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`
   = help: more complex types are supported with `#![feature(adt_const_params)]`

error: aborting due to previous error