Revamp to reflection.

Changes in brief:
1. Descriptor is now the entry point for all reflection.
2. IReflectedMessage has gone; there's now a Descriptor property in IMessage, which is explicitly implemented (due to the static property).
3. FieldAccessorTable has gone away
4. IFieldAccessor and OneofFieldAccessor still exist; we *could* put the functionality straight into FieldDescriptor and OneofDescriptor... I'm unsure about that.
5. There's a temporary property MessageDescriptor.FieldAccessorsByFieldNumber to make the test changes small - we probably want this to go away
6. Discovery for delegates is now via attributes applied to properties and the Clear method of a oneof

I'm happy with 1-3.
4 I'm unsure about - feedback welcome.
5 will go away
6 I'm unsure about, both in design and implementation. Should we have a ProtobufMessageAttribute too? Should we find all the relevant attributes in MessageDescriptor and pass them down, to avoid an O(N^2) scenario?

Generated code changes coming in the next commit.

3 files changed, 28 insertions, 26 deletions

diff --git a/csharp/src/Google.Protobuf.Test/GeneratedMessageTest.cs b/csharp/src/Google.Protobuf.Test/GeneratedMessageTest.cs
index acb20b15..180976d1 100644
--- a/csharp/src/Google.Protobuf.Test/GeneratedMessageTest.cs
+++ b/csharp/src/Google.Protobuf.Test/GeneratedMessageTest.cs
@@ -604,7 +604,7 @@ namespace Google.Protobuf
         public void Reflection_GetValue()

         {

             var message = SampleMessages.CreateFullTestAllTypes();

-            var fields = ((IReflectedMessage) message).Fields;

+            var fields = TestAllTypes.Descriptor.FieldAccessorsByFieldNumber;

             Assert.AreEqual(message.SingleBool, fields[TestAllTypes.SingleBoolFieldNumber].GetValue(message));

             Assert.AreEqual(message.SingleBytes, fields[TestAllTypes.SingleBytesFieldNumber].GetValue(message));

             Assert.AreEqual(message.SingleDouble, fields[TestAllTypes.SingleDoubleFieldNumber].GetValue(message));

@@ -639,7 +639,7 @@ namespace Google.Protobuf
 

             // Just a single map field, for the same reason

             var mapMessage = new TestMap { MapStringString = { { "key1", "value1" }, { "key2", "value2" } } };

-            fields = ((IReflectedMessage) mapMessage).Fields;

+            fields = TestMap.Descriptor.FieldAccessorsByFieldNumber;

             var dictionary = (IDictionary) fields[TestMap.MapStringStringFieldNumber].GetValue(mapMessage);

             Assert.AreEqual(mapMessage.MapStringString, dictionary);

             Assert.AreEqual("value1", dictionary["key1"]);

@@ -648,8 +648,8 @@ namespace Google.Protobuf
         [Test]

         public void Reflection_Clear()

         {

-            IReflectedMessage message = SampleMessages.CreateFullTestAllTypes();

-            var fields = message.Fields;

+            var message = SampleMessages.CreateFullTestAllTypes();

+            var fields = TestAllTypes.Descriptor.FieldAccessorsByFieldNumber;

             fields[TestAllTypes.SingleBoolFieldNumber].Clear(message);

             fields[TestAllTypes.SingleInt32FieldNumber].Clear(message);

             fields[TestAllTypes.SingleStringFieldNumber].Clear(message);

@@ -673,7 +673,7 @@ namespace Google.Protobuf
 

             // Separately, maps.

             var mapMessage = new TestMap { MapStringString = { { "key1", "value1" }, { "key2", "value2" } } };

-            fields = ((IReflectedMessage) mapMessage).Fields;

+            fields = TestMap.Descriptor.FieldAccessorsByFieldNumber;

             fields[TestMap.MapStringStringFieldNumber].Clear(mapMessage);

             Assert.AreEqual(0, mapMessage.MapStringString.Count);

         }

@@ -682,8 +682,8 @@ namespace Google.Protobuf
         public void Reflection_SetValue_SingleFields()

         {

             // Just a sample (primitives, messages, enums, strings, byte strings)

-            IReflectedMessage message = SampleMessages.CreateFullTestAllTypes();

-            var fields = message.Fields;

+            var message = SampleMessages.CreateFullTestAllTypes();

+            var fields = TestAllTypes.Descriptor.FieldAccessorsByFieldNumber;

             fields[TestAllTypes.SingleBoolFieldNumber].SetValue(message, false);

             fields[TestAllTypes.SingleInt32FieldNumber].SetValue(message, 500);

             fields[TestAllTypes.SingleStringFieldNumber].SetValue(message, "It's a string");

@@ -709,51 +709,52 @@ namespace Google.Protobuf
         [Test]

         public void Reflection_SetValue_SingleFields_WrongType()

         {

-            IReflectedMessage message = SampleMessages.CreateFullTestAllTypes();

-            var fields = message.Fields;

+            IMessage message = SampleMessages.CreateFullTestAllTypes();

+            var fields = message.Descriptor.FieldAccessorsByFieldNumber;

             Assert.Throws<InvalidCastException>(() => fields[TestAllTypes.SingleBoolFieldNumber].SetValue(message, "This isn't a bool"));

         }

 

         [Test]

         public void Reflection_SetValue_MapFields()

         {

-            IReflectedMessage message = new TestMap();

-            var fields = message.Fields;

+            IMessage message = new TestMap();

+            var fields = message.Descriptor.FieldAccessorsByFieldNumber;

             Assert.Throws<InvalidOperationException>(() => fields[TestMap.MapStringStringFieldNumber].SetValue(message, new Dictionary<string, string>()));

         }

 

         [Test]

         public void Reflection_SetValue_RepeatedFields()

         {

-            IReflectedMessage message = SampleMessages.CreateFullTestAllTypes();

-            var fields = message.Fields;

+            IMessage message = SampleMessages.CreateFullTestAllTypes();

+            var fields = message.Descriptor.FieldAccessorsByFieldNumber;

             Assert.Throws<InvalidOperationException>(() => fields[TestAllTypes.RepeatedDoubleFieldNumber].SetValue(message, new double[10]));

         }

 

         [Test]

         public void Reflection_GetValue_IncorrectType()

         {

-            IReflectedMessage message = SampleMessages.CreateFullTestAllTypes();

-            Assert.Throws<InvalidCastException>(() => message.Fields[TestAllTypes.SingleBoolFieldNumber].GetValue(new TestMap()));

+            IMessage message = SampleMessages.CreateFullTestAllTypes();

+            var fields = message.Descriptor.FieldAccessorsByFieldNumber;

+            Assert.Throws<InvalidCastException>(() => fields[TestAllTypes.SingleBoolFieldNumber].GetValue(new TestMap()));

         }

 

         [Test]

         public void Reflection_Oneof()

         {

             var message = new TestAllTypes();

-            var fields = ((IReflectedMessage) message).Fields;

-            Assert.AreEqual(1, fields.Oneofs.Count);

-            var oneof = fields.Oneofs[0];

-            Assert.AreEqual("oneof_field", oneof.Descriptor.Name);

-            Assert.IsNull(oneof.GetCaseFieldDescriptor(message));

+            var descriptor = TestAllTypes.Descriptor;

+            Assert.AreEqual(1, descriptor.Oneofs.Count);

+            var oneof = descriptor.Oneofs[0];

+            Assert.AreEqual("oneof_field", oneof.Name);

+            Assert.IsNull(oneof.Accessor.GetCaseFieldDescriptor(message));

 

             message.OneofString = "foo";

-            Assert.AreSame(fields[TestAllTypes.OneofStringFieldNumber].Descriptor, oneof.GetCaseFieldDescriptor(message));

+            Assert.AreSame(descriptor.FieldAccessorsByFieldNumber[TestAllTypes.OneofStringFieldNumber].Descriptor, oneof.Accessor.GetCaseFieldDescriptor(message));

 

             message.OneofUint32 = 10;

-            Assert.AreSame(fields[TestAllTypes.OneofUint32FieldNumber].Descriptor, oneof.GetCaseFieldDescriptor(message));

+            Assert.AreSame(descriptor.FieldAccessorsByFieldNumber[TestAllTypes.OneofUint32FieldNumber].Descriptor, oneof.Accessor.GetCaseFieldDescriptor(message));

 

-            oneof.Clear(message);

+            oneof.Accessor.Clear(message);

             Assert.AreEqual(TestAllTypes.OneofFieldOneofCase.None, message.OneofFieldCase);

         }

     }

diff --git a/csharp/src/Google.Protobuf.Test/Reflection/DescriptorsTest.cs b/csharp/src/Google.Protobuf.Test/Reflection/DescriptorsTest.cs
index 0db01a5e..0aff0a6c 100644
--- a/csharp/src/Google.Protobuf.Test/Reflection/DescriptorsTest.cs
+++ b/csharp/src/Google.Protobuf.Test/Reflection/DescriptorsTest.cs
@@ -62,6 +62,7 @@ namespace Google.Protobuf.Reflection
             Assert.AreEqual(UnittestImportProto3.Descriptor, file.Dependencies[0]);
 
             MessageDescriptor messageType = TestAllTypes.Descriptor;
+            Assert.AreSame(typeof(TestAllTypes), messageType.GeneratedType);
             Assert.AreEqual(messageType, file.MessageTypes[0]);
             Assert.AreEqual(messageType, file.FindTypeByName<MessageDescriptor>("TestAllTypes"));
             Assert.Null(file.FindTypeByName<MessageDescriptor>("NoSuchType"));
diff --git a/csharp/src/Google.Protobuf.Test/WellKnownTypes/WrappersTest.cs b/csharp/src/Google.Protobuf.Test/WellKnownTypes/WrappersTest.cs
index ad88c4eb..c617db36 100644
--- a/csharp/src/Google.Protobuf.Test/WellKnownTypes/WrappersTest.cs
+++ b/csharp/src/Google.Protobuf.Test/WellKnownTypes/WrappersTest.cs
@@ -192,7 +192,7 @@ namespace Google.Protobuf.WellKnownTypes
                 Uint32Field = 3,
                 Uint64Field = 4
             };
-            var fields = ((IReflectedMessage) message).Fields;
+            var fields = TestWellKnownTypes.Descriptor.FieldAccessorsByFieldNumber;
 
             Assert.AreEqual("x", fields[TestWellKnownTypes.StringFieldFieldNumber].GetValue(message));
             Assert.AreEqual(ByteString.CopyFrom(1, 2, 3), fields[TestWellKnownTypes.BytesFieldFieldNumber].GetValue(message));
@@ -216,7 +216,7 @@ namespace Google.Protobuf.WellKnownTypes
         {
             // Just a single example... note that we can't have a null value here
             var message = new RepeatedWellKnownTypes { Int32Field = { 1, 2 } };
-            var fields = ((IReflectedMessage) message).Fields;
+            var fields = RepeatedWellKnownTypes.Descriptor.FieldAccessorsByFieldNumber;
             var list = (IList) fields[RepeatedWellKnownTypes.Int32FieldFieldNumber].GetValue(message);
             CollectionAssert.AreEqual(new[] { 1, 2 }, list);
         }
@@ -226,7 +226,7 @@ namespace Google.Protobuf.WellKnownTypes
         {
             // Just a single example... note that we can't have a null value here
             var message = new MapWellKnownTypes { Int32Field = { { 1, 2 }, { 3, null } } };
-            var fields = ((IReflectedMessage) message).Fields;
+            var fields = MapWellKnownTypes.Descriptor.FieldAccessorsByFieldNumber;
             var dictionary = (IDictionary) fields[MapWellKnownTypes.Int32FieldFieldNumber].GetValue(message);
             Assert.AreEqual(2, dictionary[1]);
             Assert.IsNull(dictionary[3]);