rust/src/test/ui/rfc-2632-const-trait-impl/const-impl-requires-const-trait.rs

#![feature(const_trait_impl)]

pub trait A {}
//~^ NOTE: this trait must be annotated with `#[const_trait]`

impl const A for () {}
//~^ ERROR: const `impl`s must be for traits marked with `#[const_trait]`
//~| ERROR: ~const can only be applied to `#[const_trait]` traits

fn main() {}