vlib/v/checker/tests/fn_call_arg_mismatch_err_d.vv:17:26: error: cannot use `fn (string) f64` as `fn (string) ?Flag` in argument 2 to `parse_option`
   15 | 
   16 | fn main() {
   17 |     t := parse_option('45', parse_percent)?
      |                             ~~~~~~~~~~~~~
   18 |     println(t)
   19 | }