Improved fish shell completion with filename parameters

[Icelk]

Please complete the following tasks

• I have searched the discussions
• I have searched the open and rejected issues

Rust Version

rustc 1.60.0 (7737e0b5c 2022-04-04)

Clap Version

3.1.10

Minimal reproducible code

Any program which writes fish completions, has a file path as a unordered argument, and has subcommands.

use clap::{Command, AppSettings, Arg, ValueHint};
use clap_complete::{generate, Generator, Shell};
use std::io;

fn build_cli() -> Command<'static> {
    Command::new("example")
         .arg(Arg::new("file")
             .help("some input file")
             .required(true)
             .multiple(true)
                .value_hint(ValueHint::AnyPath),
        )
       .subcommand(
           Command::new("generator")
       )
}

fn print_completions<G: Generator>(gen: G, cmd: &mut Command) {
    generate(gen, cmd, cmd.get_name().to_string(), &mut io::stdout());
}

fn main() {
    let matches = build_cli().get_matches();

    if let Some(_) = matches.subcommand_matches("generator") {
        let mut cmd = build_cli();
        eprintln!("Generating completion file for {}...", generator);
        print_completions(Shell::Fish, &mut cmd);
    }
}

Steps to reproduce the bug with the above code

cargo run -- generate > ~/.config/fish/completions/<cargo project name>.fish

Actual Behaviour

When trying to complete now, files aren't completed as you'd expect. Fish expects the first argument to be a subcommand, but it can also be a file.

Expected Behaviour

Fish should complete both subcommands and files.

This was solved by prepending the following to the top of the completion file, where chute is my binary name:

complete -c chute -F

This could be done if a file path argument exists and we have subcommands.

Additional Context

No response

Debug Output

No response