error[E0038]: the trait alias `BB` is not dyn compatible
  --> $DIR/self-in-const-generics.rs:9:16
   |
LL | fn foo(x: &dyn BB) {}
   |                ^^ `BB` 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/self-in-const-generics.rs:7:12
   |
LL | trait BB = Bar<{ 2 + 1 }>;
   |       --   ^^^^^^^^^^^^^^ ...because it uses `Self` as a type parameter
   |       |
   |       this trait is not dyn compatible...
help: consider using an opaque type instead
   |
LL - fn foo(x: &dyn BB) {}
LL + fn foo(x: &impl BB) {}
   |

error: aborting due to 1 previous error

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