[muglug]

This post doesn’t make sense. It was rewritten in Rust. The rewrite itself is complete (no more Zig).

Various people have claimed that Bun in Zig had a lot of tech debt. If they’re to be believed, it seems natural to assume the rewrite does, too. Perhaps all this activity is paying down some of that debt.

[pizza234]

> This post doesn’t make sense

The author's assumption is that a rewrite is not just a mechanical translation of code - it's also a state of stability. And no release, for the author (I agree) means no stability.

It's like a developer who says that after a week of work, a feature is 90% ready, but the other 10% is still not ready (for release) after months.

[virajk_31]

Author kept "going" in title because there has been no minor/major release in last two months which unusual for this project if you review the older releases.

[muglug]

A major rewrite in another language is also unusual for this project.

It took TypeScript a year to go from announcing tsgo to releasing TypeScript 7.0. That work was done in parallel; here the work is being done serially — and it’s likely to take much less than a year for a new release.

[chmod775]

> It took TypeScript a year to go from announcing tsgo to releasing TypeScript 7.0.

These are not comparable at all. The bun "rewrite" really is more of a translation of a software that is mainly dogfooded, created with an at best loose regard for a wider ecosystem.

TypeScript 7.0. by comparison is not just a translation from one language to another. It's a true rewrite that at the same time has to consider a massive existing ecosystem (which needs to catch up first or you risk fragmenting it). Plus you might as well consider 6.x part of the effort, since that was the stepping-stone.

Also where bun really is just a runtime implemented with a bunch of glue code plus supporting tooling, TypeScript is much more complex. Change one part of TypeScript and you can get cascading issues somewhere else in the compiler easily. Change something in Bun and you'll likely just break some discrete part.

[dminik]

It's funny, but a large reason for why Go was chosen was explicitly because it has semantics close to TypeScript and that made it automatable:

https://github.com/microsoft/typescript-go/discussions/411#d...

> But this wasn't a compiler redesign, and the TypeScript to Go move was far more automatable and more one-to-one in its mapping.

So basically the opposite of what you're saying.

[chmod775]

IMHO it's not the same car, even if its engine initially was a 1:1 rebuild using other alloys. But you're right I overstated and made myself look dumb (by a lot really - this is nothing like having 2 independent C compilers for instance).

What's taken 1:1, deliberately, was the compiler core. That was almost perfectly 50% of the non-test code. A close translation of that was a starting point, but open CHANGES.md or it's history and you'll see it's quickly diverging even on its surface.

The closest matching, interesting large area of it is probably the checker. Easily recognizable on a function level, even if not being a single file anymore:

https://github.com/microsoft/typescript-go/tree/main/interna...

https://raw.githubusercontent.com/microsoft/TypeScript/refs/... (The TS file is 3MB and github won't display it inline)

You'll find a lot of the same data structures (as far as that's possible in a TS-to-Go translation + ripples from areas that were more heavily changed) and functions lying around, just in slightly different places. Because of the AST changes and TS/Go differences on a line-level each function might look different, but where there is a loop in the TS one, there's probably one in Go.

The other half of the project is heavily changed or completely new/different (like concurrency, less weird language service).

[skeledrew]

> The bun "rewrite" really is more of a translation of a software that is mainly dogfooded, created with an at best loose regard for a wider ecosystem.

This seems self-contradictory. If it's just a translation, doesn't that mean it remains fully compatible with that wider ecosystem? All the existing APIs retain identical behavior given the preexisting comprehensive test suite that had to go 100% green after all.

[chmod775]

> This seems self-contradictory.

It's not.

Passing an existing test suite just moves the optimistic lower bound to incidental compatibility, it doesn't move it to intentional - "regard" implies you gave it thought.

Plus, it's not just about code: it's also about giving the ecosystem a migration path. Dumping 500k LOC on people and discontinuing development of the zig version effective immediately (there hasn't been a release since and the zig tree is only a reference - the build script is removed afaik) is the opposite of what TypeScript did. If you broke someone's N-API module because of a regression not caught by your suite they're now between a rock and a hard place.

The good news is that there's nobody there to notice. The bun userbase is miniscule* compared to TypeScript's.

* negligible? irrelevant? laughably small? I'm struggling to find an adjective that does the difference justice.

[skeledrew]

That "incidental compatibility" point is a good place to start. Unless there are serious gaps in the test suite, one can have high confidence that there's no regression from the pre-fork version in documented behavior.

What kind of migration path beyond 0 regression do you think is needed? And if the latest Zig version is no longer available, how were at least 2 forks based on it submitted to HN? And what kind of release are you expecting when the team is working to fully migrate to the port (so far it's still marked canary)? If someone's using an untested (ie. very likely unpublished) API, well it sucks to be them but they should know the risks.

And again the self-contradictory argumentation. If the userbase is as miniscule as you imagine then your criticisms are essentially meaningless. No ecosystem worth giving a migration path and nobody's N-API module breaking because of a regression, right?

[TiredOfLife]

TypeScript 7.0 was literally a line by line translation. With essential features necessary for adoption still like a year off.

[virajk_31]

Yes, its because Anthropic took over and wanted to showcase their LLM capabilities by porting such a complex codebas.

[taormina]

Everyone’s point is “they have everything to gain by lying about being more done then they are” and “the claims seem at least a bit full of shit”.

[rk06]

bun in zig was used by many companies. some were using it in prod. how many of those are using it in prod? none, because bun in rust is not released yet.

Hence, the author concludes that rust rewrite is not complete as bun in rust is not released yet.

I agree with author's POV.

[davidgtonge]

The rust version is being used by Claude Code though - which is a fairly large product!

I was hoping for more push back against https://bun.com/blog/bun-in-rust - which is pretty thorough and has some decent arguments and reasoning for why they did the rewrite.

[reactordev]

I think they meant “released and available for use” rather than just out in the wild.

[thevinter]

It is available for use: `bun upgrade --canary`

[strobe]

it doesn't imply that lot legacy apps won't crash in prod when it will be actually released. Cool that some complex app is working but is nothing proving that everything will be fine when everyone will try to upgrade.

[flohofwoe]

How much of the Bun/Node API surface does Claude Code actually use though? Conceptually it's a relatively simple TUI application.

[nullsanity]

Yeah, but it's a TUI that has more bugs and worse performance than any other TUI in history. It's not like we'd notice a user after free.

[Aurornis]

> Various people have claimed that Bun in Zig had a lot of tech debt. If they’re to be believed,

This is one of the funnier takes on the rewrite. Bun was held up as a flagship Zig project for years. Then they chose to rewrite in Rust and everyone up to the Zig author has suddenly switched to claiming that Bun was terrible code all along.

[IsTom]

If what they're claiming is true then what were they supposed to do? Go "Hey guys, it's the biggest project in Zig and it sucks, don't look at it"? Not exactly a good PR move.

[abalashov]

> Perhaps all this activity is paying down some of that debt.

Perhaps. But were that the case, one would think they'd be quite eager to say so.

[muglug]

Maybe they will!

Are you expecting them to live-tweet their work or something?

[abalashov]

Based on the way they live-tweeted (as it were) their rewrite and their other publicity stunts? Yes, actually.

[tough]

jared was OK making this rewrite as an experiment branch in the public

why shouldnt upcoming work be as public as the rewrite itself was?

[skeledrew]

You may continue to hold your breath. You may die as a result. The maintainers continue to do what they want regardless.

[tough]

I do not really care, just pointing where people's assumptions might be coming from.

The beauty of FOSS tho is Jarred owes the community nothing, and anyone can fork bun previous to migration and keep maintaining it on zig if they so wish.

long live open source

[cowl]

tech dept is not a problem. to paraphrase captain Jack sparrow. "even if it were the most indepted working software project, IT WORKED". On the other side of the medal we have a rewritten software that although it's trumpeted for it's rewrite speed, it is not showing the same Release speed as the manualy written, "tech dept ridden" old one.