Language¶

• Reveal opaque types within the defining body for exhaustiveness checking.

• Stabilize C-string literals.

• Stabilize THIR unsafeck.

• Add lint static_mut_refs to warn on references to mutable statics.

• Support async recursive calls (as long as they have indirection).

• Undeprecate lint unstable_features and make use of it in the compiler.

• Make inductive cycles in coherence ambiguous always.

• Get rid of type-driven traversal in const-eval interning, only as a future compatiblity lint for now.

• Deny braced macro invocations in let-else.

Compiler¶

• Include lint soft_unstable in future breakage reports.

• Make i128 and u128 16-byte aligned on x86-based targets.

• Use --verbose in diagnostic output.

• Improve spacing between printed tokens.

• Merge the unused_tuple_struct_fields lint into dead_code.

• Error on incorrect implied bounds in well-formedness check, with a temporary exception for Bevy.

• Fix coverage instrumentation/reports for non-ASCII source code.

• Fix fn/const items implied bounds and well-formedness check.

• Promote riscv32{im|imafc}-unknown-none-elf targets to tier 2.

• Add several new tier 3 targets:

  • aarch64-unknown-illumos

  • hexagon-unknown-none-elf

  • riscv32imafc-esp-espidf

  • riscv32im-risc0-zkvm-elf

Refer to Rust’s platform support page for more information on Rust’s tiered platform support.

Libraries¶

• Implement From<&[T; N]> for Cow<[T]>.

• Remove special-case handling of vec.split_off(0).

Stabilized APIs¶

• array::each_ref

• array::each_mut

• core::net

• f32::round_ties_even

• f64::round_ties_even

• mem::offset_of!

• slice::first_chunk

• slice::first_chunk_mut

• slice::split_first_chunk

• slice::split_first_chunk_mut

• slice::last_chunk

• slice::last_chunk_mut

• slice::split_last_chunk

• slice::split_last_chunk_mut

• slice::chunk_by

• slice::chunk_by_mut

• Bound::map

• File::create_new

• Mutex::clear_poison

• RwLock::clear_poison

Cargo¶

• Extend the build directive syntax with cargo::.

• Stabilize metadata id format as PackageIDSpec.

• Pull out cargo-util-schemas as a crate.

• Strip all debuginfo when debuginfo is not requested.

• Inherit jobserver from env for all kinds of runners.

• Deprecate rustc plugin support in cargo.

Rustdoc¶

• Allows links in markdown headings.

• Search for tuples and unit by type with ().

• Clean up the source sidebar’s hide button.

• Prevent JS injection from localStorage.

Misc¶

• Recommend version-sorting for all sorting in style guide.

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 more weirdness to weird-exprs.rs.

Language¶

• Stabilize #[cfg(target_abi = ...)]

• Stabilize the #[diagnostic] namespace and #[diagnostic::on_unimplemented] attribute

• Make async-fn-in-trait implementable with concrete signatures

• Make matching on NaN a hard error, and remove the rest of illegal_floating_point_literal_pattern

• static mut: allow mutable reference to arbitrary types, not just slices and arrays

• Extend invalid_reference_casting to include references casting to bigger memory layout

• Add non_contiguous_range_endpoints lint for singleton gaps after exclusive ranges

• Add wasm_c_abi lint for use of older wasm-bindgen versions This lint currently only works when using Cargo.

• Update indirect_structural_match and pointer_structural_match lints to match RFC

• Make non-PartialEq-typed consts as patterns a hard error

• Split refining_impl_trait lint into _reachable, _internal variants

• Remove unnecessary type inference when using associated types inside of higher ranked where-bounds

• Weaken eager detection of cyclic types during type inference

• trait Trait: Auto {}: allow upcasting from dyn Trait to dyn Trait + Auto

Compiler¶

• Made INVALID_DOC_ATTRIBUTES lint deny by default

• Increase accuracy of redundant use checking

• Suggest moving definition if non-found macro_rules! is defined later

• Lower transmutes from int to pointer type as gep on null

Target changes:

• Windows tier 1 targets now require at least Windows 10

  • Enable CMPXCHG16B, SSE3, SAHF/LAHF and 128-bit Atomics in tier 1 Windows

• Add wasm32-wasip1 tier 2 (without host tools) target

• Add wasm32-wasip2 tier 3 target

• Rename wasm32-wasi-preview1-threads to wasm32-wasip1-threads

• Add arm64ec-pc-windows-msvc tier 3 target

• Add armv8r-none-eabihf tier 3 target for the Cortex-R52

• Add loongarch64-unknown-linux-musl tier 3 target

Refer to Rust’s platform support page for more information on Rust’s tiered platform support.

Libraries¶

• Bump Unicode to version 15.1.0, regenerate tables

• Make align_offset, align_to well-behaved in all cases

• PartialEq, PartialOrd: document expectations for transitive chains

• Optimize away poison guards when std is built with panic=abort

• Replace pthread RwLock with custom implementation

• Implement unwind safety for Condvar on all platforms

• Add ASCII fast-path for char::is_grapheme_extended

Stabilized APIs¶

• impl Read for &Stdin

• Accept non 'static lifetimes for several std::error::Error related implementations

• Make impl<Fd: AsFd> impl take ?Sized

• impl From<TryReserveError> for io::Error

These APIs are now stable in const contexts:

• Barrier::new()

Cargo¶

• Stabilize lockfile v4

• Respect rust-version when generating lockfile

• Control --charset via auto-detecting config value

• Support target.<triple>.rustdocflags officially

• Stabilize global cache data tracking

Misc¶

• rustdoc: add --test-builder-wrapper arg to support wrappers such as RUSTC_WRAPPER when building doctests

Compatibility Notes¶

• Many unsafe precondition checks now run for user code with debug assertions enabled This change helps users catch undefined behavior in their code, though the details of how much is checked are generally not stable.

• riscv only supports split_debuginfo=off for now

• Consistently check bounds on hidden types of impl Trait

• Change equality of higher ranked types to not rely on subtyping

• When called, additionally check bounds on normalized function return type

• Expand coverage for arithmetic_overflow lint

• Fix detection of potential interior mutability in const initializers This code was accidentally accepted. The fix can break generic code that borrows a value of unknown type, as there is currently no way to declare “this type has no interior mutability”. In the future, stabilizing the Freeze trait will allow proper support for such code.

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.

• Update to LLVM 18

• Build rustc with 1CGU on x86_64-pc-windows-msvc

• Build rustc with 1CGU on x86_64-apple-darwin

• Introduce run-make V2 infrastructure, a run_make_support library and port over 2 tests as example

• Windows: Implement condvar, mutex and rwlock using futex

Language¶

• Stabilize inline const {} expressions.

• Prevent opaque types being instantiated twice with different regions within the same function.

• Stabilize WebAssembly target features that are in phase 4 and 5.

• Add the redundant_lifetimes lint to detect lifetimes which are semantically redundant.

• Stabilize the unnameable_types lint for public types that can’t be named.

• Enable debuginfo in macros, and stabilize -C collapse-macro-debuginfo and #[collapse_debuginfo].

• Propagate temporary lifetime extension into if and match expressions.

• Restrict promotion of const fn calls.

• Warn against refining impls of crate-private traits with refining_impl_trait lint.

• Stabilize associated type bounds (RFC 2289).

• Stabilize importing main from other modules or crates.

• Check return types of function types for well-formedness

• Rework impl Trait lifetime inference

• Change inductive trait solver cycles to be ambiguous

Compiler¶

• Define -C strip to only affect binaries, not artifacts like .pdb.

• Stabilize -Crelro-level for controlling runtime link hardening.

• Stabilize checking of cfg names and values at compile-time with --check-cfg. Note that this only stabilizes the compiler part, the Cargo part is still unstable in this release.

• Add aarch64-apple-visionos and aarch64-apple-visionos-sim tier 3 targets.

• Add riscv32ima-unknown-none-elf tier 3 target.

• Promote several Windows targets to tier 2: aarch64-pc-windows-gnullvm, i686-pc-windows-gnullvm, and x86_64-pc-windows-gnullvm.

Refer to Rust’s platform support page for more information on Rust’s tiered platform support.

Libraries¶

• Implement FromIterator for (impl Default + Extend, impl Default + Extend).

• Implement {Div,Rem}Assign<NonZero<X>> on X.

• Document overrides of clone_from() in core/std.

• Link MSVC default lib in core.

• Caution against using transmute between pointers and integers.

• Enable frame pointers for the standard library.

Stabilized APIs¶

• {integer}::unchecked_add

• {integer}::unchecked_mul

• {integer}::unchecked_sub

• <[T]>::split_at_unchecked

• <[T]>::split_at_mut_unchecked

• <[u8]>::utf8_chunks

• str::Utf8Chunks

• str::Utf8Chunk

• <*const T>::is_aligned

• <*mut T>::is_aligned

• NonNull::is_aligned

• <*const [T]>::len

• <*mut [T]>::len

• <*const [T]>::is_empty

• <*mut [T]>::is_empty

• NonNull::<[T]>::is_empty

• CStr::count_bytes

• io::Error::downcast

• num::NonZero<T>

• path::absolute

• proc_macro::Literal::byte_character

• proc_macro::Literal::c_string

These APIs are now stable in const contexts:

• Atomic*::into_inner

• io::Cursor::new

• io::Cursor::get_ref

• io::Cursor::position

• io::empty

• io::repeat

• io::sink

• panic::Location::caller

• panic::Location::file

• panic::Location::line

• panic::Location::column

Cargo¶

• Prevent dashes in lib.name, always normalizing to _.

• Stabilize MSRV-aware version requirement selection in cargo add.

• Switch to using gitoxide by default for listing files.

Rustdoc¶

• Always display stability version even if it’s the same as the containing item.

• Show a single search result for items with multiple paths.

• Support typing / in docs to begin a search.

Misc¶

Compatibility Notes¶

• Update the minimum external LLVM to 17.

• RustcEncodable and RustcDecodable are soft-destabilized, to be removed from the prelude in next edition.

• The wasm_c_abi future-incompatibility lint will warn about use of the non-spec-compliant C ABI. Use wasm-bindgen v0.2.88 to generate forward-compatible bindings.

• Check return types of function types for well-formedness