error[E0038]: the trait `Foo` is not dyn compatible
  --> $DIR/almost-supertrait-associated-type.rs:20:20
   |
LL | impl<T, U> Dyn for dyn Foo<T, U> + '_ {
   |                    ^^^^^^^^^^^^^^^^^^ `Foo` is not dyn compatible
   |
note: for a trait to be dyn compatible it needs to allow building a vtable
      for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>
  --> $DIR/almost-supertrait-associated-type.rs:32:34
   |
LL | trait Foo<T, U>: Super<ActuallySuper, Assoc = T>
   |       --- this trait is not dyn compatible...
...
LL |     fn transmute(&self, t: T) -> <Self as Super<NotActuallySuper>>::Assoc;
   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ...because method `transmute` references the `Self` type in its return type
   = help: consider moving `transmute` to another trait

error[E0038]: the trait `Foo` is not dyn compatible
  --> $DIR/almost-supertrait-associated-type.rs:7:32
   |
LL |     (&PhantomData::<T> as &dyn Foo<T, U>).transmute(t)
   |                                ^^^^^^^^^ `Foo` is not dyn compatible
   |
note: for a trait to be dyn compatible it needs to allow building a vtable
      for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>
  --> $DIR/almost-supertrait-associated-type.rs:32:34
   |
LL | trait Foo<T, U>: Super<ActuallySuper, Assoc = T>
   |       --- this trait is not dyn compatible...
...
LL |     fn transmute(&self, t: T) -> <Self as Super<NotActuallySuper>>::Assoc;
   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ...because method `transmute` references the `Self` type in its return type
   = help: consider moving `transmute` to another trait

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0038`.