1 error: Undefined Behavior: trying to retag from <TAG> for Unique permission at ALLOC[0x4], but that tag does not exist in the borrow stack for this location
2 --> $DIR/return_invalid_mut_option.rs:LL:CC
7 | trying to retag from <TAG> for Unique permission at ALLOC[0x4], but that tag does not exist in the borrow stack for this location
8 | this error occurs as part of retag at ALLOC[0x4..0x8]
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 Unique retag at offsets [0x4..0x8]
13 --> $DIR/return_invalid_mut_option.rs:LL:CC
15 LL | let ret = Some(ret);
17 help: <TAG> was later invalidated at offsets [0x0..0x8] by a read access
18 --> $DIR/return_invalid_mut_option.rs:LL:CC
20 LL | let _val = unsafe { *xraw }; // invalidate xref
23 = note: inside `foo` at $DIR/return_invalid_mut_option.rs:LL:CC
24 note: inside `main` at $DIR/return_invalid_mut_option.rs:LL:CC
25 --> $DIR/return_invalid_mut_option.rs:LL:CC
27 LL | match foo(&mut (1, 2)) {
30 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
32 error: aborting due to previous error