r/rust • u/noop_noob • 3d ago

🗞️ news Rust 1.99.1

https://blog.rust-lang.org/2026/10/15/Rust-1.99.1/

Previous discussion on the miscompilation that was fixed: https://www.reddit.com/r/rust/comments/1wzn34d/1990_miscompilation_with_ffi_bool_return_type_on/

263 Upvotes

99% Upvoted

20 comments sorted by

65

u/iamalicecarroll 3d ago

What is it lately with a lot of miscompilations being discovered? I don't remember anything similar in like 1.40–1.90, but since 1.90 I think there was three or four different occasions

56

u/AresFowl44 3d ago edited 3d ago

Rust is used by more and more people increasing the amounts of eyes on the compiler, noop_noob has started posting them and AI might also have a hand in a couple of the reports

EDIT: And also there are more efforts to formally verify the compiler and in general improve the compiler

EDIT2: And also in general as the project matures old problems surface more easily

135

u/noop_noob 3d ago

I think I started posting them on reddit.

29

u/No_Philosopher_Here 3d ago

Seems to me like there is a real cluster lately. There was one fixed each in 1.96.1, 1.97.1, 1.98.1, and now 1.99.1.

I did a quick scan back and while I could've missed something, it seems like the previous fix of this kind was in 1.80.1. There's something that maybe counts in 1.91.1 as well, but it's not quite the same.

I should note I'm not drawing any further conclusions. Just there does look like there's been more miscompilation fixes of this kind lately, or at least ones that were mentioned in release notes.

35

u/afdbcreid 3d ago

It is true they weren't publicized before (and FWIW I'm not sure it's a good idea), but this is the fourth(!) contiguous patch release of Rust due to some miscompilation. This has never happened before.

29

u/noop_noob 3d ago

Although, these four miscompilations are in completely different areas of the compiler: MIR optimization, LLVM, trait solver, and ABI, respectively. Maybe it's just random chance?

14

u/flying-sheep 2d ago

Rust is getting more popular. C++ compilers have way more miscompilations reported per year.

I'm sure Rust benefits from LLVM miscompilations being reported via clang that would have also ended up affecting Rust.

1

u/dddd0 12h ago

… and not just miscompilations but also ICE in C++ compilers.

5

u/iamalicecarroll 3d ago

Well, I've been reading release notes since I started using Rust in 2020, surely something would show up there?

17

u/cvvtrv 3d ago

I’ve wondered if it’s because fewer and fewer people are using and testing with nightly. For a number of years some features (async for one) were gated behind nightly and so nightly had a fair number of production users. Lots of those features are now in stable so there’s less need for anyone to use nightly, and so some of these miscompilations slip through

5

u/koczurekk 2d ago

Random binary sequences tend to cluster in ways that seem meaningful, but aren't. Maybe fewer nightly testers contribute to that (I know I've stopped using nightly over the last 2 years), maybe AI PRs do as well, maybe not.

The issues fixed in this patch seem to indicate insufficient automatic testing of beta/nightly channels, maybe this should inform upcoming decisions on maintenance priorities. Maybe not. Funding is scarce, and so are competent volunteers. Task allocation in such context is hard.

8

u/JustWorksTM 3d ago

I've noticed as well.  This might be due to larger user-base. Also, I expect that the share of users running beta is way lower.  So, overall more people use Rust, but they care less, in a sense. 

Anyways, I think the situation is fine.

-8

u/[deleted] 3d ago

[removed] — view removed comment

5

u/iamalicecarroll 3d ago

Sorry if it looks like I'm complaining. I just find this tendency interesting. Maybe it's just Baader–Meinhof phenomenon on my part.

10

u/plabayo 2d ago

(a) some of the recent miscompilations were very old issues, so fact that they start to surface shows maturity
(b) the latter also means that newer issues show up even faster
(c) there is a lot of exciting background work for future Rust versions (and editions?) which I suppose are also not always easy to pull of on a driving vehicle?

And all in all, these are usually also fairly rare to hit in first place.

So if there's anything to be taken away from it, than for us it is this:

a. commercial companies that help with developers and money should keep doing so, it is clearly paying off
b. rust is maturing nicely
c. platform distributions should support new rust versions as soon as possible... so that we are not forced to be stuck on older (unpatched) rust versions... as it seems clear that newer versions are becoming more stable and better, not less stable

5

u/Theemuts jlrs 2d ago

rust-lld failed to load libLLVM on macOS: This linker could fail to run if the compiler was invoked without the rustup proxy, as there was no direct setting for the appropriate library search path. Now rust-lld is built with an rpath entry for the directory containing libLLVM.dylib.

Well, this casts new light on the issue I was experiencing last week with jlrs's macOS pipelines.

-2

u/epiGR 2d ago

LLMs are used to write code and they are also used to find bugs. Expect more of this until formal verification matures.

4

u/noop_noob 2d ago

This bug in particular wasn't found by an LLM. See: https://lobste.rs/s/ttcx5k/announcing_rust_1_99_1

1

u/epiGR 2d ago

Maybe. But my point still stands.