src/test/ui/nll/issue-31567.rs

// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

// Regression test for #31567: cached results of projections were
// causing region relations not to be enforced at all the places where
// they have to be enforced.

#![feature(nll)]

struct VecWrapper<'a>(&'a mut S);

struct S(Box<u32>);

fn get_dangling<'a>(v: VecWrapper<'a>) -> &'a u32 {
    let s_inner: &'a S = &*v.0; //~ ERROR borrow may still be in use when destructor runs [E0713]
    &s_inner.0
}

impl<'a> Drop for VecWrapper<'a> {
    fn drop(&mut self) {
        *self.0 = S(Box::new(0));
    }
}

fn main() {
    let mut s = S(Box::new(11));
    let vw = VecWrapper(&mut s);
    let dangling = get_dangling(vw);
    println!("{}", dangling);
}