feature(const_ptr_write) is broken

[AaronKutch]

As of a very recent nightly (rustc 1.54.0-nightly (0a8629bff 2021-06-11)), it appears to me that feature(const_ptr_write) is no longer working and broke my code. Sample code:

#![feature(const_ptr_write)]
const unsafe fn ex(x: *mut usize) {
    unsafe {
        x.write(0);
    }
}

error[E0015]: calls in constant functions are limited to constant functions, tuple structs and tuple variants
 --> src/lib.rs:5:9
  |
5 |         x.write(0);
  |         ^^^^^^^^^^

I see a tracking issue for many other pointer operations such as const_ptr_read, but strangely a tracking issue for const_ptr_write is missing.

[ChrisDenton]

It seems there were problems with it. See #86003.

Looks like this feature was started as an experiment which is why there's no specific tracking issue.

[AaronKutch]

This can fortunately be worked around with plain pointer dereferencing and feature(const_raw_ptr_deref), but I prefer ptr::write to make things more explicit

[slightlyoutofphase]

Yeah, this is an extremely annoying reversion that I hope is able to be un-reverted ASAP. So back to how things were a little over a week ago basically. It doesn't even just effect write, but like every single pointer method that was constified recently, basically.

[nagisa]

I'm not sure if broken is the right classification here, rather than that it is just gone. Given that this was an unstable functionality, I'm not seeing any benefit in tracking this disappearance.

Closing.

[RalfJung]

See #86295 for hopefully bringing these functions back.

[RalfJung]

There's now also a proper tracking issue for this feature: #86302