error: Undefined Behavior: attempting a write access using <TAG> at ALLOC[0x0], but that tag does not exist in the borrow stack for this location
  --> $DIR/box_exclusive_violation1.rs:LL:CC
   |
LL |         *LEAK = 7;
   |         ^^^^^^^^^
   |         |
   |         attempting a write access using <TAG> at ALLOC[0x0], but that tag does not exist in the borrow stack for this location
   |         this error occurs as part of an access at ALLOC[0x0..0x4]
   |
   = help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
help: <TAG> was created by a SharedReadOnly retag at offsets [0x0..0x4]
  --> $DIR/box_exclusive_violation1.rs:LL:CC
   |
LL |         LEAK = x as *const _ as *mut _;
   |                ^
help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
  --> $DIR/box_exclusive_violation1.rs:LL:CC
   |
LL |     *our = 5;
   |     ^^^^^^^^
   = note: backtrace:
   = note: inside `unknown_code_2` at $DIR/box_exclusive_violation1.rs:LL:CC
note: inside `demo_box_advanced_unique` at $DIR/box_exclusive_violation1.rs:LL:CC
  --> $DIR/box_exclusive_violation1.rs:LL:CC
   |
LL |     unknown_code_2();
   |     ^^^^^^^^^^^^^^^^
note: inside `main` at $DIR/box_exclusive_violation1.rs:LL:CC
  --> $DIR/box_exclusive_violation1.rs:LL:CC
   |
LL |     demo_box_advanced_unique(Box::new(0));
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

error: aborting due to previous error