Support oneofs in the Ruby code generator.

src/google/protobuf/compiler/ruby/ruby_generator.cc

@@ -100,15 +100,8 @@ std::string TypeName(const google::protobuf::FieldDescriptor* field) {
   }
 }
 
-void GenerateMessage(const google::protobuf::Descriptor* message,
+void GenerateField(const google::protobuf::FieldDescriptor* field,
                    google::protobuf::io::Printer* printer) {
-  printer->Print(
-    "add_message \"$name$\" do\n",
-    "name", message->full_name());
-  printer->Indent();
-
-  for (int i = 0; i < message->field_count(); i++) {
-    const FieldDescriptor* field = message->field(i);
   printer->Print(
     "$label$ :$name$, ",
     "label", LabelForField(field),
@@ -130,6 +123,41 @@ void GenerateMessage(const google::protobuf::Descriptor* message,
   }
 }
 
+void GenerateOneof(const google::protobuf::OneofDescriptor* oneof,
+                   google::protobuf::io::Printer* printer) {
+  printer->Print(
+      "oneof :$name$ do\n",
+      "name", oneof->name());
+  printer->Indent();
+
+  for (int i = 0; i < oneof->field_count(); i++) {
+    const FieldDescriptor* field = oneof->field(i);
+    GenerateField(field, printer);
+  }
+
+  printer->Outdent();
+  printer->Print("end\n");
+}
+
+void GenerateMessage(const google::protobuf::Descriptor* message,
+                     google::protobuf::io::Printer* printer) {
+  printer->Print(
+    "add_message \"$name$\" do\n",
+    "name", message->full_name());
+  printer->Indent();
+
+  for (int i = 0; i < message->field_count(); i++) {
+    const FieldDescriptor* field = message->field(i);
+    if (!field->containing_oneof()) {
+      GenerateField(field, printer);
+    }
+  }
+
+  for (int i = 0; i < message->oneof_decl_count(); i++) {
+    const OneofDescriptor* oneof = message->oneof_decl(i);
+    GenerateOneof(oneof, printer);
+  }
+
   printer->Outdent();
   printer->Print("end\n");