AIP-203: How should we communicate field_behavior in a oneof?

[noahdietz]

#299 attempted to take a stance on use of field_behavior = REQUIRED on oneof fields, but it is wrong. oneof and field_behavior = REQUIRED/OPTIONAL answer different questions and impact different things. One is a serialization/wire format tool, the other is a documentation of service behavior.

That said, we still need a way to communicate service expectations of oneof fields. Unfortunately, protobuf does not have a means of annotating the oneof statement itself, leaving us with field or message level annotations, each with their own issues.

cc @toumorokoshi tracking our internal discussion from a few weeks ago.

[Fleshgrinder]

Protobuf does support annotating of oneof statements.

syntax = "proto3";

import "google/api/field_behavior.proto";
import "google/protobuf/descriptor.proto";

extend .google.protobuf.OneofOptions {
  repeated .google.api.FieldBehavior oneof_behavior = 1053;
}

message Test {
  oneof something {
    option (oneof_behavior) = REQUIRED;

    string this = 1;
    string or_this = 2;
    string but_at_least_this = 3;
  }
}

[noahdietz]

Yep you are right! I hadn't updated this issue. I actually opened #1181 to start this process but had to put it on hold.