src/test/ui/feature-gates/feature-gate-async-await-2015-edition.rs

// edition:2015

#![feature(futures_api)]

async fn foo() {} //~ ERROR `async fn` is not permitted in the 2015 edition
                  //~^ ERROR async fn is unstable

fn main() {
    let _ = async {}; //~ ERROR cannot find struct, variant or union type `async`
    let _ = async || { true }; //~ ERROR cannot find value `async` in this scope
}