fix(man): Don't show default values for flags, show ellipsis for repeatable arguments

[drivasperez]

Fixes #4410.

The help generator for the main clap package uses the Arg::is_takes_value_set() method to determine whether it should show a default argument. (See Arg::stylize_arg_suffix, on line 4148 of arg.rs.)

I ported the same logic over to clap_mangen, so boolean flag arguments no longer show [default=false] (or [default=0] for repeatable options), which is not valid.

I also noticed that the generated synopsis does not add a ... ellipsis for repeatable flags, so I added that as well.

Finally, I updated the snapshot tests to reflect the above changes.

Example

For the following program (this is essentially clap_mangen/examples/man.rs):

fn main() -> Result<(), std::io::Error> {
    let cmd = Command::new("myapp")
        .version("1.0")
        .author("Kevin K. <kbknapp@gmail.com>:Ola Nordmann <old@nordmann.no>")
        .about("Does awesome things")
        .long_about(
            "With a longer description to help clarify some things.

And a few newlines.",
        )
        .after_help("This is an extra section added to the end of the manpage.")
        .after_long_help("With even more text added.")
        .arg(
            arg!(-c --config <FILE> "Sets a custom config file")
                .long_help("Some more text about how to set a custom config file")
                .default_value("config.toml")
                .env("CONFIG_FILE"),
        )
        .arg(arg!([output] "Sets an output file").default_value("result.txt"))
        .arg(
            arg!(-d --debug ... "Turn debugging information on")
                .env("DEBUG_ON")
                .hide_env(true),
        )
        .subcommand(
            Command::new("test")
                .about("does testing things")
                .arg(arg!(-l --list "Lists test values")),
        );

    Man::new(cmd).render(&mut io::stdout())
}

you previously got

myapp(1)                                                                             General Commands Manual                                                                            myapp(1)

NAME
       myapp - Does awesome things

SYNOPSIS
       myapp [-c|--config] [--thing] [-d|--debug] [-h|--help] [-V|--version] [output] [subcommands]

DESCRIPTION
       With a longer description to help clarify some things.

       And a few newlines.

OPTIONS
       -c, --config=FILE [default: config.toml]
              Some more text about how to set a custom config file
              May also be specified with the CONFIG_FILE environment variable.

       --thing [default: false]
              Does a thing with a flag

       -d, --debug [default: 0]
              Turn debugging information on

       -h, --help
              Print help information (use `-h` for a summary)

       -V, --version
              Print version information

       [output] [default: result.txt]
              Sets an output file

SUBCOMMANDS
       myapp-test(1)
              does testing things

       myapp-help(1)
              Print this message or the help of the given subcommand(s)

EXTRA
       With even more text added.

VERSION
       v1.0

AUTHORS
       Kevin K. <kbknapp@gmail.com>:Ola Nordmann <old@nordmann.no>

                                                                                            myapp 1.0                                                                                   myapp(1)

and now get

myapp(1)                                                                             General Commands Manual                                                                            myapp(1)

NAME
       myapp - Does awesome things

SYNOPSIS
       myapp [-c|--config] [--thing] [-d|--debug]... [-h|--help] [-V|--version] [output] [subcommands]

DESCRIPTION
       With a longer description to help clarify some things.

       And a few newlines.

OPTIONS
       -c, --config=FILE [default: config.toml]
              Some more text about how to set a custom config file
              May also be specified with the CONFIG_FILE environment variable.

       --thing
              Does a thing with a flag

       -d, --debug
              Turn debugging information on

       -h, --help
              Print help information (use `-h` for a summary)

       -V, --version
              Print version information

       [output] [default: result.txt]
              Sets an output file

SUBCOMMANDS
       myapp-test(1)
              does testing things

       myapp-help(1)
              Print this message or the help of the given subcommand(s)

EXTRA
       With even more text added.

VERSION
       v1.0

AUTHORS
       Kevin K. <kbknapp@gmail.com>:Ola Nordmann <old@nordmann.no>

                                                                                            myapp 1.0                                                                                   myapp(1)

[drivasperez]

It strikes me that clap_mangen also generates an incorrect synopsis for arguments with ArgAction::Append, which require a value and can also appear multiple times.

For the following program:

fn main() {
    let cmd = Command::new("testing clap").arg(
        clap::Arg::new("config")
            .action(clap::ArgAction::Append)
            .help("some config file")
            .short('c')
            .visible_short_alias('C')
            .long("config")
            .visible_alias("conf"),
    );

    clap_mangen::Man::new(cmd.clone())
        .render(&mut std::io::stdout())
        .unwrap();
}

You get the following output:

testing clap(1)                       General Commands Manual                       testing clap(1)

NAME
       testing clap

SYNOPSIS
       testing clap [-c|--config] [-h|--help]

DESCRIPTION
OPTIONS
       -c, --config
              some config file

       -h, --help
              Print help information

                                           testing clap                             testing clap(1)

I think it should be something more like the following:

testing clap [-c|--config=CONFIG]... [-h|--help]

But I'm not sure.