Help message prints argument name twice if no value name was given

[klingtnet]

Argument names are printed as values in the help message if no value_name of value_names was given for the CLI argument. The problem is located in src/args/help_writer.rs line 117. I tried to replace the line with: try!(write!(w, "<{}>", self.a.name())); but this breaks some other tests.
If no value_name was set the long or short argument name is printed twice before the arguments value.

extern crate clap;

fn main() {
    let addr = clap::Arg::with_name("address")
                   .long("address")
                   .short("a")
                   .takes_value(true)
                   .default_value("0.0.0.0")
                   .group("osc")
                   .help("Address to listen on for OSC messages.");
    let sr = clap::Arg::with_name("sample-rate")
                 .long("sample-rate")
                 .short("s")
                 .takes_value(true)
                 .default_value("48000")
                 .possible_values(&["44100", "48000", "88200", "96000"])
                 .help("Playback sample-rate");
    let ports = clap::Arg::with_name("ports")
                    .long("ports")
                    .short("p")
                    .required(true)
                    .takes_value(true)
                    .number_of_values(2)
                    .value_names(&["in", "out"])
                    .group("osc")
                    .help("OSC listening and send port.");
    let args = clap::App::new("ytterbium")
                   .version("0.1.0")
                   .author("Andreas Linz <[email protected]>")
                   .arg(addr)
                   .arg(ports)
                   .arg(sr);
    let mut buf: Vec<u8> = Vec::with_capacity(128);
    let mut out = ::std::io::stdout();
    args.write_help(&mut out);
}

This prints the following help message:

ytterbium 0.1.0
Andreas Linz <[email protected]>

USAGE:
    ytterbium [FLAGS] [OPTIONS] --ports <in> <out>

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information

OPTIONS:
    -a, --address --address <address>            Address to listen on for OSC messages. [default: 0.0.0.0] 
    -p, --ports <in> <out>             OSC listening and send port.
    -s, --sample-rate --sample-rate <sample-rate>    Playback sample-rate [default: 48000]  [values: 44100, 48000, 88200, 96000]

If you look at the OPTIONS you can see that --address is printed twice as well as --sample-rate.
Adding value_names fixes the problem:

    let addr = clap::Arg::with_name("address")
// ...
                   .takes_value(true)
                   .value_name("ip-address")
// ...
    let sr = clap::Arg::with_name("sample-rate")
// ...
                 .takes_value(true)
                 .value_name("sample-rate")
// ...

...
OPTIONS:
    -a, --address <ip-address>         Address to listen on for OSC messages. [default: 0.0.0.0] 
    -p, --ports <in> <out>             OSC listening and send port.
    -s, --sample-rate <sample-rate>    Playback sample-rate [default: 48000]  [values: 44100, 48000, 88200, 96000]

If this is intended behavior then please add a note in the documentation that setting value_names is mandatory for arguments that takes_value.

[kbknapp]

This is a bug, thanks for pointing it out! I'll get it fixed real quick and put out the updated version. Thanks!

[kbknapp]

Once #474 merges I'll put out the new version on crates.io

[klingtnet]

Thank you for the quick fix!