error: item does not constrain `ReturnType::{opaque#0}`
  --> $DIR/issue-109054.rs:14:8
   |
LL |     fn deref(&self) -> &Self::Target {
   |        ^^^^^
   |
   = note: consider removing `#[define_opaque]` or adding an empty `#[define_opaque()]`
note: this opaque type is supposed to be constrained
  --> $DIR/issue-109054.rs:7:23
   |
LL | type ReturnType<'a> = impl std::future::Future<Output = u32> + 'a;
   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to 1 previous error