[igregoryca]

The only languages that eliminate logic bugs are formally verified ones, as the article points out. (And even then, your program is only as correct as your specification.) Ordinary Rust code is not formally verified. Anyone who claims Rust eliminates errors is either very naive or lying.

Type-safe Rust code is free from certain classes of errors. But that goes out the window the moment you parse input from the outside, because Rust types can enforce invariants (i.e. internal consistency), but input has no invariants. Rust doesn't ban you from crashing the program if you see input that violates an invariant. I don't know of any mainstream language that forbids crashing the program. (Maybe something like Ada? Not sure.)

I don't understand why you bemoan that Rust hasn't solved this problem, because it seems nigh unsolvable.

[Superuser666]

As someone who's been working heavily in Rust for the last year, I have to agree with you, here.

Look, there's a lot of folks who gripe about Rust; I used to be one of them. It's like someone took C-lang and pushed it to hard mode, but the core point keeps getting lost in these conversations: Rust never claimed to solve logic bugs, and nobody serious argues otherwise. What it does is remove an entire universe of memory-unsafety pitfalls that have historically caused catastrophic outages and security incidents.

The Cloudflare issue wasn’t about memory corruption or type confusion. It was a straight logic flaw. Rust can’t save you from that any more than Ada, Go, or Haskell can. Once you accept arbitrary external input, the compiler can’t enforce the invariants for you. You need validation, you need constraints, you need a spec, and you need tests that actually reflect the real world.

The idea that "only formally verified languages eliminate logic bugs" is technically correct but practically irrelevant for the scale Cloudflare operates at. Fully verified stacks exist, like seL4, but they are extremely expensive and restrictive. Production engineering teams are not going to rewrite everything in Coq. So we operate in the real world, where Rust buys us memory safety, better concurrency guarantees, and stricter APIs, but the humans still have to get the logic right.

This is not a Rust failure. It is the nature of software. If the industry switched from Rust to OCaml, Haskell, Ada, or C#, the exact same logic bug could still have shipped. Expecting Rust to prevent it misunderstands what problems Rust is designed to eliminate.

Rust does not stop you from writing the wrong code. It stops you from writing code that explodes in ways you did not intend. This wasn't the fault of the language, it was the fault of the folks who screwed up. You don't blame the hammer when you smack your thumb instead of a nail - you should blame your piss poor aim.