Format method parameter type list more accurately

This ensures that `in`, `ref`, `out`, and `params` modifiers are in-
cluded in the formatting of parameter type lists.

src/Moq/Extensions.cs

@@ -10,6 +10,7 @@
 using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Runtime.ExceptionServices;
+using System.Text;
 
 using Moq.Properties;
 
@@ -188,6 +189,11 @@ public static bool CompareTo<TTypes, TOtherTypes>(this TTypes types, TOtherTypes
 			return true;
 		}
 
+		public static string GetParameterTypeList(this MethodInfo method)
+		{
+			return new StringBuilder().AppendParameterTypeList(method.GetParameters()).ToString();
+		}
+
 		public static ParameterTypes GetParameterTypes(this MethodInfo method)
 		{
 			return new ParameterTypes(method.GetParameters());

src/Moq/MethodCall.cs

@@ -187,14 +187,12 @@ public void SetCallbackResponse(Delegate callback)
 				var expectedParamTypes = this.Method.GetParameterTypes();
 				if (!callback.CompareParameterTypesTo(expectedParamTypes))
 				{
-					// TODO: the following won't properly distinguish between `in`, `ref`, and `out` parameters!
-					var actualParams = callback.GetMethodInfo().GetParameters();
 					throw new ArgumentException(
 						string.Format(
 							CultureInfo.CurrentCulture,
 							Resources.InvalidCallbackParameterMismatch,
-							string.Join(", ", expectedParamTypes.Select(p => p.GetFormattedName()).ToArray()),
-							string.Join(", ", actualParams.Select(p => p.ParameterType.GetFormattedName()).ToArray())));
+							this.Method.GetParameterTypeList(),
+							callback.GetMethodInfo().GetParameterTypeList()));
 				}
 
 				if (callback.GetMethodInfo().ReturnType != typeof(void))

src/Moq/StringBuilderExtensions.cs

@@ -74,6 +74,54 @@ public static StringBuilder AppendNameOf(this StringBuilder stringBuilder, Type
 			return stringBuilder.AppendFormattedName(type);
 		}
 
+		public static StringBuilder AppendParameterType(this StringBuilder stringBuilder, ParameterInfo parameter)
+		{
+			var parameterType = parameter.ParameterType;
+
+			if (parameterType.IsByRef)
+			{
+				switch (parameter.Attributes & (ParameterAttributes.In | ParameterAttributes.Out))
+				{
+					case ParameterAttributes.In:
+						stringBuilder.Append("in ");
+						break;
+
+					case ParameterAttributes.Out:
+						stringBuilder.Append("out ");
+						break;
+
+					case ParameterAttributes.In | ParameterAttributes.Out:
+					default:
+						stringBuilder.Append("ref ");
+						break;
+				}
+
+				parameterType = parameterType.GetElementType();
+			}
+
+			if (parameterType.IsArray && parameter.IsDefined(typeof(ParamArrayAttribute), true))
+			{
+				stringBuilder.Append("params ");
+			}
+
+			return stringBuilder.AppendFormattedName(parameterType);
+		}
+
+		public static StringBuilder AppendParameterTypeList(this StringBuilder stringBuilder, ParameterInfo[] parameters)
+		{
+			for (int i = 0; i < parameters.Length; ++i)
+			{
+				if (i > 0)
+				{
+					stringBuilder.Append(", ");
+				}
+
+				stringBuilder.AppendParameterType(parameters[i]);
+			}
+
+			return stringBuilder;
+		}
+
 		public static StringBuilder AppendValueOf(this StringBuilder stringBuilder, object obj)
 		{
 			if (obj == null)

tests/Moq.Tests/StringBuilderExtensionsFixture.cs

@@ -0,0 +1,45 @@
+// Copyright (c) 2007, Clarius Consulting, Manas Technology Solutions, InSTEDD.
+// All rights reserved. Licensed under the BSD 3-Clause License; see License.txt.
+
+using System.Text;
+
+using Xunit;
+
+namespace Moq.Tests
+{
+	public class StringBuilderExtensionsFixture
+	{
+		[Theory]
+		[InlineData(nameof(IMethods.Empty), "")]
+		[InlineData(nameof(IMethods.Int), "int")]
+		[InlineData(nameof(IMethods.IntAndString), "int, string")]
+		[InlineData(nameof(IMethods.InInt), "in int")]
+		[InlineData(nameof(IMethods.RefInt), "ref int")]
+		[InlineData(nameof(IMethods.OutInt), "out int")]
+		[InlineData(nameof(IMethods.BoolAndParamsString), "bool, params string[]")]
+		public void AppendParameterList_formats_parameter_lists_correctly(string methodName, string expected)
+		{
+			var actual = GetFormattedParameterListOf(methodName);
+			Assert.Equal(expected, actual);
+		}
+
+		private string GetFormattedParameterListOf(string methodName)
+		{
+			var stringBuilder = new StringBuilder();
+			var method = typeof(IMethods).GetMethod(methodName);
+			stringBuilder.AppendParameterTypeList(method.GetParameters());
+			return stringBuilder.ToString();
+		}
+
+		public interface IMethods
+		{
+			void Empty();
+			void Int(int arg1);
+			void IntAndString(int arg1, string arg2);
+			void InInt(in int arg1);
+			void RefInt(ref int arg1);
+			void OutInt(out int arg1);
+			void BoolAndParamsString(bool arg1, params string[] arg2);
+		}
+	}
+}