error: 'repr(..)' attribute must be set on the type when using 'forward' attribute
 --> tests/derive-deserial/fail-forward-without-repr.rs:5:10
  |
5 | #[derive(Deserial)]
  |          ^^^^^^^^
  |
  = note: this error originates in the derive macro `Deserial` (in Nightly builds, run with -Z macro-backtrace for more info)