#![allow(dead_code, deprecated, unused_variables, unused_mut)]
#![feature(cell_leak)]
use std::cell::RefCell;
fn main() {
    let mut c = RefCell::new(0);
    std::mem::forget(c.borrow_mut());
    assert!(c.try_borrow().is_err());
    c.undo_leak();
    assert!(c.try_borrow().is_ok());
}