//@ edition:2018 #![feature(must_not_suspend)] #![deny(must_not_suspend)] #[must_not_suspend = "You gotta use Umm's, ya know?"] struct Umm { i: i64 } fn bar() -> Box { Box::new(Umm { i: 1 }) } async fn other() {} pub async fn uhoh() { let _guard = bar(); //~ ERROR boxed `Umm` held across other().await; } fn main() { }