fix 'could destabilise runtime' error if structs threw an error; also tidied...

fix 'could destabilise runtime' error if structs threw an error; also tidied up the locals and made the func return the right type

Dapper/SqlMapper.cs

@@ -1446,11 +1446,11 @@ static List<FieldInfo> GetSettableFields(Type t)
 #endif
 )
         {
-            var dm = new DynamicMethod(string.Format("Deserialize{0}", Guid.NewGuid()), type.IsValueType ? typeof(object) : type, new[] { typeof(IDataReader) }, true);
+            var dm = new DynamicMethod(string.Format("Deserialize{0}", Guid.NewGuid()), typeof(object), new[] { typeof(IDataReader) }, true);
 
             var il = dm.GetILGenerator();
             il.DeclareLocal(typeof(int));
-            var emptyLocal = il.DeclareLocal(type);
+            il.DeclareLocal(type);
             bool haveEnumLocal = false;
             il.Emit(OpCodes.Ldc_I4_0);
             il.Emit(OpCodes.Stloc_0);
@@ -1484,18 +1484,23 @@ static List<FieldInfo> GetSettableFields(Type t)
 
             int index = startBound;
 
-            il.BeginExceptionBlock();
-            // stack is empty
-
             if (type.IsValueType)
             {
-                il.Emit(OpCodes.Ldloca, emptyLocal);
+                il.Emit(OpCodes.Ldloca_S, (byte)1);
                 il.Emit(OpCodes.Initobj, type);
-                il.Emit(OpCodes.Ldloca, emptyLocal);
             }
             else
             {
                 il.Emit(OpCodes.Newobj, type.GetConstructor(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic, null, Type.EmptyTypes, null));
+                il.Emit(OpCodes.Stloc_1);
+            }
+            il.BeginExceptionBlock();
+            if(type.IsValueType)
+            {
+                il.Emit(OpCodes.Ldloca_S, (byte)1);// [target]
+            } else
+            {
+                il.Emit(OpCodes.Ldloc_1);// [target]
             }
 
             // stack is now [target]
@@ -1640,20 +1645,13 @@ static List<FieldInfo> GetSettableFields(Type t)
             il.Emit(OpCodes.Ldloc_0); // stack is Exception, index
             il.Emit(OpCodes.Ldarg_0); // stack is Exception, index, reader
             il.EmitCall(OpCodes.Call, typeof(SqlMapper).GetMethod("ThrowDataException"), null);
-            il.Emit(OpCodes.Ldnull);
-            il.Emit(OpCodes.Stloc_1); // to make it verifiable
             il.EndExceptionBlock();
 
-           
-            if (type.IsValueType)
+            il.Emit(OpCodes.Ldloc_1); // stack is [rval]
+            if(type.IsValueType)
             {
-                il.Emit(OpCodes.Ldloc, emptyLocal); // stack is [rval]
                 il.Emit(OpCodes.Box, type);
             }
-            else 
-            {
-                il.Emit(OpCodes.Ldloc_1); // stack is [rval]
-            }
             il.Emit(OpCodes.Ret);
 
             return (Func<IDataReader, object>)dm.CreateDelegate(typeof(Func<IDataReader,object>));

Tests/Tests.cs

@@ -1192,5 +1192,22 @@ public void TestNullableUniqueIdentifierNull()
             var result = connection.Query<Guid?>("declare @foo uniqueidentifier set @foo = @guid select @foo", new { guid }).Single();
             result.IsEqualTo(guid);
         }
+
+
+        public void TestFailInASaneWayWithWrongStructColumnTypes()
+        {
+            try
+            {
+                connection.Query<CanHazInt>("select cast(1 as bigint) Value").Single();
+                throw new Exception("Should not have got here");
+            } catch(DataException ex)
+            {
+                ex.Message.IsEqualTo("Error parsing column 0 (Value=1 - Int64)");
+            }
+        }
+        struct CanHazInt
+        {
+            public int Value { get; set; }
+        }
     }
 }