protoc-gen-go: JSON struct tags are generated with the wrong naming convention

[bmhatfield]

What version of protobuf and what language are you using?
% go version
go version go1.11 darwin/amd64

What did you do?
Observed that generated code looked funny:

InviterUserId string `protobuf:"bytes,2,opt,name=inviter_user_id,json=inviterUserId,proto3" json:"inviter_user_id,omitempty"`

What did you expect to see?
I expected the json= output in the protobuf: tag to match the json: tag field name.

What did you see instead?
JSON tag field naming that doesn't match JSON field norms.

The problem is that g.goTag uses GetJsonName but the actual JSON tag generation uses *field.Name.

Reccomendation:
Switch https://github.com/golang/protobuf/blob/master/protoc-gen-go/generator/generator.go#L2488 to use GetJsonName just like https://github.com/golang/protobuf/blob/master/protoc-gen-go/generator/generator.go#L1548

[dsnet]

The situation is unfortunate and can't be changed without breaking existing code. The generation of the json tag pre-dated the formalization of the JSON<->PB specification. In it's current state, using encoding/json does not produce JSON that conforms to any particular pre-defined schema.

The jsonpb package exists to implement the aforementioned JSON specification since it is not possible to do so using the json tags alone. Rather than fixing the json tag, it should probably be removed entirely and have #256 addressed instead.

[dsnet]

Closing as there's not really any actionable to do here without breaking compatibility. The best we can do is #256.