Extend information in exception raised by ComplexTypeProvider.

Author: drewnoakes

Dasher.Tests/DeserialiserTests.cs

@@ -179,7 +179,7 @@ public void ThrowsOnNonMapData()
 
             var deserialiser = new Deserialiser<UserScore>();
             var ex = Assert.Throws<DeserialisationException>(() => deserialiser.Deserialise(bytes));
-            Assert.Equal("Message must be encoded as a MsgPack map", ex.Message);
+            Assert.Equal("Message must be encoded as a MsgPack map, not \"FixArray\".", ex.Message);
             Assert.Equal(typeof(UserScore), ex.TargetType);
         }
 

Dasher/Methods.cs

@@ -18,6 +18,7 @@ internal static class Methods
 
         public static MethodInfo String_Equals_String_String                    { get; } = typeof(string).GetMethod(nameof(string.Equals), BindingFlags.Static | BindingFlags.Public, null, new[] {typeof(string), typeof(string)}, null);
         public static MethodInfo String_Equals_String_StringComparison          { get; } = typeof(string).GetMethod(nameof(string.Equals), new[] {typeof(string), typeof(StringComparison)});
+        public static MethodInfo String_Format_String_Object                    { get; } = typeof(string).GetMethod(nameof(string.Format), new[] {typeof(string), typeof(object)});
         public static MethodInfo String_Format_String_Object_Object             { get; } = typeof(string).GetMethod(nameof(string.Format), new[] {typeof(string), typeof(object), typeof(object)});
         public static MethodInfo String_Format_String_Object_Object_Object      { get; } = typeof(string).GetMethod(nameof(string.Format), new[] {typeof(string), typeof(object), typeof(object), typeof(object)});
 

Dasher/TypeProviders/ComplexTypeProvider.cs

@@ -120,6 +120,19 @@ public bool TryEmitDeserialiseCode(ILGenerator ilg, ThrowBlockGatherer throwBloc
                 ilg.Emit(OpCodes.Throw);
             };
 
+            Action loadPeekedFormatName = () =>
+            {
+                var format = ilg.DeclareLocal(typeof(Format));
+                ilg.Emit(OpCodes.Ldloc, unpacker);
+                ilg.Emit(OpCodes.Ldloca, format);
+                ilg.Emit(OpCodes.Call, Methods.Unpacker_TryPeekFormat);
+                // Drop the return value: if false, 'format' will be 'Unknown' which is fine.
+                ilg.Emit(OpCodes.Pop);
+                ilg.Emit(OpCodes.Ldloc, format);
+                ilg.Emit(OpCodes.Box, typeof(Format));
+                ilg.Emit(OpCodes.Call, Methods.Format_ToString);
+            };
+
             #region Initialise locals for constructor args
 
             var valueLocals = new LocalBuilder[parameters.Length];
@@ -204,7 +217,9 @@ public bool TryEmitDeserialiseCode(ILGenerator ilg, ThrowBlockGatherer throwBloc
                     ilg.Emit(OpCodes.Ldstr, "Data stream empty");
                     throwException();
                     ilg.MarkLabel(lblNotEmpty);
-                    ilg.Emit(OpCodes.Ldstr, "Message must be encoded as a MsgPack map");
+                    ilg.Emit(OpCodes.Ldstr, "Message must be encoded as a MsgPack map, not \"{0}\".");
+                    loadPeekedFormatName();
+                    ilg.Emit(OpCodes.Call, Methods.String_Format_String_Object);
                     throwException();
                 });
             }
@@ -325,18 +340,9 @@ public bool TryEmitDeserialiseCode(ILGenerator ilg, ThrowBlockGatherer throwBloc
                 {
                     throwBlocks.Throw(() =>
                     {
-                        var format = ilg.DeclareLocal(typeof(Format));
-                        ilg.Emit(OpCodes.Ldloc, unpacker);
-                        ilg.Emit(OpCodes.Ldloca, format);
-                        ilg.Emit(OpCodes.Call, Methods.Unpacker_TryPeekFormat);
-                        // Drop the return value: if false, 'format' will be 'Unknown' which is fine.
-                        ilg.Emit(OpCodes.Pop);
-
                         ilg.Emit(OpCodes.Ldstr, "Encountered unexpected field \"{0}\" of MsgPack format \"{1}\" for CLR type \"{2}\".");
                         ilg.Emit(OpCodes.Ldloc, key);
-                        ilg.Emit(OpCodes.Ldloc, format);
-                        ilg.Emit(OpCodes.Box, typeof(Format));
-                        ilg.Emit(OpCodes.Call, Methods.Format_ToString);
+                        loadPeekedFormatName();
                         ilg.Emit(OpCodes.Ldstr, targetType.Name);
                         ilg.Emit(OpCodes.Call, Methods.String_Format_String_Object_Object_Object);
                         throwException();