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// Demonstrate that "rogue" `DerefMut` impls for `&T` are not allowed.
//
// https://github.com/rust-lang/rust/issues/66544
use std::cell::Cell;
use std::marker::PhantomPinned;
use std::ops::DerefMut;
use std::pin::Pin;
struct MyType<'a>(Cell<Option<&'a mut MyType<'a>>>, PhantomPinned);
impl<'a> DerefMut for &'a MyType<'a> {
//~^ ERROR E0751
fn deref_mut(&mut self) -> &mut MyType<'a> {
self.0.take().unwrap()
}
}
fn main() {
let mut unpinned = MyType(Cell::new(None), PhantomPinned);
let bad_addr = &unpinned as *const MyType<'_> as usize;
let p = Box::pin(MyType(Cell::new(Some(&mut unpinned)), PhantomPinned));
// p_ref is okay: it does not point to the bad_addr
let mut p_ref: Pin<&MyType<'_>> = p.as_ref();
assert_ne!(bad_addr, &*p_ref as *const _ as usize);
// but p_mut does point to bad_addr! this is unsound
let p_mut: Pin<&mut MyType<'_>> = p_ref.as_mut();
assert_eq!(bad_addr, &*p_mut as *const _ as usize);
println!("oh no!");
}
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