vlib/v/checker/tests/opt_is_op_check_err.vv:7:6: notice: unused parameter: `a`
    5 | }
    6 | 
    7 | fn r(a string) {}
      |      ^
    8 | 
    9 | fn t(s ?Foo) {
vlib/v/checker/tests/opt_is_op_check_err.vv:13:7: error: t.a is an Optional, it needs to be unwrapped first
   11 |         a: s
   12 |     }
   13 |     if t.a is string {
      |          ^
   14 |         r(t.a)
   15 |     }