src/test/ui/consts/const-eval/ice-packed.rs

// build-pass (FIXME(62277): could be check-pass?)
#[derive(Copy, Clone, PartialEq, Eq)]
#[repr(packed)]
pub struct Num(u64);

impl Num {
    pub const ZERO: Self = Num(0);
}

pub fn decrement(a: Num) -> Num {
    match a {
        Num::ZERO => Num::ZERO,
        a => Num(a.0 - 1)
    }
}

fn main() {
}