From b7a5924b25699ae275fed677ac0a279ebeede283 Mon Sep 17 00:00:00 2001
From: Daniel Grunwald <daniel@danielgrunwald.de>
Date: Fri, 13 Oct 2017 13:38:52 +0200
Subject: [PATCH] When possible, use implicit method group conversions to
 construct delegates.

---
 .../TestCases/Pretty/DelegateConstruction.cs      |  6 +++---
 ICSharpCode.Decompiler/CSharp/CallBuilder.cs      | 15 +++++++++------
 .../CSharp/TranslatedExpression.cs                | 11 +++++++----
 3 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/ICSharpCode.Decompiler.Tests/TestCases/Pretty/DelegateConstruction.cs b/ICSharpCode.Decompiler.Tests/TestCases/Pretty/DelegateConstruction.cs
index cd9681ddc..d4033768b 100644
--- a/ICSharpCode.Decompiler.Tests/TestCases/Pretty/DelegateConstruction.cs
+++ b/ICSharpCode.Decompiler.Tests/TestCases/Pretty/DelegateConstruction.cs
@@ -88,17 +88,17 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 
 		public static Action<string> ExtensionMethodUnbound()
 		{
-			return new Action<string>(DelegateConstruction.Test);
+			return DelegateConstruction.Test;
 		}
 
 		public static Action ExtensionMethodBound()
 		{
-			return new Action("abc".Test);
+			return "abc".Test;
 		}
 
 		public static Action ExtensionMethodBoundOnNull()
 		{
-			return new Action(((string)null).Test);
+			return ((string)null).Test;
 		}
 
 		public static object StaticMethod()
diff --git a/ICSharpCode.Decompiler/CSharp/CallBuilder.cs b/ICSharpCode.Decompiler/CSharp/CallBuilder.cs
index 2a57d77e7..23f0add1a 100644
--- a/ICSharpCode.Decompiler/CSharp/CallBuilder.cs
+++ b/ICSharpCode.Decompiler/CSharp/CallBuilder.cs
@@ -339,18 +339,21 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 			var lookup = new MemberLookup(resolver.CurrentTypeDefinition, resolver.CurrentTypeDefinition.ParentAssembly);
 			var or = new OverloadResolution(resolver.Compilation, method.Parameters.SelectArray(p => new TypeResolveResult(p.Type)));
-			var result = lookup.Lookup(target.ResolveResult, method.Name, method.TypeArguments, true) as MethodGroupResolveResult;
+			var result = lookup.Lookup(target.ResolveResult, method.Name, method.TypeArguments, false);
 
-			if (result == null) {
+			bool needsCast = true;
+			if (result is MethodGroupResolveResult mgrr) {
+				or.AddMethodLists(mgrr.MethodsGroupedByDeclaringType.ToArray());
+				needsCast = (or.BestCandidateErrors != OverloadResolutionErrors.None || !IsAppropriateCallTarget(method, or.BestCandidate, func.OpCode == OpCode.LdVirtFtn));
+			}
+			if (needsCast) {
 				target = target.ConvertTo(targetType, expressionBuilder);
-			} else {
-				or.AddMethodLists(result.MethodsGroupedByDeclaringType.ToArray());
-				if (or.BestCandidateErrors != OverloadResolutionErrors.None || !IsAppropriateCallTarget(method, or.BestCandidate, func.OpCode == OpCode.LdVirtFtn))
-					target = target.ConvertTo(targetType, expressionBuilder);
+				result = lookup.Lookup(target.ResolveResult, method.Name, method.TypeArguments, false);
 			}
 
 			var mre = new MemberReferenceExpression(target, method.Name);
 			mre.TypeArguments.AddRange(method.TypeArguments.Select(expressionBuilder.ConvertType));
+			mre.WithRR(result);
 			var oce = new ObjectCreateExpression(expressionBuilder.ConvertType(inst.Method.DeclaringType), mre)
 				.WithILInstruction(inst)
 				.WithRR(new ConversionResolveResult(
diff --git a/ICSharpCode.Decompiler/CSharp/TranslatedExpression.cs b/ICSharpCode.Decompiler/CSharp/TranslatedExpression.cs
index a4f9f2bdd..ad82d776f 100644
--- a/ICSharpCode.Decompiler/CSharp/TranslatedExpression.cs
+++ b/ICSharpCode.Decompiler/CSharp/TranslatedExpression.cs
@@ -173,11 +173,14 @@ namespace ICSharpCode.Decompiler.CSharp
 			var type = this.Type;
 			if (type.Equals(targetType)) {
 				// Make explicit conversion implicit, if possible
-				if (allowImplicitConversion && Expression is CastExpression cast && ResolveResult is ConversionResolveResult conversion) {
-					if (type.IsKnownType(KnownTypeCode.Object) && conversion.Conversion.IsBoxingConversion
-						|| type.Kind == TypeKind.Delegate && conversion.Conversion.IsAnonymousFunctionConversion)
-					{
+				if (allowImplicitConversion && ResolveResult is ConversionResolveResult conversion) {
+					if (Expression is CastExpression cast
+					&& (type.IsKnownType(KnownTypeCode.Object) && conversion.Conversion.IsBoxingConversion
+						|| type.Kind == TypeKind.Delegate && conversion.Conversion.IsAnonymousFunctionConversion
+						)) {
 						return this.UnwrapChild(cast.Expression);
+					} else if (Expression is ObjectCreateExpression oce && conversion.Conversion.IsMethodGroupConversion && oce.Arguments.Count == 1) {
+						return this.UnwrapChild(oce.Arguments.Single());
 					}
 				}
 				return this;