[Jarred]

I have learned so much reading Andrew’s code and as I said in the original post: Bun would never have happened without Zig.

> The post claims they were fuzzing their Zig code, while during our calls the whole Bun team told us that they were not fuzzing anything. This appears to be an outright fabrication.

Fuzzilli integration: https://github.com/oven-sh/bun/pull/24826

Merged PRs fixing issues Fuzzilli found in Bun’s Zig code:

- https://github.com/oven-sh/bun/pull/28926

- https://github.com/oven-sh/bun/pull/28934

- https://github.com/oven-sh/bun/pull/29255

- https://github.com/oven-sh/bun/pull/29210

- https://github.com/oven-sh/bun/pull/29199

Searching “Fuzzilli” shows more PRs: https://github.com/search?q=repo%3Aoven-sh%2Fbun+is%3Apr+Fuz...

[ovao]

Note that Andrew's since removed the “outright fabrication” bit from his post. No indication of the edit itself though, which is a choice.

[abacate]

Original post: https://archive.is/wNLqY

Updated version: https://archive.is/TpsUW

[ladyanita22]

It is a choice indeed. Well worded.

[hoppp]

Andrew means the zig build test --fuzz command probably the built in zig fuzzer, that's the tool that is in his scope.

[lolinder]

If that's what he meant that doesn't speak well for his communication in this post, because "the Bun team told us that they were not fuzzing anything" is a wildly different claim than "the Bun team told us they weren't using a specific tool for fuzzing".

[v3gas]

You're a champ, man

[tipiirai]

Not sure I follow. Is "fuzzing their Zig code" somehow related to adding a Fuzzilli integration to Bun?

[mtlynch]

Yes, "their" refers to Bun's code, not the Zig compiler's code. Fuzzili is a fuzzing engine for JavaScript, so integrating it into Bun means that Fuzzili is fuzzing Bun.[0]

From the Bun post[1]

> We fuzz Bun's runtime APIs 24/7 using Fuzzilli, the JavaScript engine fuzzer used by V8 & JavaScriptCore

From Andrew Kelley's post today[2]:

> The post claims they were fuzzing their Zig code, while during our calls the whole Bun team told us that they were not fuzzing anything. This appears to be an outright fabrication.

Sumner says that the Bun team has been fuzzing Bun's Zig code. Kelley says that this is a fabrication. Sumner showed proof that the Bun team has been fuzzing Bun's Zig code.

It looks like Kelley is incorrect and made an unfounded claim. The generous interpretation is that at the time Kelley and Sumner had a more collaborative relationship, Sumner was not fuzzing Bun's Zig code, but I'd expect Kelley to check if anything had changed since then before publicly accusing Sumner of lying in this week's Bun blog post.

[0] https://github.com/googleprojectzero/fuzzilli

[1] https://bun.com/blog/bun-in-rust

[2] https://andrewkelley.me/post/my-thoughts-bun-rust-rewrite.ht...

[xlii]

AFAIU fuzzing code != fuzzing results. Through skimming it seems that integration tests were using fuzzing, but I would call it fuzzing the code itself.

From "product" perspective there's no difference, but in program-compiler perspective (and e.g. raising bugs about compiler), Fuzilli isn't fuzzing.

Per Wikipedia > (then...) The program is then monitored for exceptions such as crashes, failing built-in code assertions, or potential memory leaks.

As for myself, I wouldn't use term fuzzing for integration testing such the one used by Fuzilla. I always caught it dynamic testing, scenario testing and in bigger cases property based tests. Fuzzing in my mind is reserved to a low-abstraction calls.

Might just be me, though.

[jsnell]

I don't understand what distinction you're trying to draw here. The very specific claim[0] in the Bun blog post that Kelley is calling a fabrication was:

> We fuzz Bun's runtime APIs 24/7 using Fuzzilli, the JavaScript engine fuzzer used by V8 & JavaScriptCore

It does not look to be a fabrication, and is very explicit just about what they meant by fuzzing.

[0] I mean, that sentence doesn't actually match Kelley's paraphrase, but it is literally the only claim in the post related to what fuzzing was done on the Zig-based bun codebase. So it has to be what Kelley was referring to, and his paraphrase is as sloppy as his fact-checking.

[xlii]

For me, using Fuzzilli for testing a Zig code is not fuzzing, it's integration testing. If you're running code externally (e.g. wrapping binary) you cannot guarantee that side effect isn't caused by IO. I consider fuzzing a low level activity with many external variables removed.

Depending on where you are and how you communicate semantics matter more or less. It's very similar to compiler/transpiler. E.g. TypeScript "Compiler" is called compiler but in fact it's transpiler (it emits other high-level language as a result).

[jsnell]

My point is that Kelley did not argue that what Bun does isn't really fuzzing. He wrote that the post's claim is a fabrication. But that claim is really specific, and to evaluate whether it is true it doesn't matter what Kelley's unstated definition of fuzzing is.

So an argument about definitions doesn't seem super valuable here.

[mtlynch]

> For me, using Fuzzilli for testing a Zig code is not fuzzing, it's integration testing. If you're running code externally (e.g. wrapping binary) you cannot guarantee that side effect isn't caused by IO. I consider fuzzing a low level activity with many external variables removed.

I've never heard anyone restrict the definition of "fuzzing" in this way. If I repeatedly generate inputs to a program and then run the program with those inputs, that's fuzzing. It doesn't matter if there's IO or not.

> Depending on where you are and how you communicate semantics matter more or less. It's very similar to compiler/transpiler. E.g. TypeScript "Compiler" is called compiler but in fact it's transpiler (it emits other high-level language as a result).

It's still a compiler. It translates code from one language to another. You can argue whether we need the term "transpiler," but a source-to-source compiler is a compiler.

[pdpi]

The conversation amounts to “You should fuzz your code” “we’re already fuzzing the big external dependency, using their own fuzzing setup that they already use upstream”.

It’s not nothing, but clearly not what Andrew meant.

[samtheprogram]

Based on timeline, it seems like both are true. They stopped communicating around the time of the acquisition per OP, which was announced December 3rd, and the PR integrating it is was merged the tail end of November.

[orangeisthe]

Why are you not using hyperlinks and adding links citation style?

[Philpax]

This is standard convention on HN for when you have more than one link. HN does not support masked links.

[nsagent]

Your links show you used a fuzzer, but that doesn't address the other half of Andrew's statement. Is Andrew misreporting/misremembering your conversations?

EDIT: It's really telling that asking a factual clarification question is somehow downvote worthy. I probably shouldn't be surprised, but this epitomizes the reason online discussions devolve in to flame wars (even moreso than real life, though it happens more and more there as well).

The answer could be as simple as we didn't use a fuzzer until recently so both are accurate. I honestly don't know, which is why I'm asking. Yet somehow just asking is triggering to people.

[lolinder]

No one's obliged to respond to hearsay by trying to guess what the other party might have misheard to arrive at a false conclusion. It's enough to demonstrate that the conclusion they came to was false, and if the other party would like to defend themselves they're welcome to explain why they came to that misunderstanding.

[mi_lk]

Or, did the whole Bun team indeed state the otherwise to Zig?

[ykurtov]

Dude, that PR is on 25th of November 2025 :) Few weeks before Anthropic acquired Bun.

[tel]

Without having any opinion on whether or not the Bun team was meaningfully fuzzing their codebase... Andrew's claim was not about whether or not they were, it was noting that the story was different between what they claimed in conversation and what they stated in this article.

[silver_silver]

All of those commits except the initial integration are from after the acquisition. How do we know this wasn’t done without anyone on the call’s knowledge?

[zamadatix]

Since there are multiple ways to interpret Andrew's original comment, multiple ways to interpret what his newer edit of it implies, multiple logical reasons each way could have come about, and likely multiple opinions on what the expectations from each side should be... I'm finding myself getting stuck in a loop of trying to understand how/why these considerations are important.

Could you help further explain which interpretations & ways you feel this info is relevant to?