Output attributes on lambda expressions

ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj

@@ -33,11 +33,11 @@
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">
-    <DefineConstants>TRACE;DEBUG;NET46;ROSLYN;CS60;CS70;CS71;CS72;CS73</DefineConstants>
+    <DefineConstants>TRACE;DEBUG;ROSLYN;CS60;CS70;CS71;CS72;CS73;CS80;CS90;CS100</DefineConstants>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|AnyCPU'">
-    <DefineConstants>TRACE;NET46;ROSLYN;CS60;CS70;CS71;CS72;CS73</DefineConstants>
+    <DefineConstants>TRACE;ROSLYN;CS60;CS70;CS71;CS72;CS73;CS80;CS90;CS100</DefineConstants>
   </PropertyGroup>
 
   <Import Project="..\packages.props" />

ICSharpCode.Decompiler.Tests/TestCases/Pretty/DelegateConstruction.cs

@@ -20,8 +20,11 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
+#if CS100
+using System.Threading.Tasks;
+#endif
 
-namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty.DelegateConstruction
 {
 	public static class DelegateConstruction
 	{
@@ -527,6 +530,46 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			return (int _, int _, int _) => 0;
 		}
 #endif
+
+#if CS100
+		public static Func<int> LambdaWithAttribute0()
+		{
+			return [My] () => 0;
+		}
+
+		public static Func<int, int> LambdaWithAttribute1()
+		{
+			return [My] (int x) => 0;
+		}
+
+		public static Func<int, int> LambdaWithAttributeOnParam()
+		{
+			return ([My] int x) => 0;
+		}
+
+		public static Func<Task<int>> AsyncLambdaWithAttribute0()
+		{
+			return [My] async () => 0;
+		}
+		public static Action StatementLambdaWithAttribute0()
+		{
+			return [My] () => {
+			};
+		}
+
+		public static Action<int> StatementLambdaWithAttribute1()
+		{
+			return [return: My] (int x) => {
+				Console.WriteLine(x);
+			};
+		}
+		public static Action<int> StatementLambdaWithAttribute2()
+		{
+			return ([My] int x) => {
+				Console.WriteLine(x);
+			};
+		}
+#endif
 	}
 
 	public class Issue1867
@@ -551,4 +594,9 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			return () => m1.value + 1 == 4 && m2.value > 5;
 		}
 	}
+
+	[AttributeUsage(AttributeTargets.All)]
+	internal class MyAttribute : Attribute
+	{
+	}
 }

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -2302,6 +2302,24 @@ namespace ICSharpCode.Decompiler.CSharp
 			{
 				body.InsertChildAfter(prev, prev = new Comment(warning), Roles.Comment);
 			}
+			var attributeSections = new List<AttributeSection>();
+			foreach (var attr in method?.GetAttributes() ?? Enumerable.Empty<IAttribute>())
+			{
+				if (attr.AttributeType.IsKnownType(KnownAttribute.CompilerGenerated))
+					continue;
+				if (function.IsAsync)
+				{
+					if (attr.AttributeType.IsKnownType(KnownAttribute.AsyncStateMachine))
+						continue;
+					if (attr.AttributeType.IsKnownType(KnownAttribute.DebuggerStepThrough))
+						continue;
+				}
+				attributeSections.Add(new AttributeSection(astBuilder.ConvertAttribute(attr)));
+			}
+			foreach (var attr in method?.GetReturnTypeAttributes() ?? Enumerable.Empty<IAttribute>())
+			{
+				attributeSections.Add(new AttributeSection(astBuilder.ConvertAttribute(attr)) { AttributeTarget = "return" });
+			}
 
 			bool isLambda = false;
 			if (ame.Parameters.Any(p => p.Type.IsNull))
@@ -2309,6 +2327,11 @@ namespace ICSharpCode.Decompiler.CSharp
 				// if there is an anonymous type involved, we are forced to use a lambda expression.
 				isLambda = true;
 			}
+			else if (attributeSections.Count > 0 || ame.Parameters.Any(p => p.Attributes.Any()))
+			{
+				// C# 10 lambdas can have attributes, but anonymous methods cannot
+				isLambda = true;
+			}
 			else if (settings.UseLambdaSyntax && ame.Parameters.All(p => p.ParameterModifier == ParameterModifier.None))
 			{
 				// otherwise use lambda only if an expression lambda is possible
@@ -2331,6 +2354,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			if (isLambda)
 			{
 				LambdaExpression lambda = new LambdaExpression();
+				lambda.Attributes.AddRange(attributeSections);
 				lambda.IsAsync = ame.IsAsync;
 				lambda.CopyAnnotationsFrom(ame);
 				ame.Parameters.MoveTo(lambda.Parameters);

ICSharpCode.Decompiler/CSharp/OutputVisitor/CSharpOutputVisitor.cs

@@ -1007,6 +1007,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 		public virtual void VisitLambdaExpression(LambdaExpression lambdaExpression)
 		{
 			StartNode(lambdaExpression);
+			WriteAttributes(lambdaExpression.Attributes);
 			if (lambdaExpression.IsAsync)
 			{
 				WriteKeyword(LambdaExpression.AsyncModifierRole);
@@ -1502,6 +1503,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 					break;
 				case TypeParameterDeclaration _:
 				case ComposedType _:
+				case LambdaExpression _:
 					Space();
 					break;
 				default:

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

@@ -31,11 +31,16 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 	/// </summary>
 	public class LambdaExpression : Expression
 	{
+		public static readonly Role<AttributeSection> AttributeRole = new Role<AttributeSection>("Attribute", null);
 		public readonly static TokenRole AsyncModifierRole = new TokenRole("async");
 		public static readonly Role<AstNode> BodyRole = new Role<AstNode>("Body", AstNode.Null);
 
 		bool isAsync;
 
+		public AstNodeCollection<AttributeSection> Attributes {
+			get { return base.GetChildrenByRole(AttributeRole); }
+		}
+
 		public bool IsAsync {
 			get { return isAsync; }
 			set { ThrowIfFrozen(); isAsync = value; }