Can UB be triggered by mem::forget of a ScopeGuard? #1
Description
Attempts at guarding a lifetime in this manner typically are unsound as leaking - whether via RC cycles or mem::forget or any other mechanism - can be done in safe code.
use scoped_static::{ScopeGuard, Scoped};
#[tokio::main]
async fn main() {
let value = Box::new(1.0);
let ref_value = &value;
// `guard` ensures no derived "lifted" values exist when dropped
let guard = ScopeGuard::new(ref_value);
// `lifted` holds a `'static` reference to `'ref_value`
let lifted: Scoped<Box<f64>> = guard.lift();
tokio::spawn(async move {
// lifted moved here
let value = **lifted + 1.0;
assert_eq!(value, 2.0);
// lifted dropped
})
.await
.unwrap();
std::mem::forget(guard);
}There have been proposals to add a new auto trait to make this sort of usage safe, called Forget or Leak or Forgettable.