rust/tests/fail/stacked_borrows/interior_mut2.rs
2022-07-11 11:48:56 +00:00

31 lines
1.0 KiB
Rust

use std::cell::UnsafeCell;
use std::mem;
// Like `&mut *x.get()`, but without intermediate raw pointers.
#[allow(mutable_transmutes)]
unsafe fn unsafe_cell_get<T>(x: &UnsafeCell<T>) -> &'static mut T {
mem::transmute(x)
}
fn main() {
unsafe {
let c = &UnsafeCell::new(UnsafeCell::new(0));
let inner_uniq = &mut *c.get();
let inner_shr = &*inner_uniq;
// stack: [c: SharedReadWrite, inner_uniq: Unique, inner_shr: SharedReadWrite]
let _val = c.get().read(); // invalidates inner_uniq
// stack: [c: SharedReadWrite, inner_uniq: Disabled, inner_shr: SharedReadWrite]
// We have to be careful not to add any raw pointers above inner_uniq in
// the stack, hence the use of unsafe_cell_get.
let _val = *unsafe_cell_get(inner_shr); // this still works
*c.get() = UnsafeCell::new(0); // now inner_shr gets invalidated
// stack: [c: SharedReadWrite]
// now this does not work any more
let _val = *inner_shr.get(); //~ ERROR: borrow stack
}
}