src/tools/miri/tests/fail/stacked_borrows/interior_mut2.rs

   1 use std::cell::UnsafeCell;
   2 use std::mem;
   3
   4 // Like `&mut *x.get()`, but without intermediate raw pointers.
   5 #[allow(mutable_transmutes)]
   6 unsafe fn unsafe_cell_get<T>(x: &UnsafeCell<T>) -> &'static mut T {
   7     mem::transmute(x)
   8 }
   9
  10 fn main() {
  11     unsafe {
  12         let c = &UnsafeCell::new(UnsafeCell::new(0));
  13         let inner_uniq = &mut *c.get();
  14         let inner_shr = &*inner_uniq;
  15         // stack: [c: SharedReadWrite, inner_uniq: Unique, inner_shr: SharedReadWrite]
  16
  17         let _val = c.get().read(); // invalidates inner_uniq
  18         // stack: [c: SharedReadWrite, inner_uniq: Disabled, inner_shr: SharedReadWrite]
  19
  20         // We have to be careful not to add any raw pointers above inner_uniq in
  21         // the stack, hence the use of unsafe_cell_get.
  22         let _val = *unsafe_cell_get(inner_shr); // this still works
  23
  24         *c.get() = UnsafeCell::new(0); // now inner_shr gets invalidated
  25         // stack: [c: SharedReadWrite]
  26
  27         // now this does not work any more
  28         let _val = *inner_shr.get(); //~ ERROR: /retag .* tag does not exist in the borrow stack/
  29     }
  30 }