…function

…Simulacrum

allow unions with mutable references and tuples of allowed types

We currently allow shared references in unions, but not mutable references. That seems somewhat inconsistent. So let's allow all references, and while we are at it, let's make sure the set of allowed types is closed under tuples.

This will need T-lang FCP (at least).

Then remove the `tagged_unions` feature, since we do not plan to stabilize any more of it.
Closes rust-lang#55149

…non_exhaustive, r=oli-obk

check non_exhaustive attr and private fields for transparent types

Fixes rust-lang#78586.

…, r=oli-obk

Use constant eval to do strict mem::uninit/zeroed validity checks

I'm not sure about the code organisation here, I just dumped the check in rustc_const_eval at the root. Not hard to move it elsewhere, in any case.

Also, this means cranelift codegen intrinsics lose the strict checks, since they don't seem to depend on rustc_const_eval, and I didn't see a point in keeping around two copies.

I also left comments in the is_zero_valid methods about "uhhh help how do i do this", those apply to both methods equally.

Also rustc_codegen_ssa now depends on rustc_const_eval... is this okay?

Pinging `@RalfJung` since you were the one who mentioned this to me, so I'm assuming you're interested.

Haven't had a chance to run full tests on this since it's really warm, and it's 1AM, I'll check out any failures/comments in the morning :)

Add some autolabels for A-bootstrap and T-infra

…=lnicola

⬆️ rust-analyzer

r? `@ghost`