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Merged
merged 2 commits into from
May 20, 2025

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@compiler-errors compiler-errors commented Apr 5, 2025

"Non-trivially recursive" opaques are opaques whose hidden types are inferred to be equal to something other than themselves. For example, if we have a TAIT like type TAIT = impl Sized, if we infer the hidden type to be TAIT := (TAIT,), that would be a non-trivial recursive definition. We don't want to support opaques that are non-trivially recursive, since they will (almost!! -- see caveat below) always result in borrowck errors, and are generally a pain to deal with.

On the contrary, trivially recursive opaques may occur today because the old solver overagerly uses replace_opaque_types_with_inference_vars. This infer var can then later be constrained to be equal to the opaque itself. These cases will not necessarily result in borrow-checker errors, since other uses of the opaque may properly constrain the opaque. If there are no other uses we may instead fall back to () today.

The only weird case that we have to unfortunately deal with was discovered in #139406:

#![allow(unconditional_recursion)]

fn what1<T>(x: T) -> impl Sized {
    what1(x)
}

fn what2<T>(x: T) -> impl Sized {
    what2(what2(x))
}

fn print_return_type<T, U>(_: impl Fn(T) -> U) {
    println!("{}", std::any::type_name::<U>())
}

fn main() {
    print_return_type(what1::<i32>); // ()
    print_return_type(what2::<i32>); // i32
}

HIR typeck eagerly replaces the return type with an infer var, ending up with RPIT<T> = RPIT<RPIT<T>> in the storage. While we return this in the TypeckResults, it's never actually used anywhere.

MIR building then results in the following statement

let _0: impl RPIT<T> /* the return place */ = build<RPIT<T>>(_some_local);

Unlike HIR typeck MIR typeck now directly equates RPIT<T> with RPIT<RPIT<T>>. This does not try to define RPIT but instead relates its generic arguments

(
&ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, .. }),
&ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, .. }),
) if a_def_id == b_def_id => {
super_combine_tys(infcx, self, a, b)?;
}

This means we relate T with RPIT<T>, which results in a defining use RPIT<T> = T

I think it's pretty obvious that this is not desirable behavior, and according to the crater run there were no regressions, so let's break this so that we don't have any inference hazards in the new solver.

In the future what2 may end up compiling again by also falling back to (). However, that is not yet guaranteed and the transition to this state is made significantly harder by not temporarily breaking it on the way. It is also concerning to change the inferred hidden type like this without any notification to the user, even if likely not an issue in this concrete case.

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Apr 5, 2025
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compiler-errors commented Apr 5, 2025

@bors try

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@rustbot rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Apr 5, 2025
bors added a commit to rust-lang-ci/rust that referenced this pull request Apr 5, 2025
…<try>

Just error on recursive opaque ty in HIR typeck

Opening just to gauge fallout.

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bors commented Apr 5, 2025

⌛ Trying commit 99e7ce9 with merge f45c1ab...

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bors commented Apr 5, 2025

☀️ Try build successful - checks-actions
Build commit: f45c1ab (f45c1ab62d4de6b63f69b4daa9d1f0b90c38a208)

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Finished benchmarking commit (f45c1ab): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

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This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results (secondary -2.2%)

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mean range count
Regressions ❌
(primary)
- - 0
Regressions ❌
(secondary)
- - 0
Improvements ✅
(primary)
- - 0
Improvements ✅
(secondary)
-2.2% [-2.2%, -2.2%] 1
All ❌✅ (primary) - - 0

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Bootstrap: 775.534s -> 775.663s (0.02%)
Artifact size: 365.93 MiB -> 365.92 MiB (-0.00%)

@rustbot rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Apr 5, 2025
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👌 Experiment pr-139419 created and queued.
🤖 Automatically detected try build f45c1ab
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

@craterbot craterbot added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 5, 2025
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🚧 Experiment pr-139419 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

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🎉 Experiment pr-139419 is completed!
📊 3 regressed and 2 fixed (610052 total)
📰 Open the full report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

@craterbot craterbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-crater Status: Waiting on a crater run to be completed. labels Apr 7, 2025
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lcnr commented Apr 7, 2025

all spurious, can you think of a test case which actually compiled before this PR?

I would expect us to error for them already, just after rustc_borrowck

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lcnr commented Apr 7, 2025

This is a breaking change, see #139406. We should very much break this, explaining what's going on in that issue

@compiler-errors compiler-errors changed the title Just error on recursive opaque ty in HIR typeck Error on recursive opaque ty in HIR typeck Apr 16, 2025
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@compiler-errors compiler-errors marked this pull request as ready for review April 28, 2025 20:45
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rustbot commented Apr 28, 2025

Some changes occurred in exhaustiveness checking

cc @Nadrieril

@compiler-errors compiler-errors removed the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Apr 28, 2025
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rfcbot commented May 6, 2025

🔔 This is now entering its final comment period, as per the review above. 🔔

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bors commented May 8, 2025

☔ The latest upstream changes (presumably #140106) made this pull request unmergeable. Please resolve the merge conflicts.

@rfcbot rfcbot added finished-final-comment-period The final comment period is finished for this PR / Issue. to-announce Announce this issue on triage meeting and removed final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. labels May 16, 2025
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rfcbot commented May 16, 2025

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

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lcnr commented May 20, 2025

r=me after rebase

@compiler-errors compiler-errors force-pushed the recursive-opaque branch 3 times, most recently from 34f7cbe to 56c206c Compare May 20, 2025 09:38
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lcnr commented May 20, 2025

@bors r+ rollup

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bors commented May 20, 2025

📌 Commit 47b9e37 has been approved by lcnr

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 20, 2025
bors added a commit to rust-lang-ci/rust that referenced this pull request May 20, 2025
…iaskrgr

Rollup of 7 pull requests

Successful merges:

 - rust-lang#139419 (Error on recursive opaque ty in HIR typeck)
 - rust-lang#141236 (Resolved issue with mismatched types triggering ICE in certain scenarios)
 - rust-lang#141253 (Warning added when dependency crate has async drop types, and the feature is disabled)
 - rust-lang#141269 (rustc-dev-guide subtree update)
 - rust-lang#141275 (`gather_locals`: only visit guard pattern guards when checking the guard)
 - rust-lang#141279 (`lower_to_hir` cleanups)
 - rust-lang#141285 (Add tick to `RePlaceholder` debug output)

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 7e3af74 into rust-lang:master May 20, 2025
6 checks passed
@rustbot rustbot added this to the 1.89.0 milestone May 20, 2025
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request May 20, 2025
Rollup merge of rust-lang#139419 - compiler-errors:recursive-opaque, r=lcnr

Error on recursive opaque ty in HIR typeck

"Non-trivially recursive" opaques are opaques whose hidden types are inferred to be equal to something other than themselves. For example, if we have a TAIT like `type TAIT = impl Sized`, if we infer the hidden type to be `TAIT := (TAIT,)`, that would be a non-trivial recursive definition. We don't want to support opaques that are non-trivially recursive, since they will (almost!! -- see caveat below) always result in borrowck errors, and are generally a pain to deal with.

On the contrary, trivially recursive opaques may occur today because the old solver overagerly uses `replace_opaque_types_with_inference_vars`. This infer var can then later be constrained to be equal to the opaque itself. These cases will not necessarily result in borrow-checker errors, since other uses of the opaque may properly constrain the opaque. If there are no other uses we may instead fall back to `()` today.

The only weird case that we have to unfortunately deal with was discovered in rust-lang#139406:

```rust
#![allow(unconditional_recursion)]

fn what1<T>(x: T) -> impl Sized {
    what1(x)
}

fn what2<T>(x: T) -> impl Sized {
    what2(what2(x))
}

fn print_return_type<T, U>(_: impl Fn(T) -> U) {
    println!("{}", std::any::type_name::<U>())
}

fn main() {
    print_return_type(what1::<i32>); // ()
    print_return_type(what2::<i32>); // i32
}
```

> HIR typeck eagerly replaces the return type with an infer var, ending up with `RPIT<T> = RPIT<RPIT<T>>` in the storage. While we return this in the `TypeckResults`, it's never actually used anywhere.
>
> MIR building then results in the following statement
> ```rust
> let _0: impl RPIT<T> /* the return place */ = build<RPIT<T>>(_some_local);
> ```
> Unlike HIR typeck MIR typeck now directly equates `RPIT<T>` with `RPIT<RPIT<T>>`. This does not try to define `RPIT` but instead relates its generic arguments https://github.com/rust-lang/rust/blob/b9856b6e400709392dd14599265b6fd52fc19f3e/compiler/rustc_infer/src/infer/relate/type_relating.rs#L185-L190
>
> This means we relate `T` with `RPIT<T>`, which results in a defining use `RPIT<T> = T`

I think it's pretty obvious that this is not desirable behavior, and according to the crater run there were no regressions, so let's break this so that we don't have any inference hazards in the new solver.

In the future `what2` may end up compiling again by also falling back to `()`. However, that is not yet guaranteed and the transition to this state is made significantly harder by not temporarily breaking it on the way. It is also concerning to change the inferred hidden type like this without any notification to the user, even if likely not an issue in this concrete case.
@apiraino apiraino removed the to-announce Announce this issue on triage meeting label Jun 5, 2025
wip-sync pushed a commit to NetBSD/pkgsrc-wip that referenced this pull request Aug 11, 2025
Pkgsrc changes:
 * Adjust patches to adapt to upstream changes and new versions.
 * assosicated checksums

Upstream changes relative to 1.88.0:

Version 1.89.0 (2025-08-07)
==========================

Language
--------
- [Stabilize explicitly inferred const arguments (`feature(generic_arg_infer)`)]
  (rust-lang/rust#141610)
- [Add a warn-by-default `mismatched_lifetime_syntaxes` lint.]
  (rust-lang/rust#138677)
  This lint detects when the same lifetime is referred to by
  different syntax categories between function arguments and return
  values, which can be confusing to read, especially in unsafe
  code.  This lint supersedes the warn-by-default `elided_named_lifetimes`
  lint.
- [Expand `unpredictable_function_pointer_comparisons` to also lint
  on function pointer comparisons in external macros]
  (rust-lang/rust#134536)
- [Make the `dangerous_implicit_autorefs` lint deny-by-default]
  (rust-lang/rust#141661)
- [Stabilize the avx512 target features]
  (rust-lang/rust#138940)
- [Stabilize `kl` and `widekl` target features for x86]
  (rust-lang/rust#140766)
- [Stabilize `sha512`, `sm3` and `sm4` target features for x86]
  (rust-lang/rust#140767)
- [Stabilize LoongArch target features `f`, `d`, `frecipe`, `lasx`,
  `lbt`, `lsx`, and `lvz`]
  (rust-lang/rust#135015)
- [Remove `i128` and `u128` from `improper_ctypes_definitions`]
  (rust-lang/rust#137306)
- [Stabilize `repr128` (`#[repr(u128)]`, `#[repr(i128)]`)]
  (rust-lang/rust#138285)
- [Allow `#![doc(test(attr(..)))]` everywhere]
  (rust-lang/rust#140560)
- [Extend temporary lifetime extension to also go through tuple
  struct and tuple variant constructors]
  (rust-lang/rust#140593)

Compiler
--------
- [Default to non-leaf frame pointers on aarch64-linux]
  (rust-lang/rust#140832)
- [Enable non-leaf frame pointers for Arm64EC Windows]
  (rust-lang/rust#140862)
- [Set Apple frame pointers by architecture]
  (rust-lang/rust#141797)

Platform Support
----------------
- [Add new Tier-3 targets `loongarch32-unknown-none` and
  `loongarch32-unknown-none-softfloat`]
  (rust-lang/rust#142053)

Refer to Rust's [platform support page][platform-support-doc]
for more information on Rust's tiered platform support.

[platform-support-doc]: https://doc.rust-lang.org/rustc/platform-support.html

Libraries
---------
- [Specify the base path for `file!`]
  (rust-lang/rust#134442)
- [Allow storing `format_args!()` in a variable]
  (rust-lang/rust#140748)
- [Add `#[must_use]` to `[T; N]::map`]
  (rust-lang/rust#140957)
- [Implement `DerefMut` for `Lazy{Cell,Lock}`]
  (rust-lang/rust#129334)
- [Implement `Default` for `array::IntoIter`]
  (rust-lang/rust#141574)
- [Implement `Clone` for `slice::ChunkBy`]
  (rust-lang/rust#138016)
- [Implement `io::Seek` for `io::Take`]
  (rust-lang/rust#138023)

Stabilized APIs
---------------

- [`NonZero<char>`]
  (https://doc.rust-lang.org/stable/std/num/struct.NonZero.html)
- Many intrinsics for x86, not enumerated here
  - [AVX512 intrinsics](rust-lang/rust#111137)
  - [`SHA512`, `SM3` and `SM4` intrinsics]
    (rust-lang/rust#126624)
- [`File::lock`]
  (https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.lock)
- [`File::lock_shared`]
  (https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.lock_shared)
- [`File::try_lock`]
  (https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.try_lock)
- [`File::try_lock_shared`]
  (https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.try_lock_shared)
- [`File::unlock`]
  (https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.unlock)
- [`NonNull::from_ref`]
  (https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.from_ref)
- [`NonNull::from_mut`]
  (https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.from_mut)
- [`NonNull::without_provenance`]
  (https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.without_provenance)
- [`NonNull::with_exposed_provenance`]
  (https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.with_exposed_provenance)
- [`NonNull::expose_provenance`]
  (https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.expose_provenance)
- [`OsString::leak`]
  (https://doc.rust-lang.org/stable/std/ffi/struct.OsString.html#method.leak)
- [`PathBuf::leak`]
  (https://doc.rust-lang.org/stable/std/path/struct.PathBuf.html#method.leak)
- [`Result::flatten`]
  (https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.flatten)
- [`std::os::linux::net::TcpStreamExt::quickack`]
  (https://doc.rust-lang.org/stable/std/os/linux/net/trait.TcpStreamExt.html#tymethod.quickack)
- [`std::os::linux::net::TcpStreamExt::set_quickack`]
  (https://doc.rust-lang.org/stable/std/os/linux/net/trait.TcpStreamExt.html#tymethod.set_quickack)

These previously stable APIs are now stable in const contexts:

- [`<[T; N]>::as_mut_slice`]
  (https://doc.rust-lang.org/stable/std/primitive.array.html#method.as_mut_slice)
- [`<[u8]>::eq_ignore_ascii_case`]
  (https://doc.rust-lang.org/stable/std/primitive.slice.html#impl-%5Bu8%5D/method.eq_ignore_ascii_case)
- [`str::eq_ignore_ascii_case`]
  (https://doc.rust-lang.org/stable/std/primitive.str.html#impl-str/method.eq_ignore_ascii_case)

Cargo
-----
- [`cargo fix` and `cargo clippy --fix` now default to the same
  Cargo target selection as other build commands.]
  (rust-lang/cargo#15192) Previously it
  would apply to all targets (like binaries, examples, tests, etc.).
  The `--edition` flag still applies to all targets.

- [Stabilize doctest-xcompile.]
  (rust-lang/cargo#15462) Doctests are
  now tested when cross-compiling. Just like other tests, it will
  use the [`runner` setting]
  (https://doc.rust-lang.org/cargo/reference/config.html#targettriplerunner)
  to run the tests. If you need to disable tests for a target, you
  can use the [ignore doctest attribute]
  (https://doc.rust-lang.org/rustdoc/write-documentation/documentation-tests.html#ignoring-targets)
  to specify the targets to ignore.

Rustdoc
-----
- [On mobile, make the sidebar full width and linewrap]
  (rust-lang/rust#139831). This makes long
  section and item names much easier to deal with on mobile.

Compatibility Notes
-------------------
- [Make `missing_fragment_specifier` an unconditional error]
  (rust-lang/rust#128425)
- [Enabling the `neon` target feature on `aarch64-unknown-none-softfloat`
  causes a warning]
  (rust-lang/rust#135160) because mixing
  code with and without that target feature is not properly supported
  by LLVM
- [Sized Hierarchy: Part I](rust-lang/rust#137944)
  - Introduces a small breaking change affecting `?Sized` bounds
    on impls on recursive types which contain associated type
    projections. It is not expected to affect any existing published
    crates. Can be fixed by refactoring the involved types or opting
    into the `sized_hierarchy` unstable feature. See the [FCP report]
    (rust-lang/rust#137944 (comment))
    for a code example.
- The warn-by-default `elided_named_lifetimes` lint is [superseded
  by the warn-by-default `mismatched_lifetime_syntaxes` lint.]
  (rust-lang/rust#138677)
- [Error on recursive opaque types earlier in the type checker]
  (rust-lang/rust#139419)
- [Type inference side effects from requiring element types of
  array repeat expressions are `Copy` are now only available at the
  end of type checking]
  (rust-lang/rust#139635)

- [The deprecated accidentally-stable
  `std::intrinsics::{copy,copy_nonoverlapping,write_bytes}` are now
  proper intrinsics]
  (rust-lang/rust#139916). There are no
  debug assertions guarding against UB, and they cannot be coerced
  to function pointers.
- [Remove long-deprecated `std::intrinsics::drop_in_place`]
  (rust-lang/rust#140151)
- [Make well-formedness predicates no longer coinductive]
  (rust-lang/rust#140208)
- [Remove hack when checking impl method compatibility]
  (rust-lang/rust#140557)
- [Remove unnecessary type inference due to built-in trait object impls]
  (rust-lang/rust#141352)
- [Lint against "stdcall", "fastcall", and "cdecl" on non-x86-32 targets]
  (rust-lang/rust#141435)
- [Future incompatibility warnings relating to the never type (`!`)
  are now reported in dependencies]
  (rust-lang/rust#141937)
- [Ensure `std::ptr::copy_*` intrinsics also perform the static
  self-init checks]
  (rust-lang/rust#142575)

Internal Changes
----------------

These changes do not affect any public interfaces of Rust, but they represent
significant improvements to the performance or internals of rustc and related
tools.

- [Correctly un-remap compiler sources paths with the `rustc-dev` component]
  (rust-lang/rust#142377)
tmeijn pushed a commit to tmeijn/dotfiles that referenced this pull request Aug 12, 2025
This MR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [rust](https://github.com/rust-lang/rust) | minor | `1.88.0` -> `1.89.0` |

MR created with the help of [el-capitano/tools/renovate-bot](https://gitlab.com/el-capitano/tools/renovate-bot).

**Proposed changes to behavior should be submitted there as MRs.**

---

### Release Notes

<details>
<summary>rust-lang/rust (rust)</summary>

### [`v1.89.0`](https://github.com/rust-lang/rust/blob/HEAD/RELEASES.md#Version-1890-2025-08-07)

[Compare Source](rust-lang/rust@1.88.0...1.89.0)

\==========================

<a id="1.89.0-Language"></a>

## Language

- [Stabilize explicitly inferred const arguments (`feature(generic_arg_infer)`)](rust-lang/rust#141610)
- [Add a warn-by-default `mismatched_lifetime_syntaxes` lint.](rust-lang/rust#138677)
  This lint detects when the same lifetime is referred to by different syntax categories between function arguments and return values, which can be confusing to read, especially in unsafe code.
  This lint supersedes the warn-by-default `elided_named_lifetimes` lint.
- [Expand `unpredictable_function_pointer_comparisons` to also lint on function pointer comparisons in external macros](rust-lang/rust#134536)
- [Make the `dangerous_implicit_autorefs` lint deny-by-default](rust-lang/rust#141661)
- [Stabilize the avx512 target features](rust-lang/rust#138940)
- [Stabilize `kl` and `widekl` target features for x86](rust-lang/rust#140766)
- [Stabilize `sha512`, `sm3` and `sm4` target features for x86](rust-lang/rust#140767)
- [Stabilize LoongArch target features `f`, `d`, `frecipe`, `lasx`, `lbt`, `lsx`, and `lvz`](rust-lang/rust#135015)
- [Remove `i128` and `u128` from `improper_ctypes_definitions`](rust-lang/rust#137306)
- [Stabilize `repr128` (`#[repr(u128)]`, `#[repr(i128)]`)](rust-lang/rust#138285)
- [Allow `#![doc(test(attr(..)))]` everywhere](rust-lang/rust#140560)
- [Extend temporary lifetime extension to also go through tuple struct and tuple variant constructors](rust-lang/rust#140593)
- [`extern "C"` functions on the `wasm32-unknown-unknown` target now have a standards compliant ABI](https://blog.rust-lang.org/2025/04/04/c-abi-changes-for-wasm32-unknown-unknown/)

<a id="1.89.0-Compiler"></a>

## Compiler

- [Default to non-leaf frame pointers on aarch64-linux](rust-lang/rust#140832)
- [Enable non-leaf frame pointers for Arm64EC Windows](rust-lang/rust#140862)
- [Set Apple frame pointers by architecture](rust-lang/rust#141797)

<a id="1.89.0-Platform-Support"></a>

## Platform Support

- [Add new Tier-3 targets `loongarch32-unknown-none` and `loongarch32-unknown-none-softfloat`](rust-lang/rust#142053)
- [`x86_64-apple-darwin` is in the process of being demoted to Tier 2 with host tools](rust-lang/rfcs#3841)

Refer to Rust's [platform support page][platform-support-doc]
for more information on Rust's tiered platform support.

[platform-support-doc]: https://doc.rust-lang.org/rustc/platform-support.html

<a id="1.89.0-Libraries"></a>

## Libraries

- [Specify the base path for `file!`](rust-lang/rust#134442)
- [Allow storing `format_args!()` in a variable](rust-lang/rust#140748)
- [Add `#[must_use]` to `[T; N]::map`](rust-lang/rust#140957)
- [Implement `DerefMut` for `Lazy{Cell,Lock}`](rust-lang/rust#129334)
- [Implement `Default` for `array::IntoIter`](rust-lang/rust#141574)
- [Implement `Clone` for `slice::ChunkBy`](rust-lang/rust#138016)
- [Implement `io::Seek` for `io::Take`](rust-lang/rust#138023)

<a id="1.89.0-Stabilized-APIs"></a>

## Stabilized APIs

- [`NonZero<char>`](https://doc.rust-lang.org/stable/std/num/struct.NonZero.html)
- Many intrinsics for x86, not enumerated here
  - [AVX512 intrinsics](rust-lang/rust#111137)
  - [`SHA512`, `SM3` and `SM4` intrinsics](rust-lang/rust#126624)
- [`File::lock`](https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.lock)
- [`File::lock_shared`](https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.lock_shared)
- [`File::try_lock`](https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.try_lock)
- [`File::try_lock_shared`](https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.try_lock_shared)
- [`File::unlock`](https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.unlock)
- [`NonNull::from_ref`](https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.from_ref)
- [`NonNull::from_mut`](https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.from_mut)
- [`NonNull::without_provenance`](https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.without_provenance)
- [`NonNull::with_exposed_provenance`](https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.with_exposed_provenance)
- [`NonNull::expose_provenance`](https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.expose_provenance)
- [`OsString::leak`](https://doc.rust-lang.org/stable/std/ffi/struct.OsString.html#method.leak)
- [`PathBuf::leak`](https://doc.rust-lang.org/stable/std/path/struct.PathBuf.html#method.leak)
- [`Result::flatten`](https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.flatten)
- [`std::os::linux::net::TcpStreamExt::quickack`](https://doc.rust-lang.org/stable/std/os/linux/net/trait.TcpStreamExt.html#tymethod.quickack)
- [`std::os::linux::net::TcpStreamExt::set_quickack`](https://doc.rust-lang.org/stable/std/os/linux/net/trait.TcpStreamExt.html#tymethod.set_quickack)

These previously stable APIs are now stable in const contexts:

- [`<[T; N]>::as_mut_slice`](https://doc.rust-lang.org/stable/std/primitive.array.html#method.as_mut_slice)
- [`<[u8]>::eq_ignore_ascii_case`](https://doc.rust-lang.org/stable/std/primitive.slice.html#impl-%5Bu8%5D/method.eq_ignore_ascii_case)
- [`str::eq_ignore_ascii_case`](https://doc.rust-lang.org/stable/std/primitive.str.html#impl-str/method.eq_ignore_ascii_case)

<a id="1.89.0-Cargo"></a>

## Cargo

- [`cargo fix` and `cargo clippy --fix` now default to the same Cargo target selection as other build commands.](rust-lang/cargo#15192) Previously it would apply to all targets (like binaries, examples, tests, etc.). The `--edition` flag still applies to all targets.
- [Stabilize doctest-xcompile.](rust-lang/cargo#15462) Doctests are now tested when cross-compiling. Just like other tests, it will use the [`runner` setting](https://doc.rust-lang.org/cargo/reference/config.html#targettriplerunner) to run the tests. If you need to disable tests for a target, you can use the [ignore doctest attribute](https://doc.rust-lang.org/rustdoc/write-documentation/documentation-tests.html#ignoring-targets) to specify the targets to ignore.

<a id="1.89.0-Rustdoc"></a>

## Rustdoc

- [On mobile, make the sidebar full width and linewrap](rust-lang/rust#139831). This makes long section and item names much easier to deal with on mobile.

<a id="1.89.0-Compatibility-Notes"></a>

## Compatibility Notes

- [Make `missing_fragment_specifier` an unconditional error](rust-lang/rust#128425)
- [Enabling the `neon` target feature on `aarch64-unknown-none-softfloat` causes a warning](rust-lang/rust#135160) because mixing code with and without that target feature is not properly supported by LLVM
- [Sized Hierarchy: Part I](rust-lang/rust#137944)
  - Introduces a small breaking change affecting `?Sized` bounds on impls on recursive types which contain associated type projections. It is not expected to affect any existing published crates. Can be fixed by refactoring the involved types or opting into the `sized_hierarchy` unstable feature. See the [FCP report](rust-lang/rust#137944 (comment)) for a code example.
- The warn-by-default `elided_named_lifetimes` lint is [superseded by the warn-by-default `mismatched_lifetime_syntaxes` lint.](rust-lang/rust#138677)
- [Error on recursive opaque types earlier in the type checker](rust-lang/rust#139419)
- [Type inference side effects from requiring element types of array repeat expressions are `Copy` are now only available at the end of type checking](rust-lang/rust#139635)
- [The deprecated accidentally-stable `std::intrinsics::{copy,copy_nonoverlapping,write_bytes}` are now proper intrinsics](rust-lang/rust#139916). There are no debug assertions guarding against UB, and they cannot be coerced to function pointers.
- [Remove long-deprecated `std::intrinsics::drop_in_place`](rust-lang/rust#140151)
- [Make well-formedness predicates no longer coinductive](rust-lang/rust#140208)
- [Remove hack when checking impl method compatibility](rust-lang/rust#140557)
- [Remove unnecessary type inference due to built-in trait object impls](rust-lang/rust#141352)
- [Lint against "stdcall", "fastcall", and "cdecl" on non-x86-32 targets](rust-lang/rust#141435)
- [Future incompatibility warnings relating to the never type (`!`) are now reported in dependencies](rust-lang/rust#141937)
- [Ensure `std::ptr::copy_*` intrinsics also perform the static self-init checks](rust-lang/rust#142575)
- [`extern "C"` functions on the `wasm32-unknown-unknown` target now have a standards compliant ABI](https://blog.rust-lang.org/2025/04/04/c-abi-changes-for-wasm32-unknown-unknown/)

<a id="1.89.0-Internal-Changes"></a>

## Internal Changes

These changes do not affect any public interfaces of Rust, but they represent
significant improvements to the performance or internals of rustc and related
tools.

- [Correctly un-remap compiler sources paths with the `rustc-dev` component](rust-lang/rust#142377)

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