alt Hacker NewsSure, but you need to consider that, in this case we are talking about the language runtime. It isn't just some other library dep. It's basically the base layer of the stack. It has a huge blast radius. It is, imo, a nontrivial decision to swap runtimes. If problems emerge you can't easily plug some other runtime, that's a major technical decision and should be treated as such.
In the past at least you could assume the maintainers of the runtime had some kind of mental model of how it worked. In my view, with the way this rewrite has been approached, you can't assume that at all. It's good the test suite passes, but who knows how this will affect the evolution of the codebase? Do we even know if the code is good? How much is just slop? Tests do not test architecture. Is this new rewrite even going to be maintainable? How is the team going to get up to speed on a new codebase in a new language that the main author presumably doesn't even fully understand?
There are many reasons to be concerned. Treating this as no big deal would make me question one's ability to make assessments of technology. There's a world of difference between relying on gen AI heavily in products and leaf nodes of the stack, using it in a purely assistive way, and using it to drive a massive scale rewrite of a base component in a language the maintains team has an unproven amount of experience with. From a reliability standpoint the way this project was executed is completely preposterous, and it's very clearly a marketing stunt more than a sound technical decision on how to drive a project. It's not about the use of LLMs, it's about thee stupid and blatantly obvious generation of cognitive debt all to help sell claude. I'd have way fewer qualms if they used LLMs to do a rewrite in a way that retained developer understanding (i.e. not driven by one person and in such a short timespan that having a robust mental model, even for that person, is highly unlikely)
You're implying that reckless rewrites within the JS ecosystem are a novel event, or more specifically that surprise language changes over a short period of time are. And yet... I can think of at least six times in which exactly this has happened and little fuss was made because the polarizing element of "AI" was not involved. Not just JS to Typescript, but to Dart, Go, C, Rust, Zig, Nim etc.
From any reasonable perspective, this is business as usual in the house of cards we all operate in. Perhaps the sensationalization would be justified if the lang migration wasn't one of less correct -> enforced correctness by default?
To your point in general about maintainers holding a mental model of the runtime: I would challenge that to say that it is very likely that there is no developer who holds a complete mental model of an entire runtime at any given point. As with anything of this scale you understand individual parts in their entirety and have general assertions about the rest until specifically revisited, even if you are the sole developer. In this case specifically, Bun has been largely AI driven for quite a while anyway so it is even more unlikely that the developers ever had a complete picture in the first place. If you trusted them before, then nothing has changed.
It's not lost on me that code logic can be subtly incorrect even as tests are passing either, but there isn't exactly a lot of grey area in this particular context. Does your code compile or not? If it builds as expected, then your own unit tests will highlight the difference.