error: `bool` cannot be used as positional parameter with default parser

  = help: if you want to create a flag add `long` or `short`
  = help: If you really want a boolean parameter add an explicit parser, for example `parse(try_from_str)`
  = note: see also https://github.com/clap-rs/clap_derive/tree/master/examples/true_or_false.rs

 --> $DIR/positional_bool.rs:5:14
  |
5 |     verbose: bool,
  |              ^^^^