error[E0700]: hidden type for `impl Debug` captures lifetime that does not appear in bounds
  --> $DIR/impl-fn-hrtb-bounds-2.rs:5:9
   |
LL | fn a() -> impl Fn(&u8) -> impl Debug {
   |                           ---------- opaque type defined here
LL |     |x| x
   |     --- ^
   |     |
   |     hidden type `&u8` captures the anonymous lifetime #1 defined here

error: aborting due to previous error

For more information about this error, try `rustc --explain E0700`.