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Rewrite Bun in Rust has been merged

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Re: Rewrite Bun in Rust has been merged

#371

Post by ryanschaefer »

carllerche wrote: post #361
konart wrote: post #267

Earlier quoted context omitted.

Rust vs Zig "wars" etc. Also at some point Bun was acquired by Anthropic. And some people feared that this will greatly influence Bun's development.

I don't think Rust vs. Zig has anything to do with why people are talking about this. It is a large piece of "real software" that underwent a full language transition in ~1 week using LLMs. That is a big deal regardless of the language and will be a case study regardless of how it turns out.

It’s a watershed moment. Basically one of the most controlled applications of an LLM into a robust codebase without regard for the implications of doing so.

Anthropic needed something like this and it must proceed flawlessly. My guess is that nothing will explicitly break. But that’s the difficulty of LLM generated code: nothing breaks. You sit with a codebase that swallows all errors and appears to be working. Silently failing makes debugging performance and behavior much harder.

Re: Rewrite Bun in Rust has been merged

#372

Post by user142 »

bhaak wrote: post #335
losvedir wrote: post #276

Wow. This is going to be interesting to follow. There's absolutely no way any of this code was reviewed, but maybe we're in a post-human world now where you can trust the models to write and review the code. This is like Gastown but on a higher profile project. Will be fascinating to see how this project is able to add new features going forward (or even _if_ it will be able to). Does anyone know how exactly Bun is u…

It passed all the tests. If you can't trust your test suite to catch an automatic language translation you shouldn't trust it at all. :)

Tests can only prove the presence of bugs, but not their absence. If the AI can access the tests, it can easily make them pass by just adding additional if statements. It doesn't mean the code is actually correct.

Re: Rewrite Bun in Rust has been merged

#373

Post by jaccola »

sesm wrote: post #368

When announcements say that rewrite took 1 week, I wonder how much time went into preparing this file with very detailed instructions on mapping Zig to Rust idioms: https://github.com/oven-sh/bun/commit/46d3bc29f270fa881dd573... On top of that, if you look at 'Pointers & ownership' and 'Collections' sections, the Bun codebase is already prepared, using internal smart pointer types that map 1-to-1 to Rust equivalents,…

Yeah I don’t know what’s true when reading about LLMs. Same with comments here on hacker news. So much money on the line it’s clear they would seed communities with marketing shills (and some people are just tribal).

Same since they own Bun, they have every incentive to make this seem easier than it was.

Re: Rewrite Bun in Rust has been merged

#374

Post by nsagent »

rudedogg wrote: post #332
tayo42 wrote: post #293

Earlier quoted context omitted.

Rust has a ton of other features besides safe. Like exhaustive checking of enum variants and the ability to avoid using null with option and result.

Zig has these modern language features too fwiw. I think the goal was to do a massive rewrite for Anthropic (they acquired bun) and show that rewriting projects from lang -> lang with Claude can reduce security vulnerabilities to help with the hype for an IPO. I don’t use/know Rust so I can’t comment on the quality, but there was a public security review that found issues with the new Rust code: https://x.com/SwivalA…

There's a reasonable request to run the same analysis for the Zig version of the code as a comparison.

In lieu of that, it seems the Swivel devs ran an analysis on Tigerbeetle, one of the other major Zig projects, and found only 7 medium/low priority issues:

https://xcancel.com/SwivalAgent/status/2054063291266113994

Re: Rewrite Bun in Rust has been merged

#375

Post by dgellow »

randusername wrote: post #366
dgellow wrote: post #324

If the bun team is around I would be interested to get their opinion on this: in the old time migrating a 1M codebase from one language to another meant you would pretty much become an expert in the target language. The output of the work is team experience/knowledge + the actual rewrite. With that Bun rewrite do you feel that the Bun team learned something other than “Claude can rewrite a very large codebase in no t…

I used to think software was inherently valuable. Then I decided that software is of limited value without a team to maintain it. Not necessarily because they fix it, but because they represent a bunch of humans who collectively understand it and therefore give it more possibilities. And now this. I'm not sure what to make of it.

Same

Re: Rewrite Bun in Rust has been merged

#376

Post by lightamulet »

serial_dev wrote: post #348
tshaddox wrote: post #274

Earlier quoted context omitted.

Bun isn't a node.js wrapper. It's an alternative to node.js that sits at roughly the same spot in the stack. Node.js is a distribution of the V8 JavaScript engine (the thing that executes JavaScript in the Chrome browser), along with a bunch of standard library code written mostly in C++. Bun is a distribution of the JavaScriptCore engine (the thing that executes JavaScript in the Safari browser), along with a bunch…

Answering “who is even using this software” is unfortunately missing in your answer. I am honestly curious. I’ve never seen it “in the wild” (in job descriptions, hearing from past colleagues, meetups etc). Only place I heard about it is HN and Twitter.

I'd say the most prominent user (and the reason why Anthropic acquired Bun) is Claude Code

Re: Rewrite Bun in Rust has been merged

#377

Post by sunrunner »

layer8 wrote: post #358
sunrunner wrote: post #306

Earlier quoted context omitted.

I'm not sure if it's just the leading '+' or if there are other factors for phone number detection on iOS, but on mobile the line count changes are underlined and I can tap it to start a call, which, if it is because of the diff size, is something I find pretty amusing.

The leading “+” is not needed. Numbers with seven digits are automatically hyperlinked (possibly depends on locale). 123456 1234567 12345678

Interestingly, the entire line gets formatted once it reaches seven digits, +lines and -lines both, so I guess the -lines is just interpreted as a dash. But your eight digit string doesn't. Perhaps it's not interesting, though I've never really given it a second thought before.

Re: Rewrite Bun in Rust has been merged

#378

Post by q3k »

kllrnohj wrote: post #312
q3k wrote: post #74

Earlier quoted context omitted.

No matter how I look at this, it's churn for the sake of churn. Even if the translation was free and into ideal idiomatic Rust (and it's obviously not - it's now Zig with Rust syntax) then this would be churn for the sake of churn. At some project scale the language really stops being any limiting factor, and you're instead mostly dealing with working past past architectural decisions, integration of large changes, d…

> At some project scale the language really stops being any limiting factor That's not entirely true. At a certain scale, some languages start becoming increasingly more of a factor. Memory issues in C/C++ codebases, for example. This is pretty well established at this point, which is why there's a push to move away from memory-unsafe languages. Which likely would include Zig, for better or worse.

I agree that new software should avoid memory unsafe languages, but I would disagree that rewriting existing projects in a memory safe language at all cost is a universally good idea.

Re: Rewrite Bun in Rust has been merged

#379

Post by sobellian »

petcat wrote: post #308
gm678 wrote: post #249

$ rg 'unsafe [{]' src/ | wc -l 10428 $ rg 'unsafe [{]' src/ -l | wc -l 736 Language Files Lines Code Comments Blanks ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Rust 1443 929213 732281 116293 80639 Zig 1298 711112 574563 59118 77431 TypeScript 2604 654684 510464 82254 61966 JavaScript 4370 364928 293211 36108 35609 C 111 305123 205875 79077 20171 C++ 586 262475 217111 19004 26360 C Header 779 100979…

Cool you can just search specifically for potentially unsafe code in Rust. How do you search for unsafe code in Zig? Or do you just have to assume it's everywhere?

If half of your code is unsafe then unless you exercise tremendous discipline (Claude basically doesn't) you will just end up with a big ball of unsafe, peppered with hallucinations in whatever random documentary comments Claude decided to make. I doubt they enforced the confinement of unsafe to a specific architectural layer or anything like that.

Re: Rewrite Bun in Rust has been merged

#380

Post by zozbot234 »

12_throw_away wrote: post #360
Aurornis wrote: post #336

Earlier quoted context omitted.

unsafe just means that you take responsibility for the safety of the code contained within. Calling into non-Rust libraries has to be wrapped in unsafe. Making syscalls has to be wrapped in unsafe. Bun needs to interact with FFI code. This gets wrapped in unsafe blocks. There are many places where a JavaScript interpreter and library would need to make unsafe calls and operations. It doesn't literally mean the code i…

There's actually a good example of this in the rewrite [1], in `PathString::slice`. They are doing an unsafe operation to return a slice that could be a use-after-free, if the caller had not already guaranteed that an invariant will remain true. Following proper rust idiomatic practices, claude has added a SAFETY comment to the unsafe block to explain why it's safe: "caller guarantees the borrowed memory outlives thi…

One potential way to solve this in a principled manner is to turn at least some "unsafe" annotations into ghost capability tokens that are explicitly threaded through the code and consistently checked by the compiler. Manufacturing the capability could itself be left as an unsafe operation, or require a runtime check of some kind.

You already see this in some cases, for example the NonZero generic type can be viewed as a T endowed with a capability or token that just says "this particular value of type T is nonzero, so the zero value is available for niche purposes". But this could be expanded a lot, especially with some AI assistance.

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