rust/tests/ui/const-generics/issue-80471.rs

#![feature(adt_const_params)]
//~^ WARN the feature `adt_const_params` is incomplete and may not be safe to use and/or cause compiler crashes [incomplete_features]

#[derive(PartialEq, Eq)]
enum Nat {
    Z,
    S(Box<Nat>),
}

fn foo<const N: Nat>() {}
//~^ ERROR `Nat` must implement `ConstParamTy` to be used as the type of a const generic parameter

fn main() {}