#![feature(generators, generator_trait, box_leak)]

use std::cell::RefCell;
use std::ops::Generator;

fn main() {
    let (mut gen, cell);
    cell = Box::new(RefCell::new(0));
    let ref_ = Box::leak(Box::new(Some(cell.borrow_mut())));
    //~^ ERROR `*cell` does not live long enough [E0597]
    // the upvar is the non-dropck `&mut Option<Ref<'a, i32>>`.
    gen = || {
        // but the generator can use it to drop a `Ref<'a, i32>`.
        let _d = ref_.take(); //~ ERROR `ref_` does not live long enough
        yield;
    };
    unsafe { gen.resume(); }
    // drops the RefCell and then the Ref, leading to use-after-free
}