Overriding --help produces a different message than the default

[brianp]

When overriding the help flag using long("help"), the auto-generated help output is different from the default.

Differences include:

• The app bin_name in the usage example
• No version flag is displayed

---

Example app, with expected default output:

fn main() {
    let app = App::new("test").get_matches();
}

Output:

$ cargo run -- --help
     Running `target/debug/clapapp --help`
test

USAGE:
    clapapp [FLAGS]

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

---

Example app overriding help, and different output:

fn main() {
    let app = App::new("test")
                  .arg(Arg::with_name("help")
                       .short("h")
                       .long("help")
                       .help("Prints help information")
                       .takes_value(false));

    let matches = &app.clone().get_matches();

    if matches.is_present("help") {
        let _ = &app.print_help();
        println!("\n");
    };
}

Output:

$ cargo run -- --help
     Running `target/debug/clapapp --help`
test

USAGE:
    test [FLAGS]

FLAGS:
    -h, --help    Prints help information

[kbknapp]

I'm on mobile so I can't give a good link at the moment, but if you look at line 460 of src/app/parser.rs you'll see a call to build_help_and_version which never gets called when print_help is called.

Simply inserting that call will fix it, but also have the side effect that it's called twice on a normal run. So we either need to find a way to not call it twice, minimize the runtime impact if it is called twice, or something to the like.

Something that might help is use the Parser::is_set methods to check the internal AppSettings for things like NeedsLongHelp (or Version) instead of iterating all flags.