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Announcing Rust 1.89.0
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‎content/Rust-1.89.0.md

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path = "2025/08/07/Rust-1.89.0"
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title = "Announcing Rust 1.89.0"
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authors = ["The Rust Release Team"]
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aliases = ["releases/1.89.0"]
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[extra]
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release = true
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The Rust team is happy to announce a new version of Rust, 1.89.0. Rust is a programming language empowering everyone to build reliable and efficient software.
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If you have a previous version of Rust installed via `rustup`, you can get 1.89.0 with:
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```console
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$ rustup update stable
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```
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If you don't have it already, you can [get `rustup`](https://www.rust-lang.org/install.html) from the appropriate page on our website, and check out the [detailed release notes for 1.89.0](https://doc.rust-lang.org/stable/releases.html#version-1890-2025-08-07).
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If you'd like to help us out by testing future releases, you might consider updating locally to use the beta channel (`rustup default beta`) or the nightly channel (`rustup default nightly`). Please [report](https://github.com/rust-lang/rust/issues/new/choose) any bugs you might come across!
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## What's in 1.89.0 stable
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### Explicitly inferred arguments to const generics
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Rust now supports `_` as an argument to const generic parameters, inferring the value from surrounding context:
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```rust
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pub fn all_false<const LEN: usize>() -> [bool; LEN] {
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[false; _]
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}
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```
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Similar to the rules for when `_` is permitted as a type, `_` is not permitted as an argument to const generics when in a signature:
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```rust
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// This is not allowed
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pub const fn all_false<const LEN: usize>() -> [bool; _] {
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[false; LEN]
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}
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// Neither is this
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pub const ALL_FALSE: [bool; _] = all_false::<10>();
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```
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### Mismatched lifetime syntaxes lint
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[Lifetime elision][elision] in function signatures is an ergonomic aspect of the Rust language, but it can also be a stumbling point for newcomers and experts alike. This is especially true when lifetimes are inferred in types where it isn't syntactically obvious that a lifetime is even present:
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```rust
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// The returned type `std::slice::Iter` has a lifetime,
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// but there's no visual indication of that.
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//
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// Lifetime elision infers the lifetime of the return
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// type to be the same as that of `scores`.
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fn items(scores: &[u8]) -> std::slice::Iter<u8> {
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scores.iter()
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}
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```
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Code like this will now produce a warning by default:
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```text
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warning: hiding a lifetime that's elided elsewhere is confusing
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--> src/lib.rs:1:18
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|
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1 | fn items(scores: &[u8]) -> std::slice::Iter<u8> {
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| ^^^^^ -------------------- the same lifetime is hidden here
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| |
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| the lifetime is elided here
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|
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= help: the same lifetime is referred to in inconsistent ways, making the signature confusing
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= note: `#[warn(mismatched_lifetime_syntaxes)]` on by default
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help: use `'_` for type paths
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|
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1 | fn items(scores: &[u8]) -> std::slice::Iter<'_, u8> {
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| +++
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```
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We [first attempted][elided_lifetime_in_path] to improve this situation back in 2018 as part of the [`rust_2018_idioms`][2018-by-default] lint group, but [strong feedback][bevy] about the `elided_lifetimes_in_paths` lint showed that it was too blunt of a hammer as it warns about lifetimes which don't matter to understand the function:
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```rust
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use std::fmt;
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struct Greeting;
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impl fmt::Display for Greeting {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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// -----^^^^^^^^^ expected lifetime parameter
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// Knowing that `Formatter` has a lifetime does not help the programmer
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"howdy".fmt(f)
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}
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}
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```
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We then realized that the confusion we want to eliminate occurs when both
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1. lifetime elision inference rules *connect* an input lifetime to an output lifetime
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2. it's not syntactically obvious that a lifetime exists
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There are two pieces of Rust syntax that indicate that a lifetime exists: `&` and `'`, with `'` being subdivided into the inferred lifetime `'_` and named lifetimes `'a`. When a type uses a named lifetime, lifetime elision will not infer a lifetime for that type. Using these criteria, we can construct three groups:
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| Self-evident it has a lifetime | Allow lifetime elision to infer a lifetime | Examples |
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|--------------------------------|--------------------------------------------|---------------------------------------|
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| No | Yes | `ContainsLifetime` |
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| Yes | Yes | `&T`, `&'_ T`, `ContainsLifetime<'_>` |
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| Yes | No | `&'a T`, `ContainsLifetime<'a>` |
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The `mismatched_lifetime_syntaxes` lint checks that the inputs and outputs of a function belong to the same group. For the initial motivating example above, `&[u8]` falls into the second group while `std::slice::Iter<u8>` falls into the first group. We say that the lifetimes in the first group are *hidden*.
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Because the input and output lifetimes belong to different groups, the lint will warn about this function, reducing confusion about when a value has a meaningful lifetime that isn't visually obvious.
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The `mismatched_lifetime_syntaxes` lint supersedes the `elided_named_lifetimes` lint, which did something similar for named lifetimes specifically.
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Future work on the `elided_lifetimes_in_paths` lint intends to split it into more focused sub-lints with an eye to warning about a subset of them eventually.
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[elision]: https://doc.rust-lang.org/1.89/book/ch10-03-lifetime-syntax.html#lifetime-elision
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[elided_lifetime_in_path]: https://github.com/rust-lang/rust/pull/46254
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[2018-by-default]: https://github.com/rust-lang/rust/issues/54910
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[bevy]: https://github.com/rust-lang/rust/issues/131725
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### More x86 target features
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The `target_feature` attribute now supports the `sha512`, `sm3`, `sm4`, `kl` and `widekl` target features on x86. Additionally a number of `avx512` intrinsics and target features are also supported on x86:
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```rust
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#[target_feature(enable = "avx512bw")]
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pub fn cool_simd_code(/* .. */) -> /* ... */ {
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/* ... */
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}
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```
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### Cross-compiled doctests
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Doctests will now be tested when running `cargo test --doc --target other_target`, this may result in some amount of breakage due to would-be-failing doctests now being tested.
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Failing tests can be disabled by annotating the doctest with `ignore-<target>`:
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```rust
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/// ```ignore-x86_64
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/// panic!("something")
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/// ```
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pub fn my_function() { }
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```
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### `i128` and `u128` in `extern "C"` functions
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`i128` and `u128` no longer trigger the `improper_ctypes_definitions` lint, meaning these types may be used in `extern "C"` functions without warning. This comes with some caveats:
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* The Rust types are ABI- and layout-compatible with (unsigned) `__int128` in C when the type is available.
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* On platforms where `__int128` is not available, `i128` and `u128` do not necessarily align with any C type.
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* `i128` is _not_ necessarily compatible with `_BitInt(128)` on any platform, because `_BitInt(128)` and `__int128` may not have the same ABI (as is the case on x86-64).
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This is the last bit of follow up to the layout changes from last year: https://blog.rust-lang.org/2024/03/30/i128-layout-update/.
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### Demoting `x86_64-apple-darwin` to Tier 2 with host tools
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GitHub will soon [discontinue][gha-sunset] providing free macOS x86\_64 runners for public repositories. Apple has also announced their [plans][apple] for discontinuing support for the x86\_86 architecture.
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In accordance with these changes, the Rust project is in the [process of demoting the `x86_64-apple-darwin` target][rfc] from Tier 1 to Tier 2 with host tools. This means that the target, including tools like `rustc` and `cargo`, will be guaranteed to build but is not guaranteed to pass our automated test suite.
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We expect that the RFC for the demotion to Tier 2 with host tools will be accepted between the releases of Rust 1.89 and 1.90, which means that Rust 1.89 will be the last release of Rust where `x86_64-apple-darwin` is a Tier 1 target.
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For users, nothing will change. Builds of both the standard library and the compiler will still be distributed by the Rust Project for use via `rustup` or alternative installation methods.
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[apple]: https://en.wikipedia.org/wiki/Mac_transition_to_Apple_silicon#Timeline
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[gha-sunset]: https://github.blog/changelog/2025-07-11-upcoming-changes-to-macos-hosted-runners-macos-latest-migration-and-xcode-support-policy-updates/#macos-13-is-closing-down
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[rfc]: https://github.com/rust-lang/rfcs/pull/3841
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### Standards Compliant C ABI on the `wasm32-unknown-unknown` target
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`extern "C"` functions on the `wasm32-unknown-unknown` target now have a standards compliant ABI. See this blog post for more information: https://blog.rust-lang.org/2025/04/04/c-abi-changes-for-wasm32-unknown-unknown.
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### Platform Support
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- [`x86_64-apple-darwin` is in the process of being demoted to Tier 2 with host tools](https://github.com/rust-lang/rfcs/pull/3841)
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- [Add new Tier-3 targets `loongarch32-unknown-none` and `loongarch32-unknown-none-softfloat`](https://github.com/rust-lang/rust/pull/142053)
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Refer to Rust’s [platform support page][platform_support_page] for more information on Rust’s tiered platform support.
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### Stabilized APIs
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- [`NonZero<char>`](https://doc.rust-lang.org/stable/std/num/struct.NonZero.html)
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- Many intrinsics for x86, not enumerated here
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- [AVX512 intrinsics](https://github.com/rust-lang/rust/issues/111137)
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- [`SHA512`, `SM3` and `SM4` intrinsics](https://github.com/rust-lang/rust/issues/126624)
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- [`File::lock`](https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.lock)
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- [`File::lock_shared`](https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.lock_shared)
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- [`File::try_lock`](https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.try_lock)
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- [`File::try_lock_shared`](https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.try_lock_shared)
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- [`File::unlock`](https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.unlock)
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- [`NonNull::from_ref`](https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.from_ref)
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- [`NonNull::from_mut`](https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.from_mut)
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- [`NonNull::without_provenance`](https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.without_provenance)
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- [`NonNull::with_exposed_provenance`](https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.with_exposed_provenance)
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- [`NonNull::expose_provenance`](https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.expose_provenance)
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- [`OsString::leak`](https://doc.rust-lang.org/stable/std/ffi/struct.OsString.html#method.leak)
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- [`PathBuf::leak`](https://doc.rust-lang.org/stable/std/path/struct.PathBuf.html#method.leak)
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- [`Result::flatten`](https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.flatten)
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- [`std::os::linux::net::TcpStreamExt::quickack`](https://doc.rust-lang.org/stable/std/os/linux/net/trait.TcpStreamExt.html#tymethod.quickack)
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- [`std::os::linux::net::TcpStreamExt::set_quickack`](https://doc.rust-lang.org/stable/std/os/linux/net/trait.TcpStreamExt.html#tymethod.set_quickack)
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These previously stable APIs are now stable in const contexts:
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- [`<[T; N]>::as_mut_slice`](https://doc.rust-lang.org/stable/std/primitive.array.html#method.as_mut_slice)
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- [`<[u8]>::eq_ignore_ascii_case`](https://doc.rust-lang.org/stable/std/primitive.slice.html#impl-%5Bu8%5D/method.eq_ignore_ascii_case)
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- [`str::eq_ignore_ascii_case`](https://doc.rust-lang.org/stable/std/primitive.str.html#impl-str/method.eq_ignore_ascii_case)
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### Other changes
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Check out everything that changed in [Rust](https://github.com/rust-lang/rust/releases/tag/1.89.0), [Cargo](https://doc.rust-lang.org/nightly/cargo/CHANGELOG.html#cargo-189-2025-08-07), and [Clippy](https://github.com/rust-lang/rust-clippy/blob/master/CHANGELOG.md#rust-189).
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## Contributors to 1.89.0
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Many people came together to create Rust 1.89.0. We couldn't have done it without all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.89.0/)
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[platform_support_page]: https://doc.rust-lang.org/rustc/platform-support.html

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