How do I indicate that an argument must be passed?

Question

I'm writing a CLI tool using Clap. Usage should look like this:

$ my_tool command argument

The argument is necessary for the command to work. This is the code I have at the moment:

use::clap::{Parser, Subcommand};

#[derive(Parser)]
#[clap(author, version,  about)]
struct Cli {
    #[clap(subcommand)]
    subcommand: Subcommands,
}

#[derive(Subcommand)]
enum Subcommands {
    Command {
        #[clap(value_parser)]
        argument: Vec<String>,
    }
    // --snip--
}

fn main() {
    let _cli = Cli::parse();
    // --snip--
}

I get this when trying to use the tool:

~/my_tool$ cargo run -- command
Compiling my_tool v0.1.0 (/home/derch/my_tool)
Finished dev [unoptimized + debuginfo] target(s) in 0.78s
 Running `target/debug/my_tool command`
~/my_tool$

I was expecting an error message because I didn't provide an argument after the command. How do I make the program to require the argument?

Answer 1

Because this is a Vec, by default it allows zero values. You can fix that by making it explicitly required:

#[derive(Subcommand)]
enum Subcommands {
    Command {
        #[clap(value_parser, required = true)]
        argument: Vec<String>,
    }
    // --snip--
}