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  • Took me a good couple minutes to wrap my head around. Man, what a nasty bug. I guess this specific use-case is rare. Time to see if any of the big libs are affected...
    by j4k0bfr
  • This makes me feel better about my programming language I'm building. No amount of eyes can solve every problem.

    I'm using sqlite's testing principles that Dr Hipp explains (MC/DC, mutation testing, fuzzy checking, property testing) and even some loose lean proofs written by LLMs, but in the end, it's all just kayfabe. I'll find out some bug one day anyway.

    by ashkankiani
  • Shoulda coded it in C
    by glennfiedler
  • Type systems are hard! Check out https://counterexamples.org/

    I gave it a quick scan for Rust examples; there are 11 samples among the following pages:

      https://counterexamples.org/eventually-nothing.html
  https://counterexamples.org/mutable-matching.html
  https://counterexamples.org/selfishness.html
  https://counterexamples.org/scope-escape.html
  https://counterexamples.org/nearly-universal.html
    The first thing I always look for is mutability (combined with some other tricky feature), e.g. "Now it's a Just(3):Maybe<Int>, now it's a Nothing:Maybe<Int>, now it's a Nothing:Maybe<String>."

    I wonder if TFA's example could be reproduced without mutability.

    by mrkeen
  • I feel like these things get waved around as gotchas without any sense for whether any real code is impacted.

    It will be interesting to see if fixing this bug actually causes any crates to not compile.

    by Eridrus
  • Perhaps ironically, AI-based searching of the Rust compiler for bugs is likely to find more of these, pushing Rust closer and closer to the point of complete reliability.

    The eventual formalization of Rust and a creation of a formally proven compiler is presumably going to be the end point of this process.

    by lambdaone
  • This is remarkable but not super unusual. There are more than 100 issues labeled unsound currently. Some are long standing but from what I understand the new trait solver will unblock fixes for some of them (but probably not the one in OP).
    by weinzierl
  • It's surprising this bug went unnoticed for so long, but at least it's easy to fix, since it's not a bug with the type system itself; it's just a bug in the compiler. The compiler should always have been rejecting that code according to lifetime rules of Rust's type system, so the fix is to just make it reject the code, rather than having to change the fundamental rules of lifetimes.
    by GrantMoyer

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