fn main() {
    let x = &mut 0u32;
    let p = x as *mut u32;
    foo(x, p);
}

fn foo(a: &mut u32, y: *mut u32) -> u32 {
    *a = 1;
    let _b = &*a;
    unsafe { *y = 2; } //~ ERROR: not granting access to tag
    return *a;
}