error[E0277]: the type `&mut i32` may not be safely transferred across an unwind boundary
  --> $DIR/not-panic-safe.rs:9:5
   |
LL | fn assert<T: UnwindSafe + ?Sized>() {}
   |    ------    ---------- required by this bound in `assert`
...
LL |     assert::<&mut i32>();
   |     ^^^^^^^^^^^^^^^^^^ `&mut i32` may not be safely transferred across an unwind boundary
   |
   = help: the trait `std::panic::UnwindSafe` is not implemented for `&mut i32`
   = note: `std::panic::UnwindSafe` is implemented for `&i32`, but not for `&mut i32`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.