Language¶

• Don’t make statement nonterminals match pattern nonterminals

• Patterns matching empty types can now be omitted in common cases

• Enforce supertrait outlives obligations when using trait impls

• addr_of(_mut)! macros and the newly stabilized &raw (const|mut) are now safe to use with all static items

• size_of_val_raw: for length 0 this is safe to call

• Reorder trait bound modifiers after for<...> binder in trait bounds

• Stabilize + use<'lt> opaque type precise capturing (RFC 3617)

• Stabilize &raw const and &raw mut operators (RFC 2582)

• Stabilize unsafe extern blocks (RFC 3484)

• Stabilize nested field access in offset_of!

• Do not require T to be live when dropping [T; 0]

• Stabilize const operands in inline assembly

• Stabilize floating-point arithmetic in const fn

• Stabilize explicit opt-in to unsafe attributes

• Document NaN bit patterns guarantees

Compiler¶

• Promote riscv64gc-unknown-linux-musl to tier 2

• Promote Mac Catalyst targets aarch64-apple-ios-macabi and x86_64-apple-ios-macabi to Tier 2, and ship them with rustup

• Add tier 3 NuttX based targets for RISC-V and ARM

• Add tier 3 powerpc-unknown-linux-muslspe target

• Improved diagnostics to explain why a pattern is unreachable

• The compiler now triggers the unreachable code warning properly for async functions that don’t return/are -> !

• Promote aarch64-apple-darwin to Tier 1

• Add Trusty OS target aarch64-unknown-trusty and armv7-unknown-trusty as tier 3 targets

• Promote wasm32-wasip2 to Tier 2.

Libraries¶

• Generalize {Rc,Arc}::make_mut() to Path, OsStr, and CStr.

Stabilized APIs¶

• std::thread::Builder::spawn_unchecked

• std::str::CharIndices::offset

• std::option::Option::is_none_or

• [T]::is_sorted

• [T]::is_sorted_by

• [T]::is_sorted_by_key

• Iterator::is_sorted

• Iterator::is_sorted_by

• Iterator::is_sorted_by_key

• std::future::Ready::into_inner

• std::iter::repeat_n

• impl<T: Clone> DoubleEndedIterator for Take<Repeat<T>>

• impl<T: Clone> ExactSizeIterator for Take<Repeat<T>>

• impl<T: Clone> ExactSizeIterator for Take<RepeatWith<T>>

• impl Default for std::collections::binary_heap::Iter

• impl Default for std::collections::btree_map::RangeMut

• impl Default for std::collections::btree_map::ValuesMut

• impl Default for std::collections::vec_deque::Iter

• impl Default for std::collections::vec_deque::IterMut

• Rc<T>::new_uninit

• Rc<MaybeUninit<T>>::assume_init

• Rc<[T]>::new_uninit_slice

• Rc<[MaybeUninit<T>]>::assume_init

• Arc<T>::new_uninit

• Arc<MaybeUninit<T>>::assume_init

• Arc<[T]>::new_uninit_slice

• Arc<[MaybeUninit<T>]>::assume_init

• Box<T>::new_uninit

• Box<MaybeUninit<T>>::assume_init

• Box<[T]>::new_uninit_slice

• Box<[MaybeUninit<T>]>::assume_init

• core::arch::x86_64::_bextri_u64

• core::arch::x86_64::_bextri_u32

• core::arch::x86::_mm_broadcastsi128_si256

• core::arch::x86::_mm256_stream_load_si256

• core::arch::x86::_tzcnt_u16

• core::arch::x86::_mm_extracti_si64

• core::arch::x86::_mm_inserti_si64

• core::arch::x86::_mm_storeu_si16

• core::arch::x86::_mm_storeu_si32

• core::arch::x86::_mm_storeu_si64

• core::arch::x86::_mm_loadu_si16

• core::arch::x86::_mm_loadu_si32

• core::arch::wasm32::u8x16_relaxed_swizzle

• core::arch::wasm32::i8x16_relaxed_swizzle

• core::arch::wasm32::i32x4_relaxed_trunc_f32x4

• core::arch::wasm32::u32x4_relaxed_trunc_f32x4

• core::arch::wasm32::i32x4_relaxed_trunc_f64x2_zero

• core::arch::wasm32::u32x4_relaxed_trunc_f64x2_zero

• core::arch::wasm32::f32x4_relaxed_madd

• core::arch::wasm32::f32x4_relaxed_nmadd

• core::arch::wasm32::f64x2_relaxed_madd

• core::arch::wasm32::f64x2_relaxed_nmadd

• core::arch::wasm32::i8x16_relaxed_laneselect

• core::arch::wasm32::u8x16_relaxed_laneselect

• core::arch::wasm32::i16x8_relaxed_laneselect

• core::arch::wasm32::u16x8_relaxed_laneselect

• core::arch::wasm32::i32x4_relaxed_laneselect

• core::arch::wasm32::u32x4_relaxed_laneselect

• core::arch::wasm32::i64x2_relaxed_laneselect

• core::arch::wasm32::u64x2_relaxed_laneselect

• core::arch::wasm32::f32x4_relaxed_min

• core::arch::wasm32::f32x4_relaxed_max

• core::arch::wasm32::f64x2_relaxed_min

• core::arch::wasm32::f64x2_relaxed_max

• core::arch::wasm32::i16x8_relaxed_q15mulr

• core::arch::wasm32::u16x8_relaxed_q15mulr

• core::arch::wasm32::i16x8_relaxed_dot_i8x16_i7x16

• core::arch::wasm32::u16x8_relaxed_dot_i8x16_i7x16

• core::arch::wasm32::i32x4_relaxed_dot_i8x16_i7x16_add

• core::arch::wasm32::u32x4_relaxed_dot_i8x16_i7x16_add

These APIs are now stable in const contexts:

• std::task::Waker::from_raw

• std::task::Context::from_waker

• std::task::Context::waker

• {integer}::from_str_radix

• std::num::ParseIntError::kind

Cargo¶

• feat: Add info cargo subcommand

Compatibility Notes¶

• We now disallow setting some built-in cfgs via the command-line with the newly added explicit_builtin_cfgs_in_flags lint in order to prevent incoherent state, eg. windows cfg active but target is Linux based. The appropriate rustc flag should be used instead.

• The standard library has a new implementation of binary_search which is significantly improves performance (#128254). However when a sorted slice has multiple values which compare equal, the new implementation may select a different value among the equal ones than the old implementation.

• illumos/Solaris now sets MSG_NOSIGNAL when writing to sockets. This avoids killing the process with SIGPIPE when writing to a closed socket, which matches the existing behavior on other UNIX targets.

• Removes a problematic hack that always passed the –whole-archive linker flag for tests, which may cause linker errors for code accidentally relying on it.

• The WebAssembly target features multivalue and reference-types are now both enabled by default. These two features both have subtle changes implied for generated WebAssembly binaries. For the multivalue feature, WebAssembly target support has changed when upgrading to LLVM 19. Support for generating functions with multiple returns no longer works and -Ctarget-feature=+multivalue has a different meaning than it did in LLVM 18 and prior. There is no longer any supported means to generate a module that has a function with multiple returns in WebAssembly from Rust source code. For the reference-types feature the encoding of immediates in the call_indirect, a commonly used instruction by the WebAssembly backend, has changed. Validators and parsers which don’t understand the reference-types proposal will no longer accept modules produced by LLVM due to this change in encoding of immediates. Additionally these features being enabled are encoded in the target_features custom section and may affect downstream tooling such as wasm-opt consuming the module. Generating a WebAssembly module that disables default features requires -Zbuild-std support from Cargo and more information can be found at rust-lang/rust#128511.

• Rust now raises unsafety errors for union patterns in parameter-position

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 19

Language¶

• Stabilize &mut, *mut, &Cell, and *const Cell in const.

• Allow creating references to statics in const initializers.

• Implement raw lifetimes and labels ('r#ident).

• Define behavior when atomic and non-atomic reads race.

• Non-exhaustive structs may now be empty.

• Disallow implicit coercions from places of type !

• const extern functions can now be defined for other calling conventions.

• Stabilize expr_2021 macro fragment specifier in all editions.

• The non_local_definitions lint now fires on less code and warns by default.

Compiler¶

• Deprecate unsound -Csoft-float flag.

• Add many new tier 3 targets:

  • aarch64_unknown_nto_qnx700

  • arm64e-apple-tvos

  • armv7-rtems-eabihf

  • loongarch64-unknown-linux-ohos

  • riscv32-wrs-vxworks and riscv64-wrs-vxworks

  • riscv32{e|em|emc}-unknown-none-elf

  • x86_64-unknown-hurd-gnu

  • x86_64-unknown-trusty

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

Libraries¶

• Implement PartialEq for ExitCode.

• Document that catch_unwind can deal with foreign exceptions without UB, although the exact behavior is unspecified.

• Implement Default for HashMap/HashSet iterators that don’t already have it.

• Bump Unicode to version 16.0.0.

• Change documentation of ptr::add/sub to not claim equivalence with offset.

Stabilized APIs¶

• BufRead::skip_until

• ControlFlow::break_value

• ControlFlow::continue_value

• ControlFlow::map_break

• ControlFlow::map_continue

• DebugList::finish_non_exhaustive

• DebugMap::finish_non_exhaustive

• DebugSet::finish_non_exhaustive

• DebugTuple::finish_non_exhaustive

• ErrorKind::ArgumentListTooLong

• ErrorKind::Deadlock

• ErrorKind::DirectoryNotEmpty

• ErrorKind::ExecutableFileBusy

• ErrorKind::FileTooLarge

• ErrorKind::HostUnreachable

• ErrorKind::IsADirectory

• ErrorKind::NetworkDown

• ErrorKind::NetworkUnreachable

• ErrorKind::NotADirectory

• ErrorKind::NotSeekable

• ErrorKind::ReadOnlyFilesystem

• ErrorKind::ResourceBusy

• ErrorKind::StaleNetworkFileHandle

• ErrorKind::StorageFull

• ErrorKind::TooManyLinks

• Option::get_or_insert_default

• Waker::data

• Waker::new

• Waker::vtable

• char::MIN

• hash_map::Entry::insert_entry

• hash_map::VacantEntry::insert_entry

These APIs are now stable in const contexts:

• Cell::into_inner

• Duration::as_secs_f32

• Duration::as_secs_f64

• Duration::div_duration_f32

• Duration::div_duration_f64

• MaybeUninit::as_mut_ptr

• NonNull::as_mut

• NonNull::copy_from

• NonNull::copy_from_nonoverlapping

• NonNull::copy_to

• NonNull::copy_to_nonoverlapping

• NonNull::slice_from_raw_parts

• NonNull::write

• NonNull::write_bytes

• NonNull::write_unaligned

• OnceCell::into_inner

• Option::as_mut

• Option::expect

• Option::replace

• Option::take

• Option::unwrap

• Option::unwrap_unchecked

• Option::<&_>::copied

• Option::<&mut _>::copied

• Option::<Option<_>>::flatten

• Option::<Result<_, _>>::transpose

• RefCell::into_inner

• Result::as_mut

• Result::<&_, _>::copied

• Result::<&mut _, _>::copied

• Result::<Option<_>, _>::transpose

• UnsafeCell::get_mut

• UnsafeCell::into_inner

• array::from_mut

• char::encode_utf8

• {float}::classify

• {float}::is_finite

• {float}::is_infinite

• {float}::is_nan

• {float}::is_normal

• {float}::is_sign_negative

• {float}::is_sign_positive

• {float}::is_subnormal

• {float}::from_bits

• {float}::from_be_bytes

• {float}::from_le_bytes

• {float}::from_ne_bytes

• {float}::to_bits

• {float}::to_be_bytes

• {float}::to_le_bytes

• {float}::to_ne_bytes

• mem::replace

• ptr::replace

• ptr::slice_from_raw_parts_mut

• ptr::write

• ptr::write_unaligned

• <*const _>::copy_to

• <*const _>::copy_to_nonoverlapping

• <*mut _>::copy_from

• <*mut _>::copy_from_nonoverlapping

• <*mut _>::copy_to

• <*mut _>::copy_to_nonoverlapping

• <*mut _>::write

• <*mut _>::write_bytes

• <*mut _>::write_unaligned

• slice::from_mut

• slice::from_raw_parts_mut

• <[_]>::first_mut

• <[_]>::last_mut

• <[_]>::first_chunk_mut

• <[_]>::last_chunk_mut

• <[_]>::split_at_mut

• <[_]>::split_at_mut_checked

• <[_]>::split_at_mut_unchecked

• <[_]>::split_first_mut

• <[_]>::split_last_mut

• <[_]>::split_first_chunk_mut

• <[_]>::split_last_chunk_mut

• str::as_bytes_mut

• str::as_mut_ptr

• str::from_utf8_unchecked_mut

Cargo¶

• Introduced a new CARGO_MANIFEST_PATH environment variable, similar to CARGO_MANIFEST_DIR but pointing directly to the manifest file.

• Added package.autolib to the manifest, allowing [lib] auto-discovery to be disabled.

• Declare support level for each crate in Cargo’s Charter / crate docs.

• Declare new Intentional Artifacts as ‘small’ changes.

Rustdoc¶

• The sidebar / hamburger menu table of contents now includes the # headers from the main item’s doc comment. This is similar to a third-party feature provided by the rustdoc-search-enhancements browser extension.

Compatibility Notes¶

• Warn against function pointers using unsupported ABI strings.

• Check well-formedness of the source type’s signature in fn pointer casts. This partly closes a soundness hole that comes when casting a function item to function pointer

• Use equality instead of subtyping when resolving type dependent paths.

• Linking on macOS now correctly includes Rust’s default deployment target. Due to a linker bug, you might have to pass MACOSX_DEPLOYMENT_TARGET or fix your #[link] attributes to point to the correct frameworks. See https://github.com/rust-lang/rust/pull/129369.

• Rust will now correctly raise an error for repr(Rust) written on non-struct/enum/union items, since it previous did not have any effect.

• The future incompatibility lint deprecated_cfg_attr_crate_type_name has been made into a hard error. It was used to deny usage of #![crate_type] and #![crate_name] attributes in #![cfg_attr], which required a hack in the compiler to be able to change the used crate type and crate name after cfg expansion. Users can use --crate-type instead of #![cfg_attr(..., crate_type = "...")] and --crate-name instead of #![cfg_attr(..., crate_name = "...")] when running rustc/cargo rustc on the command line. Use of those two attributes outside of #![cfg_attr] continue to be fully supported.

• Until now, paths into the sysroot were always prefixed with /rustc/$hash in diagnostics, codegen, backtrace, e.g.

  thread 'main' panicked at 'hello world', map-panic.rs:2:50
  stack backtrace:
     0: std::panicking::begin_panic
               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/panicking.rs:616:12
     1: map_panic::main::{{closure}}
               at ./map-panic.rs:2:50
     2: core::option::Option<T>::map
               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/option.rs:929:29
     3: map_panic::main
               at ./map-panic.rs:2:30
     4: core::ops::function::FnOnce::call_once
               at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/ops/function.rs:248:5
  note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
  

  RFC 3127 said

  We want to change this behaviour such that, when rust-src source files can be discovered, the virtual path is discarded and therefore the local path will be embedded, unless there is a --remap-path-prefix that causes this local path to be remapped in the usual way.

  #129687 implements this behaviour, when rust-src is present at compile time, rustc replaces /rustc/$hash with a real path into the local rust-src component with best effort. To sanitize this, users must explicitly supply --remap-path-prefix=<path to rust-src>=foo or not have the rust-src component installed.

• The allow-by-default missing_docs lint used to disable itself when invoked through rustc --test/cargo test, resulting in #[expect(missing_docs)] emitting false positives due to the expectation being wrongly unfulfilled. This behavior has now been removed, which allows #[expect(missing_docs)] to be fulfilled in all scenarios, but will also report new missing_docs diagnostics for publicly reachable #[cfg(test)] items, integration test crate-level documentation, and publicly reachable items in integration tests.

• The armv8r-none-eabihf target now uses the Armv8-R required set of floating-point features.

• Fix a soundness bug where rustc wouldn’t detect unconstrained higher-ranked lifetimes in a dyn Trait’s associated types that occur due to supertraits.

• Update the minimum external LLVM version to 18.

• Remove aarch64-fuchsia and x86_64-fuchsia target aliases in favor of aarch64-unknown-fuchsia and x86_64-unknown-fuchsia respectively.

• The ABI-level exception class of a Rust panic is now encoded with native-endian bytes, so it is legible in hex dumps.

• Visual Studio 2013 is no longer supported for MSVC targets.

• The sysroot no longer contains the std dynamic library in its top-level lib/ dir.