A non-structural-match type was used as the type of a const generic parameter.
Erroneous code example:
#![feature(adt_const_params)]
struct A;
struct B<const X: A>; // error!Only structural-match types (that is, types that derive PartialEq and Eq)
may be used as the types of const generic parameters.
To fix the previous code example, we derive PartialEq and Eq:
#![feature(adt_const_params)]
#[derive(PartialEq, Eq)] // We derive both traits here.
struct A;
struct B<const X: A>; // ok!