Rust 1.81.0

Language

• Abort on uncaught panics in extern "C" functions.
• Fix ambiguous cases of multiple & in elided self lifetimes.
• Stabilize #[expect] for lints (RFC 2383), like #[allow] with a warning if the lint is not fulfilled.
• Change method resolution to constrain hidden types instead of rejecting method candidates.
• Bump elided_lifetimes_in_associated_constant to deny.
• offset_from: always allow pointers to point to the same address.
• Allow constraining opaque types during subtyping in the trait system.
• Allow constraining opaque types during various unsizing casts.
• Deny keyword lifetimes pre-expansion.

Compiler

• Make casts of pointers to trait objects stricter.
• Check alias args for well-formedness even if they have escaping bound vars.
• Deprecate no-op codegen option -Cinline-threshold=....
• Re-implement a type-size based limit.
• Properly account for alignment in transmute size checks.
• Remove the box_pointers lint.
• Ensure the interpreter checks bool/char for validity when they are used in a cast.
• Improve coverage instrumentation for functions containing nested items.
• Target changes:
  • Add Tier 3 no_std Xtensa targets: xtensa-esp32-none-elf, xtensa-esp32s2-none-elf, xtensa-esp32s3-none-elf
  • Add Tier 3 std Xtensa targets: xtensa-esp32-espidf, xtensa-esp32s2-espidf, xtensa-esp32s3-espidf
  • Add Tier 3 i686 Redox OS target: i686-unknown-redox
  • Promote arm64ec-pc-windows-msvc to Tier 2.
  • Promote loongarch64-unknown-linux-musl to Tier 2 with host tools.
  • Enable full tools and profiler for LoongArch Linux targets.
  • Unconditionally warn on usage of wasm32-wasi. (see compatibility note below)
  • Refer to Rust's platform support page for more information on Rust's tiered platform support.

Libraries

• Split core's PanicInfo and std's PanicInfo. (see compatibility note below)
• Generalize {Rc,Arc}::make_mut() to unsized types.
• Replace sort implementations with stable driftsort and unstable ipnsort. All slice::sort* and slice::select_nth* methods are expected to see significant performance improvements. See the research project for more details.
• Document behavior of create_dir_all with respect to empty paths.
• Fix interleaved output in the default panic hook when multiple threads panic simultaneously.

Stabilized APIs

• core::error
• hint::assert_unchecked
• fs::exists
• AtomicBool::fetch_not
• Duration::abs_diff
• IoSlice::advance
• IoSlice::advance_slices
• IoSliceMut::advance
• IoSliceMut::advance_slices
• PanicHookInfo
• PanicInfo::message
• PanicMessage

These APIs are now stable in const contexts:

• char::from_u32_unchecked (function)
• char::from_u32_unchecked (method)
• CStr::count_bytes
• CStr::from_ptr

Cargo

• Generated .cargo_vcs_info.json is always included, even when --allow-dirty is passed.
• Disallow package.license-file and package.readme pointing to non-existent files during packaging.
• Disallow passing --release/--debug flag along with the --profile flag.
• Remove lib.plugin key support in Cargo.toml. Rust plugin support has been deprecated for four years and was removed in 1.75.0.

Compatibility Notes

• 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 is being done to enable removing wasm32-wasi in January 2025.

• 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.

  The reason is that these types have different roles: std::panic::PanicHookInfo is the argument to the panic hook in std context (where panics can have an arbitrary payload), while core::panic::PanicInfo is the argument to the #[panic_handler] 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().

• The new sort implementations may panic if a type's implementation of Ord (or the given comparison function) does not implement a total order as the trait requires. Ord's supertraits (PartialOrd, Eq, and PartialEq) must also be consistent. The previous implementations would not "notice" any problem, but the new implementations have a good chance of detecting inconsistencies, throwing a panic rather than returning knowingly unsorted data.

• In very rare cases, a change in the internal evaluation order of the trait solver may result in new fatal overflow errors.

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.

• Add a Rust-for Linux auto CI job to check kernel builds.