Support for proto3 field presence

[stanley-cheung]

Proto3 introduced the optional syntax to support field presence tracking in release 3.12.0. We need to add support in our grpc protoc plugin.

See this doc for more details. Basically we need to add a function GetSupportedFeatures() to our grpc protoc plugin to mark our compliance.

Please plan to do this in the next release. If not, please let me know. Thanks!

[stanley-cheung]

FYI, grpc/grpc PR: grpc/grpc#22998

[menghanl]

Is this for the proto messages or grpc stubs?
If for proto messages, https://github.com/protocolbuffers/protobuf-go would be the repo for it.

[stanley-cheung]

This is for grpc stubs. The proto3 'optional' feature won't directly affect us because we are not generating classes for messages. But, we still need to add that GetSupportedFeatures() function in our grpc plugin to mark compliance. This is asked for by the protobuf team.

[dfawley]

@mt-inside

code generator protoc-gen-gogo hasn't been updated to support optional fields in proto3
...
I installed protoc-gen-gogo just now, with go get -u github.com/gogo/protobuf/protoc-gen-gogo

You should file this in the gogo proto repo (github.com/gogo/protobuf) instead.

[mt-inside]

Oh wow sorry, I've literally pasted this into the wrong brower tab.