badarity must always include the stacktrace in the error reason

[KronicDeth]

When Lumen raises badarity and it is passed through a monitor, it has Info as {badarity, {Fun, Args}}, but it is supposed to be {{badarity, {Fun, Args}}, Stacktrace}. I believe this is the case because when badarity happens it counts as exit reason, which is always {reason, stacktrace}.

Lumen

init.erl

-module(init).
-export([start/0]).
-import(erlang, [display/1]).
-import(lumen, [log_exit/1]).

start() ->
  log_exit(false),
  {ParentPid, ParentMonitorReference} = spawn_monitor(fun () ->
    Options = [link, monitor],
    spawn_opt(fun (_) ->
      ok
    end, Options),
    wait_to_shutdown()
  end),
  receive
    {'DOWN', ParentMonitorReference, process, _, Info} ->
      case Info of
        {Reason = badarity, _FunArgs} ->
          display({parent, Reason});
        _ ->
          display({parent, Info})
      end
  after
    10 ->
      display({parent, alive, is_process_alive(ParentPid)})
  end.

wait_to_shutdown() ->
  receive
    shutdown -> ok
  end.

BEAM

start.erl

-module(start).
-export([start/0]).
-import(erlang, [display/1]).

start() ->
  {ParentPid, ParentMonitorReference} = spawn_monitor(fun () ->
    Options = [link, monitor],
    spawn_opt(fun (_) ->
      ok
    end, Options),
    wait_to_shutdown()
  end),
  receive
    {'DOWN', ParentMonitorReference, process, _, Info} ->
      case Info of
        {{Reason = badarity, _FunArgs}, _Stacktrace} ->
          display({parent, Reason});
        _ ->
          display({parent, Info})
      end
  after
    10 ->
      display({parent, alive, is_process_alive(ParentPid)})
  end,
  ok.

wait_to_shutdown() ->
  receive
    shutdown -> ok
  end.

Commands

1. erl
2. c(start).
3. start:start().

Output

{parent,badarity}
ok
=ERROR REPORT==== 24-Aug-2020::11:52:33.289409 ===
Error in process <0.146.0> with exit value:
{{badarity,{#Fun<start.1.105435764>,[]}},[{erlang,apply,2,[]}]}

Difference with exit/1

It should be noted that exit(reason) DOES NOT include the stack trace and so counts whatever is passed to exit/1 as the "exit reason"

Commands

1. erl
2. catch exit(reason)

Output

{'EXIT', reason}