error: `Bar` is forbidden as the type of a const generic parameter
  --> $DIR/feature-gate-adt_const_params.rs:3:21
   |
LL | struct Foo<const N: Bar>;
   |                     ^^^
   |
   = note: the only supported types are integers, `bool`, and `char`
help: add `#![feature(adt_const_params)]` to the crate attributes to enable more complex and user defined types
   |
LL + #![feature(adt_const_params)]
   |

error: aborting due to 1 previous error