src/test/ui/no_share-enum.rs

#![feature(optin_builtin_traits)]

use std::marker::Sync;

struct NoSync;
impl !Sync for NoSync {}

enum Foo { A(NoSync) }

fn bar<T: Sync>(_: T) {}

fn main() {
    let x = Foo::A(NoSync);
    bar(x);
    //~^ ERROR `NoSync` cannot be shared between threads safely [E0277]
}