error: Undefined Behavior: trying to retag from <TAG> for SharedReadOnly permission at ALLOC[0x4], but that tag does not exist in the borrow stack for this location
  --> tests/fail/stacked_borrows/zst_slice.rs:LL:CC
   |
LL |         assert_eq!(*s.as_ptr().add(1), 2);
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this error occurs as part of retag at ALLOC[0x4..0x8]
   |
   = 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> would have been created here, but this is a zero-size retag ([0x0..0x0]) so the tag in question does not exist anywhere
  --> tests/fail/stacked_borrows/zst_slice.rs:LL:CC
   |
LL |         assert_eq!(*s.as_ptr().add(1), 2);
   |                     ^^^^^^^^^^
   = note: BACKTRACE (of the first span):
   = note: inside `main` at RUSTLIB/core/src/macros/mod.rs:LL:CC
   = note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)

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

error: aborting due to 1 previous error