warning: opaque type `Traitable` does not satisfy its associated type bounds
  --> $DIR/nested-return-type2-tait2.rs:21:29
   |
LL |     type Assoc: Duh;
   |                 --- this associated type bound is unsatisfied for `Sendable`
...
LL | type Traitable = impl Trait<Assoc = Sendable>;
   |                             ^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(opaque_hidden_inferred_bound)]` on by default

warning: 1 warning emitted