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Comment by insanitybit | Hacker News Reader

For a long time `loop {}` was undefined behavior. Lots of l-unsounds are really nuts but a few are not.

The reality is that if this were actually code that people wrote, well, it wouldn't have sat around for a decade.

Afaik loop {} has never been UB, however because llvm started as a c++ compiled where it is, this has been causing miscompilations in rust and C for… nearly two decades (llvm issue 965).

Since the Rust language is defined by the Rust compiler and has no other specification, if it's UB in the compiler then it's UB in the language.

Rust has no formal spec? Really?

It's a work in progress. The Reference (https://doc.rust-lang.org/reference) is slowly getting more complete over time. Other ongoing efforts include a-mir-formality (https://github.com/rust-lang/a-mir-formality), minirust (https://github.com/minirust/minirust), the FLS (https://github.com/rust-lang/fls), and Rust via Desugarings (https://nadrieril.github.io/rust-via-desugarings/). But writing a 100% complete and correct formal spec is hard! Not even C gets this right, the C standard has holes which lead to miscompilations and UB in practice: https://www.ralfj.de/blog/2020/12/14/provenance.html

Sure, I think it was still under the same unsound tag regardless.

Unsoundness and UB are very different things, UB tells users of the language "don't do that it's wrong", unsoundness tells users of the language "be careful we need to fix that", it's a bug.

I don't care, nor should anyone else

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