Fix #2506: NamedArgumentTransform loses information, if the original variable is of StackType.Ref

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -1618,7 +1618,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 			else
 			{
-				return compilation.FindType(stackType.ToKnownTypeCode(sign));
+				return compilation.FindType(stackType, sign);
 			}
 		}
 
@@ -1644,7 +1644,7 @@ namespace ICSharpCode.Decompiler.CSharp
 					stackType = StackType.I8;
 				}
 			}
-			return compilation.FindType(stackType.ToKnownTypeCode(sign));
+			return compilation.FindType(stackType, sign);
 		}
 
 		/// <summary>
@@ -3568,7 +3568,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				}
 				else if (!value.Type.Equals(SpecialType.NullType) && !fallback.Type.Equals(SpecialType.NullType) && !value.Type.Equals(fallback.Type))
 				{
-					targetType = compilation.FindType(inst.UnderlyingResultType.ToKnownTypeCode());
+					targetType = compilation.FindType(inst.UnderlyingResultType);
 				}
 				else
 				{
@@ -3731,7 +3731,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 			else
 			{
-				resultType = compilation.FindType(inst.ResultType.ToKnownTypeCode());
+				resultType = compilation.FindType(inst.ResultType);
 			}
 
 			foreach (var section in inst.Sections)

ICSharpCode.Decompiler/IL/ILReader.cs

@@ -1170,7 +1170,7 @@ namespace ICSharpCode.Decompiler.IL
 		ILInstruction Push(ILInstruction inst)
 		{
 			Debug.Assert(inst.ResultType != StackType.Void);
-			IType type = compilation.FindType(inst.ResultType.ToKnownTypeCode());
+			IType type = compilation.FindType(inst.ResultType);
 			var v = new ILVariable(VariableKind.StackSlot, type, inst.ResultType);
 			v.HasGeneratedName = true;
 			currentStack = currentStack.Push(v);

ICSharpCode.Decompiler/IL/Transforms/CopyPropagation.cs

@@ -148,7 +148,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			for (int j = 0; j < uninlinedArgs.Length; j++)
 			{
 				var arg = copiedExpr.Children[j];
-				var type = context.TypeSystem.FindType(arg.ResultType.ToKnownTypeCode());
+				var type = context.TypeSystem.FindType(arg.ResultType);
 				uninlinedArgs[j] = new ILVariable(VariableKind.StackSlot, type, arg.ResultType) {
 					Name = "C_" + arg.StartILOffset,
 					HasGeneratedName = true,

ICSharpCode.Decompiler/IL/Transforms/ILExtraction.cs

@@ -62,7 +62,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		{
 			FlagsBeingMoved |= predecessor.Flags;
 			MoveActions.Add(delegate {
-				var type = context.TypeSystem.FindType(predecessor.ResultType.ToKnownTypeCode());
+				var type = context.TypeSystem.FindType(predecessor.ResultType);
 				var v = Function.RegisterVariable(VariableKind.StackSlot, type);
 				predecessor.ReplaceWith(new LdLoc(v));
 				return new StLoc(v, predecessor);
@@ -119,7 +119,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				{
 					// We've reached the target block, and extraction is possible all the way.
 					int insertIndex = inst.ChildIndex;
-					var type = context.TypeSystem.FindType(instToExtract.ResultType.ToKnownTypeCode());
+					var type = context.TypeSystem.FindType(instToExtract.ResultType);
 					// Move instToExtract itself:
 					var v = function.RegisterVariable(VariableKind.StackSlot, type);
 					instToExtract.ReplaceWith(new LdLoc(v));

ICSharpCode.Decompiler/IL/Transforms/NamedArgumentTransform.cs

@@ -87,7 +87,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		{
 			var call = (CallInstruction)arg.Parent;
 			Debug.Assert(context.Function == call.Ancestors.OfType<ILFunction>().First());
-			var type = context.TypeSystem.FindType(arg.ResultType.ToKnownTypeCode());
+			var type = context.TypeSystem.FindType(arg.ResultType);
 			var v = context.Function.RegisterVariable(VariableKind.NamedArgument, type);
 			context.Step($"Introduce named argument '{v.Name}'", arg);
 			if (!(call.Parent is Block namedArgBlock) || namedArgBlock.Kind != BlockKind.CallWithNamedArgs)

ICSharpCode.Decompiler/IL/Transforms/NullableLiftingTransform.cs

@@ -630,7 +630,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			if (!MatchNullableCtor(trueInst, out var utype, out var exprToLift))
 			{
 				isNullCoalescingWithNonNullableFallback = true;
-				utype = context.TypeSystem.FindType(trueInst.ResultType.ToKnownTypeCode());
+				utype = context.TypeSystem.FindType(trueInst.ResultType);
 				exprToLift = trueInst;
 				if (nullableVars.Count == 1 && exprToLift.MatchLdLoc(nullableVars[0]))
 				{

ICSharpCode.Decompiler/TypeSystem/ReflectionHelper.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 
+using ICSharpCode.Decompiler.IL;
 using ICSharpCode.Decompiler.TypeSystem.Implementation;
 
 namespace ICSharpCode.Decompiler.TypeSystem
@@ -66,6 +67,19 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		{
 			return type.ToTypeReference().Resolve(new SimpleTypeResolveContext(compilation));
 		}
+
+		public static IType FindType(this ICompilation compilation, StackType stackType, Sign sign = Sign.None)
+		{
+			switch (stackType)
+			{
+				case StackType.Unknown:
+					return SpecialType.UnknownType;
+				case StackType.Ref:
+					return new ByReferenceType(SpecialType.UnknownType);
+				default:
+					return compilation.FindType(stackType.ToKnownTypeCode(sign));
+			}
+		}
 		#endregion
 
 		#region Type.ToTypeReference()