error: `<i32 as Identity>::Identity` is forbidden as the type of a const generic parameter
  --> $DIR/projection-as-arg-const.rs:13:21
   |
LL | pub fn foo<const X: <i32 as Identity>::Identity>() {
   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: the only supported types are integers, `bool`, and `char`

error: aborting due to 1 previous error