error[E0792]: expected generic lifetime parameter, found `'_`
  --> $DIR/impl-fn-predefined-lifetimes.rs:6:9
   |
LL | fn a<'a>() -> impl Fn(&'a u8) -> (impl Debug + '_) {
   |                                                -- this generic parameter must be used with a generic lifetime parameter
LL |
LL |     |x| x
   |         ^

error[E0720]: cannot resolve opaque type
  --> $DIR/impl-fn-predefined-lifetimes.rs:4:35
   |
LL | fn a<'a>() -> impl Fn(&'a u8) -> (impl Debug + '_) {
   |                                   ^^^^^^^^^^^^^^^ cannot resolve opaque type

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0720, E0792.
For more information about an error, try `rustc --explain E0720`.