error[E0277]: the trait bound `&_: main::Ref` is not satisfied
  --> $DIR/trait-selection-sanity.rs:28:19
   |
LL |     let (&_, b) = generic();
   |                   ^^^^^^^^^ the trait `main::Ref` is not implemented for `&_`
   |
   = help: the trait `main::Ref` is implemented for `&'static mut [(); 0]`
note: required by a bound in `generic`
  --> $DIR/trait-selection-sanity.rs:7:19
   |
LL |     fn generic<R: Ref>() -> (R, bool) {
   |                   ^^^ required by this bound in `generic`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.