test for validity of references pointing to uninhabited types

[RalfJung]

The new tests for rust-lang/rust#97116

[oli-obk]

What are the plans for types like &Option<!> if the discriminant is for Some?

Is it possible to hit other {kind}s than references? The diagnostics are versatile enough. Maybe some tests for boxes or similar could give us more coverage?

[RalfJung]

The code is the same for references and boxes, and I don't want to have a bazillion tests.^^

But I guess I could change one of these tests to use Box rather than a reference.

What are the plans for types like &Option<!> if the discriminant is for Some?

My plan is to never look at the memory a reference points to (as part of validity checking). So we cannot know the value of the discriminant, and hence &Option<!> is fine (as long as it is aligned and dereferencable, as usual).

[RalfJung]

@bors r+

[bors]

📌 Commit 439f861 has been approved by RalfJung

[bors]

⌛ Testing commit 439f861 with merge c5f1cdb...

[bors]

☀️ Test successful - checks-actions
Approved by: RalfJung
Pushing c5f1cdb to master...

[RalfJung]

@saethlin if you see crates fail that used to work, this might be why.
I'd actually be curious if anything in the wild is affected by this change.