iiinova — where your digital self keeps evolving

Michael (compiler-errors) Goulet @errs.io · 27/12/2025

i wonder how'd it get there? did they switch to the jamaica line at b'way junction, then up go 6 av?

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Michael (compiler-errors) Goulet @errs.io · 03/11/2025

starting work next week… hopefully i remember how to program

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Michael (compiler-errors) Goulet @errs.io · 02/11/2025

lexington was horrendous earlier today, northbound 4 trains already 100% packed pulling into fulton and 5 trains were just skipping the station altogether

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Michael (compiler-errors) Goulet @errs.io · 28/10/2025

don’t forget 8av and central park west

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Jared @jaredjct.bsky.social · 27/10/2025

121 years of the greatest subway in the world ! #subwayday

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Michael (compiler-errors) Goulet @errs.io · 11/10/2025

khadija al hanafi set was insane last night

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Michael (compiler-errors) Goulet @errs.io · 26/09/2025

how hard is it to paste an image into an image 😭

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Michael (compiler-errors) Goulet @errs.io · 23/09/2025

i dislike that one in particular. i'd be fine if it were a cheeky custom error message when the unresolved break target is `rust`, but it's implemented as a custom ICE in the compiler which is kinda annoying

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Michael (compiler-errors) Goulet @errs.io · 09/09/2025

not afaict, they’re ocaml as far as i can tell :)

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Michael (compiler-errors) Goulet @errs.io · 09/09/2025

oh right, this all does remind me of implicits in scala. thanks for the terminology :)

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Michael (compiler-errors) Goulet @errs.io · 09/09/2025

I will note that the Rust compiler does distinguish "instance resolution" from plain ol' "solving goals". In typeck, we only care that a where clause holds, but it doesn't necessarily know what impl a solution comes from until codegen b/c of things like opaques, where clauses that shadow impls, etc.

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Michael (compiler-errors) Goulet @errs.io · 09/09/2025

but it is a very good point that there is some flexibility lost, though I'm not sure if there isn't a way for traits to themselves implement some kind of rank-2 "kind" and make signatures generic over *those*, for example. it wouldn't be generalizable like functors are, tho.

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Michael (compiler-errors) Goulet @errs.io · 09/09/2025

Right, but I find that often I want my API to be meant for a single "kind" of trait. When I write `sum_values<T: Add>`, I don't want callers to provide an implementation of `Mul`, even tho it provides some binary `t -> t -> output`. So in a way it also kinda makes the API more self descriptive 🤔.

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Michael (compiler-errors) Goulet @errs.io · 09/09/2025

Another rust could be smarter about this or have chosen a different solver strategy, but lots of reasonable code relies on this incompleteness (we've encountered a lot of cases when working on the new solver lol).

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Michael (compiler-errors) Goulet @errs.io · 09/09/2025

The compiler today either just bails out with ambiguity if we don't know what to return from `.borrow()` (like we sometimes do) or be incomplete, and I guess we settled on reasonable heuristic of preferring where clauses + associated bounds which is (possibly surprisingly) often what the user wants.

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Michael (compiler-errors) Goulet @errs.io · 09/09/2025

Yeah. The issue stems from the fact that there are essentially two things we're proving here that both involve inference: `O: Borrow<?0>` and `?0: PartialEq<?1>` here, and we don't really do solving at the "intersection" of two different goals even if both taken together would find a valid solution.

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Michael (compiler-errors) Goulet @errs.io · 09/09/2025

the important part of (2.) is that modules (i.e. impls) themselves don't need names, since theyre uniquely identified by the `module type` being impl'd + the params, and we don't ever *need* to name them directly as a consequence of them being retrievable by this name

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Michael (compiler-errors) Goulet @errs.io · 09/09/2025

by 1. treating `modules type`s nominally rather than structurally, 2. and uniquely identifying each module with a set of input parameter types (i.e. no impl overlap), we can look up a module's components by name without referencing it directly, via the `module type` + generics

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Michael (compiler-errors) Goulet @errs.io · 09/09/2025

trying to make sense of ocaml modules and their conceptual relationship to rust traits... rust essentially enables "module inference" which i think is neat, especially thinking about what constraints this requires compared to ocaml where modules need to be named directly in functors

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Michael (compiler-errors) Goulet @errs.io · 09/09/2025

Second example, yeah we prefer associated type bounds over impls so `owned.borrow()` is `&B`, which requires `B: PartialEq`.

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Michael (compiler-errors) Goulet @errs.io · 09/09/2025

third example shouldn't be a mystery. `owned.borrow()` requires `O: Borrow<_>`. We prefer where clauses over the built-in reflexive `Borrow` impl, so we end up with type `&B`. That means we end up selecting the `B: PartialEq` impl in the where clause (elaborated from `B: Eq`) for the `==`.

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Michael (compiler-errors) Goulet @errs.io · 06/09/2025

we dont have the implication that the type U in `T: Tr<Assoc = U>` implies all of the bounds of Assoc onto U, unfortunately. Doing so leads to a complexity blowup that the old solver can’t handle and the new solver would probably also choke on.

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Graydon Hoare @graydon-pub.bsky.social · 05/09/2025

I wrote about this sort of corporate mis-allocation of maintainer roles a while back and it's tragic to see such a vivid example. Let maintainers be maintainers! graydon2.dreamwidth.org/306832.html

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Michael (compiler-errors) Goulet @errs.io · 05/09/2025

thanks! it’s a shame i didn’t get to work on rust for longer, but i hope i made my mark and i’m glad i’m settled job-wise. hope i get to work on rust or something equivalently impactful in the future, we shall see.

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Michael (compiler-errors) Goulet @errs.io · 05/09/2025

I urge companies to take funding contributors seriously, in ways that aren’t tied to projects and goals. Being a generalist in the compiler meant that often I wasn’t working towards a roadmap, but my contributions *always* paid off in the long term extensibility of the language.

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Michael (compiler-errors) Goulet @errs.io · 05/09/2025

That does mean I’ll be scaling back my Rust contributions over the next few months before I start my new job. Sorry to the folks who were looking forward to stuff I had in the pipeline. I really would’ve liked to deliver async fn in dyn traits or `-Zhigher-ranked-assumptions`.

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Michael (compiler-errors) Goulet @errs.io · 05/09/2025

Unfortunately, it was not possible to snag a new job working on Rust in the way that I do today (type system/compiler frontend) especially with the freedom I have today, and I couldn't possibly be jobless for an indeterminate amount of time waiting for the right role to show up.

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Michael (compiler-errors) Goulet @errs.io · 05/09/2025

I’m glad I got the opportunity to do amazing work on Rust over the last 3 years. It’s hard to quantify, but I hope people saw a difference due to my work on async traits/closures, the type system, diagnostics, style team, ICE fixes, internal refactors, speedups, edition 2024 etc.

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Michael (compiler-errors) Goulet @errs.io · 05/09/2025

Today’s my last day at AWS working on the Rust compiler. Unfortunately, back in July I received notice that I had to choose between moving to Boston from NYC, or leaving the company due to RTO policy. I unfortunately couldn’t abandon the city I plan on being my long term home.

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Michael (compiler-errors) Goulet @errs.io · 28/07/2025

unfortunately i really don’t think i have that leverage 😅

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Michael (compiler-errors) Goulet @errs.io · 27/07/2025

that sounds really fun. especially if the interviewers already knew rust, you can just dive into the subtleties and tradeoffs.

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Michael (compiler-errors) Goulet @errs.io · 27/07/2025

that is so funny, did they just not read anything about your background or experience?

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Michael (compiler-errors) Goulet @errs.io · 27/07/2025

i wish i could just sit down and talk for an hour about a really complex change that i did, i've got plenty of those

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Michael (compiler-errors) Goulet @errs.io · 27/07/2025

coding interviews are a joke and i'm gonna be so pissed if i can't get a job because i don't know how to find some "trick" to solve some toy problem that has nothing to do with developing and maintaining a massively complex compiler codebase, which is a thing that i *am* actually good at doing.

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sophie alpert @sophiebits.com · 22/07/2025

I wrote a blog post sophiebits.com/2025/07/21/t...

sophiebits.com

TODOs aren’t for doing

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Michael (compiler-errors) Goulet @errs.io · 14/07/2025

also someone find me a job so that i can keep doing work like this 🦀

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Michael (compiler-errors) Goulet @errs.io · 14/07/2025

The PR is pretty technical, so I don't expect that many people to understand what's going on in it, but hopefully when it lands I can ask people to test their code with `-Zhigher-ranked-assumptions` and see if it fixes their code :)

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Michael (compiler-errors) Goulet @errs.io · 14/07/2025

github.com/rust-lang/ru... is the beginning of a fix for all the nonsense lifetime errors you probably encounter when writing async code in Rust that heavily uses lifetimes. github.com/rust-lang/ru... If you've ever hit any of these issues, I'd like your feedback when that PR lands.

github.com

Consider WF of coroutine witness when proving outlives assumptions by compiler-errors · Pull Request #143545 · rust-lang/rust

TL;DR This PR introduces an unstable flag -Zhigher-ranked-assumptions which tests out a new algorithm for dealing with some of the higher-ranked outlives problems that come from auto trait bounds o...

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Michael (compiler-errors) Goulet @errs.io · 02/07/2025

Howdy all. I'm unfortunately not going to be with my employer for much longer due to team relocation. If anyone has any info on roles that would allow me to continue my Rust compiler work (in New York City), they'd be greatly appreciated.

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Alona @alona.page · 03/06/2025

don't talk to me or my son ever again

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Erik Jonkers @erikjee.bsky.social · 17/05/2025

On my way back home after RustWeek 2025. So, so proud that we hosted the Rust Project All-Hands, the 10 years of Rust celebration, and the biggest Rust conference yet. See you all next year! Thanks to my co-organizers Jana, Laura, @tertsdiepraam.bsky.social and @mara.bsky.social ❤️ #rustlang #rust

10 years of Rust celebration - by rust-lang.org

RustWeek closing with all speakers on stage

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Rust Language @rust-lang.org · 15/05/2025

Live from the 10 Years of Rust celebration in Utrecht, Netherlands, we are very happy to announce a new version of Rust, 1.87.0! See the blog post and release notes for all the details! blog.rust-lang.org/2025/05/15/R...

Many happy Rustaceans at the release party.

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Michael (compiler-errors) Goulet @errs.io · 08/05/2025

I feel like the work i did to improve diagnostics in github.com/rust-lang/ru... is paying off a lot now. I see it all the time. We now report "purely additive" typo fixes for things like methods using an inline syntax that highlights what to *add*, rather than the whole identifier.

A method resolution error:

```
error[E0599]: no method named `try_structurally_resolve` found for reference `&fn_ctxt::FnCtxt<'a, 'tcx>` in the current scope
--> compiler/rustc_hir_typeck/src/pat.rs:694:31
|
694 | *self.try_structurally_resolve(pat.span, peeled_ty).kind()
| ^^^^^^^^^^^^^^^^^^^^^^^^
|
help: there is a method `try_structurally_resolve_type` with a similar name
|
694 | *self.try_structurally_resolve_type(pat.span, peeled_ty).kind()
| +++++
```

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Michael (compiler-errors) Goulet @errs.io · 07/05/2025

same but mine is 60 minutes and it’s already a 200 bullet point list

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Michael (compiler-errors) Goulet @errs.io · 21/04/2025

how the heck do i write a conference talk

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