1 error: Undefined Behavior: trying to retag from <TAG> for SharedReadWrite permission at ALLOC[0x0], but that tag does not exist in the borrow stack for this location
2 --> $DIR/box-cell-alias.rs:LL:CC
4 LL | unsafe { (*ptr).set(20) };
7 | trying to retag from <TAG> for SharedReadWrite permission at ALLOC[0x0], but that tag does not exist in the borrow stack for this location
8 | this error occurs as part of retag at ALLOC[0x0..0x1]
10 = help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
11 = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
12 help: <TAG> was created by a SharedReadWrite retag at offsets [0x0..0x1]
13 --> $DIR/box-cell-alias.rs:LL:CC
15 LL | let ptr: *const Cell<u8> = &*val;
17 help: <TAG> was later invalidated at offsets [0x0..0x1] by a Unique retag
18 --> $DIR/box-cell-alias.rs:LL:CC
20 LL | let res = helper(val, ptr);
23 = note: inside `helper` at $DIR/box-cell-alias.rs:LL:CC
24 note: inside `main` at $DIR/box-cell-alias.rs:LL:CC
25 --> $DIR/box-cell-alias.rs:LL:CC
27 LL | let res = helper(val, ptr);
30 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
32 error: aborting due to previous error