error[E0277]: the trait bound `for<'b> fn(&'b ()): Foo` is not satisfied
  --> $DIR/higher-ranked-fn-type.rs:20:5
   |
LL |     called()
   |     ^^^^^^ the trait `for<'b> Foo` is not implemented for `fn(&'b ())`
   |
note: required by a bound in `called`
  --> $DIR/higher-ranked-fn-type.rs:12:25
   |
LL | fn called()
   |    ------ required by a bound in this function
LL | where
LL |     for<'b> fn(&'b ()): Foo,
   |                         ^^^ required by this bound in `called`

error: aborting due to previous error

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