Other than memory leaks, we also saw a bug in Bun.SQL's connection pool that would consistently lead to deadlocks after restoring the VM from scale-to-zero. It was also fixed by the Rust rewrite/translation.

Overall, the empirical evidence we got clearly showed that the Rust version was much more stable and reliable.

There was a lot of discourse on the internet about the trustworthiness of the automatic rewrite, but my understanding is that it was essentially a glorified machine translation and not a re-implementation from specs and tests, akin to using Google Translate or DeepL but for code. Of course it's a simplification, and I'm looking forward to reading Jarred's upcoming blog post about all of the non-trivial aspects of it, but it's still essentially the same code, largely written by humans and translated by an LLM. The main differences are the bugfixes that the codebase got for free thanks to Rust having destructors (a lot of Bun's bugs and memory leaks seem to have been caused by manual resource management in Zig), as well as whatever issues the Rust compiler found even in the non-idiomatic code.

One valid area of concern is the amount of unsafe code and it potentially adding new kinds of UB for things that wouldn't have been UB in Zig, for example, by converting raw pointers to Rust references and inadvertently violating aliasing rules. As long as those things have been audited for, I wouldn't be any more concerned to use the rewritten version than the original even if basically nothing else was reviewed. And as long as the code is being refactored to get rid of those unsafe blocks and refactor it to idiomatic Rust in reviewable chunks, the surface area for bugs will continue to shrink and more pre-existing bugs will be uncovered and fixed.