Issue 50: The XML serializer will fail to deserialize a message with empty child message

src/ProtocolBuffers.Serialization/XmlFormatReader.cs

@@ -225,15 +225,18 @@ namespace Google.ProtocolBuffers.Serialization
                 stopNode = _elements.Peek();
             }
 
-            while (!_input.IsStartElement() && _input.Depth > stopNode.Depth && _input.Read())
+            if (!stopNode.IsEmpty)
             {
-                continue;
-            }
+                while (!_input.IsStartElement() && _input.Depth > stopNode.Depth && _input.Read())
+                {
+                    continue;
+                }
 
-            if (_input.IsStartElement())
-            {
-                field = _input.LocalName;
-                return true;
+                if (_input.IsStartElement() && _input.Depth > stopNode.Depth)
+                {
+                    field = _input.LocalName;
+                    return true;
+                }
             }
             field = null;
             return false;

src/ProtocolBuffers.Test/Compatibility/CompatibilityTests.cs

@@ -25,6 +25,40 @@ namespace Google.ProtocolBuffers.Compatibility
             Assert.AreEqual<object>(lhs, rhs);
         }
 
+        [TestMethod]
+        public virtual void RoundTripWithEmptyChildMessageSize()
+        {
+            SizeMessage1 msg = SizeMessage1.CreateBuilder()
+                .SetField100(100)
+                .SetField15(SizeMessage1SubMessage.DefaultInstance)
+                .BuildPartial();
+            byte[] contents = msg.ToByteArray();
+            object content = SerializeMessage<SizeMessage1, SizeMessage1.Builder>(msg);
+
+            SizeMessage1 copy = DeserializeMessage<SizeMessage1, SizeMessage1.Builder>(content, SizeMessage1.CreateBuilder(), ExtensionRegistry.Empty).BuildPartial();
+
+            Assert.AreEqual(msg, copy);
+            AssertOutputEquals(content, SerializeMessage<SizeMessage1, SizeMessage1.Builder>(copy));
+            Assert.AreEqual(Convert.ToBase64String(contents), Convert.ToBase64String(copy.ToByteArray()));
+        }
+
+        [TestMethod]
+        public virtual void RoundTripWithEmptyChildMessageSpeed()
+        {
+            SpeedMessage1 msg = SpeedMessage1.CreateBuilder()
+                .SetField100(100)
+                .SetField15(SpeedMessage1SubMessage.DefaultInstance)
+                .BuildPartial();
+            byte[] contents = msg.ToByteArray();
+            object content = SerializeMessage<SpeedMessage1, SpeedMessage1.Builder>(msg);
+
+            SpeedMessage1 copy = DeserializeMessage<SpeedMessage1, SpeedMessage1.Builder>(content, SpeedMessage1.CreateBuilder(), ExtensionRegistry.Empty).BuildPartial();
+
+            Assert.AreEqual(msg, copy);
+            AssertOutputEquals(content, SerializeMessage<SpeedMessage1, SpeedMessage1.Builder>(copy));
+            Assert.AreEqual(Convert.ToBase64String(contents), Convert.ToBase64String(copy.ToByteArray()));
+        }
+
         [TestMethod]
         public virtual void RoundTripMessage1OptimizeSize()
         {