---
title: "Lang/RfL meeting 2025-10-08"
tags: ["T-lang", "design-meeting", "minutes"]
date: 2025-10-08
discussion: https://rust-lang.zulipchat.com/#narrow/channel/410673-t-lang.2Fmeetings/topic/RfL.20meeting.202025-10-08/
url: https://hackmd.io/iSCyY3JTTz-g8YM-nnzTTA
---

# Lang/RfL meeting 2025-10-08

## Attendance

People: TC, Alejandra Gonzalez, Alice Ryhl, Gary Guo, Miguel Ojeda, Xiangfei Ding, Aapo Alasuufari, Benno Lossin, Josh, tmandry

Driver: TC

## Tracking

[RfL lang features tracking issue](https://github.com/rust-lang/rust-project-goals/issues/116)
[RfL compiler features tracking issue](https://github.com/rust-lang/rust-project-goals/issues/407)
[Rust unstable features needed for the kernel](https://github.com/Rust-for-Linux/linux/issues/2)
[Rust wanted features from RfL](https://github.com/Rust-for-Linux/linux/issues/354)

### 2025H2 Goals

* Lang features: https://rust-lang.github.io/rust-project-goals/2025h2/Rust-for-Linux-language.html
* Compiler features: https://rust-lang.github.io/rust-project-goals/2025h2/Rust-for-Linux-compiler.html

## Announcements or custom items

### rustfmt

Miguel worked out an agreement with Linus for what to do here (https://lore.kernel.org/all/CANiq72kDB1cX1XXX7sc3yQvnaUUYB8q1wVKNxykv8=OV-=[e-mail]/). He also has a proposal for rustfmt.

#### Merge driver

Gary: Merge driver [`mergiraf`](https://docs.rs/mergiraf/latest/mergiraf/) could be helpful, but it does more than imports which can be worrying. A merge driver that just does absolute minimal in solving the simplest case could be very useful (and leave complex case to humans).

Miguel: that works, although it may make diffs bigger nevertheless (especially given `rustfmt`'s default behavior that may change the formatting significantly after the merge). It may be fine if we use vertical layout.

#### Always Vertical

Miguel: one approach is to always use the vertical layout, possibly even for single item import statements (and possibly with the merge multiple statements behavior). This should be generally compatible with the trailing comment trick.

#### Magic Comma

Miguel: one approach is for a trailing comma to indicate "you want to expand this list later" so it'll get reformatted as multiline (or at least not attempt to make it single line). I tried to implement this and the diff resulting from applying to the kernel doesn't look large. The implementation is also fairly small (if done tweaking the logic of handling the lists). This should be generally compatible with the trailing comment trick.

#### What rustc did with rustfmt and `use` imports

It might be worth having a look at the discussion the compiler team had on a similar matter:

https://github.com/rust-lang/compiler-team/issues/750

Also maybe interesting:

- https://github.com/rust-lang/rust/issues/88029

## Other news

- [Upcoming Rust language features for kernel development](https://lwn.net/SubscriberLink/1039073/abf96f38b178f988/)
- [Linting Rust code in the kernel](https://lwn.net/SubscriberLink/1038750/6aa9769e0b875235/)

## T-content and LWN syndication

We'll have interviews coming out, from Kangregos, of Benno and Greg KH. We'll want to be sure to reach out to Jonathan Corbet for potential syndication when these go out.

It'll probably be important to give them a good text summary of the video so that they don't need to watch it to do that.

## Compiler features

* -Zharden-sls / https://github.com/rust-lang/rust/pull/136597
* Waiting on review? No change.
* `#![register_tool]` / https://github.com/rust-lang/rust/issues/66079
* Waiting on [RFC#3808](https://github.com/rust-lang/rfcs/pull/3808)
* Tyler planned to take a look and see if can be resolved with an FCP or will schedule a design meeting
* -Zno-jump-tables / https://github.com/rust-lang/rust/pull/145974
* Waiting on t-compiler
* FCP missing 2 check boxes
* Anything else?

## Lang features

#### `Deref` / `Receiver`

https://rust-lang.zulipchat.com/#narrow/channel/213817-t-lang/topic/Consequences.20of.20making.20Deref.20a.20subtrait.20of.20Receiver/

*Last time, Ding was working on a document that would explain how PR [#146095](https://github.com/rust-lang/rust/pull/146095) would change the feature.*

Ding: Diagnostics are fixed and a new changeset will be published. What comes next is a second feature flag to reflect the old `Deref->Receiver` one-chain method resolution, so that we could compare and experiment.

### Arbitrary Self Types and `derive(CoercePointee)`
[Arbitrary Self Types: Tracking issue #44874](https://github.com/rust-lang/rust/issues/44874)
- Waiting on the Deref/Receiver

[derive(CoercePointee) Tracking issue #123430](https://github.com/rust-lang/rust/issues/123430)
- Stabilization PR: https://github.com/rust-lang/rust/pull/133820
- Waiting on Arbitrary self types
- https://github.com/rust-lang/rust/pull/136776

#### [RFC #3851: Supertrait Auto-impl](https://github.com/rust-lang/rfcs/pull/3851)

Ding: I am still responding to the review comments.

#### [RFC #3848: Pass pointers to `const` in assembly](https://github.com/rust-lang/rfcs/pull/3848)

[Lang design meeting scheduled for 2025-10-08](https://github.com/rust-lang/lang-team/issues/347)

Tomas: The design meeting just happened. Updates?

TC: This is now in FCP.

#### Field projections (2025H2 Goal)

https://rust-lang.github.io/rust-project-goals/2025h2/field-projections.html

Goal tracking issue: https://github.com/rust-lang/rust-project-goals/issues/390

Feature tracking issue: https://github.com/rust-lang/rust/issues/145383

Field representing types (FRT) PR: https://github.com/rust-lang/rust/pull/146307. Status?

### Other topics