const-eval ICE: allocation missing in dead_alloc_map

[pnkfelix]

Spawned off of @oli-obk 's example on #55223:

play

#![feature(const_let)]

union Foo<'a> {
    y: &'a (),
    long_live_the_unit: &'static (),
}

const FOO: &() = {
    let y = ();
    unsafe { Foo { y: &y }.long_live_the_unit }
};

fn main() {
}

[pnkfelix]

@oli-obk to be clear: we don't need to use feature(const_let) to reproduce the problem, right? I.e. hypothetically examples exist that don't use that feature?

In particular I know this problem is in some way related to #55288, which is definitely a true regression of stable code.

[oli-obk]

Right, this here is not really a regression. It is just an ICE that should be an error and it is fixed by #55262

We can probably do this without const_let, but I couldn't come up with an example.

[kornelski]

A user is reporting the same ICE in simplewiki crate

[sighol]

I have tried to reduce the problem. This repository is smaller, but still fails on nightly-2018-10-25: rustc-panic-dead_alloc_map. The same crate builds on stable.

[oli-obk]

I think you are encountering #55288 which has a fix in #55385 (making everything work again)

This issue is different, even though the symptom is the same right now. When this issue is fixed (via #55262), the ICE will become a hard error.