Fix merging with message-valued oneof

If messages A and B have the same oneof case, which is a message
type, and we merge B into A, those sub-messages should be merged.

Fixes #3200.

Note that I haven't regenerated all the code, as some of the protos
have been changed, breaking generation.

csharp/protos/unittest_issues.proto

@@ -124,3 +124,18 @@ message TestJsonName {
   string description = 2 [json_name = "desc"];
   string guid = 3 [json_name = "exid"];
 }
+
+// Issue 3200: When merging two messages which use the same
+// oneof case, which is itself a message type, the submessages should
+// be merged.
+message OneofMerging {
+  message Nested {
+    int32 x = 1;
+    int32 y = 2;
+  }
+
+  oneof value {
+    string text = 1;
+    Nested nested = 2;
+  }
+}
\ No newline at end of file

csharp/src/Google.Protobuf.Test/IssuesTest.cs

@@ -33,7 +33,7 @@
 using Google.Protobuf.Reflection;
 using UnitTest.Issues.TestProtos;
 using NUnit.Framework;
-
+using static UnitTest.Issues.TestProtos.OneofMerging.Types;
 
 namespace Google.Protobuf
 {
@@ -78,5 +78,17 @@ namespace Google.Protobuf
             Assert.AreEqual("{ \"name\": \"test\", \"desc\": \"test2\", \"exid\": \"test3\" }",
                 JsonFormatter.Default.Format(message));
         }
+
+        [Test]
+        public void OneofMerging()
+        {
+            var message1 = new OneofMerging { Nested = new Nested { X = 10 } };
+            var message2 = new OneofMerging { Nested = new Nested { Y = 20 } };
+            var expected = new OneofMerging { Nested = new Nested { X = 10, Y = 20 } };
+
+            var merged = message1.Clone();
+            merged.MergeFrom(message2);
+            Assert.AreEqual(expected, merged);
+        }
     }
 }

csharp/src/Google.Protobuf/WellKnownTypes/Struct.cs

@@ -466,10 +466,16 @@ namespace Google.Protobuf.WellKnownTypes {
           BoolValue = other.BoolValue;
           break;
         case KindOneofCase.StructValue:
-          StructValue = other.StructValue;
+          if (StructValue == null) {
+            StructValue = new global::Google.Protobuf.WellKnownTypes.Struct();
+          }
+          StructValue.MergeFrom(other.StructValue);
           break;
         case KindOneofCase.ListValue:
-          ListValue = other.ListValue;
+          if (ListValue == null) {
+            ListValue = new global::Google.Protobuf.WellKnownTypes.ListValue();
+          }
+          ListValue.MergeFrom(other.ListValue);
           break;
       }
 

src/google/protobuf/compiler/csharp/csharp_enum_field.cc

@@ -89,6 +89,10 @@ EnumOneofFieldGenerator::EnumOneofFieldGenerator(
 EnumOneofFieldGenerator::~EnumOneofFieldGenerator() {
 }
 
+void EnumOneofFieldGenerator::GenerateMergingCode(io::Printer* printer) {
+  printer->Print(variables_, "$property_name$ = other.$property_name$;\n");
+}
+
 void EnumOneofFieldGenerator::GenerateParsingCode(io::Printer* printer) {
   // TODO(jonskeet): What about if we read the default value?
   printer->Print(

src/google/protobuf/compiler/csharp/csharp_enum_field.h

@@ -64,6 +64,7 @@ class EnumOneofFieldGenerator : public PrimitiveOneofFieldGenerator {
                           const Options *options);
   ~EnumOneofFieldGenerator();
 
+  virtual void GenerateMergingCode(io::Printer* printer);
   virtual void GenerateParsingCode(io::Printer* printer);
   virtual void GenerateSerializationCode(io::Printer* printer);
   virtual void GenerateSerializedSizeCode(io::Printer* printer);

src/google/protobuf/compiler/csharp/csharp_message.cc

@@ -463,9 +463,12 @@ void MessageGenerator::GenerateMergingMethods(io::Printer* printer) {
       vars["field_property_name"] = GetPropertyName(field);
       printer->Print(
         vars,
-        "case $property_name$OneofCase.$field_property_name$:\n"
-        "  $field_property_name$ = other.$field_property_name$;\n"
-        "  break;\n");
+        "case $property_name$OneofCase.$field_property_name$:\n");
+      printer->Indent();
+      scoped_ptr<FieldGeneratorBase> generator(CreateFieldGeneratorInternal(field));
+      generator->GenerateMergingCode(printer);
+      printer->Print("break;\n");
+      printer->Outdent();
     }
     printer->Outdent();
     printer->Print("}\n\n");

src/google/protobuf/compiler/csharp/csharp_message_field.cc

@@ -171,6 +171,14 @@ void MessageOneofFieldGenerator::GenerateMembers(io::Printer* printer) {
     "}\n");
 }
 
+void MessageOneofFieldGenerator::GenerateMergingCode(io::Printer* printer) {
+  printer->Print(variables_, 
+    "if ($property_name$ == null) {\n"
+    "  $property_name$ = new $type_name$();\n"
+    "}\n"
+    "$property_name$.MergeFrom(other.$property_name$);\n");
+}
+
 void MessageOneofFieldGenerator::GenerateParsingCode(io::Printer* printer) {
   // TODO(jonskeet): We may be able to do better than this
   printer->Print(

src/google/protobuf/compiler/csharp/csharp_message_field.h

@@ -74,6 +74,7 @@ class MessageOneofFieldGenerator : public MessageFieldGenerator {
 
   virtual void GenerateCloningCode(io::Printer* printer);
   virtual void GenerateMembers(io::Printer* printer);
+  virtual void GenerateMergingCode(io::Printer* printer);
   virtual void WriteToString(io::Printer* printer);
   virtual void GenerateParsingCode(io::Printer* printer);
 

src/google/protobuf/compiler/csharp/csharp_primitive_field.cc

@@ -196,6 +196,10 @@ void PrimitiveOneofFieldGenerator::GenerateMembers(io::Printer* printer) {
       "}\n");
 }
 
+void PrimitiveOneofFieldGenerator::GenerateMergingCode(io::Printer* printer) {
+  printer->Print(variables_, "$property_name$ = other.$property_name$;\n");
+}
+
 void PrimitiveOneofFieldGenerator::WriteToString(io::Printer* printer) {
   printer->Print(variables_,
     "PrintField(\"$descriptor_name$\", $has_property_check$, $oneof_name$_, writer);\n");

src/google/protobuf/compiler/csharp/csharp_primitive_field.h

@@ -78,6 +78,7 @@ class PrimitiveOneofFieldGenerator : public PrimitiveFieldGenerator {
 
   virtual void GenerateCloningCode(io::Printer* printer);
   virtual void GenerateMembers(io::Printer* printer);
+  virtual void GenerateMergingCode(io::Printer* printer);
   virtual void WriteToString(io::Printer* printer);
   virtual void GenerateParsingCode(io::Printer* printer);
 

src/google/protobuf/compiler/csharp/csharp_wrapper_field.cc

@@ -181,6 +181,10 @@ void WrapperOneofFieldGenerator::GenerateMembers(io::Printer* printer) {
     "}\n");
 }
 
+void WrapperOneofFieldGenerator::GenerateMergingCode(io::Printer* printer) {
+  printer->Print(variables_, "$property_name$ = other.$property_name$;\n");
+}
+
 void WrapperOneofFieldGenerator::GenerateParsingCode(io::Printer* printer) {
   printer->Print(
     variables_,

src/google/protobuf/compiler/csharp/csharp_wrapper_field.h

@@ -75,6 +75,7 @@ class WrapperOneofFieldGenerator : public WrapperFieldGenerator {
   ~WrapperOneofFieldGenerator();
 
   virtual void GenerateMembers(io::Printer* printer);
+  virtual void GenerateMergingCode(io::Printer* printer);
   virtual void GenerateParsingCode(io::Printer* printer);
   virtual void GenerateSerializationCode(io::Printer* printer);
   virtual void GenerateSerializedSizeCode(io::Printer* printer);