vlib/v/checker/tests/for_c_stmt_with_optional_call.vv:15:31: error: optionals are not allowed in `for statement increment` (yet)
   13 |     for t := 0; t < tests; t++ {
   14 |         mut v := []bool{len: nmax, init: false}
   15 |         for x := 0; !v[x]; x = rand.intn(n) or { 0 } {
      |                                     ~~~~~~~
   16 |             v[x] = true
   17 |             sum++