error[E0277]: `NonError` doesn't implement `std::fmt::Display`
 --> $DIR/result_no_display.rs:4:19
  |
4 |         fn f() -> Result<()>;
  |                   ^^^^^^^^^^ `NonError` cannot be formatted with the default formatter
  |
  = help: the trait `std::fmt::Display` is not implemented for `NonError`
  = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead