Rust Project Goals

Key developments

• rust-lang/rust#148051

Blockers:

• rustdoc deciding on and implementing how they want frontmatter handled in doctests

Key developments:

• Overall polish
  • https://github.com/rust-lang/rust/pull/145751
  • https://github.com/rust-lang/rust/pull/145754
  • https://github.com/rust-lang/rust/pull/146106
  • https://github.com/rust-lang/rust/pull/146137
  • https://github.com/rust-lang/rust/pull/146211
  • https://github.com/rust-lang/rust/pull/146340
  • https://github.com/rust-lang/rust/pull/145568
  • https://github.com/rust-lang/cargo/pull/15878
  • https://github.com/rust-lang/cargo/pull/15886
  • https://github.com/rust-lang/cargo/pull/15899
  • https://github.com/rust-lang/cargo/pull/15914
  • https://github.com/rust-lang/cargo/pull/15927
  • https://github.com/rust-lang/cargo/pull/15939
  • https://github.com/rust-lang/cargo/pull/15952
  • https://github.com/rust-lang/cargo/pull/15972
  • https://github.com/rust-lang/cargo/pull/15975
• rustfmt work
  • https://github.com/rust-lang/rust/pull/145617
  • https://github.com/rust-lang/rust/pull/145766
• Reference work
  • https://github.com/rust-lang/reference/pull/1974

We're putting together a prototype/demo of our reference changes at https://rust-lang.github.io/project-goal-reference-expansion/ . This includes a demonstration of tooling changes to provide stability markers (both "documenting unstable Rust" and "unstable documentation of stable Rust").

The work on this goal has led to many ongoing discussions on the current status of the Reference. Those discussions are still in progress.

Meanwhile, many people working on this goal have successfully written outlines or draft chapters, at various stages of completeness. There's a broken-out status report at https://github.com/rust-lang/project-goal-reference-expansion/issues/11 .

Update from the 2025-12-03 meeting.

Deref / Receiver

Ding keeps working on the Reference draft. The idea is still not well-proliferated and people are not convinced this is a good way to go. We hope the method-probing section in Reference PR could clear thins up.

We're keeping the supertrait auto-impl experiment as an alternative.

RFC #3851: Supertrait Auto-impl

Ding addressed Predrag's requests on SemVer compatibility. He's also opened an implementation PR: https://github.com/rust-lang/rust/pull/149335. Here's the tracking issue: https://github.com/rust-lang/rust/issues/149556.

derive(CoercePointee)

Ding opened a PR to require additional checks for DispatchFromDyn: https://github.com/rust-lang/rust/pull/149068

In-place initialization

Ding will prepare material for a discussion at the LPC (Linux Plumbers Conference). We're looking to hear feedback on the end-user syntax for it.

The feature is going quite large, Ding will check with Tyler on the whether this might need a series of RFCs.

The various proposals on the table continue being discussed and there are signs (albeit slow) of convergence. The placing function and guaranteed return ones are superseded by outpointer. The more ergonomic ideas can be built on top. The guaranteed value placement one would be valuable in the compiler regardless and we're waiting for Olivier to refine it.

The feeling is that we've now clarified the constraints that the proposals must operate under.

Field projections

Nadri's Custom places proposal is looking good at least for the user-facing bits, but the whole thing is growing into a large undertaking. Benno's been focused on academic work that's getting wrapped up soon. The two will sync afterwards.

Update from the 2025-11-19 meeting.

rustdoc checking for private and hidden items (rust##149105 & rust#149106)

Miguel proposed Rust Doc checking for invalid links to items that are hidden or private even if no docs are built for them. This can help catch typos or dead links because the docs became out of date.

Guillaume was much more open to this being a toggle, lolbinarycat opened a PR here: https://github.com/rust-lang/rust/pull/141299

unsafe_op_in_unsafe_fn not respected in imported declarative macros rust#112504

This lint doesn't trigger when importing a declarative macro that's calling unsafe code without having an unsafe block and without a SAFETY comment.

The lint is only triggered when the macro was actually used.

Fix for imports_granularity is not respected for #[cfg]'d items / rustfmt#6666

Ding opened a PR to fix this: https://github.com/rust-lang/rustfmt/issues/6666

rustfmt trailing comma hack

Ding and Manish were talking about writing up a proper fix for the vertical layout that's currently being solved by the , //, hack

TypeId layout

This has been discussed in https://github.com/rust-lang/rust/pull/148265 and https://rust-lang.zulipchat.com/#narrow/channel/213817-t-lang/topic/TypeID.20design/near/560189854.

Apiraino proposed a compiler design meeting here: https://github.com/rust-lang/compiler-team/issues/941. That meeting has not been scheduled yet, though.

Deref / Receiver

Following TC's recommendation, Ding is drafting the Reference PR.

Arbitrary Self Types and derive(CoercePointee)

Ding opened a PR to fix unsoundness in the DispatchFromDyn trait: https://github.com/rust-lang/rust/pull/149068

Theemathas opened a question on whether Receiver should by dyn-compatible: https://github.com/rust-lang/rust/issues/149094

RFC #3848: Pass pointers to const in assembly

Merged!

In-place initialization

Benno noted that Effects and In-place Init are not compatible with each other: https://rust-lang.zulipchat.com/#narrow/channel/528918-t-lang.2Fin-place-init/topic/Fundamental.20Issue.20of.20Effects.20and.20In-place-init/with/558268061

This is going to affect any in-place init proposal.

Benno proposes fixing this with keyword generics. This is a topic that will receive a lot of discussion doing forward.

Alice has been nominated and accepted as language-advisor. Fantastic news and congratulations!

Update from the 2025-11-05 meeting.

Deref/Receiver

Ding Xiang Fei posted his reasoning for the trait split in the Zulip thread and suggested adding a second RFC to explain.

TC recommended writing a Reference PR. The style forces one to explain the model clearly which should then make writing the RFC easier.

The lang experiment PR for arbitrary self types have feature gates for the two options we're exploring.

Arbitrary Self Types and derive(CoercePointee) / tracking issue #44874

theemathas opened an issue derive(CoercePointee) accepts ?Sized + Sized #148399. This isn't a critical issue, just an error that arguably should be a lint.

Boxy opened a fix for a derive(CoercePointee) blocker: Forbid freely casting lifetime bounds of dyn-types .

RFC #3851: Supertrait Auto-impl

Ding Xiang Fei is working on the implementation (the parser and HIR interface for it). Ding's also working on a more complete section dedicated to questions raised by obi1kenobi

Field projections

Benno Lossin has been posting super detailed updates on the tracking issue

We've discussed the idea of virtual places (see Zulip thread where they were proposed).

Inlining C code into Rust code

Matt Mauer had an idea to compile C code into LLVM bytecode (instead of object file) and then the llvm-link tool to merge them together and treat everything in the second bytecode file as a static inlined function. Matt suggested we could integrate this into the rustc passes.

This would make it easy to inline certain functions into Rust code without full LTO.

Relevant Zulip thread.

This sounds like a good candidate for the next Project Goals period.

Layout of core::any::TypeId

Danilo asked about the layout of TypeId -- specifically its size and whether they can rely on it because they want to store it in a C struct. The struct's size is currently 16 bytes, but that's an implementation detail.

As a vibe check, Josh Triplett and Tyler Mandry were open to guaranteeing that it's going to be at most 16 bytes, but they wanted to reserve the option to reduce the size at some point. The next step is to have the full Lang and Libs teams discuss the proposal.

Danilo will open a PR to get that discussion started.

rustfmt

Miguel brought up the "trailing empty comment" workaround for the formatting issue that made the rounds on the Linux kernel a few weeks ago. The kernel style places each import on a single line:

#![allow(unused)]
fn main() {
    use crate::{
        fmt,
        page::AsPageIter,
    };
}

rustfmt compresses this to:

#![allow(unused)]
fn main() {
    use crate::{fmt, page::AsPageIter};
}

The workaround is to put an empty trailing comment at the end

#![allow(unused)]
fn main() {
    use crate::{
        fmt,
        page::AsPageIter, //
    };
}

This was deemed acceptable (for the time being) and merged into the mainline kernel: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4a9cb2eecc78fa9d388481762dd798fa770e1971

Miguel is in contact with rustfmt to support this behaviour without a workaround.

// PANIC: ... comments / clippy#15895

This is a proposal to add a lint that would require a PANIC comment (modeled after the SAFETY comment) to explain the circumstances during which the code will or won't panic.

Alejandra González was open to the suggestion and Henry Barker stepped up to implement it.

Deref/Receiver

During the experimentation work, Ding ran into an issue with overlapping impls (that was present even with #[unstable_feature_bound(..)]). We ran out of time but we'll discuss this offline and return to it at the next meeting.

Deref/Receiver

• Ding Xiang Fei keeps updating the PR: https://github.com/rust-lang/rust/pull/146095
• They're also working on a document to explain the consequences of this split

Arbitrary Self Types

• https://github.com/rust-lang/rust/issues/44874
• Waiting on the Deref/Receiver work, no updates

derive(CoercePointee)

• https://github.com/rust-lang/rust/pull/133820
• Waiting on Arbitrary self types

Pass pointers to const in asm! blocks

• RFC: https://github.com/rust-lang/rfcs/pull/3848
• The Lang team went through the RFC with Alice Ryhl on 2025-10-08 and it's in FCP now

Field projections

• Benno Lossin opened a PR here: https://github.com/rust-lang/rust/pull/146307
• Being reviewed by the compiler folks

Providing \0 terminated file names with #[track_caller]

• The feature has been implemented and stabilized with file_as_c_str as the method name: https://github.com/rust-lang/rust/pull/145664

Supertrait auto impl RFC

• Ding Xiang Fei opened the RFC and works with the reviewers: https://github.com/rust-lang/rfcs/pull/3851

Other

• Miguel Ojeda spoke to Linus about rustfmt and they came to agreement.

I've updated the top-level description to show everything we're tracking here (please let me know if anything's missing or incorrect!).