---
# System prepended metadata

title: Triage meeting 2024-10-02
tags: [triage-meeting, T-lang, minutes]

---

---
title: Triage meeting 2024-10-02
tags: ["T-lang", "triage-meeting", "minutes"]
date: 2024-10-02
discussion: https://rust-lang.zulipchat.com/#narrow/stream/410673-t-lang.2Fmeetings/topic/Triage.20meeting.202024-10-02
url: https://hackmd.io/PhjTTh1QRd-2wZyhAR0eVw
---

# T-lang meeting agenda

- Meeting date: 2024-10-02

## Attendance

- People: TC, nikomatsakis, tmandry, Josh, scottmcm, yosh, Santiago, CE, Xiang, eholk

## Meeting roles

- Minutes, driver: TC

## Scheduled meetings

- 2024-10-02: Planning meeting

Edit the schedule here: https://github.com/orgs/rust-lang/projects/31/views/7.

## Announcements or custom items

(Meeting attendees, feel free to add items here!)

scottmcm: New RFC for a wrapping conversions trait, https://github.com/rust-lang/rfcs/pull/3703 (Just FYI; offline discussion is fine.)


## New Leadership Council member

Congratulations to TC :tada:

And much appreciation for Jack's work as our Council member for the last year.

### Guest attendee items

TC: For any guests who are present, please note in this section if you're attending for the purposes of any items on (or off) the agenda in particular.

### Moving right along

TC: As we've been doing recently, due to the impressive backlog, I'm going to push the pace a bit.  If it's ever too fast or you need a moment before we move on, please raise a hand and we'll pause.

### Design meeting at 12:30 EST / 09:30 PST / 17:30 CET

TC: Remember that we have a design/planning meeting that starts half an hour after this call ends.

### Next meeting with RfL

We're next meeting with RfL on 2024-10-09 to review the status of RfL project goals.

https://github.com/rust-lang/rfcs/pull/3614

## Rust 2024 review

Project board: https://github.com/orgs/rust-lang/projects/43/views/5

None.

### Meta

TC: We have tracking issues for the Rust 2024 aspects of every item queued for the edition:

https://github.com/rust-lang/rust/issues?q=label%3AA-edition-2024+label%3AC-tracking-issue

For each item, we've identified an *owner*.

Our motivating priorities are:

- Make this edition a success.
- Do so without requiring heroics from anyone.
    - ...or stressing anyone or everyone out.

The current timeline is:

| Date       | Version       | Edition stage                  |
|------------|---------------|--------------------------------|
| 2024-09-05 | Release v1.81 | Checking off items...          |
| 2024-10-11 | Branch  v1.83 | Go / no go on all items        |
| 2024-10-17 | Release v1.82 | Rust 2024 nightly beta         |
| 2024-11-22 | Branch  v1.84 | Prepare to stabilize...        |
| 2024-11-28 | Release v1.83 | Stabilize Rust 2024 on master  |
| 2025-01-03 | Branch  v1.85 | Cut Rust 2024 to beta          |
| 2025-01-09 | Release v1.84 | Announce Rust 2024 is pending! |
| 2025-02-20 | Release v1.85 | Release Rust 2024              |

All lang priority items are ready for Rust 2024.  The remaining not-ready lang items are:


### "Tracking Issue for match ergonomics 2024 (RFC 3627)" rust#123076

**Link:** https://github.com/rust-lang/rust/issues/123076

Josh: Let's use the latter part of today's design meeting to discuss the bare minimum consensus proposal (which reserves space for improving further in the future after shipping the edition).

### "Tracking Issue for RFC 3593: Reserve unprefixed guarded string literals in Edition 2024" rust#123735

**Link:** https://github.com/rust-lang/rust/issues/123735

### "Tracking Issue for RFC 3606: Drop temporaries in tail expressions before local variables" rust#123739

**Link:** https://github.com/rust-lang/rust/issues/123739

### "Tracking Issue for Rust 2024: Deny references to static mut" rust#123758

**Link:** https://github.com/rust-lang/rust/issues/123758

### "Tracking Issue for Rust 2024: Rescope temporary lifetimes with respect to `else`" rust#124085

**Link:** https://github.com/rust-lang/rust/issues/124085

## Nominated RFCs, PRs, and issues

### "Proposal: stabilize if_let_rescope for Edition 2024" rust#131154

**Link:** https://github.com/rust-lang/rust/issues/131154

TC: This is the stabilization of an edition item, rescoping temporary lifetimes with respect to else.

TC: What do we think?

NM: This introduces a disparity between match and if-let, which I don't like, *but* it moves towards earlier drop, which I *do* like, and it also means that `if` and `if let` work consistently:

```rust
struct DropOrder;

impl DropOrder {
    fn test(&self) -> bool {
        false
    }
}

impl Drop for DropOrder {
    fn drop(&mut self) {
        eprintln!("drop");
    }
}

fn main() {
    if DropOrder.test() {
    // ^^^^^^^^^ dropped before entering else
        eprintln!("this body");
    } else {
        eprintln!("else body");
    }
}
```

TM: It could be confusing if you refactor from match to if-let

NM: Yes, definitely, but also confusing if you refactor from `if let Ok(_) = foo` and `if foo.is_ok()` today. I feel like the next step here is to work towards lints because relying on side-effecting drop order and temporary drop is very subtle and bound to bite you.

TM: Yes, there's no clear answer to what language should do here. Dropping before the else is reasonable.

TC: We've talked before about changing this behavior for `match`.

NM: We have, and I'm interested in doing that.  There are some complexities.

TC: I'm interested in doing that if we can in a future edition.  It doesn't need to block this change though.  They're both improvements.

tmandry: I'm checking my box.

TC: And this is now in FCP.

### "Fixup Windows verbatim paths when used with the `include!` macro" rust#125205

**Link:** https://github.com/rust-lang/rust/pull/125205

TC: Chris Denton asks us:

> On Windows, the following code can fail if the `OUT_DIR` environment variable is a [verbatim path](https://doc.rust-lang.org/std/path/enum.Prefix.html) (i.e. begins with `\\?\`):
>
> ```rust
> include!(concat!(env!("OUT_DIR"), "/src/repro.rs"));
> ```
>
> This is because verbatim paths treat `/` literally, as if it were just another character in the file name.
>
> The good news is that the standard library already has code to fix this. We can simply use `components` to normalize the path so it works as intended.
>
> I think it could just be considered a bug fix but it might also be considered a change in language.

TC: What do we think, is this a bug fix or a change to the language, and if the latter, do we want it?

NM/tmandry: Sounds good.

TC: This will go into FCP.

### "Check ABI target compatibility for function pointers" rust#128784

**Link:** https://github.com/rust-lang/rust/pull/128784

TC: This comes to us as a proposed FCW for cases like:

```rust
// These raise E0570
extern "thiscall" fn foo() {}
extern "thiscall" { fn bar() }

// This did not raise any error
fn baz(f: extern "thiscall" fn()) { f() }
```

There's been extensive analysis using crater here.  CE says it looks good to him at this point.  RalfJ says this should be relatively uncontroversial.

TC: What do we think?

NM: Sounds right.

TC: This will go into FCP.

scottmcm: Note that it's only a FCW at this point.  If people really wants to do this, they'll show up when we do this.

### "Stabilize 7 `const_mut_refs`-dependent API" rust#130954

**Link:** https://github.com/rust-lang/rust/pull/130954

TC: RalfJ brings to us:

> There's in fact 3 intrinsics marked as const-stable here (meaning they are indirectly exposed to stable const code), which needs wg-const-eval approval, and t-lang should be in the loop as well:
>
> * `forget`
> * `write_via_move`
> * `write_bytes`
>
> None of them do anything odd. In fact `forget` does nothing at all; the other two just copy some bytes around -- basic stuff we can confidently commit const-eval to support. The implementation of these has been battle-tested in Miri.
>
> @rust-lang/lang this should be an easy one.

TC: Sound right to us?  I proposed FCP here:

https://github.com/rust-lang/rust/pull/130954#issuecomment-2382226349

Josh: Should this be for us or wg-const-eval?

scottmcm: This is us.  We approve the stabilization of const on these intrinsics.  We did this as a correction to some earlier stabilizations that were surprising to us.

scottmcm: These particular intrinsics are particularly fine.

tmandry: You could forget in `const` before stabilizing this `forget` intrinsic?

scottmcm: Yes, because you could construct `ManuallyDrop` in `const`.

scottmcm: https://doc.rust-lang.org/nightly/std/mem/struct.ManuallyDrop.html#method.new is const stable since 1.32

TC: This will move into FCP.

### "Add `&pin (mut|const) T` type position sugar" rust#130635

**Link:** https://github.com/rust-lang/rust/pull/130635

In Rust 1.41, we broke this program...

```rust
macro_rules! m {
    ($x:expr) => { compile_error!("bad") };
    ($($t:tt)*) => {}
}
m!(&raw const ());
```

...even though we didn't end up stabilizing `&raw const ..` until Rust 1.82.

Then we broke this in Rust 1.77:

```rust
macro_rules! m {
    ($x:ty) => { compile_error!("bad") };
    ($($t:tt)*) => {}
}
m!(impl const Sized);
```

(We haven't stabilized `const` trait modifiers yet.)  And then in Rust 1.78, we broke:

```rust
macro_rules! m {
    ($x:ty) => { compile_error!("bad") };
    ($($t:tt)*) => {}
}
m!(impl async Sized);
```

(We haven't stabilized `async` trait modifiers yet.)

Now we plan to break this program when this PR lands:

```rust
macro_rules! m {
    ($x:ty) => { compile_error!("bad") };
    ($($t:tt)*) => {}
}
m!(&pin const ());
```

CE gives further background:

> The breakage specifically represents an inherent limitation to the "macro follow-set" formulation which is _supposed_ to make us more resilient against breakages due to extensions to the grammar like this.
>
> Given two macro matcher arms:
>
> * `($ty:ty) => ...`
> * `(($tt:tt)*) => ...`
>
> And given tokens like:
>
> * `&` `pin` `mut` [...more tokens may follow...]
>
> On nightly today, `&pin` gets parsed as a type. However, we run out of matchers but still have tokens left (the `mut` token is next), so we fall through to the next arm. Since it's written like `($tt:tt)*`, everything is allowed, and we match the second arm successfully...
>
> I think that's weird, because if this second arm were written like `$ty:ty mut`, that would be illegal, since `mut` is not in the follow-set of the `:ty` matcher. Thus, we can use `:tt` matchers to observe whether the compiler _actually_ parses things not in our grammar that should otherwise be protected against, which seems pretty gross.
>
> I think this breakage is purely theoretical, though. I would like to hear any suggestions to close this hole and make macros a bit more resilient, but nothing really comes to mind :(

This breakage is believed to be theoretical-only.  Does this sound OK to us?

NM: Where we have seen real breakage of this kind of thing in the past is where someone was emulating the language construct that we were adding.  It's the language version of the `itertools` problem.  I think we have to live with it, we basically botched the follow-set design, which doesn't serve its intended purpose. We would have to modify macros so that if you *start* parsing as a given fragment, then that parse must succeed and it must consume all the tokens up until some predefined boundary (e.g., the follow-set). This was, they would be independent of the specific grammar (which is the property we want). It would mean macro authors have to write LL(1)-grammars, which is kind of restrictive. i.e., you should know what you are parsing when you get there.

eholk: It'd be nice if this didn't break until we stabilize.

CE: But that doesn't really work with how feature gate parsing works.

tmandry: I'm OK with doing this.

Josh: Should we do a crater run for it?

CE: It would come up in the beta crater runs.

scottmcm: We could make sure it's in the relnotes as a theoretically breaking change.  The people doing the crater runs would probably make note of that.

TC: I'll leave a note that this is OK to go forward.

### "Strengthen the follow-set rule for macros" rust#131025

**Link:** https://github.com/rust-lang/rust/issues/131025

TC: Over in:

- https://github.com/rust-lang/rust/pull/130635

@compiler-errors describes this general problem:

> The breakage specifically represents an inherent limitation to the "macro follow-set" formulation which is _supposed_ to make us more resilient against breakages due to extensions to the grammar like this.
>
> Given two macro matcher arms:
>
> * `($ty:ty) => ...`
> * `(($tt:tt)*) => ...`
>
> And given tokens like:
>
> * `&` `pin` `mut` [...more tokens may follow...]
>
> On nightly today, `&pin` gets parsed as a type. However, we run out of matchers but still have tokens left (the `mut` token is next), so we fall through to the next arm. Since it's written like `($tt:tt)*`, everything is allowed, and we match the second arm successfully...
>
> I think that's weird, because if this second arm were written like `$ty:ty mut`, that would be illegal, since `mut` is not in the follow-set of the `:ty` matcher. Thus, we can use `:tt` matchers to observe whether the compiler _actually_ parses things not in our grammar that should otherwise be protected against, which seems pretty gross.

And @Noratrieb proposes a general solution:

> I believe a solution to this would be the following new logic:
>
> * after the end of a macro matcher arm has been reached
> * and there are still input tokens remaining
> * and if the last part of the matcher is a metavar
> * ensure that the first remaining token is in the follow set of this metavar
> * if it is, move on to the next arm
> * if it is not, **emit an error**
>
> What this semantically does is strengthen the "commit to fully matching metavars or error" behavior such that it extends past the end. I don't know how many macros rely on this, but it seems like emitting an FCW (instead of error) on such macro invocations would find all these cases and ensure that the follow-set logic is actually robust past the end. But imo this shouldn't block this PR (which should probably just ship as-is) and can be done separately.

TC: Do we like this solution?

NM: I don't think this proposal is sufficient but I am interested in pursuing a real fix to this for a future edition.

Example:

```rust
macro_rules! test {
    (if $x:ty { }) => {};
    (if $x:expr { }) => {};
}
```

This basically says to pick one arm if something is a type, another if it's an expression. Extending the type grammar to cover new cases could change which arm you go down to.

I *think* the most general fix is to say: when you would start parsing a fragment, first skip ahead to find the extent of it (i.e., until you see an entry from the follow-set). Then parse it as the fragment. If the parsing fails or there are unconsumed tokens, report a hard error.

I suspect it would break a lot in practice and we would need an opt-in.

### "Retire the `unnamed_fields` feature for now" rust#131045

**Link:** https://github.com/rust-lang/rust/pull/131045

TC: CE brings to us:

> `#![feature(unnamed_fields)]` was implemented in part in #115131 and #115367, however work on that feature has (afaict) stalled and in the mean time there have been some concerns raised (e.g.[1](#user-content-fn-1-fbd97f98128fee12ec63ced80b4c193f)[2](#user-content-fn-2-fbd97f98128fee12ec63ced80b4c193f)) about whether `unnamed_fields` is worthwhile to have in the language, especially in its current desugaring. Because it represents a compiler implementation burden including a new kind of anonymous ADT and additional complication to field selection, and is quite prone to bugs today, I'm choosing to remove the feature.
>
> However, since I'm not one to really write a bunch of words, I'm specifically _not_ going to de-RFC this feature. This PR essentially _rolls back_ the state of this feature to "RFC accepted but not yet implemented"; however if anyone wants to formally unapprove the RFC from the t-lang side, then please be my guest. I'm just not totally willing to summarize the various language-facing reasons for why this feature is or is not worthwhile, since I'm coming from the compiler side mostly.
>
> I'm nominating this for T-lang _somewhat_ out of courtesy; my understanding is that whether or not an RFC-approved _unstable_ implementation of a feature moves forwards or backwards really is a T-compiler judgement call, but I would like to hear T-lang's take on this.
>
> I generally think that "let's go back to the drawing board" is the right call here, and in the mean time, I'd like to remove this from the compiler since there's a fair chance that a future design could be implemented some other way, and it's always easier to add things back into the compiler -- and I would be glad to either mentor or implement that work myself when that time comes, of course.

TC: Sound OK to us?

scottmcm: This sounds OK.

NM: Sounds fine.

tmandry: +1.

TC: I'll leave a note that we appreciate the courtesy and are OK with this.

(The meeting ended here.)

---

### "improper_ctypes lint allows all "Option-like" enums, but we only guarantee this specifically for Option" rust#130652

**Link:** https://github.com/rust-lang/rust/issues/130652

TC: Way back when...

https://github.com/rust-lang/rust/pull/60300#issuecomment-488798080

...we FCPed a decision to make FFI guarantees not just for `Option<T>`, but for any `Option`-like enum.  Specifically, we adopted these rules:

> ...an enum `E` (is) FFI-safe if:
>
> * `E` has no explicit `#[repr(...)]`.
> * It only has two variants.
> * One of those variants is empty (meaning it has no fields).
> * The other variant has only one field.
> * That field is one of the following:
>
>   * `&T`
>   * `&mut T`
>   * `extern "C" fn`
>   * `core::num::NonZero*`
>   * `core::ptr::NonNull<T>`
>   * `#[repr(transparent)] struct` wrapper around one of the types in this list.
> * The size of `E` and its field are both known and are both the same size (implying `E` is participating in the nonnull optimization).

We apparently never documented this outside of the behavior of the `improper_ctypes` lint.  The question to us is whether we meant for this to be a stable guarantee and whether we'd like it documented.

TC: What do we think?

### "Finish stabilization of `result_ffi_guarantees`" rust#130628

**Link:** https://github.com/rust-lang/rust/pull/130628

TC: Originally this came to us as a request to stabilize FFI guarantees for `Result` as we do for `Option`, following on from RFC 3391:

https://github.com/rust-lang/rfcs/pull/3391

However, it's since been observed that we earlier...

https://github.com/rust-lang/rust/pull/60300#issuecomment-488798080

...decided to make these guarantees not just for `Option<T>`, but for any `Option`-like enum.

So the question now to us is whether we actually want to make these guarantees for any `Result<T, U>`-like enum.  Specifically, RalfJ proposes these rules as being symmetric with the `Option<T>` ones:

> An enum `E` is guaranteed to be layout- and ABI-compatible with type `T` if
>
> * `E` has exactly two variants
> * One variant has exactly one field, of type `T`
> * `T` is a `rustc_nonnull_optimization_guaranteed` type
> * The other variant either has no field, or exactly one field of type `U` that satisfies all of the following:
>
>   * `U` is a 1-ZST
>   * `U` must have no fields
>   * `U` must not have the `#[non_exhaustive]` attribute

...and proposes that we strengthen the guarantee by dropping the last two bullet points.

TC: What do we think?

### "Emit error when calling/declaring functions with vectors that require missing target feature" rust#127731

**Link:** https://github.com/rust-lang/rust/pull/127731

TC: RalfJ nominates for us:

> There's only 2 crates.io failures and they are both spurious. And the github failures I checked were also all spurious. So looking pretty good I would say. :)
>
> Seems like the next step process-wise is to check back in with the lang team, now that we have crater results. (That's based on [this message](https://github.com/rust-lang/lang-team/issues/235#issuecomment-1865489298).) @rust-lang/lang this aims to fix #116558, which is part of the discussion we had in [rust-lang/lang-team#235](https://github.com/rust-lang/lang-team/issues/235). The way it is fixed is by making it a hard error to call or declare an `extern "C"` function that passes a SIMD type by-value without enabling the target feature that enables SIMD vectors of the appropriate size. The reason it is made a hard error is that these functions end up having a different ABI depending on whether that target feature is enabled or not. "Rust" ABI functions are not affected as those functions pass SIMD vectors indirectly (they do that precisely to avoid these ABI issues).
>
> There are two points we'd like your take on:
>
> * How to stage this. Should it become a hard error immediately, or first be reported as a future-compat lint (I would say we can make it show up in dependencies immediately)? Crater found no regressions (probably because `extern "C"` functions are generally fairly rare), but of course crater doesn't see all the codebases out there.
> * What exactly should be checked? Right now, the check is extremely low-level and looks at the computed effective ABI of the function, ensuring it doesn't end up with a too large by-value SIMD vector argument. The check is done during monomorphization, each time a function is instantiated, to make sure that we can even know the actual effective ABI. More mono-time checks are unfortunate, but there's no good way to test this in generic code since we can't know whether a generic argument is a SIMD vector or not. Give that it should be rather rare to run into this, hopefully a mono-time check is acceptable.
>   The other concern is semver compatibility: if a library changes a public type, e.g., from being an array of `i32` to being a SIMD vector instead, that can now break downstream code. However, it can only break downstream code that passes types of this library by-value across an  `extern "C"`. If that is an FFI boundary, this is already extremely sketchy to do due to all the concerns around FFI safety and ABI compatibility. The most realistic scenario I could come up with is code using `extern "C"` for Rust-to-Rust calls; not sure how much we worry about such code -- I presume it is fairly rare. Still, we could try to mitigate this by making the check some sort of overapproxomation that generally refuses to pass types from other crates across an `extern "C"` boundary if those types could in the future be changed such that the ABI ends up with a by-value SIMD vector (i.e., `(i32, ForeignType)` would be okay but `TransparentWrapper<ForeignType>` would not). I personally am not convinced that is worth the effort.

TC: What do we think?

### "Lint against `&T` to `&mut T` and `&T` to `&UnsafeCell<T>` transmutes" rust#128351

**Link:** https://github.com/rust-lang/rust/pull/128351

TC: CE nominates for us a proposal by ChayimFriedman2:

> Conversion from `&` to `&mut` are and always were immediate UB, and we already lint against them, but until now the lint did not catch the case were the reference was in a field.
>
> Conversion from `&` to `&UnsafeCell` is more nuanced: Stacked Borrows makes it immediate UB, but in Tree Borrows it is sound.
>
> However, even in Tree Borrows it is UB to write into that reference (if the original value was `Freeze`). In all cases crater found where the lint triggered, the reference was written into.

More details here:

https://github.com/rust-lang/rust/pull/128351#issue-2435783651

TC: What do we think?

### "`optimize` attribute applied to things other than methods/functions/c…" rust#128943

**Link:** https://github.com/rust-lang/rust/pull/128943

TC: jieyouxu nominates for us:

> This needs a T-lang FCP since it diverges from the original [RFC 2412](https://github.com/rust-lang/rust/issues/54882) specified behavior. cc @rust-lang/lang
>
> ### Summary for T-lang
>
> **This PR proposes to elevate `#[optimize]` attribute (as specified in [RFC 2412](https://github.com/rust-lang/rfcs/blob/master/text/2412-optimize-attr.md)) applied to unsupported HIR nodes from a warn-by-default `unused_attributes` lint to a hard error.**

More details are here:

https://github.com/rust-lang/rust/pull/128943#issuecomment-2282357407

TC: What do we think?

### "edition lint: migrating `extern crate` with `#[macro_use]`" rust#52043

**Link:** https://github.com/rust-lang/rust/issues/52043

TC: Code like this today isn't idiomatic, since we would use `use` to import any macros, but it doesn't lint:

```
#[macro_use]
extern crate rayon;

fn main() { }
```

TC: Josh nominates as it seems perhaps beyond time that we do so.  What do we think?

### "Consider deprecation of UB-happy `static mut`" rust#53639

**Link:** https://github.com/rust-lang/rust/issues/53639

TC: Long ago, eddyb opened an issue to consider deprecating `static mut`.  This is because handling long-lived references to `static mut` items is hard to do right.

We decided for Rust 2024 to lint at `deny-by-default` against long-lived references to `static mut` items, thus apparently solving the problem that motivated opening the issue.  And there seem to be use cases for `static mut`.  As RalfJ says:

> Sometimes, you need global mutable state. We already had several cases of people being quite confused and concerned by the lints we started emitting, and it turns out that what they were doing is completely fine and we basically told them to add a bit of noise to their code to silence the lint. Those people will be even more confused if we now tell them that `static mut` will be banned entirely, and I am not convinced that replacing `addr_of_mut!(STATIC)` with `STATIC.get()` is really doing anything for ensuring the safety of global mutable state.
>
> Many people that use `static mut` now are entirely aware of what they are doing, they didn't accidentally stumble into global mutable state. People that just mindlessly run into `static mut` will equally mindlessly start using `SyncUnsafeCell` (probably by copying some online resource telling them how to silence that annoying borrow checker, or by following helpful compiler hints).
>
> So overall I am not convinced that the churn caused on existing code, and the overhead caused for people that know what they are doing, is balanced by a sufficient risk reduction for people that don't know what they are doing.

Given all this, it's hard to me to imagine that we've soon depracet `static mut`, so I propose FCP close.

TC: What do we think?

### "Tracking Issue for the C-cmse-nonsecure-call ABI" rust#81391

**Link:** https://github.com/rust-lang/rust/issues/81391

TC: T-compiler nominates for us:

> Nominating for both T-lang and T-compiler discussion: there is a request for the stabilization of the `C-cmse-nonsecure-call` ABI (posted above at [#81391 (comment)](https://github.com/rust-lang/rust/issues/81391#issuecomment-2258346708)), there's also the seemingly related `#[cmse_nonsecure_entry]` attribute (#75835). This is mostly nominated for several reasons stated below.
>
> ...
>
> For **T-lang**:
>
> * Procedure questions:
>
>   * Does this need T-lang sign-off, like a T-lang FCP or a joint T-lang/T-compiler FCP?
>
> For **both T-compiler and T-lang**:
>
> * Is the cmse-related efforts being tracked anywhere?

TC: What do we think?

### "Tracking Issue for enum access in offset_of" rust#120141

**Link:** https://github.com/rust-lang/rust/issues/120141

TC: There's a proposed FCP merge for us:

https://github.com/rust-lang/rust/issues/120141#issuecomment-2161507356

TC: What do we think?

### "Support for pointers with asm_const" rust#128464

**Link:** https://github.com/rust-lang/rust/issues/128464

TC: Josh nominates for us the question:

> Nominating this for lang to discuss the question of whether we should support use of `const` in `asm!` for things that can't just be textually substituted, or whether we should give that a different name.
>
> @Amanieu, any input you'd like to provide would be helpful.

To which Amanieu replies:

> After thinking about it a bit, I think it's probably fine to add this functionality to `const`. I'm a bit bothered about the duplication with `sym`, which is already stable.

TC: What do we think?

### "Decide on name for `derive(SmartPtr)`" rust#129104

**Link:** https://github.com/rust-lang/rust/issues/129104

TC: We need to resolve the open question on:

- https://github.com/rust-lang/rfcs/pull/3621

...regarding what name to use.

Tracking:

- https://github.com/rust-lang/rust/issues/123430

TC: What do we think?

### "Remove unstable cfg `target(...)` compact feature" rust#130780

**Link:** https://github.com/rust-lang/rust/pull/130780

TC: Urgau suggests that we remove the `cfg_target_compact` unstable feature.  Its tracking issue is:

https://github.com/rust-lang/rust/issues/96901

TC: What do we think?

### "Stabilize `count`, `ignore`, `index`, and `length` (`macro_metavar_expr`)" rust#122808

**Link:** https://github.com/rust-lang/rust/pull/122808

TC: c410-f3r proposes the following for stabilization:

> # Stabilization proposal
>
> This PR proposes the stabilization of a subset of `#![feature(macro_metavar_expr)]` or more specifically, the stabilization of `count`, `ignore`, `index` and `length`.
>
> ## What is stabilized
>
> ### Count
> The number of times a meta variable repeats in total.
>
```rust
macro_rules! count_idents {
    ( $( $i:ident ),* ) => {
        ${count($i)}
    };
}

fn main() {
    assert_eq!(count_idents!(a, b, c), 3);
}
```
>
> ### Ignore
> Binds a meta variable for repetition, but expands to nothing.
>
```rust
macro_rules! count {
    ( $( $i:stmt ),* ) => {{
        0 $( + 1 ${ignore($i)} )*
    }};
}

fn main() {
    assert_eq!(count!(if true {} else {}, let _: () = (), || false), 3);
}
```
>
> ### Index
> The current index of the inner-most repetition.
>
```rust
trait Foo {
    fn bar(&self) -> usize;
}

macro_rules! impl_tuple {
    ( $( $name:ident ),* ) => {
        impl<$( $name, )*> Foo for ($( $name, )*)
        where
            $( $name: AsRef<[u8]>, )*
        {
            fn bar(&self) -> usize {
                let mut sum: usize = 0;
                $({
                    const $name: () = ();
                    sum = sum.wrapping_add(self.${index()}.as_ref().len());
                })*
                sum
            }
        }
    };
}

impl_tuple!(A, B, C, D);

fn main() {
}
```
>
> ### Length
>
> The current index starting from the inner-most repetition.
>
```rust
macro_rules! array_3d {
    ( $( $( $number:literal ),* );* ) => {
        [
            $(
                [
                    $( $number + ${length()}, )*
                ],
            )*
        ]
    };
}

fn main() {
    assert_eq!(array_3d!(0, 1; 2, 3; 4, 5), [[2, 3], [4, 5], [6, 7]]);
}
```
>
> ## Motivation
>
> Meta variable expressions not only facilitate the use of macros but also allow things that can't be done today like in the `$index` example.
>
> An initial effort to stabilize this feature was made in #111908 but ultimately reverted because of possible obstacles related to syntax and expansion.
>
> Nevertheless, [#83527 (comment)](https://github.com/rust-lang/rust/issues/83527#issuecomment-1744822345) tried to address some questions and fortunately the lang team accept #117050 the unblocking suggestions.
>
> Here we are today after ~4 months so everything should be mature enough for wider use.
>
> ## What isn't stabilized
> `$$` is not being stabilized due to unresolved concerns.

TC: I asked WG-macros for feedback on this here:

https://rust-lang.zulipchat.com/#narrow/stream/404510-wg-macros/topic/Partial.20macro_metavar_expr.20stabilization

TC: Josh proposed FCP merge on this stabilization.

### "Supertrait item shadowing v2" rfcs#3624

**Link:** https://github.com/rust-lang/rfcs/pull/3624

TC: This RFC is in FCP.  One of the main motivations for this RFC is so that libs-api can stabilize methods whose names match those used by `itertools`.  Since the FCP started, one of the maintainers of `itertools` chimed in to say:

> tmandry said:
> > We'll be creating a slightly bad experience for users of itertools with the lint, and that will only be resolved by the crate releasing a new semver-incompatible version or a new trait (or perhaps doing rustc version hacks, if the signatures are compatible).
>
> This is going to create a slightly bad experience for the maintainers of itertools, too. We _will_ get issues filed by users who would like us to remove now-shadowing methods for their toolchain because of the lint. (If we're very unlucky, those users will have also discovered that the rationale for the lint is to avoid supply chain attacks.) We won't be able to readily remove these methods, because that conflicts with our longstanding policy of maintaining a conservative MSRV. The only way we'll be able to reconcile these interests is by using `build.rs`-rustc-version-detection hacks, something we've intentionally avoided _because `build.rs` is a vector for supply chain attacks_.
>
> Please consider making this lint allow-by-default.

I nominated so we could consider that feedback.  We could of course handle the setting of the lint level during stabilization, but it seems worth discussing this feedback while it's fresh.

TC: What do we think?

### "Trait method impl restrictions" rfcs#3678

**Link:** https://github.com/rust-lang/rfcs/pull/3678

TC: This RFC just went into FCP.  I'd like to check my box, as I want something like this, but there are some things I'd like to talk though.

This RFC is about restricting where trait methods can be implemented, e.g. preventing any but default impls.

There's an existing accepted RFC 3323 for restricting where traits can be implemented, e.g.:

```rust
pub impl(crate) trait Tr {
    fn method(&self) { .. }
}
```

...and where fields can be mutated...

```rust
pub struct S {
    pub mut(crate) inner: u8,
}
```

...so the original draft of the RFC extended this "restrictions" RFC to support where methods can be implemented, e.g.:

```rust
pub trait Tr {
    impl(crate) fn method1(&self) { .. }
    impl(trait) fn method2(&self) { .. }
}
```

(RFC 3323 itself left the exact syntax as an open question, and this RFC would have inherited that by building on RFC 3323.)

Later drafts updated this to use the `final` keyword:

```rust
pub trait Tr {
    final fn method(&self) { .. }
}
```

Things to talk through:

#### Keyword vs attribute

TC: In the issue, we've received feedback that an attribute would feel more consistent to some, e.g.:

```rust
pub trait Tr {
    #[final]
    fn method(&self) { .. }
}
```

The argument is that it feels closer to something like `#[non_exhaustive]` than to `async`, `const`, or `pub`.

I wonder how much having the keyword reserved should change our thinking here.  If we didn't, it feels likely we wouldn't have thought twice about this being an attribute.

#### Is `final` too OO, and is the analogy correct?

TC: Probably also -- admittedly very subjectively -- the `final` keyword to me feels a bit too "OO" for Rust.  A trait isn't a base class, but that's kind of what my brain sees with `final` there.

Less subjectively, given its meaning for inheritance, it suggests another plausible meaning in Rust.  Traits can "extend" other traits, i.e. be subtraits ("typeclass inheritance"?).  So, arguable, especially in the context of supertrait item shadowing...

https://github.com/rust-lang/rfcs/pull/3624

...where we're preferring subtrait methods of the same name, one might expect `final` to be a designation on the supertrait that indicates that a subtrait cannot "override" the method.  This is actually a more intuitive meaning, given what `final` means in OO systems, than meaning some restriction about how an "interface" (to use the OO term) can be implemented.

#### Are there no use cases for overriding within the crate?

TC: I wonder, given how a crate providing traits often provides various blanket impls, are there really no use cases for a restriction that allows for overriding the method within the crate but not otherwise?  If there are, it seems a bit strange to me to break parity with RFC 3323.

(If we don't like the syntax of RFC 3323, we can still change that.)

#### Alternate syntax proposal

TC: In the RFC thread, there's recently been a proposal by PoignardAzur for:

```rust
trait MyTrait<T> {
    fn output(&self) -> T;
}

impl<T: Display> MyTrait<T> {
    fn method(&self) {
        println!("{}", self.output());
    }
}
```

> This syntax would basically be an inherent impl block, for traits. It would have the same properties as final in this RFC.

TC: If this makes sense semantically, this does syntactically feel more Rust-like to me.

#### Guaranteed devirtualization?

TC: I had assumed that `final` (in whatever form) would guarantee devirtualization so that it could be used for cases like the `next` method for `AsyncGen`, but now I see discussion that we may never want to do that (for reasonable reasons) and such methods should continue to live on separate traits with blanket impls.  This seems a major class of use cases we'd be cutting out.  I wonder if we want a way for users to control this.

Cutting this out also causes me to reconsider the distribution of use cases.  Guaranteed devirtualization is a good reason for restricting impls to the trait and not to the rest of the crate.  Without this, I start to imagine again reasons why one might want such crate-local but not trait-local impls.

### "Simplify lightweight clones, including into closures and async blocks" rfcs#3680

**Link:** https://github.com/rust-lang/rfcs/pull/3680

TC: Josh nominates a new RFC for us.  What do we think?

### "[RFC] Default field values" rfcs#3681

**Link:** https://github.com/rust-lang/rfcs/pull/3681

TC: This RFC adds a way to set field defaults, e.g.:

```rust
struct Point {
    x: u8 = 0,
    y: u8 = 0,
}

let p = Point { .. };
```

But, unfortunately, the interaction with `Default` here is a bit weird.  If we write:

```rust
struct Point {
    x: u8,
    y: u8,
    // We just want to override the default `None` on this field,
    // but we can leave the others alone because `Default::default`
    // for those is fine, right?
    z: Option<u8> = Some(0),
}

let p = Point { .. }; //~ ERROR
let p = Point::default(); //~ OK!
```

In general, under this RFC, `Point { .. }` and `Point::default()` can each work when the other can fail and can have arbitrarily different behaviors.  So it's in that context that I [nominate](https://github.com/rust-lang/rfcs/pull/3681#issuecomment-2370130867), suggestion a nightly experiment, and propose a design meeting.

https://github.com/rust-lang/lang-team/issues/291

TC: What do we think?

### "Declarative `macro_rules!` attribute macros" rfcs#3697

**Link:** https://github.com/rust-lang/rfcs/pull/3697

TC: Josh proposes an RFC for us:

> Many crates provide attribute macros. Today, this requires defining proc macros, in a separate crate, typically with several additional dependencies adding substantial compilation time, and typically guarded by a feature that users need to remember to enable.
>
> However, many common cases of attribute macros don't require any more power than an ordinary `macro_rules!` macro. Supporting these common cases would allow many crates to avoid defining proc macros, reduce dependencies and compilation time, and provide these macros unconditionally without requiring the user to enable a feature.

E.g.:

```rust
macro_rules! main {
    attr() ($func:item) => { make_async_main!($func) };
    attr(threads = $threads:literal) ($func:item) => { make_async_main!($threads, $func) };
}

#[main]
async fn main() { ... }

#[main(threads = 42)]
async fn main() { ... }
```

TC: What do we think?

### "Declarative `macro_rules!` derive macros" rfcs#3698

**Link:** https://github.com/rust-lang/rfcs/pull/3698

TC: Josh proposes an RFC for us:

> Many crates support deriving their traits with `derive(Trait)`. Today, this requires defining proc macros, in a separate crate, typically with several additional dependencies adding substantial compilation time, and typically guarded by a feature that users need to remember to enable.
>
> However, many common cases of derives don't require any more power than an ordinary `macro_rules!` macro. Supporting these common cases would allow many crates to avoid defining proc macros, reduce dependencies and compilation time, and provide these macros unconditionally without requiring the user to enable a feature.

E.g.:

```rust
trait Answer { fn answer(&self) -> u32; }

#[macro_derive]
macro_rules! Answer {
    // Simplified for this example
    (struct $n:ident $_:tt) => {
        impl Answer for $n {
            fn answer(&self) -> u32 { 42 }
        }
    };
}

#[derive(Answer)]
struct Struct;

fn main() {
    let s = Struct;
    assert_eq!(42, s.answer());
}
```

TC: What do we think?

### "Add support for `use Trait::func`" rfcs#3591

**Link:** https://github.com/rust-lang/rfcs/pull/3591

This RFC would add support for:

```rust
use Default::default;

struct S {
    a: HashMap<i32, i32>,
}

impl S {
    fn new() -> S {
        S {
            a: default()
        }
    }
}
```

Josh has proposed FCP merge and has nominated.  There are outstanding concerns about the handling of turbofish and associated constants.

TC: What do we think?

### "Tracking issue for the `start` feature" rust#29633

**Link:** https://github.com/rust-lang/rust/issues/29633

TC: Nils proposes to us that we delete the unstable `#[start]` attribute:

> I think this issue should be closed and `#[start]` should be deleted. It's nothing but an accidentally leaked implementation detail that's a not very useful mix between "portable" entrypoint logic and bad abstraction.
>
> I think the way the stable user-facing entrypoint should work (and works today on stable) is pretty simple:
>
> * `std`-using cross-platform programs should use `fn main()`. the compiler, together with `std`, will then ensure that code ends up at `main` (by having a platform-specific entrypoint that gets directed through `lang_start` in `std` to `main` - but that's just an implementation detail)
> * `no_std` platform-specific programs should use `#![no_main]` and define their own platform-specific entrypoint symbol with `#[no_mangle]`, like `main`, `_start`, `WinMain` or `my_embedded_platform_wants_to_start_here`. most of them only support a single platform anyways, and need cfg for the different platform's ways of passing arguments or other things _anyways_
>
> `#[start]` is in a super weird position of being neither of those two. It tries to pretend that it's cross-platform, but its signature is a total lie. Those arguments are just stubbed out to zero on Windows, for example. It also only handles the platform-specific entrypoints for a few platforms that are supported by `std`, like Windows or Unix-likes. `my_embedded_platform_wants_to_start_here` can't use it, and neither could a libc-less Linux program. So we have an attribute that only works in some cases anyways, that has a signature that's a total lie (and a signature that, as I might want to add, has changed recently, and that I definitely would not be comfortable giving _any_ stability guarantees on), and where there's a pretty easy way to get things working without it in the first place.
>
> Note that this feature has **not** been RFCed in the first place.

TC: What do we think?

### "Coercing &mut to *const should not create a shared reference" rust#56604

**Link:** https://github.com/rust-lang/rust/issues/56604

TC: It's currently UB to write:

```
fn main() {
    let x = &mut 0;
    let y: *const i32 = x;
    unsafe { *(y as *mut i32) = 1; }
    assert_eq!(*x, 1);
}
```

This is due to the fact that we implicitly first create a shared reference when coercing a `&mut` to a `*const`.  See:

TC: What do we think about this?

### "Stabilize `anonymous_lifetime_in_impl_trait`" rust#107378

**Link:** https://github.com/rust-lang/rust/pull/107378

TC: We unnominated this back in October 2023 as more analysis seemed to be needed. Since then, nikomatsakis and tmandry have posted substantive analysis that it seems we should discuss.

### "#[cold] on match arms" rust#120193

**Link:** https://github.com/rust-lang/rust/pull/120193

TC: Apparently our unstable `likely` and `unlikely` intrinsics don't work.  There's a proposal to do some work on fixing that and stabilizing a solution here.  The nominated question is whether we want to charter this as an experiment.

### "Disallow deriving (other than Copy/Clone) on types with unnamed fields" rust#121270

**Link:** https://github.com/rust-lang/rust/pull/121270

TC: pnkfelix nominates this for us:

> This PR that addresses some ICEs arising for the unstable `feature(unnamed_fields)`, by conservatively mapping the ICE'ing cases to static errors instead.
>
> The T-compiler team wants to know the opinion of T-lang of whether `feature(unnamed_fields)` is sufficiently likely, in the near future, to be removed (or significantly reworked) to such a degree that it would make more sense to close this PR rather than have contributors spend further time on it.
>
> (See also the context established by https://hackmd.io/7r0i-EWyR8yO6po2LnS2rA#Tracking-issue-for-RFC-2102-Unnamed-fields-of-struct-and-union-type-rust49804 (where I think there was supposed to be an eventual writeup of the concerns people had with `feature(unnamed_fields)`) and [#49804 (comment)](https://github.com/rust-lang/rust/issues/49804#issuecomment-2106381721) )

On 2024-05-12, Josh said:

> It sounds like, from the minutes, that some folks would like to see this feature designed differently than it was when it was previously accepted. It wouldn't be the first or last feature to need some design adjustments when lang design met compiler reality. Happy to help with that, so that we can find a design that meets the requirements in the original RFC and any new issues that have arisen since then.

This is about RFC 2102:

https://github.com/rust-lang/rfcs/pull/2102

We discussed this in the meeting on 2024-06-12 without consensus.

Some felt that this was still needed, others first wanted to look for a more minimal approach.

We left this for further discussion.

TC: What do we think?

### "Emit a warning if a `match` is too complex" rust#122685

**Link:** https://github.com/rust-lang/rust/pull/122685

TC: Nadri nominates this for us and describes the situation:

> Dear T-lang, this PR adds a warning that cannot be silenced, triggered when a match takes a really long time to analyze (in the order of seconds). This is to help users figure out what's taking so long and fix it.
>
> We _could_ make the limit configurable or the warning `allow`able. I argue that's not necessary because [crater](https://github.com/rust-lang/rust/pull/121979#issuecomment-2003089646) showed zero regressions with the current limit, and it's be pretty easy in general to split up a `match` into smaller `match`es to avoid blowup.
>
> We're still figuring out the exact limit, but does the team approve in principle?

(As an aside, awhile back someone [showed](https://niedzejkob.p4.team/rust-np/) how to [lower](https://github.com/NieDzejkob/rustc-sat) SAT to exhaustiveness checking with `match`.  Probably that would hit this limit.)

TC: What do we think?

### "Tracking Issue for unicode and escape codes in literals" rust#116907

**Link:** https://github.com/rust-lang/rust/issues/116907

TC: nnethercote has implemented most of RFC 3349 ("Mixed UTF-8 literals") and, based on implementation experience, argues that the remainder of the RFC should not be implemented:

> I have a partial implementation of this RFC working locally (EDIT: now at #120286). The RFC proposes five changes to literal syntax. I think three of them are good, and two of them aren't necessary.

TC: What do we think?

### "Proposal: Remove `i128`/`u128` from the `improper_ctypes` lint" lang-team#255

**Link:** https://github.com/rust-lang/lang-team/issues/255

TC: Trevor Gross describes the situation:

> For a while, Rust's 128-bit integer types have been incompatible with those from C. The original issue is here [rust-lang/rust#54341](https://github.com/rust-lang/rust/issues/54341), with some more concise background information at the MCP here [rust-lang/compiler-team#683](https://github.com/rust-lang/compiler-team/issues/683)
>
> The current Beta of 1.77 will have [rust-lang/rust#116672](https://github.com/rust-lang/rust/pull/116672), which manually sets the alignment of `i128` to make it ABI-compliant with any version of LLVM (`clang` does something similar now). 1.78 will have LLVM18 as the vendored version which fixes the source of this error.
>
> Proposal: now that we are ABI-compliant, do not raise `improper_ctypes` on our 128-bit integers. I did some testing with abi-cafe and a more isolated https://github.com/tgross35/quick-abi-check during the time https://reviews.llvm.org/D86310 was being worked on, and verified everything lines up. (It would be great to have some fork of abi-cafe in tree, but that is a separate discussion.)
>
> @joshtriplett mentioned that changing this lint needs a lang FCP https://rust-lang.zulipchat.com/#narrow/stream/187780-t-compiler.2Fwg-llvm/topic/LLVM.20alignment.20of.20i128/near/398422037. cc @maurer
>
> Reference change from when I was testing [rust-lang/rust@c742908](https://github.com/rust-lang/rust/commit/c742908c4b9abde264b8c5e9663e31c649a47f2f)

TC: Josh nominates this for our discussion.  What do we think?

### "`is` operator for pattern-matching and binding" rfcs#3573

**Link:** https://github.com/rust-lang/rfcs/pull/3573

TC: Josh proposes for us that we should accept:

```rust
if an_option is Some(x) && x > 3 {
    println!("{x}");
}
```

And:

```rust
func(x is Some(y) && y > 3);
```

TC: The main topic discussed in the issue thread so far has been the degree to which Rust should have "two ways to do things".  Probably the more interesting issue is how the binding and drop scopes for this should work.

TC: In the 2024-02-21 meeting (with limited attendance), we discussed how we should prioritize stabilizing let chains, and tmandry suggested we may want to allow those to settle first.

TC: What do we think, as a gut check?

### "Unsafe fields" rfcs#3458

**Link:** https://github.com/rust-lang/rfcs/pull/3458

TC: Nearly ten years ago, on 2014-10-09, pnkfelix proposed unsafe fields in RFC 381:

https://github.com/rust-lang/rfcs/issues/381

On 2017-05-04, Niko commented:

> I am pretty strongly in favor of unsafe fields at this point. The only thing that holds me back is some desire to think a bit more about the "unsafe" model more generally.

Then, in 2023, Jacob Pratt refreshed this proposal with RFC 3458.  It proposes that:

> Fields may be declared `unsafe`. Unsafe fields may only be mutated (excluding interior mutability) or initialized in an unsafe context. Reading the value of an unsafe field may occur in either safe or unsafe contexts. An unsafe field may be relied upon as a safety invariant in other unsafe code.

E.g.:

```rust
struct Foo {
    safe_field: u32,
    /// Safety: Value must be an odd number.
    unsafe unsafe_field: u32,
}

// Unsafe field initialization requires an `unsafe` block.
// Safety: `unsafe_field` is odd.
let mut foo = unsafe {
    Foo {
        safe_field: 0,
        unsafe_field: 1,
    }
};
```

On 2024-05-21, Niko nominated this for us:

> I'd like to nominate this RFC for discussion. I've not read the details of the thread but I think the concept of unsafe fields is something that comes up continuously and some version of it is worth doing.

TC: What do we think?

### "RFC: Allow symbol re-export in cdylib crate from linked staticlib" rfcs#3556

**Link:** https://github.com/rust-lang/rfcs/pull/3556

TC: This seems to be about making the following work:

```rust
// kind is optional if it's been specified elsewhere, e.g. via the `-l` flag to rustc
#[link(name="ext", kind="static")]
extern {
    #[no_mangle]
    pub fn foo();

    #[no_mangle]
    pub static bar: std::ffi::c_int;
}
```

There are apparently use cases for this.

What's interesting is that apparently it already does, but we issue a warning that is wrong:

```rust
warning: `#[no_mangle]` has no effect on a foreign function
  --> src/lib.rs:21:5
   |
21 |     #[no_mangle]
   |     ^^^^^^^^^^^^ help: remove this attribute
22 |     pub fn foo_rfc3556_pub_with_no_mangle();
   |     ---------------------------------------- foreign function
   |
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: symbol names in extern blocks are not mangled
```

TC: One of the author's asks of us is that we don't make this into a hard error (e.g. with the new edition).

TC: What do we think?

### "Better errors with bad/missing identifiers in MBEs" rust#118939

**Link:** https://github.com/rust-lang/rust/pull/118939

TC: The idea here seems to be to improve some diagnostics around `macro_rules`, but this seems to be done by way of reserving the `macro_rules` token more widely, which is a breaking change.  Petrochenkov has objected to it on that basis, given that reserving `macro_rules` minimally has been the intention since we hope it will one day disappear in favor of `macro`.  What do we think?

### "Uplift `clippy::invalid_null_ptr_usage` lint" rust#119220

**Link:** https://github.com/rust-lang/rust/pull/119220

TC: Urgau proposes this for us:

> This PR aims at uplifting the `clippy::invalid_null_ptr_usage` lint into rustc, this is similar to the [`clippy::invalid_utf8_in_unchecked` uplift](https://github.com/rust-lang/rust/pull/111543) a few months ago, in the sense that those two lints lint on invalid parameter(s), here a null pointer where it is unexpected and UB to pass one.
>
> ## `invalid_null_ptr_usages`
>
> (deny-by-default)
>
> The `invalid_null_ptr_usages` lint checks for invalid usage of null pointers.
>
> ### Example
>
```rust
// Undefined behavior
unsafe { std::slice::from_raw_parts(ptr::null(), 0); }
// Not Undefined behavior
unsafe { std::slice::from_raw_parts(NonNull::dangling().as_ptr(), 0); }
```
>
> Produces:
>
```
error: calling this function with a null pointer is undefined behavior, even if the result of the function is unused, consider using a dangling pointer instead
  --> $DIR/invalid_null_ptr_usages.rs:14:23
   |
LL |     let _: &[usize] = std::slice::from_raw_parts(ptr::null(), 0);
   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^-----------^^^^
   |                                                  |
   |                                                  help: use a dangling pointer instead: `core::ptr::NonNull::dangling().as_ptr()`
```
>
> ### Explanation
>
> Calling methods who's safety invariants requires non-null pointer with a null pointer is undefined behavior.
>
> The lint use a list of functions to know which functions and arguments to checks, this could be improved in the future with a rustc attribute, or maybe even with a `#[diagnostic]` attribute.

TC: What do we think?

### "Uplift `clippy::double_neg` lint as `double_negations`" rust#126604

**Link:** https://github.com/rust-lang/rust/pull/126604

TC: This proposes to lint against cases like this:

```
fn main() {
    let x = 1;
    let _b = --x; //~ WARN use of a double negation
}
```

TC: What do we think?

### "Language vs. implementation threat models and implications for TypeId collision resistance" rust#129030

**Link:** https://github.com/rust-lang/rust/issues/129030

TC: We use SipHash-1-3-128 in Rust for hashing types to form TypeIds.  If these TypeIds collide in a single program, UB may result.

If SipHash-1-3-128 is a secure PRF, then the probability of such collisions happening accidentally in a program that contains an enormous 1M types is one in 2^-89.

But, if someone wanted to brute-force a collision -- that is, find two entirely random types that would have the same TypeId -- the work factor for that is no more than about 2^64 on average.

The question being nominated for lang is whether we consider that good enough for soundness, for now.

TC: What do we think?

### "Lang discussion: Item-level `const {}` blocks, and `const { assert!(...) }`" lang-team#251

**Link:** https://github.com/rust-lang/lang-team/issues/251

TC: This issue was raised due to discussion in a T-libs-api call.  Josh gives the context:

> In discussion of [rust-lang/libs-team#325](https://github.com/rust-lang/libs-team/issues/325) (a proposal for a compile-time assert macro), the idea came up to allow `const {}` blocks at item level, and then have people use `const { assert!(...) }`.
>
> @rust-lang/libs-api would like some guidance from @rust-lang/lang about whether lang is open to toplevel `const { ... }` blocks like this, which would influence whether we want to add a compile-time assert macro, as well as what we want to call it (e.g. `static_assert!` vs `const_assert!` vs some other name).
>
> Filing this issue to discuss in a lang meeting. This issue is _not_ seeking any hard commitment to add such a construct, just doing a temperature check.

CAD97 noted:

> To ensure that it's noted: if both item and expression `const` blocks are valid in the same position (i.e. in statement position), a rule to disambiguate would be needed (like for statement versus expression `if`-`else`). IMO it would be quite unfortunate for item-level `const` blocks to be evaluated pre-mono if that same `const` block but statement-level would be evaluated post-mono.
>
> Additionally: since `const { assert!(...) }` is post-mono (due to using the generic context), it's potentially desirable to push people towards using `const _: () = assert!(...);` (which is pre-mono) whenever possible (not capturing generics).

TC: What do we think?

### "Add lint against function pointer comparisons" rust#118833

**Link:** https://github.com/rust-lang/rust/pull/118833

TC: In the 2024-01-03 call, we developed a tentative consensus to lint against direct function pointer comparison and to push people toward using `ptr::fn_addr_eq`.  We decided to ask T-libs-api to add this.  There's now an open proposal for that here:

https://github.com/rust-lang/libs-team/issues/323

One question that has come up is whether we would expect this to work like `ptr::addr_eq` and have separate generic parameters, e.g.:

```rust
/// Compares the *addresses* of the two pointers for equality,
/// ignoring any metadata in fat pointers.
///
/// If the arguments are thin pointers of the same type,
/// then this is the same as [`eq`].
pub fn addr_eq<T: ?Sized, U: ?Sized>(p: *const T, q: *const U) -> bool { .. }
```

Or whether we would prefer that `fn_addr_eq` enforced type equality of the function pointers.  Since we're the ones asking for this, we probably want to develop a consensus here.  We discussed this in the call on 2024-01-10, then we opened a Zulip thread:

https://rust-lang.zulipchat.com/#narrow/stream/213817-t-lang/topic/Signature.20of.20.60ptr.3A.3Afn_addr_eq.60

TC: On this subject, scottmcm raised this point, with which pnkfelix seemed to concur:

> I do feel like if I saw code that had `fn1.addr() == fn2.addr()` (if `FnPtr` were stabilized), I'd write a comment saying "isn't that what `fn_addr_eq` is for?"
>
> If the answer ends up being "no, actually, because I have different types", that feels unfortunate even if it's rare.
>
> (Like how `addr_eq(a, b)` is nice even if with strict provenance I could write `a.addr() == b.addr()` anyway.)

TC: scottmcm also asserted confidence that allowing mixed-type pointer comparisons is correct for `ptr::addr_eq` since comparing the addresses of `*const T`, `*const [T; N]`, and `*const [T]` are all reasonable.  I pointed out that, if that's reasonable, then `ptr::fn_addr_eq` is the higher-ranked version of that, since for the same use cases, it could be reasonable to compare function pointers that return those three different things or accept them as arguments.

TC: Adding to that, scottmcm noted that comparing addresses despite lifetime differences is also compelling, e.g. comparing `fn(Box<T>) -> &'static mut T` with `for<'a> fn(Box<T>) -> &'a mut T`.

TC: Other alternatives we considered were not stabilizing `ptr::fn_addr_eq` at all and instead stabilizing `FnPtr` so people could write `ptr::addr_eq(fn1.addr(), fn2.addr())`, or expecting that people would write instead `fn1 as *const () == fn2 as *const ()`.

TC: Recently CAD97 raised an interesting alternative:

> From the precedent of `ptr::eq` and `ptr::addr_eq`, I'd expect a "`ptr::fn_eq`" to have one generic type and a "`ptr::fn_addr_eq`" to have two. Even if `ptr::fn_eq`'s implementation is just an address comparison, it still serves as a documentation point to call out the potential pitfalls with comparing function pointers.

TC: What do we think?

---

TC: Separately, on the 2024-01-10 call, we discussed some interest use cases for function pointer comparison, especially when it's indirected through `PartialEq`.  We had earlier said we didn't want to lint when such comparisons were indirected through generics, but we did address the non-generic case of simply composing such comparisons.

One example of how this is used is in the standard library, in `Waker::will_wake`:

https://doc.rust-lang.org/core/task/struct.Waker.html#method.will_wake

It's comparing multiple function pointers via a `#[derive(PartialEq)]` on the `RawWakerVTable`.

We decided on 2024-01-01 that this case was interesting and we wanted to think about it further.  We opened a discussion thread about this:

https://rust-lang.zulipchat.com/#narrow/stream/213817-t-lang/topic/Function.20pointer.20comparison.20and.20.60PartialEq.60

Since then, another interesting use case in the standard library was raised, in the formatting machinery:

https://doc.rust-lang.org/src/core/fmt/rt.rs.html

What do we think about these, and would we lint on derived `PartialEq` cases like these or no?

### "RFC: inherent trait implementation" rfcs#2375

**Link:** https://github.com/rust-lang/rfcs/pull/2375

TC: We had a design meeting on 2023-09-12 about inherent trait impls.  In that meeting, I proposed a `use` syntax for this:

> In the discussion above, we had left two major items unresolved.
>
> - How do we make blanket trait impls inherent?
> - How can we allow only *some* items from the trait impl to be made inherent?
>   - This is especially tricky for associated functions and methods with a default implementation.
>
> (Part of the motivation for wanting to allow only some items to be made inherent is to prevent or to fix breakage caused when a trait later adds a new method with a default implementation whose name conflicts with the name of an existing inherent method.)
>
> Coming up with a syntax for these that combines well with the `#[inherent]` attribute could be challenging.
>
> One alternative that would make solving these problems straightforward is to add some syntax to the inherent `impl` block for the type.  Given the desugaring in the RFC, there is some conceptual appeal here.  (quaternic proposed this arrangement; TC is proposing the concrete syntax.)
>
> We can use `use` syntax to make this concise and intuitive.
>
> Here's an example:

```rust
trait Trait1<Tag, T> {
    fn method0(&self) -> u8 { 0 }
    fn method1(&self) -> u8 { 1 }
}
trait Trait2<Tag, T> {
    fn method2(&self) -> u8 { 2 }
    fn method3(&self) -> u8 { 3 }
    fn method4(&self) -> u8 { 4 }
}

struct Tag;

struct Foo<T>(T);
impl<T> Foo<T> {
    // All methods and associated items of Trait1 become inherent,
    // except for `method0`.  The inherent items are only visible
    // within this crate.
    pub(crate) use Trait1<Tag, T>::*;
    // Only `method2` and `method3` on Trait2 become inherent.
    pub use Trait2<Tag, T>::{method2, method3};

    fn method0(&self) -> u64 { u64::MAX }
}

impl<T> Trait1<Tag, T> for Foo<T> {}
impl<U: Trait1<Tag, T>, T> Trait2<Tag, T> for U {}
```

> This solves another problem that we discussed above.  How do we prevent breakage in downstream crates when a trait later adds a new method with a default implementation?  Since a downstream crate might have made an impl of this trait for some local type inherent and might have an inherent method with a conflicting name, this could be breaking.
>
> We already handle this correctly for `use` declarations with wildcards.  Any locally-defined items override an item that would otherwise be brought into scope with a wildcard import.  We can reuse that same behavior and intuition here.  When a wildcard is used to make all items in the trait inherent, any locally-defined inherent items in the `impl` prevent those items from the trait with the same name from being made inherent.
>
> Advantages:
>
> - It provides a syntax for adopting as inherent a blanket implementation of a trait for the type.
> - It provides a syntax for specifying which methods should become inherent, including methods with default implementations.
> - The wildcard import (`use Trait::*`) makes it very intuitive what exactly is happening and what exactly your API is promising.
> - The `use` syntax makes it natural for a locally-defined item to override an item from the wildcard import because that's exactly how other `use` declarations work.
> - `rust-analyzer` would probably support expanding a wildcard `use Trait::*` to an explicit `use Trait::{ .. }` just as it does for other `use` declarations, which would help people to avoid breakage.
> - We can support any visibility (e.g. `use`, `pub use`, `pub(crate) use`, etc.) for the items made inherent.
>
> Disadvantages:
>
> - There's some redundancy, especially when the items to make inherent are specifically named.

During the meeting, this emerged as the presumptive favorite, and we took on a TODO item to updated the RFC.

After follow-on discussion in Zulip, Niko agreed, and also raised a good question:

> Per the discussion on zulip, I have become convinced that it would be better to make this feature use the syntax `use`, like:
>
```rust
impl SomeType {
    pub use SomeTrait::*;  // re-export the methods for the trait implementation
}
```
>
> This syntax has a few advantages:
>
> * We can give preference to explicit method declared in the impl blocks over glob re-exports, eliminating one source of breakage (i.e., trait adds a method with a name that overlaps one of the inherent methods defined on `SomeType`)
> * Can make just specific methods (not all of them) inherent.
> * Easier to see the inherent method when scanning source.
> * You can re-export with different visibility levels (e.g., `pub(crate)`)
> * It would work best if we planned to permit `use SomeTrait::some_method;` as a way to import methods as standalone fns, but I wish we did that.
>
> However, in writing this, I realize an obvious disadvantage -- if the trait has more generics and things, it's not obvious how those should map. i.e., consider
>
```rust
struct MyType<T> {
}

impl<T> MyType<T> {
    pub use MyTrait::foo;
}

impl<T: Debug> MyTrait for MyType<T> {
    fn foo(&self) { }
}
```
>
> This would be weird -- is this an error, because the impl block says it's for all `T`? And what if it were `trait MyTRait<X>`?

TC: My sense is that we've just been awaiting someone digging in and updating the RFC here.

### "Raw Keywords" rfcs#3098

**Link:** https://github.com/rust-lang/rfcs/pull/3098

TC: We've at various times discussed that we had earlier decided that if we wanted to use a new keyword within an edition, we would write it as `k#keyword`, and for that reason, we prefer to not speculatively reserve keywords ahead of an edition (except, perhaps, when it's clear we plan to use it in the near future).

TC: Somewhat amusingly, however, we never in fact accepted that RFC.  Back in 2021, we accepted scottmcm's proposal to **cancel**:

> We discussed this RFC again in the lang team triage meeting today.
>
> For the short-term goal of the reservation for the edition, we'll be moving forward on #3101 instead. As such, we wanted to leave more time for conversations about this one, and maybe use crater results from 3101 to make design changes,
>
> @rfcbot cancel

Instead we accepted RFC 3101 that reserved `ident#foo`, `ident"foo"`, `ident'f'`, and `ident#123` starting in the 2023 edition.

Reading through the history, here's what I see:

- What do we want to do about Rust 2015 and Rust 2018?  It's a breaking change to add this there.  Is this OK?  Do we want to do a crater run on this?
- Would we have the stomach to actually do this?  It's one thing to *say* that if we wanted to use a new keyword within an edition, we'd write `k#keyword`, but it's another to actually do it in the face of certain criticism about that being e.g. unergonomic.  Would we follow through?

TC: What do we think?

### "RFC: Implementable trait aliases" rfcs#3437

**Link:** https://github.com/rust-lang/rfcs/pull/3437

TC: We discussed this in the lang planning meeting in June, and it looks like there have been updates since we last looked at this, so it's time for us to have another look since we seemed interested in this happening.

TC: What do we think?

### "Should Rust still ignore SIGPIPE by default?" rust#62569

**Link:** https://github.com/rust-lang/rust/issues/62569

TC: Prior to `main()` being executed, the Rust startup code makes a syscall to change the handling of `SIGPIPE`.  Many believe that this is wrong thing for a low-level language like Rust to do, because 1) it makes it impossible to recover what the original value was, and 2) means things like `seccomp` filters must be adjusted for this.

It's also just, in a practical sense, wrong for most CLI applications.

This seems to have been added back when Rust had green threads and then forgotten about.  But it's been an ongoing footgun.

Making a celebrity appearance, Rich Felker, the author of MUSL libc, notes:

> As long as Rust is changing signal dispositions inside init code in a way that the application cannot suppress or undo, it is _fundamentally unusable to implement standard unix utilities that run child processes_ or anything that needs to preserve the signal dispositions it was invoked with and pass them on to children. Changing inheritable process state behind the application's back is just unbelievably bad behavior and does not belong in a language runtime for a serious language...
>
> As an example, if you implement `find` in Rust, the `-exec` option will invoke its commands with `SIGPIPE` set to `SIG_IGN`, so that they will not properly terminate on broken pipe. But if you just made it set `SIGPIPE` to `SIG_DFL` before invoking the commands, now it would be broken in the case where the invoking user intentionally set `SIGPIPE` to `SIG_IGN` so that the commands would not die on broken pipe.

There was discussion in 2019 about fixing this over an edition, but nothing came of it.

Are we interested in fixing it over this one?

Strawman (horrible) proposal: We could stop making this pre-main syscall in Rust 2024 and have `cargo fix` insert this syscall at the start of every `main` function.

(In partial defense of the strawman, it gets us directly to the arguably best end result while having an automatic semantics-preserving edition migration and it avoids the concerns about lang/libs coupling that Mara raised.  The edition migration could add a comment above this inserted code telling people under what circumstances they should either keep or delete the added line.)

### "types team / lang team interaction" rust#116557

**Link:** https://github.com/rust-lang/rust/issues/116557

TC: nikomatsakis nominated this:

> We had some discussion about types/lang team interaction. We concluded a few things:
>
> * Pinging the team like @rust-lang/lang is not an effective way to get attention. Nomination is the only official way to get attention.
> * It's ok to nominate things in an "advisory" capacity but not block (e.g., landing a PR), particularly as most any action can ultimately be reversed. But right now, triagebot doesn't track closed issues, so that's a bit risky.
>
> Action items:
>
> * We should fix triagebot to track closed issues.

TC: What do we think?

### "[RFC] `core::marker::Freeze` in bounds" rfcs#3633

**Link:** https://github.com/rust-lang/rfcs/pull/3633

TC: There's a proposal on the table for the stabilization of the `Freeze` trait in bounds.

We discussed this in our design meeting on 2024-07-24.

TC: What's next here?

### "Implement `PartialOrd` and `Ord` for `Discriminant`" rust#106418

**Link:** https://github.com/rust-lang/rust/pull/106418

TC: We discussed this last in the meeting on 2024-03-13.  scottmcm has now raised on concern on the issue and is planning to make a counter-proposal:

> I remain concerned about exposing this with no opt-out on an unrestricted generic type @rfcbot concern overly-broad
>
> I'm committing to making an alternative proposal because I shouldn't block without one. Please hold my feet to the fire if that's no up in a week.
>
> Basically, I have an idea for how we might be able to do this, from [#106418 (comment)](https://github.com/rust-lang/rust/pull/106418#issuecomment-1698887324)
>
> > 2. Expose the variant ordering privately, only accessible by the type owner/module.
> >
> > Solution 2. is obviously more desirable, but AFAIK Rust can't do that and there is no proposal to add a feature like that.

https://github.com/rust-lang/rust/pull/106418#issuecomment-1994833151

### "Fallout from expansion of redundant import checking" rust#121708

**Link:** https://github.com/rust-lang/rust/issues/121708

TC: We discussed this in the meeting on 2024-03-13.  The feelings expressed included:

- We don't want to create a perverse incentive for people to expand existing lints rather than to create new ones where appropriate just because there's less process for expanding the meaning of an existing lint.
- It would be good if potentially-disruptive expansions of an existing lint either:
  - Had a machine-applicable fix.
  - Or had a new name.
- We don't want to require a new lint name for each expansion.
- We don't want to require a crater run for each change to a lint.
- There are two ways to prevent disruption worth exploring:
  - Prevent potentially-disruptive changes from hitting master.
  - Respond quickly to early indications of disruption once the changes hit master.
- Compiler maintainers have a sense of what might be disruptive and are cautious to avoid it.  It may be OK to have a policy that is not perfectly measurable.

TC: tmandry volunteered to draft a policy proposal.

### "What are the guarantees around which constants (and callees) in a function get monomorphized?" rust#122301

**Link:** https://github.com/rust-lang/rust/issues/122301

TC: The8472 asks whether this code, which compiles today, can be relied upon:

```rust
const fn panic<T>() {
    struct W<T>(T);
    impl<T> W<T> {
        const C: () = panic!();
    }
    W::<T>::C
}

struct Invoke<T, const N: usize>(T);

impl<T, const N: usize> Invoke<T, N> {
    const C: () = match N {
        0 => (),
        // Not called for `N == 0`, so not monomorphized.
        _ => panic::<T>(),
    };
}

fn main() {
    let _x = Invoke::<(), 0>::C;
}
```

The8472 notes that this is a useful property and that there are use cases for this in the compiler and the standard library, at least unless or until we adopt something like `const if`:

https://github.com/rust-lang/rfcs/issues/3582

RalfJ has pointed out to The8472 that the current behavior might not be intentional and notes:

> It's not opt-dependent, but it's also unclear how we want to resolve the opt-dependent issue. Some [proposals](https://github.com/rust-lang/rust/issues/122814#issuecomment-2015090501) involve also walking all items "mentioned" in a const. That would be in direct conflict with your goal here I think. To be clear I think that's a weakness of those proposals. But if that turns out to be the only viable strategy then we'll have to decide what we want more: using `const` tricks to control what gets monomorphized, or not having optimization-dependent errors.
>
> One crucial part of this construction is that everything involved is generic. If somewhere in the two "branches" you end up calling a monomorphic function, then that may have its constants evaluated even if it is in the "dead" branch -- or it may not, it depends on which functions are deemed cross-crate-inlinable. That's basically what #122814 is about.

TC: The question to us is whether we want to guarantee this behavior.  What do we think?

### "Policy for lint expansions" rust#122759

**Link:** https://github.com/rust-lang/rust/issues/122759

TC: In the call on 2024-03-13, we discussed this issue raised by tmandry:

"Fallout from expansion of redundant import checking"

https://github.com/rust-lang/rust/issues/121708

During the call, the thoughts expressed included:

- We don't want to create a perverse incentive for people to expand existing lints rather than to create new ones where appropriate just because there's less process for expanding the meaning of an existing lint.
- It would be good if potentially-disruptive expansions of an existing lint either:
  - Had a machine-applicable fix.
  - Or had a new name.
- We don't want to require a new lint name for each expansion.
- We don't want to require a crater run for each change to a lint.
- There are two ways to prevent disruption worth exploring:
  - Prevent potentially-disruptive changes from hitting master.
  - Respond quickly to early indications of disruption once the changes hit master.
- Compiler maintainers have a sense of what might be disruptive and are cautious to avoid it.  It may be OK to have a policy that is not perfectly measurable.

TC: tmandry volunteered to draft a policy proposal.  He's now written up this proposal in this issue.

TC: What do we think?

### "Decide on path forward for attributes on expressions" rust#127436

**Link:** https://github.com/rust-lang/rust/issues/127436

TC: We decided recently to unblock progress on attributes on expressions (RFC 16) by allowing attributes on blocks.  We have a proposed FCP to this effect.

After we did this, the question came up what we want to do about attributes in list contexts, e.g.:

```rust
call(#[foo] { block1 }, #[bar] { block2 })
```

...in particular, macro attributes.

Petrochenkov says:

> It needs to be decided how proc macros see the commas, or other separators in similar cases.
>
> Ideally proc macros should be able to turn 1 expression into multiple (including 0) expressions in this position, similarly to `cfg`s or macros in list contexts without separators. So it would be reasonable if the separators were included into both input and output tokens streams (there are probably other alternatives, but they do not fit into the token-based model as well). The "reparse context" bit from [#61733 (comment)](https://github.com/rust-lang/rust/issues/61733#issuecomment-509626449) is likely relevant to this case as well.

We filed a concern to figure this all out.

We discussed this on 2024-07-24 and came up with these options:

> Options ordered from least to most conservative (and then from most to least expressive):
>
> - Option A: Punt this case and don't support attributes in this position without parens (e.g. `call((#[attr] arg), (#[attr] arg2))`)
> - Option B (exactly one): Specify that, for now, if you use a macro attribute on an expression, that macro can only expand to a single expresion (not zero tokens, and no tokens following in the output).
> - Option C (zero or one): Specify that, for now, if you use a macro attribute on an expression, that macro can only expand to zero tokens or an expression with nothing following (extra tokens, including `,`, are an error for now)
> - Option D (zero or more): Specify that an attribute in this position can expand to tokens that may include a `,`, and that if they expand to zero tokens then we elide the comma.
> - Option E (flexible): include comma, let macro decide, etc
>    - We find it surprising that comma would be included.

In discussion, we seemed generally interested in allowing at least zero and 1.  We weren't sure about N, and we weren't sure about the handling of the comma in the input.

TC: What do we think?

### "Decide on bounds syntax for async closures (RFC 3668)" rust#128129

**Link:** https://github.com/rust-lang/rust/issues/128129

In the special design meeting 2024-07-23, we discussed five syntaxes for async closures:

- `F: async FnMut() -> T`
- `F: AsyncFnMut() -> T`
- `F: async mut fn() -> T`
- `F: async mut () -> T`
- `F: async mut || -> T`

Our current straw poll is:

| name         | `async Fn*() -> T` | `AsyncFn*() -> T` | `async fn * () -> T` | `async * () -> T` | `async * \|A, B\| -> T` |
|--------------|--------------------|-------------------|----------------------|-------------------|-------------------------|
| nikomatsakis |       +1           |         +0        |         -1           |          -1       |          -1             |
| tmandry      |       +1           |         +1        |         -0.5         |          -1       |          -0.5           |
| Josh         |       -1           |         +0.75     |         +0.5         |          +1       |          +0.5           |
| pnkfelix     |       +0           |         -0        |         -0.5         |          +0       |          -1             |
| scottmcm     |                    |                   |                      |                   |                         |
| TC           |       +1           |         -0.5      |         -1           |          -1       |          -1             |
| CE           |       +1           |         -1        |         -1           |          -0.5     |          -1             |
| eholk        |       +1           |         +0        |         -1           |          -0.75    |          -0.5           |

- +1: "This is what I would do."
- +0: "I'm OK with this, leaning positive."
- -0: "I'm neutral to this, leaning negative."
- -1: "I would block this."

We agreed to:

- Move this to an unresolved question in RFC 3668.
- Allow that RFC to proceed to FCP.
- Implement both of the two main syntax options in nightly.
- Give both syntaxes equal billing in any blog posts about this.

There was substantial discussion of this after the design meeting itself in the thread here:

https://rust-lang.zulipchat.com/#narrow/stream/410673-t-lang.2Fmeetings/topic/Design.20meeting.202024-07-23

TC: This is just an FYI for those that didn't follow this closely.

### "Effective breakage to `jiff` due to `ambiguous_negative_literals`" rust#128287

**Link:** https://github.com/rust-lang/rust/issues/128287

We recently adopted a lint againstn `ambiguous_negative_literals` like:

```rust
assert_eq!(-1.abs(), -1);
```

However, immediately after this landed, BurntSushi reported that this effectively breaks a pattern he had used in the API of his `jiff` datetime library:

> This completely broke Jiff once the change landed. Because it specifically supports negating spans like `-1.hour()`. [In the case of Jiff, there is no ambiguity because `-1.hour()` and `(-1).hour()` and `-(1.hour())` are all precisely equivalent.](https://docs.rs/jiff/latest/jiff/struct.Span.html#negative-spans)

This seems worth our consideration.

One option proposed is that, perhaps, we should have a way to notate functions that are sensitive to the order of operations here, and lint on calls to those with unparenthesized negative literals.

Another option proposed is to go the other way, and introduce some way to notate functions that are *not* sensitive to the order of operations.

TC: What do we think?

### "Tracking issue for const `<*const T>::is_null`" rust#74939

**Link:** https://github.com/rust-lang/rust/issues/74939

### "Lint against getting pointers from immediately dropped temporaries" rust#128985

**Link:** https://github.com/rust-lang/rust/pull/128985

### "Tracking issue for release notes of #127672: Stabilize opaque type precise capturing (RFC 3617)" rust#129577

**Link:** https://github.com/rust-lang/rust/issues/129577

## Action item review

- [Action items list](https://hackmd.io/gstfhtXYTHa3Jv-P_2RK7A)

## Pending lang team project proposals

None.

## PRs on the lang-team repo

### "Add soqb`s design doc to variadics notes" lang-team#236

**Link:** https://github.com/rust-lang/lang-team/pull/236

### "Update auto traits design notes with recent discussion" lang-team#237

**Link:** https://github.com/rust-lang/lang-team/pull/237

### "Update hackmd link to a public link" lang-team#258

**Link:** https://github.com/rust-lang/lang-team/pull/258

### "Adding a link to "how to add a feature gate" in the experimenting how-to" lang-team#267

**Link:** https://github.com/rust-lang/lang-team/pull/267

### "text describing how other teams are enabled to make decisions." lang-team#290

**Link:** https://github.com/rust-lang/lang-team/pull/290

## RFCs waiting to be merged

### "RFC: Allow boolean literals as `cfg` predicates" rfcs#3695

**Link:** https://github.com/rust-lang/rfcs/pull/3695

## `S-waiting-on-team`

### "Stabilize `extended_varargs_abi_support`" rust#116161

**Link:** https://github.com/rust-lang/rust/pull/116161

### "Check ABI target compatibility for function pointers" rust#128784

**Link:** https://github.com/rust-lang/rust/pull/128784

### "Allow dropping `dyn Trait` principal" rust#126660

**Link:** https://github.com/rust-lang/rust/pull/126660

### "Emit error when calling/declaring functions with vectors that require missing target feature" rust#127731

**Link:** https://github.com/rust-lang/rust/pull/127731

### "`optimize` attribute applied to things other than methods/functions/c…" rust#128943

**Link:** https://github.com/rust-lang/rust/pull/128943

### "`repr(tag = ...)` for type aliases" rfcs#3659

**Link:** https://github.com/rust-lang/rfcs/pull/3659

### "Stabilize `count`, `ignore`, `index`, and `length` (`macro_metavar_expr`)" rust#122808

**Link:** https://github.com/rust-lang/rust/pull/122808

### "Emit a warning if a `match` is too complex" rust#122685

**Link:** https://github.com/rust-lang/rust/pull/122685

### "Better errors with bad/missing identifiers in MBEs" rust#118939

**Link:** https://github.com/rust-lang/rust/pull/118939

### "Uplift `clippy::double_neg` lint as `double_negations`" rust#126604

**Link:** https://github.com/rust-lang/rust/pull/126604

### "Rename `AsyncIterator` back to `Stream`, introduce an AFIT-based `AsyncIterator` trait" rust#119550

**Link:** https://github.com/rust-lang/rust/pull/119550

### "Allow `#[deny]` inside `#[forbid]` as a no-op" rust#121560

**Link:** https://github.com/rust-lang/rust/pull/121560

### "Lint against getting pointers from immediately dropped temporaries" rust#128985

**Link:** https://github.com/rust-lang/rust/pull/128985

## Proposed FCPs

**Check your boxes!**

### "Fixup Windows verbatim paths when used with the `include!` macro" rust#125205

**Link:** https://github.com/rust-lang/rust/pull/125205

### "Check ABI target compatibility for function pointers" rust#128784

**Link:** https://github.com/rust-lang/rust/pull/128784

### "Stabilize 7 `const_mut_refs`-dependent API" rust#130954

**Link:** https://github.com/rust-lang/rust/pull/130954

### "Finish stabilization of `result_ffi_guarantees`" rust#130628

**Link:** https://github.com/rust-lang/rust/pull/130628

### "`repr(tag = ...)` for type aliases" rfcs#3659

**Link:** https://github.com/rust-lang/rfcs/pull/3659

### "Consider deprecation of UB-happy `static mut`" rust#53639

**Link:** https://github.com/rust-lang/rust/issues/53639

### "Tracking Issue for enum access in offset_of" rust#120141

**Link:** https://github.com/rust-lang/rust/issues/120141

### "Stabilize `count`, `ignore`, `index`, and `length` (`macro_metavar_expr`)" rust#122808

**Link:** https://github.com/rust-lang/rust/pull/122808

### "Supertrait item shadowing v2" rfcs#3624

**Link:** https://github.com/rust-lang/rfcs/pull/3624

### "Trait method impl restrictions" rfcs#3678

**Link:** https://github.com/rust-lang/rfcs/pull/3678

### "[RFC] Default field values" rfcs#3681

**Link:** https://github.com/rust-lang/rfcs/pull/3681

### "Add support for `use Trait::func`" rfcs#3591

**Link:** https://github.com/rust-lang/rfcs/pull/3591

### "Stabilize `anonymous_lifetime_in_impl_trait`" rust#107378

**Link:** https://github.com/rust-lang/rust/pull/107378

### "[RFC] externally implementable functions" rfcs#3632

**Link:** https://github.com/rust-lang/rfcs/pull/3632

### "Implement `PartialOrd` and `Ord` for `Discriminant`" rust#106418

**Link:** https://github.com/rust-lang/rust/pull/106418

### "Policy for lint expansions" rust#122759

**Link:** https://github.com/rust-lang/rust/issues/122759

### "Decide on path forward for attributes on expressions" rust#127436

**Link:** https://github.com/rust-lang/rust/issues/127436

### "Don't allow unwinding from Drop impls" rfcs#3288

**Link:** https://github.com/rust-lang/rfcs/pull/3288

### "Add text for the CFG OS Version RFC" rfcs#3379

**Link:** https://github.com/rust-lang/rfcs/pull/3379

### "[RFC] Add `#[export_ordinal(n)]` attribute" rfcs#3641

**Link:** https://github.com/rust-lang/rfcs/pull/3641

### "Stabilize associated type position impl Trait (ATPIT)" rust#120700

**Link:** https://github.com/rust-lang/rust/pull/120700

## Active FCPs

None.

## P-critical issues

None.
