Solution to clap issue #1820 (having an argument that is both a flag and positional)

clap_issue_1820.rs

use clap::{self, App, AppSettings, Arg};

fn main() {
    let matches = App::new("glif2svg")
        .setting(AppSettings::ArgRequiredElseHelp)
        .version("0.1.0")
        .author("Fredrick R. Brennan <copypasteⒶkittens⊙ph>; MFEK Authors")
        .about("Convert between glif to SVG")
        .arg(Arg::with_name("input_file")
            .short("in")
            .long("input")
            .takes_value(true)
            .conflicts_with("input")
            .hidden(true))
        .arg(Arg::with_name("input")
            .index(1)
            .help("The path to the input file.")
            .conflicts_with("input_file")
            .required_unless("input_file"))
        .arg(Arg::with_name("output_file")
            .short("out")
            .long("output")
            .takes_value(true)
            .conflicts_with("output")
            .required_unless("output")
            .display_order(1)
            .help("The path to the output file.\n\n\n"))
        .arg(Arg::with_name("output")
            .index(2)
            .hidden(true))
        .arg(Arg::with_name("no-transform")
            .short("T")
            .long("no-transform")
            .help("Don't put transform=\"translate(…)\" in SVG"))
        .arg(Arg::with_name("no-glif-metrics")
            .short("M")
            .long("no-glif-metrics")
            .help("Don't consider glif's height/width when writing SVG, use minx/maxx/miny/maxy"))
        .arg(Arg::with_name("fontinfo")
            .short("F")
            .long("fontinfo")
            .takes_value(true)
            .help("fontinfo file (for metrics, should point to fontinfo.plist path)\n\n"))
        .get_matches();

    let input = matches.value_of("input").unwrap_or_else(||matches.value_of("input_file").unwrap());

    //let glif: glifparser::Glif<()> = glifparser::glif::read_from_filename(matches.value_of("input").unwrap()).unwrap();
    
    eprintln!("Input: {}", input);
    eprintln!("{:?}", matches);
}