rust/tests/compile-fail/validity/transmute_through_ptr.rs

#[repr(u32)]
#[derive(Debug)]
enum Bool { True }

fn evil(x: &mut Bool) {
    let x = x as *mut _ as *mut u32;
    unsafe { *x = 44; } // out-of-bounds enum tag
}

fn main() {
    let mut x = Bool::True;
    evil(&mut x);
    let y = x; // reading this ought to be enough to trigger validation
    //~^ ERROR type validation failed at .<enum-tag>: encountered 0x0000002c, but expected a valid enum tag
    println!("{:?}", y); // make sure it is used (and not optimized away)
}