error[E0605]: non-primitive cast: `&dyn Foo<i32>` as `&dyn Bar<u32>`
  --> $DIR/type-checking-test-2.rs:19:13
   |
LL |     let _ = x as &dyn Bar<u32>; // Error
   |             ^^^^^^^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object

error[E0605]: non-primitive cast: `&dyn Foo<u32>` as `&dyn Bar<_>`
  --> $DIR/type-checking-test-2.rs:24:13
   |
LL |     let a = x as &dyn Bar<_>; // Ambiguous
   |             ^^^^^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0605`.