Allow Custom types in java JsonFormat utility

[Gaff]

We have a problem where we want to represent a date as an ISO format string in JSON, but we wish to use google.type.Date in protobuf. I'm using the JsonFormat tool to build the protobuf from the JSON, but this fails since it sees a string in the JSON but the mergeMessage method expects it to be a JsonObject.

So would you consider a change where people can register custom parsers, so that users can extend the JsonFormat to support any types?

My proposal would involve the following steps:
1, Expose WellKnownTypeParser as a public interface.
2. Make wellKnownTypePrasers in ParserImpl non-static, add constructor params.
3. Add a usingTypeParser() method to Parser

And analogous steps for Printer.

Would this be viable?

[elharo]

My gut is that this won't fly. JsonFormat is designed to supprot a single consistent and reproducible JSON format for protos across languages, not as a general purpose converter between arbitrary JSON formats and protos. I don't think we want to add complexity to the API to support this. However this could be a viable third party library.