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.

1 files changed, 8 insertions, 2 deletions

diff --git a/csharp/src/Google.Protobuf/WellKnownTypes/Struct.cs b/csharp/src/Google.Protobuf/WellKnownTypes/Struct.cs
index 1fa35521..65119894 100644
--- a/csharp/src/Google.Protobuf/WellKnownTypes/Struct.cs
+++ b/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;
       }