1.81.0 release announcement

posts/2024-09-05-Rust-1.81.0.md

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+---
+layout: post
+title: "Announcing Rust 1.81.0"
+author: The Rust Release Team
+release: true
+---
+
+The Rust team is happy to announce a new version of Rust, 1.81.0. 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 1.81.0 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 1.81.0](https://doc.rust-lang.org/nightly/releases.html#version-1810-2024-09-05).
+
+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 1.81.0 stable
+
+### `core::error::Error`
+
+1.81 stabilizes the `Error` trait in `core`, allowing usage of the trait in `#![no_std]` libraries.
+
+TODO: What can we actually say about this? It seems like this mostly enables
+things in the ecosystem, but from the langauge/standard library not much has
+actually changed in *this* release?
+
+### New sort implementations
+
+Both the stable and unstable sort implementations in the standard library have
+been updated to new algorithms, improving their runtime performance and
+compilation time. Both of the new sort algorithms try to detect
+incorrect implementations of `Ord` and will panic on such cases if detected.
+
+Users encountering these panics should audit any custom Ord implementations to
+ensure they satisfy the requirements documented in [PartialOrd] and [Ord].
+
+TODO: Ideally we'd have text somewhere specific to the new detection that helps
+explain how to do this audit or otherwise helps users. This otherwise feels
+pretty opaque to me. We might also want to consider whether some kind of
+transition rather than panic! is best (not sure how else users would find out
+about the problem though). See https://github.com/rust-lang/rust/issues/129561.
+
+[PartialOrd]: https://doc.rust-lang.org/nightly/std/cmp/trait.PartialOrd.html
+[Ord]: https://doc.rust-lang.org/nightly/std/cmp/trait.Ord.html
+
+### `#[expect(lint)]`
+
+1.81 stabilizes a new lint level, `expect`, which allows explicitly noting that
+a particular lint *should* occur, and warning if it doesn't.  The intended use
+case for this is temporarily silencing a lint, whether due to lint
+implementation bugs or ongoing refactoring, while wanting to know when the lint
+is no longer required.
+
+For example, if you're moving a code base to comply with a new restriction
+enforced via a Clippy lint like
+[`undocumented_unsafe_blocks`](https://rust-lang.github.io/rust-clippy/stable/index.html#/undocumented_unsafe_blocks),
+you can use `#[expect(clippy::undocumented_unsafe_blocks)]` as you transition,
+ensuring that once all unsafe blocks are documented you can opt into denying
+the lint to enforce it.
+
+### Lint reasons
+
+Changing the lint level is often done for some particular reason. For example,
+if code runs in an environment without floating point support, you could use
+Clippy to lint on such usage with `#![deny(clippy::float_arithmetic)]`.
+However, if a new developer to the project sees this lint fire, they need to
+look for (hopefully) a comment on the deny explaining why it was added. With
+Rust 1.71, they can be informed directly in the compiler message:
+
+```text
+error: floating-point arithmetic detected
+ --> src/lib.rs:4:5
+  |
+4 |     a + b
+  |     ^^^^^
+  |
+  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#float_arithmetic
+  = note: no hardware float support
+note: the lint level is defined here
+ --> src/lib.rs:1:9
+  |
+1 | #![deny(clippy::float_arithmetic, reason = "no hardware float support")]
+  |         ^^^^^^^^^^^^^^^^^^^^^^^^
+```
+
+### Stabilized APIs
+
+- [`core::error`](https://doc.rust-lang.org/stable/core/error/index.html)
+- [`hint::assert_unchecked`](https://doc.rust-lang.org/stable/core/hint/fn.assert_unchecked.html)
+- [`fs::exists`](https://doc.rust-lang.org/stable/std/fs/fn.exists.html)
+- [`AtomicBool::fetch_not`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicBool.html#method.fetch_not)
+- [`Duration::abs_diff`](https://doc.rust-lang.org/stable/core/time/struct.Duration.html#method.abs_diff)
+- [`IoSlice::advance`](https://doc.rust-lang.org/stable/std/io/struct.IoSlice.html#method.advance)
+- [`IoSlice::advance_slices`](https://doc.rust-lang.org/stable/std/io/struct.IoSlice.html#method.advance_slices)
+- [`IoSliceMut::advance`](https://doc.rust-lang.org/stable/std/io/struct.IoSliceMut.html#method.advance)
+- [`IoSliceMut::advance_slices`](https://doc.rust-lang.org/stable/std/io/struct.IoSliceMut.html#method.advance_slices)
+- [`PanicHookInfo`](https://doc.rust-lang.org/stable/std/panic/struct.PanicHookInfo.html)
+- [`PanicInfo::message`](https://doc.rust-lang.org/stable/core/panic/struct.PanicInfo.html#method.message)
+- [`PanicMessage`](https://doc.rust-lang.org/stable/core/panic/struct.PanicMessage.html)
+
+These APIs are now stable in const contexts:
+
+- [`char::from_u32_unchecked`](https://doc.rust-lang.org/stable/core/char/fn.from_u32_unchecked.html) (function)
+- [`char::from_u32_unchecked`](https://doc.rust-lang.org/stable/core/primitive.char.html#method.from_u32_unchecked) (method)
+- [`CStr::count_bytes`](https://doc.rust-lang.org/stable/core/ffi/c_str/struct.CStr.html#method.count_bytes)
+- [`CStr::from_ptr`](https://doc.rust-lang.org/stable/core/ffi/c_str/struct.CStr.html#method.from_ptr)
+
+### Compatibility notes
+
+#### Split panic hook and panic handler arguments
+
+We have renamed [`std::panic::PanicInfo`] to [`std::panic::PanicHookInfo`]. The old
+name will continue to work as an alias, but will result in a deprecation
+warning starting in Rust 1.82.0.
+
+`core::panic::PanicInfo` will remain unchanged, however, as this is now a
+*different type*.  cuviper marked this conversation as resolved.
+
+ The reason is that these types have different roles:
+`std::panic::PanicHookInfo` is the argument to the [panic hook](https://doc.rust-lang.org/stable/std/panic/fn.set_hook.html) in std
+context (where panics can have an arbitrary payload), while
+`core::panic::PanicInfo` is the argument to the
+[`#[panic_handler]`](https://doc.rust-lang.org/nomicon/panic-handler.html) in
+`#![no_std]` context (where panics always carry a formatted *message*). Separating
+these types allows us to add more useful methods to these types, such as
+[`std::panic::PanicHookInfo::payload_as_str()`]() and
+[`core::panic::PanicInfo::message()`](https://doc.rust-lang.org/stable/core/panic/struct.PanicInfo.html#method.message).
+
+[`std::panic::PanicInfo`]: https://doc.rust-lang.org/stable/std/panic/type.PanicInfo.html
+[`std::panic::PanicHookInfo`]: https://doc.rust-lang.org/stable/std/panic/type.PanicHookInfo.html
+
+#### Abort on uncaught panics in `extern "C"` functions
+
+This completes the transition started in [1.71](https://blog.rust-lang.org/2023/07/13/Rust-1.71.0.html#c-unwind-abi),
+which added dedicated `"C-unwind"` (amongst other `-unwind` variants) ABIs for
+when unwinding across the ABI boundary is expected. As of 1.81, the non-unwind
+ABIs (e.g., `"C"`) will now abort on uncaught unwinds, closing the longstanding soundess problem.
+
+Programs relying on unwinding should transition to using `-unwind` suffixed ABI
+variants.
+
+TODO: Check on status of https://github.com/rust-lang/rust/issues/123231
+
+#### WASI target naming changed
+
+Usage of the `wasm32-wasi` target will now issue a compiler warning and request
+users switch to the `wasm32-wasip1` target instead. Both targets are the same,
+`wasm32-wasi` is only being renamed, and this [change to the WASI target](https://blog.rust-lang.org/2024/04/09/updates-to-rusts-wasi-targets.html)
+is being done to enable removing `wasm32-wasi` in January 2025.
+
+### Other changes
+
+Check out everything that changed in [Rust](https://github.com/rust-lang/rust/releases/tag/1.81.0), [Cargo](https://github.com/rust-lang/cargo/blob/master/CHANGELOG.md#cargo-181-2024-09-05), and [Clippy](https://github.com/rust-lang/rust-clippy/blob/master/CHANGELOG.md#rust-181).
+
+## Contributors to 1.81.0
+
+Many people came together to create Rust 1.81.0. We couldn't have done it without all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.81.0/)