argparse help shows arguments in the wrong order

[rlipscombe]

Describe the bug
In experimenting with argparse -- https://www.erlang.org/doc/man/argparse.html, it seems that the help text displays positional arguments for nested commands in the wrong order.

To Reproduce

main(Args) ->
    argparse:run(
        Args,
        #{
            arguments => [#{name => global}],
            commands => #{
                "list" => #{
                    arguments => [#{name => what}],
                    handler => fun(A) -> io:format("~p~n", [A]) end
                }
            }
        },
        #{progname => ?MODULE}
    ).

Here we have an example that takes a "list" command, taking two arguments: "global" (common to all commands) and "what" (specific to the "list" command).

The help text shows the following:

% ./example list
error: example list: required argument missing: global
Usage:
  example list <what> <global>

Arguments:
  what   what
  global global

You can see that it claims to expect "what" and then "global".

However, the parser expects "global" and then "what" as seen here:

./example list global what
#{global => "global",what => "what"}

Expected behavior

The help text should display the positional arguments in the correct order.

Affected versions

OTP-26.1.2

Additional context

I guess you could argue that it's kinda weird to use positional arguments in the face of sub-commands, but argparse allows it, so it should do it correctly.

[jhogberg]

Thanks for your report! We're a bit swamped at the moment so we're not going to be able to fix this in the near future, a PR would be much appreciated.

[rlipscombe]

While investigating, I came up with another repro:

1> io:put_chars(argparse:help(#{arguments => [#{name => first}, #{name => second}], commands => #{"cmd" => #{arguments => [#{name => third}, #{name => fourth}]}}}, #{progname => example, command => ["cmd"]})).
Usage:
  example cmd <third> <fourth> <first> <second>

Arguments:
  third  third
  fourth fourth
  first  first
  second second
ok

This shows that each group of arguments is in the correct order, but the groups are reversed.

[max-au]

Thanks for reporting, taking a look at it.

[rlipscombe]

And to be explicit about the expected order of the arguments when run:

1> argparse:run(["cmd", "1", "2", "3", "4"], #{arguments => [#{name => first}, #{name => second}], commands => #{"cmd" => #{handler => {maps, to_list}, arguments => [#{name => third}, #{name => fourth}]}}}, #{progname => example}).
[{first,"1"},{second,"2"},{third,"3"},{fourth,"4"}]