Add Rust 1.90.0 announcement

Author: Mark-Simulacrum

content/Rust-1.90.0.md

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+path = "2025/09/18/Rust-1.90.0"
+title = "Announcing Rust 1.90.0"
+authors = ["The Rust Release Team"]
+aliases = ["releases/1.90.0"]
+
+[extra]
+release = true
++++
+
+The Rust team is happy to announce a new version of Rust, 1.90.0. Rust is a programming language empowering everyone to build reliable and efficient software.
+
+If you have a previous version of Rust installed via `rustup`, you can get 1.90.0 with:
+
+```console
+$ rustup update stable
+```
+
+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 1.90.0](https://doc.rust-lang.org/stable/releases.html#version-1900-2025-09-18).
+
+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!
+
+## What's in 1.90.0 stable
+
+### `lld` by default on `x86_64-unknown-linux-gnu`
+
+As [previously announced](https://blog.rust-lang.org/2025/09/01/rust-lld-on-1.90.0-stable/),
+1.90 brings a change in the default linker to `lld` on
+`x86_64-unknown-linux-gnu`. As discussed in that blog, for the vast majority of
+users this change should just be a compile time reduction. In some edge cases,
+`lld` may have different behavior: please file
+[issues](https://github.com/rust-lang/rust/issues/new/choose) if you run into
+problems as part of the migration.
+
+### Cargo adds native support for workspace publishing
+
+`cargo publish --workspace` is now supported, automatically publishing all of
+the crates in a workspace in the right order (following any dependencies
+between them). This has long been possible with external tooling or manual
+ordering of individual publishes, but this brings the functionality into Cargo
+itself.
+
+### Demoting `x86_64-apple-darwin` to Tier 2 with host tools
+
+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\_64 architecture.
+
+In accordance with these changes, as of Rust 1.90, the project has [demoted the `x86_64-apple-darwin` target][rfc] from [Tier 1 with host tools](https://doc.rust-lang.org/stable/rustc/platform-support.html#tier-1-with-host-tools) to [Tier 2 with host tools](https://doc.rust-lang.org/stable/rustc/platform-support.html#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.
+
+For users, this change will not immediately cause impact. 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 while the target remains at Tier 2. Over time, it's likely that reduced test coverage for this target will cause things to break or fall out of compatibility with no further announcements.
+
+[apple]: https://en.wikipedia.org/wiki/Mac_transition_to_Apple_silicon#Timeline
+[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
+[rfc]: https://github.com/rust-lang/rfcs/pull/3841
+
+### Stabilized APIs
+
+- [`u{n}::checked_sub_signed`](https://doc.rust-lang.org/stable/std/primitive.usize.html#method.checked_sub_signed)
+- [`u{n}::overflowing_sub_signed`](https://doc.rust-lang.org/stable/std/primitive.usize.html#method.overflowing_sub_signed)
+- [`u{n}::saturating_sub_signed`](https://doc.rust-lang.org/stable/std/primitive.usize.html#method.saturating_sub_signed)
+- [`u{n}::wrapping_sub_signed`](https://doc.rust-lang.org/stable/std/primitive.usize.html#method.wrapping_sub_signed)
+- [`impl Copy for IntErrorKind`](https://doc.rust-lang.org/stable/std/num/enum.IntErrorKind.html#impl-Copy-for-IntErrorKind)
+- [`impl Hash for IntErrorKind`](https://doc.rust-lang.org/stable/std/num/enum.IntErrorKind.html#impl-Hash-for-IntErrorKind)
+- [`impl PartialEq<&CStr> for CStr`](https://doc.rust-lang.org/stable/std/ffi/struct.CStr.html#impl-PartialEq%3C%26CStr%3E-for-CStr)
+- [`impl PartialEq<CString> for CStr`](https://doc.rust-lang.org/stable/std/ffi/struct.CStr.html#impl-PartialEq%3CCString%3E-for-CStr)
+- [`impl PartialEq<Cow<CStr>> for CStr`](https://doc.rust-lang.org/stable/std/ffi/struct.CStr.html#impl-PartialEq%3CCow%3C'_,+CStr%3E%3E-for-CStr)
+- [`impl PartialEq<&CStr> for CString`](https://doc.rust-lang.org/stable/std/ffi/struct.CString.html#impl-PartialEq%3C%26CStr%3E-for-CString)
+- [`impl PartialEq<CStr> for CString`](https://doc.rust-lang.org/stable/std/ffi/struct.CString.html#impl-PartialEq%3CCStr%3E-for-CString)
+- [`impl PartialEq<Cow<CStr>> for CString`](https://doc.rust-lang.org/stable/std/ffi/struct.CString.html#impl-PartialEq%3CCow%3C'_,+CStr%3E%3E-for-CString)
+- [`impl PartialEq<&CStr> for Cow<CStr>`](https://doc.rust-lang.org/stable/std/borrow/enum.Cow.html#impl-PartialEq%3C%26CStr%3E-for-Cow%3C'_,+CStr%3E)
+- [`impl PartialEq<CStr> for Cow<CStr>`](https://doc.rust-lang.org/stable/std/borrow/enum.Cow.html#impl-PartialEq%3CCStr%3E-for-Cow%3C'_,+CStr%3E)
+- [`impl PartialEq<CString> for Cow<CStr>`](https://doc.rust-lang.org/stable/std/borrow/enum.Cow.html#impl-PartialEq%3CCString%3E-for-Cow%3C'_,+CStr%3E)
+
+These previously stable APIs are now stable in const contexts:
+
+- [`<[T]>::reverse`](https://doc.rust-lang.org/stable/std/primitive.slice.html#method.reverse)
+- [`f32::floor`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.floor)
+- [`f32::ceil`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.ceil)
+- [`f32::trunc`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.trunc)
+- [`f32::fract`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.fract)
+- [`f32::round`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.round)
+- [`f32::round_ties_even`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.round_ties_even)
+- [`f64::floor`](https://doc.rust-lang.org/stable/std/primitive.f64.html#method.floor)
+- [`f64::ceil`](https://doc.rust-lang.org/stable/std/primitive.f64.html#method.ceil)
+- [`f64::trunc`](https://doc.rust-lang.org/stable/std/primitive.f64.html#method.trunc)
+- [`f64::fract`](https://doc.rust-lang.org/stable/std/primitive.f64.html#method.fract)
+- [`f64::round`](https://doc.rust-lang.org/stable/std/primitive.f64.html#method.round)
+- [`f64::round_ties_even`](https://doc.rust-lang.org/stable/std/primitive.f64.html#method.round_ties_even)
+
+### Platform Support
+
+- `x86_64-apple-darwin` is now a tier 2 target
+
+Refer to Rust’s [platform support page][platform_support_page] for more information on Rust’s tiered platform support.
+
+### Other changes
+
+Check out everything that changed in [Rust](https://github.com/rust-lang/rust/releases/tag/1.90.0), [Cargo](https://doc.rust-lang.org/nightly/cargo/CHANGELOG.html#cargo-190-2025-09-18), and [Clippy](https://github.com/rust-lang/rust-clippy/blob/master/CHANGELOG.md#rust-190).
+
+## Contributors to 1.90.0
+
+Many people came together to create Rust 1.90.0. We couldn't have done it without all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.90.0/)
+
+[platform_support_page]: https://doc.rust-lang.org/rustc/platform-support.html