alt Hacker NewsIt does apply, of course (even if not to this case specifically). The implemented Rust semantics are not sound, as evidenced by this issue. We need to find (or adjust) sound semantics. Which, mathematically, is equivalent to designing Rust from scratch (ignoring things like RustBelt because they did not formalize the entire system). Due to Rice's theorem we know we need to give up some sound programs. Can we give up exactly the programs we already gave up for the previous Rust? Maybe, maybe not.
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> The implemented Rust semantics are not sound, as evidenced by this issue. We need to find (or adjust) sound semantics.
You’re ignoring the possibility that Rust semantics are sound, and the implementation doesn’t fully implement them. In that case, we do not have to find sound semantics.
That, I think, by far is the most likely option.
Reason: I’ve not seen a single comment claiming the example should compile, and zillions (implicitly) acknowledging this is not what Rust should do.
It could be that I'm totally yapping bullshit, but the "designing from scratch" can vary depending which field of maths you're talking about. For instance, if we model the semantics as a series of composable functions, then you only have to scratch only the specific dependency tree of the functions. Basically everything can be reused with no wasted work, and the output space gets culled.
The tricky thing about formalization is that you usually have to reimplement the type checker into a proof assistant in order to do formal soundness proofs. It's not necessarily clear that this reimplementation is identical to the actual Rust compiler (in fact, you often have to massively simplify the type system to make the proofs tractable), so bugs in implementation can cause unsoundness without being related to fundamental flaws in the soundness of the type system.