s.PropertyName);
+						string field = FieldName(slots[k].PropertyName);
-					builder.AppendLine($"\t\t{{ int n = {field}?.Count ?? 0; if (i < n) return {field}![i]; i -= n; }}");
+						builder.AppendLine("\t\t{");
+						builder.AppendLine($"\t\t\tint n = {field}?.Count ?? 0;");
+						builder.AppendLine("\t\t\tif (i < n)");
+						builder.AppendLine($"\t\t\t\treturn {collectionExpr(k)};");
+						if (!last)
+							builder.AppendLine("\t\t\ti -= n;");
+						builder.AppendLine("\t\t}");
 					}
 					else
 					{
-					builder.AppendLine($"\t\tif (i == 0) return {FieldName(s.PropertyName)}; i -= 1;");
+						builder.AppendLine("\t\tif (i == 0)");
+						builder.AppendLine($"\t\t\treturn {singleExpr(k)};");
+						if (!last)
+							builder.AppendLine("\t\ti--;");
 					}
 				}
 				builder.AppendLine("\t\tthrow new System.ArgumentOutOfRangeException(nameof(index));");
+			}
+
+			builder.AppendLine("\tinternal override AstNode? GetChild(int index)");
+			builder.AppendLine("\t{");
+			EmitReturnDispatch(k => FieldName(slots[k].PropertyName), k => $"{FieldName(slots[k].PropertyName)}![i]");
 			builder.AppendLine("\t}");
 			builder.AppendLine();
 
 			builder.AppendLine("\tinternal override void SetChild(int index, AstNode? value)");
 			builder.AppendLine("\t{");
+			if (!anyCollection)
+			{
+				builder.AppendLine("\t\tswitch (index)");
+				builder.AppendLine("\t\t{");
+				for (int k = 0; k < slots.Count; k++)
+				{
+					builder.AppendLine($"\t\t\tcase {k}:");
+					builder.AppendLine($"\t\t\t\tSetChildNode(ref {FieldName(slots[k].PropertyName)}, ({slots[k].PropertyType}?)value);");
+					builder.AppendLine("\t\t\t\treturn;");
+				}
+				builder.AppendLine("\t\t\tdefault:");
+				builder.AppendLine("\t\t\t\tthrow new System.ArgumentOutOfRangeException(nameof(index));");
+				builder.AppendLine("\t\t}");
+			}
+			else
+			{
 				builder.AppendLine("\t\tint i = index;");
-			foreach (var s in slots)
+				for (int k = 0; k < slots.Count; k++)
 				{
+					bool last = k == slots.Count - 1;
+					var s = slots[k];
+					string field = FieldName(s.PropertyName);
 					if (s.IsCollection)
 					{
-					string field = FieldName(s.PropertyName);
+						builder.AppendLine("\t\t{");
-					builder.AppendLine($"\t\t{{ int n = {field}?.Count ?? 0; if (i < n) {{ {field}![i] = ({s.ElementType})value!; return; }} i -= n; }}");
+						builder.AppendLine($"\t\t\tint n = {field}?.Count ?? 0;");
+						builder.AppendLine("\t\t\tif (i < n)");
+						builder.AppendLine("\t\t\t{");
+						builder.AppendLine($"\t\t\t\t{field}![i] = ({s.ElementType})value!;");
+						builder.AppendLine("\t\t\t\treturn;");
+						builder.AppendLine("\t\t\t}");
+						if (!last)
+							builder.AppendLine("\t\t\ti -= n;");
+						builder.AppendLine("\t\t}");
 					}
 					else
 					{
-					builder.AppendLine($"\t\tif (i == 0) {{ SetChildNode(ref {FieldName(s.PropertyName)}, ({s.PropertyType}?)value); return; }} i -= 1;");
+						builder.AppendLine("\t\tif (i == 0)");
+						builder.AppendLine("\t\t{");
+						builder.AppendLine($"\t\t\tSetChildNode(ref {field}, ({s.PropertyType}?)value);");
+						builder.AppendLine("\t\t\treturn;");
+						builder.AppendLine("\t\t}");
+						if (!last)
+							builder.AppendLine("\t\ti--;");
 					}
 				}
 				builder.AppendLine("\t\tthrow new System.ArgumentOutOfRangeException(nameof(index));");
+			}
 			builder.AppendLine("\t}");
 			builder.AppendLine();
 
@@ -515,15 +589,7 @@ internal class DecompilerSyntaxTreeGenerator : IIncrementalGenerator
 
 			builder.AppendLine("\tinternal override CSharpSlotInfo GetChildSlotInfo(int index)");
 			builder.AppendLine("\t{");
-			builder.AppendLine("\t\tint i = index;");
+			EmitReturnDispatch(k => $"{slots[k].PropertyName}Slot", k => $"{slots[k].PropertyName}Slot");
-			foreach (var s in slots)
-			{
-				if (s.IsCollection)
-					builder.AppendLine($"\t\t{{ int n = {FieldName(s.PropertyName)}?.Count ?? 0; if (i < n) return {s.PropertyName}Slot; i -= n; }}");
-				else
-					builder.AppendLine($"\t\tif (i == 0) return {s.PropertyName}Slot; i -= 1;");
-			}
-			builder.AppendLine("\t\tthrow new System.ArgumentOutOfRangeException(nameof(index));");
 			builder.AppendLine("\t}");
 			builder.AppendLine();
 
@@ -547,7 +613,11 @@ internal class DecompilerSyntaxTreeGenerator : IIncrementalGenerator
 			{
 				string field = FieldName(s.PropertyName);
 				if (s.IsCollection)
-					builder.AppendLine($"\t\tif ({field} != null) foreach (var c in {field}) copy.{s.PropertyName}.Add(({s.ElementType})c.Clone());");
+				{
+					builder.AppendLine($"\t\tif ({field} != null)");
+					builder.AppendLine($"\t\t\tforeach (var c in {field})");
+					builder.AppendLine($"\t\t\t\tcopy.{s.PropertyName}.Add(({s.ElementType})c.Clone());");
+				}
 				else
 					builder.AppendLine($"\t\tif ({field} != null) copy.{s.PropertyName} = ({s.PropertyType}){field}.Clone();");
 			}
@@ -558,9 +628,9 @@ internal class DecompilerSyntaxTreeGenerator : IIncrementalGenerator
 			// and the visitors' VisitChildren, instead of the per-step O(slots) index scan (NextSibling).
 			// Collection slots iterate via their own enumerator, which tolerates removing/replacing the
 			// current child during traversal.
-			builder.AppendLine("\tinternal override System.Collections.Generic.IEnumerable<AstNode> GetChildNodes()");
+			builder.AppendLine("\tinternal override IEnumerable<AstNode> GetChildNodes()");
 			builder.AppendLine("\t{");
-			builder.AppendLine("\t\tvar children = new System.Collections.Generic.List<AstNode>(GetChildCount());");
+			builder.AppendLine("\t\tvar children = new List<AstNode>(GetChildCount());");
 			foreach (var s in slots)
 			{
 				string field = FieldName(s.PropertyName);
@@ -574,32 +644,38 @@ internal class DecompilerSyntaxTreeGenerator : IIncrementalGenerator
 			builder.AppendLine();
 		}
 
-		builder.AppendLine("}");
+		// Close the class, trimming the blank line the per-member spacer leaves before the brace.
+		string body = builder.ToString().TrimEnd() + "\n}\n";
 
-		context.AddSource(source.NodeName + ".g.cs", SourceText.From(builder.ToString().Replace("\r\n", "\n"), Encoding.UTF8));
+		context.AddSource(source.NodeName + ".g.cs", SourceText.From(body.Replace("\r\n", "\n"), Encoding.UTF8));
 	}
 
 	void WriteVisitors(SourceProductionContext context, ImmutableArray<AstNodeAdditions> source)
 	{
 		var builder = new StringBuilder();
 
+		builder.AppendLine("// <auto-generated/>");
+		builder.AppendLine("#nullable enable");
+		builder.AppendLine();
 		builder.AppendLine("namespace ICSharpCode.Decompiler.CSharp.Syntax;");
+		builder.AppendLine();
 
 		source = source
 			.Concat([new("PatternPlaceholder", true, false, true, false, "PatternPlaceholder", "AstNode", null, null, null, null)])
 			.ToImmutableArray();
 
 		WriteInterface("IAstVisitor", "void", "");
+		builder.AppendLine();
 		WriteInterface("IAstVisitor<out S>", "S", "");
+		builder.AppendLine();
 		WriteInterface("IAstVisitor<in T, out S>", "S", ", T data");
 
-		context.AddSource("IAstVisitor.g.cs", SourceText.From(builder.ToString(), Encoding.UTF8));
+		context.AddSource("IAstVisitor.g.cs", SourceText.From(builder.ToString().Replace("\r\n", "\n"), Encoding.UTF8));
 
 		void WriteInterface(string name, string ret, string param)
 		{
 			builder.AppendLine($"public interface {name}");
 			builder.AppendLine("{");
-
 			foreach (var type in source.OrderBy(t => t.VisitMethodName))
 			{
 				if (!type.NeedsVisitor)
@@ -696,6 +772,8 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		}
 
 		var builder = new StringBuilder();
+		builder.AppendLine("// <auto-generated/>");
+		builder.AppendLine();
 		builder.AppendLine("namespace ICSharpCode.Decompiler.CSharp.Syntax;");
 		builder.AppendLine();
 		builder.AppendLine("/// <summary>Identifies the kind of an AST child slot, shared across node types.</summary>");
@@ -706,7 +784,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			builder.AppendLine($"\t{k},");
 		builder.AppendLine("}");
 
-		context.AddSource("SlotKind.g.cs", SourceText.From(builder.ToString(), Encoding.UTF8));
+		context.AddSource("SlotKind.g.cs", SourceText.From(builder.ToString().Replace("\r\n", "\n"), Encoding.UTF8));
 	}
 }