error[E0224]: at least one trait is required for an object type
  --> $DIR/issue-65673.rs:9:16
   |
LL | trait Alias<T> = where T: Trait;
   | -------------- this alias does not contain a trait
...
LL |     type Ctx = dyn Alias<T>;
   |                ^^^^^^^^^^^^

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0224`.