tests/ui/borrowck/borrow-immutable-deref-box.rs

//! regression test for issue <https://github.com/rust-lang/rust/issues/36400>
fn f(x: &mut u32) {}

fn main() {
    let x = Box::new(3);
    f(&mut *x); //~ ERROR cannot borrow `*x` as mutable, as `x` is not declared as mutable
}