fix: support binary map keys in unions

[thalesmg]

Previously, when using maps with binary keys, flat unions and verification, unions would not work, even with binary map keys as expected.

For example, with the following definitions:

Src = """
syntax = "proto3";

message test {
  map<string, string> args = 1;
}

message union {
  oneof u {
    int32 a = 1;
    string b = 2;
  }
}
""".
{ok, Mod, Bin} = gpb_compile:string(aaa, Src, [binary, strings_as_binaries, {maps, true}, {maps_oneof, flat}, {maps_key_type, binary}, {verify, always}, {maps_unset_optional, omitted}]).
code:load_binary(Mod, "aaa.erl", Bin).

... normal maps work as expected:

7>   Encoded1 = Mod:encode_msg(#{<<"args">> => #{<<"hey">> => <<"hi">>}}, test).
 <<10,9,10,3,104,101,121,18,2,104,105>>
8>   Mod:decode_msg(Encoded1, test).
 #{<<"args">> => #{<<"hey">> => <<"hi">>}}

... but unions break, due to verifier failing to consider binary keys when encoding:

20>   %% Should produce <<8, 1>>.
      Mod:encode_msg(#{<<"a">> => 1}, union).
** exception error: {gpb_type_error,{{multiple_oneof_keys,[],u},
                                     [{value,#{<<"a">> => 1}},{path,"union.u"}]}}
     in function  aaa:mk_type_error/3 (aaa.erl, line 567)
     in call from aaa:encode_msg/3 (aaa.erl, line 79)

... and decoding due to incorrect generated code which produced <<(atom_to_list(SomeAtom))>> for the map key:

21>   Mod:decode_msg(<<8, 1>>, union).
** exception error: {gpb_error,{decoding_failure,{<<8,1>>,
                                                  union,
                                                  {error,badarg,
                                                         [{aaa,dfp_read_field_def_union,6,
                                                               [{file,"aaa.erl"},
                                                                {line,292},
                                                                {error_info,#{cause => {1,integer,type,"a"},
                                                                              function => format_bs_fail,module => erl_erts_errors}}]},
                                                          {aaa,decode_msg_1_catch,3,[{file,"aaa.erl"},{line,227}]},
                                                          {erl_eval,do_apply,7,[{file,"erl_eval.erl"},{line,919}]},
                                                          {shell,exprs,7,[{file,"shell.erl"},{line,916}]},
                                                          {shell,eval_exprs,7,[{file,"shell.erl"},{line,872}]},
                                                          {shell,restricted_eval_loop,5,
                                                                 [{file,"shell.erl"},{line,866}]}]}}}}
     in function  aaa:decode_msg_1_catch/3 (aaa.erl, line 231)

[tomas-abrahamsson]

Thanks for a good report and fix. I'll merge it and make a new release.

[tomas-abrahamsson]

Merged and included in 4.21.5.

[thalesmg]

Thanks! 🍻