error[E0308]: mismatched types
  --> $DIR/issue-99387.rs:23:5
   |
LL | pub type Successors<'a> = impl Iterator<Item = &'a ()>;
   |                           ---------------------------- the expected opaque type
...
LL | pub fn ohno<'a>() -> <&'a () as Tr>::Item {
   |                      -------------------- expected `Successors<'a>` because of return type
LL |     None.into_iter()
   |     ^^^^^^^^^^^^^^^^ expected opaque type, found `IntoIter<_>`
   |
   = note: expected opaque type `Successors<'a>`
                   found struct `std::option::IntoIter<_>`
note: this item must have a `#[define_opaque(Successors)]` attribute to be able to define hidden types
  --> $DIR/issue-99387.rs:22:8
   |
LL | pub fn ohno<'a>() -> <&'a () as Tr>::Item {
   |        ^^^^

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0308`.