Usage message is misleading when SubcommandsNegateReqs is used

[malbarbo]

Affected Version of clap

2.20.5

Expected Behavior Summary

Show a usage message that is more accurate, like

USAGE:
    16_app_settings (<input> | SUBCOMMAND)

or

USAGE:
    16_app_settings <input>
    16_app_settings SUBCOMMAND

With flags it become more difficult to write a usage message...

Actual Behavior Summary

Show a usage message that is misleading

myapp 

USAGE:
    16_app_settings <input> [SUBCOMMAND]

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

ARGS:
    <input>    input file to use

SUBCOMMANDS:
    help    Prints this message or the help of the given subcommand(s)
    test    does some testing

This suggests that a subcommand can be used after <input> but it cannot.

Steps to Reproduce the issue

cargo run --example 16_app_settings -- -h

[kbknapp]

Good catch, I agree. I tend to like the dual line usage, but that may be slightly harder to implement in current clap. I'll play with it and see.

[wfraser]

I noticed that in addition to showing the arg in the help for the main command, it also shows it in the help for the subcommand, but DOES NOT show it if you give a value for it. Really weird.

I.e.:

extern crate clap;
use clap::{Arg, SubCommand};

fn main() {
    let args = clap::App::new("")
        .arg(Arg::with_name("input")
            .required(true)
            .help("the input"))
        .subcommand(SubCommand::new("test"))
        .get_matches();

    println!("{:#?}", args);
}

$ cargo run -- --help
   Compiling clap-experiments v0.1.0 (file:///D:/code/clap-experiments)
    Finished dev [unoptimized + debuginfo] target(s) in 1.22 secs
     Running `target\debug\clap-experiments.exe --help`


USAGE:
    clap-experiments.exe <input> [SUBCOMMAND]

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

ARGS:
    <input>    the input

SUBCOMMANDS:
    help    Prints this message or the help of the given subcommand(s)
    test

$ cargo run -- test --help
    Finished dev [unoptimized + debuginfo] target(s) in 0.0 secs
     Running `target\debug\clap-experiments.exe test --help`
clap-experiments.exe-test

USAGE:
    clap-experiments.exe <input> test

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

$ cargo run -- foo test --help
    Finished dev [unoptimized + debuginfo] target(s) in 0.0 secs
     Running `target\debug\clap-experiments.exe foo test --help`
clap-experiments.exe-test

USAGE:
    clap-experiments.exe test

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

Note how in the last example, the <input> parameter is gone from the help text.