Requiring another argument by name from an argument that is itself required creates a duplicate error message

[stensonowen]

Hopefully the title is clear. In the example, argument foo is required, and it also requires bar.

let matches = App::new("MyApp")
                        .arg(Arg::with_name("foo")
                                    .help("FOO")
                                    .short("f")
                                    .required(true)
                                    .takes_value(true)
                                    .conflicts_with("c")
                                    .requires("bar")
                            )
                         .arg(Arg::with_name("bar")
                                    .short("b")
                                    .takes_value(true)
                                    .help("BAR")
                                    //.required(true)
                            )
                        .get_matches();

Calling ./prog --help returns what you'd expect (foo and bar are required, with the correct usage string), but supplying the -f flag produces the following error:

error: The following required arguments were not provided:
    -b <bar>
    -b <bar>

USAGE:
    repeat_errors [FLAGS] [OPTIONS] -f <foo> -b <bar> -b <bar>

(Uncommenting the bar.required(true) adds another -b <bar> to the error and usage.)
It's conceivable that someone would want a required argument that requires another, so there is understandably a use case in which this error occurs. Additionally, it is certainly possible for a user to have accidentally made bar required, and the usage mistake might easily go unnoticed.
Apologies if there's already a way to avoid these kinds of redundancies, but I didn't see any.
It seems like an interesting (albiet niche) problem, so I'll probably take a crack at solving it and make a pull request.

[kbknapp]

Thanks for filing! Yep, the title is clear 😄

I agree it's possible someone could end up doing this either by accident, or just not knowing there are other ways to accomplish this (i.e. if an arg is required by another required arg, it's not necessary to set).

I should have this fixed shortly!