Announcing Rust 1.81.0

1.81 stabilizes the Error trait in core, allowing usage of the trait in #![no_std] libraries. This primarily enables the wider Rust ecosystem to standardize on the same Error trait, regardless of what environments the library targets.

Both the stable and unstable sort implementations in the standard library have been updated to new algorithms, improving their runtime performance and compilation time.

Additionally, both of the new sort algorithms try to detect incorrect implementations of Ord that prevent them from being able to produce a meaningfully sorted result, and will now panic on such cases rather than returning effectively randomly arranged data. Users encountering these panics should audit their ordering implementations to ensure they satisfy the requirements documented in PartialOrd and Ord.

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, 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.

Clippy also has two lints to enforce the usage of this feature and help with migrating existing attributes:

• clippy::allow_attributes to restrict allow attributes in favor of #[expect] or to migrate #[allow] attributes to #[expect]
• clippy::allow_attributes_without_reason To require a reason for #[allow] attributes

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 1.81, they can be informed directly in the compiler message:

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")]
  |         ^^^^^^^^^^^^^^^^^^^^^^^^