json_name is not respected for proto.Field objects using Python proto impl

[software-dov]

E.g.

import os
os.environ["PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION"] = "python"

import proto
class Squid(proto.Message):
    massKg = proto.Field(proto.INT32, number=1, json_name="mass_in_kilograms")

s = Squid(massKg=20)
j = Squid.to_json(s)
print(j)    # '{"massKg" : 20}', or something like that.

This is only reproducible with the python protobuf implementation.

Editorial: my gut feeling is that this is a bug in proto-plus, or at least that a workaround/fix/correct solution is entirely possible within proto-plus.

[software-dov]

Nope, this is a protobuf bug.

[software-dov]

Depends on protocolbuffers/protobuf#7910