error[E0596]: cannot borrow `*x` as mutable, as it is behind a `&` reference
  --> $DIR/slice-mut-2.rs:7:18
   |
LL |     let x: &[isize] = &[1, 2, 3, 4, 5];
   |                       ---------------- help: consider changing this to be a mutable reference: `&mut [1, 2, 3, 4, 5]`
...
LL |     let _ = &mut x[2..4];
   |                  ^ `x` is a `&` reference, so the data it refers to cannot be borrowed as mutable

error: aborting due to previous error

For more information about this error, try `rustc --explain E0596`.