Cannot compile when enum is map value

[quininer]

syntax = "proto2";

enum Command {
	AAA = 0;
}

message CommandMap {
	map<string, Command> map = 1;
}

error[E0277]: the trait bound `bad::Command: std::default::Default` is not satisfied
  --> src/bad.rs:74:21
   |
74 |                     ::protobuf::rt::read_map_into::<::protobuf::types::ProtobufTypeString, ::protobuf::types::ProtobufTypeEnum<Command>>(wire_type, is, &mut self.map)?;
   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::default::Default` is not implemented for `bad::Command`
   |
   = note: required by `protobuf::rt::read_map_into`

[stepancheg]

The issue is implicitly fixed in master where all enums implement Default.

I decided to create a new stable branch — v2.3 — and cherry-pick that change from master. I think it would be backwards compatible, and proper fix not very trivial.

[stepancheg]

Published v2.3.0. Thanks!