`clap` does have magic for enums:

  use clap::{Parser, ValueEnum};

  #[derive(ValueEnum, Debug, Clone)]
  pub enum Foo {
    Bar,
    Baz,
  }

  #[derive(Parser, Debug)]
  #[command(author, version, about, long_about = None)]
  pub struct Args {
    /// description
    #[arg(short = 'f', long = "foo", value_enum, default_value = "bar")]
    foo: Foo,
  }

The output of `--help` will look like:

  -f, --foo <FOO>  description [default: bar] [possible values: bar, baz]

This is with clap >= 4.4 with the derive feature.