`--version` and `--help` permit invalid arguments

[ysndr]

Most unix utilities require valid arguments passed to them, even in the presence of --help or --version, e.g. git:

$ git --badarg --version
unknown option: --badarg
usage: git [-v | --version] [-h | --help] [-C <path>] [-c <name>=<value>]
           [--exec-path[=<path>]] [--html-path] [--man-path] [--info-path]
           [-p | --paginate | -P | --no-pager] [--no-replace-objects] [--bare]
           [--git-dir=<path>] [--work-tree=<path>] [--namespace=<name>]
           [--super-prefix=<path>] [--config-env=<name>=<envvar>]
           <command> [<args>]

$ git --badarg --help
unknown option: --badarg
usage: git [-v | --version] [-h | --help] [-C <path>] [-c <name>=<value>]
           [--exec-path[=<path>]] [--html-path] [--man-path] [--info-path]
           [-p | --paginate | -P | --no-pager] [--no-replace-objects] [--bare]
           [--git-dir=<path>] [--work-tree=<path>] [--namespace=<name>]
           [--super-prefix=<path>] [--config-env=<name>=<envvar>]
           <command> [<args>]

Doing the same with bpaf, does not catch any bad arguments:

use bpaf::*;

#[allow(dead_code)]
#[derive(Debug, Bpaf)]
#[bpaf(options, version)]
pub struct Options {
    /// Message to print in a big friendly letters
    #[bpaf(positional("MESSAGE"))]
    message: String,
}

fn main() {
    println!("{:?}", options().run())
}

cargo run -- --badarg --version
Version: 0.1.0

[pacak]

Behavior for --help is partially intentional, behavior for --version is mostly because it uses the same mechanism as --help.

Main motivation for --help is often I find myself wondering "how do I use this again?" for apps that don't have shell completion. With this behavior I simply slap --help at the end and get the info, without it this means getting the command line to a state here it can be parsed, checking help and then restoring the original.

This behavior is not unique either: cargo (clap?) is undecided if it supports invalid arguments along with help or not: cargo --help --nosuch works, cargo --nosuch --help fails to work. ghc (Haskell compiler) works either way, gcc complains about invalid argument but produces help message anyway.

I'll fix the --verbose behavior when I'm around it since there's no reason to accept invalid names along with it. Any particular reason you want the same behavior for help?