JSON parsing of overlapping oneof keys

[sttawm]

Would it make sense for the JSON parser to complain if multiple fields of a oneof are defined?

Or maybe the compiler could be configured to generate code (a Reads[T]) that complains if the oneof is oversubscribed?

I looked into passing a custom formatter via .registerMessageFormatter to gain access to the e.g. JValue before passing it along to the default parser, but I don't have access to a default parser, and I don't want to have to specify a writer as well.

I may be able to take a pass at it if this could be helpful to others or if there's a suggested way to handle this.

[thesamet]

I think that it would be reasonable to add an option for this that should be opt-in (in order to avoid breaking existing user). Can you check how this is handled in protobuf-java? If there's some pre-existing behavior then we should follow that here. A PR to address this will be welcome.

[thesamet]

Hi @sttawm , are you interested in working on this?

[sttawm]

Yes I am interested, let me see if I can make some progress.

So far, I've found that google's json to protobuf conversion fails with an InvalidProtocolBufferException when parsing json with overlapping oneof keys.

So I guess we can follow that behavior by doing the equivalent in scalapb.

[sttawm]

See this PR