---
title: "Lang/RfL meeting 2025-01-29"
tags: ["T-lang", "design-meeting", "minutes"]
date: 2025-01-29
discussion: https://rust-lang.zulipchat.com/#narrow/channel/410673-t-lang.2Fmeetings/topic/RfL.20meeting.202025-01-29
url: https://hackmd.io/Jq3Xo0ZARAKNsRBC3lXkEA
---

# Lang/RfL meeting 2025-01-29

## Attendance

People: TC, nikomatsakis, Josh, Miguel Ojeda, Alice Ryhl, Andreas Hindborg, Benno Lossin, Boqun Feng, Guillaume Gomez, Wesley Wiser, Jubilee Young

## Rust 1.85 in Debian Trixie

Apparently the Debian folks are planning to upload Rust 1.85 to Debian Trixie, and due to the freeze timing, they'll be able to do that as a normal upload without asking for any exceptions.

## Tracking

[Tracking issue](https://github.com/rust-lang/rust-project-goals/issues/116)

### Older items

#### Arbitrary self types v2

* Arbitrary self types v2: stabilize #135881.
* Reference is under development, has a stabilization report, will hopefully be stabilized soon.

#### Stabilize CoercePointee

* Ding is working on solving some of the concerns that were brought up.
* Alice wants to see how the problem of leaking unstable impls of `Unsize` gets solved.
* It might be that it's possible to support unstable impls in the compiler, that would help.
* Some soundness concerns raised by Boxy on the #135881 thread
* `derive(CoercePointee)` is now in use in mainline Linux (for v6.14).

#### ABI-modifying flags

* RFC rust-lang/rfcs#3716 has [completed FCP](https://github.com/rust-lang/rfcs/pull/3716#issuecomment-2614078103) and needs to be merged.
* PR [#133138](https://github.com/rust-lang/rust/pull/133138) authored by azhogin@ remains under review.

#### Other compiler flags

Order of operations

* [ ] `-Zdwarf-version` -- wesley wiser
* [ ] `-Zdebuginfo-compression`, unblocked
* [ ] `-Zcrate-attr`, used to configure no-std without requiring it in the source file, no real concerns
* [ ] `-Zunpretty=expanded`, unblocked, maybe needs a PR that says "don't rely on this", Linux only uses it for debugging macros (i.e. not in the normal build, so it is less critical). Needs a stable name, e.g., `--emit macro-expanded`, and we should make sure output cannot be piped to rustc.
+ `rustfmt` told us (Rust for Linux) that they will try their best to keep `rustfmt` able to format the output of the expansion.
* [ ] `-Zno-jump-tables`, considered an ABI-modifying flag
* [ ] `-Zbinary_dep_depinfo=y` -- basically ready to stabilize
* tmandry: Do you want toolchain runtimes (libstd, compiler-rt) in your dep info? In my experience this features does 90% of what I want it to do, but removing the inclusion of runtimes is the only question I have before stabilizing. (we don't understand this point)

Easy next step:

* [ ] rename all the above to something other than `-Z` (e.g., `-C`) with `-Zunstable-features`
* maybe an MCP for this?

#### stable rustdoc features

PR https://github.com/rust-lang/rust/pull/134531 is still open. Some small back-and-forth in the issue, it will land soon.

Once that is done, need to

#### clippy configuration

Want to have the file format be stable and to have a policy on the options in the file. Flags are also ok for RFL, need something.

What happens if you remove a key from the file? Don't want it to crash and burn.

Either we go one by one through the options kernel uses or just declare that

* once a name is added it will always be recognized
* msrv, check-private-items, disallow=macros
* using the last one to disallow dbe macro. Normal lint that would deal with it doesn't work with the custom macro.

Could have a "allow-unrecognized-options" that will never go away and be done with it, that is the only one that is stable forever?

Not super critical because kernel builds are not production.

Seems like it just needs someone to write down what is expected and someone does the finishing work. Maybe there will be clippy folks at FOSDEM.

Clippy team lead is flip1995, Manishearth

#### rebuild libcore

Progress but no update.

### publicity

How to get the word out about how this has gone?

* Alice will be speaking at Rust Nation
* Rust blog post, perhaps once the language items are done done done?
* LWN article might be an option

### discussion about a flag we don't yet have

`Cgeneral-regs-only` -- something to disable floating point registers.

The language has always exposed floating point as a "always available" feature, but sometimes you want to ban them.

Removing floats from language may not be needed as there are other ways to achieve the same goal. Compiler can have a "way that this should work" instead of having a bunch of flags.