Language¶

• Document MaybeUninit representation and validity

• Allow &raw [mut | const] for union field in safe code

• Prefer item bounds of associated types over where-bounds for auto-traits and Sized

• Do not materialize X in [X; 0] when X is unsizing a const

• Support combining #[track_caller] and #[no_mangle] (requires every declaration specifying #[track_caller] as well)

• Make never type lints never_type_fallback_flowing_into_unsafe and dependency_on_unit_never_type_fallback deny-by-default

• Allow specifying multiple bounds for same associated item, except in trait objects

• Slightly strengthen higher-ranked region handling in coherence

• The unused_must_use lint no longer warns on Result<(), Uninhabited> (for instance, Result<(), !>), or ControlFlow<Uninhabited, ()>. This avoids having to check for an error that can never happen.

Compiler¶

• Make mips64el-unknown-linux-muslabi64 link dynamically

• Remove current code for embedding command-line args in PDB Command-line information is typically not needed by debugging tools, and the removed code was causing problems for incremental builds even on targets that don’t use PDB debuginfo.

Libraries¶

• Specialize Iterator::eq{_by} for TrustedLen iterators

• Simplify Extend for tuples

• Added details to Debug for EncodeWide.

• iter::Repeat::last and count will now panic, rather than looping infinitely.

Stabilized APIs¶

• NonZero<u{N}>::div_ceil

• Location::file_as_c_str

• RwLockWriteGuard::downgrade

• Box::new_zeroed

• Box::new_zeroed_slice

• Rc::new_zeroed

• Rc::new_zeroed_slice

• Arc::new_zeroed

• Arc::new_zeroed_slice

• btree_map::Entry::insert_entry

• btree_map::VacantEntry::insert_entry

• impl Extend<proc_macro::Group> for proc_macro::TokenStream

• impl Extend<proc_macro::Literal> for proc_macro::TokenStream

• impl Extend<proc_macro::Punct> for proc_macro::TokenStream

• impl Extend<proc_macro::Ident> for proc_macro::TokenStream

These previously stable APIs are now stable in const contexts:

• <[_]>::rotate_left

• <[_]>::rotate_right

Cargo¶

• Added a new chapter to the Cargo book, “Optimizing Build Performance”.

Rustdoc¶

• If a trait item appears in rustdoc search, hide the corresponding impl items. Previously a search for “last” would show both Iterator::last as well as impl methods like std::vec::IntoIter::last. Now these impl methods will be hidden, freeing up space for inherent methods like BTreeSet::last.

• Relax rules for identifiers in search. Previously you could only search for identifiers that were valid in rust code, now searches only need to be valid as part of an identifier. For example, you can now perform a search that starts with a digit.

Compatibility Notes¶

• Fix backtraces with -C panic=abort on Linux by generating unwind tables by default. Build with -C force-unwind-tables=no to keep omitting unwind tables.

• As part of the larger effort refactoring compiler built-in attributes and their diagnostics, the future-compatibility lint invalid_macro_export_arguments is upgraded to deny-by-default and will be reported in dependencies too.

• Update the minimum external LLVM to 20

• Prevent downstream impl DerefMut for Pin<LocalType>

• Don’t apply temporary lifetime extension rules to the arguments of non-extended pin! and formatting macros

Language¶

• Stabilize several s390x vector-related target features and the is_s390x_feature_detected! macro

• Stabilize declaration of C-style variadic functions for the system ABI

• Emit error when using some keyword as a cfg predicate

• Stabilize asm_cfg

• During const-evaluation, support copying pointers byte-by-byte

• LUB coercions now correctly handle function item types, and functions with differing safeties

• Allow const items that contain mutable references to static (which is very unsafe, but not always UB)

• Add warn-by-default const_item_interior_mutations lint to warn against calls which mutate interior mutable const items

• Add warn-by-default function_casts_as_integer lint

Compiler¶

• Stabilize -Cjump-tables=bool. The flag was previously called -Zno-jump-tables.

Platform Support¶

• Promote riscv64a23-unknown-linux-gnu to Tier 2 (without host tools)

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

Libraries¶

• Stop internally using specialization on the Copy trait as it is unsound in the presence of lifetime dependent Copy implementations. This may result in some performance regressions as some standard library APIs may now call Clone::clone instead of performing bitwise copies

• Allow the global allocator to use thread-local storage and std::thread::current()

• Make BTree::append not update existing keys when appending an entry which already exists

• Don’t require T: RefUnwindSafe for vec::IntoIter<T>: UnwindSafe

Stabilized APIs¶

• <[MaybeUninit<T>]>::assume_init_drop

• <[MaybeUninit<T>]>::assume_init_ref

• <[MaybeUninit<T>]>::assume_init_mut

• <[MaybeUninit<T>]>::write_copy_of_slice

• <[MaybeUninit<T>]>::write_clone_of_slice

• String::into_raw_parts

• Vec::into_raw_parts

• <iN>::unchecked_neg

• <iN>::unchecked_shl

• <iN>::unchecked_shr

• <uN>::unchecked_shl

• <uN>::unchecked_shr

• <[T]>::as_array

• <[T]>::as_mut_array

• <*const [T]>::as_array

• <*mut [T]>::as_mut_array

• VecDeque::pop_front_if

• VecDeque::pop_back_if

• Duration::from_nanos_u128

• char::MAX_LEN_UTF8

• char::MAX_LEN_UTF16

• std::fmt::from_fn

• std::fmt::FromFn

Cargo¶

• Enable CARGO_CFG_DEBUG_ASSERTIONS in build scripts based on profile

• In cargo tree, support long forms for --format variables

• Add --workspace to cargo clean

Rustdoc¶

• Remove #![doc(document_private_items)]

• Include attribute and derive macros in search filters for “macros”

• Include extern crates in search filters for import

• Validate usage of crate-level doc attributes. This means if any of html_favicon_url, html_logo_url, html_playground_url, issue_tracker_base_url, or html_no_source either has a missing value, an unexpected value, or a value of the wrong type, rustdoc will emit the deny-by-default lint rustdoc::invalid_doc_attributes.

Compatibility Notes¶

• Introduce pin_v2 into the builtin attributes namespace

• Update bundled musl to 1.2.5

• On Emscripten, the unwinding ABI used when compiling with panic=unwind was changed from the JS exception handling ABI to the wasm exception handling ABI. If linking C/C++ object files with Rust objects, -fwasm-exceptions must be passed to the linker now. On nightly Rust, it is possible to get the old behavior with -Zwasm-emscripten-eh=false -Zbuild-std, but it will be removed in a future release.

• The #[test] attribute, used to define tests, was previously ignored in various places where it had no meaning (e.g on trait methods or types). Putting the #[test] attribute in these places is no longer ignored, and will now result in an error; this may also result in errors when generating rustdoc. Error when test attribute is applied to structs

• Cargo now sets the CARGO_CFG_DEBUG_ASSERTIONS environment variable in more situations. This will cause crates depending on static-init versions 1.0.1 to 1.0.3 to fail compilation with “failed to resolve: use of unresolved module or unlinked crate parking_lot”. See the linked issue for details.

• User written types in the offset_of! macro are now checked to be well formed.

• cargo publish no longer emits .crate files as a final artifact for user access when the build.build-dir config is unset

• Upgrade the deref_nullptr lint from warn-by-default to deny-by-default

• Add future-incompatibility warning for ... function parameters without a pattern outside of extern blocks

• Introduce future-compatibility warning for repr(C) enums whose discriminant values do not fit into a c_int or c_uint

• Introduce future-compatibility warning against ignoring repr(C) types as part of repr(transparent)

Language¶

• Impls and impl items inherit dead_code lint level of the corresponding traits and trait items

• Stabilize additional 29 RISC-V target features including large portions of the RVA22U64 / RVA23U64 profiles

• Add warn-by-default unused_visibilities lint for visibility on const _ declarations

• Update to Unicode 17

• Avoid incorrect lifetime errors for closures

Platform Support¶

• Add riscv64im-unknown-none-elf as a tier 3 target

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

Libraries¶

• Relax T: Ord bound for some BinaryHeap<T> methods.

Stabilized APIs¶

• <[T]>::array_windows

• <[T]>::element_offset

• LazyCell::get

• LazyCell::get_mut

• LazyCell::force_mut

• LazyLock::get

• LazyLock::get_mut

• LazyLock::force_mut

• impl TryFrom<char> for usize

• std::iter::Peekable::next_if_map

• std::iter::Peekable::next_if_map_mut

• x86 avx512fp16 intrinsics (excluding those that depend directly on the unstable f16 type)

• AArch64 NEON fp16 intrinsics (excluding those that depend directly on the unstable f16 type)

• f32::consts::EULER_GAMMA

• f64::consts::EULER_GAMMA

• f32::consts::GOLDEN_RATIO

• f64::consts::GOLDEN_RATIO

These previously stable APIs are now stable in const contexts:

• f32::mul_add

• f64::mul_add

Cargo¶

• Stabilize the config include key. The top-level include config key allows loading additional config files, enabling better organization, sharing, and management of Cargo configurations across projects and environments. docs #16284

• Stabilize the pubtime field in registry index. This records when a crate version was published and enables time-based dependency resolution in the future. Note that crates.io will gradually backfill existing packages when a new version is published. Not all crates have pubtime yet. #16369 #16372

• Cargo now parses TOML v1.1 for manifests and configuration files. Note that using these features in Cargo.toml will raise your development MSRV, but the published manifest remains compatible with older parsers. #16415

• Make CARGO_BIN_EXE_<crate> available at runtime

Compatibility Notes¶

• Forbid freely casting lifetime bounds of dyn-types

• Make closure capturing have consistent and correct behaviour around patterns Some finer details of how precise closure captures get affected by pattern matching have been changed. In some cases, this can cause a non-move closure that was previously capturing an entire variable by move, to now capture only part of that variable by move, and other parts by borrow. This can cause the borrow checker to complain where it previously didn’t, or cause Drop to run at a different point in time.

• Standard library macros are now imported via prelude, not via injected #[macro_use] This will raise an error if macros of the same name are glob imported. For example if a crate defines their own matches macro and then glob imports that, it’s now ambiguous whether the custom or standard library matches is meant and an explicit import of the name is required to resolve the ambiguity. One exception is core::panic and std::panic, if their import is ambiguous a new warning (ambiguous_panic_imports) is raised. This may raise a new warning (ambiguous_panic_imports) on #![no_std] code glob importing the std crate. Both core::panic! and std::panic! are then in scope and which is used is ambiguous.

• Don’t strip shebang in expression-context include!(…)s This can cause previously working includes to no longer compile if they included files which started with a shebang.

• Ambiguous glob reexports are now also visible cross-crate This unifies behavior between local and cross-crate errors on these exports, which may introduce new ambiguity errors.

• Don’t normalize where-clauses before checking well-formedness

• Introduce a future compatibility warning on codegen attributes on body-free trait methods These attributes currently have no effect in this position.

• On Windows std::time::SystemTime::checked_sub_duration will return None for times before the Windows epoch (1/1/1601)

• Lifetime identifiers such as 'a are now NFC normalized.

• Overhaul filename handling for cross-compiler consistency Any paths emitted by compiler now always respect the relative-ness of the paths and --remap-path-prefix given originally. One side-effect of this change is that paths emitted for local crates in Cargo (path dependencies and workspace members) are no longer absolute but relative when emitted as part of a diagnostic in a downstream crate.

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.

• Switch to annotate-snippets for error emission This should preserve mostly the same outputs in rustc error messages.

Language¶

• Stabilize if let guards on match arms

• irrefutable_let_patterns lint no longer lints on let chains

• Support importing path-segment keywords with renaming

• Stabilize inline assembly for PowerPC and PowerPC64

• const-eval: be more consistent in the behavior of padding during typed copies

• Const blocks are no longer evaluated to determine if expressions involving fallible operations can implicitly be constant-promoted.. Expressions whose ability to implicitly be promoted would depend on the result of a const block are no longer implicitly promoted.

• Make operational semantics of pattern matching independent of crate and module

Compiler¶

• Stabilize --remap-path-scope for controlling the scoping of how paths get remapped in the resulting binary

• Apply patches for CVE-2026-6042 and CVE-2026-40200 to vendored musl

Platform Support¶

• Promote powerpc64-unknown-linux-musl to Tier 2 with host tools

• Promote aarch64-apple-tvos to Tier 2

• Promote aarch64-apple-tvos-sim to Tier 2

• Promote aarch64-apple-watchos to Tier 2

• Promote aarch64-apple-watchos-sim to Tier 2

• Promote aarch64-apple-visionos to Tier 2

• Promote aarch64-apple-visionos-sim to Tier 2

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

Libraries¶

• thread::scope: document how join interacts with TLS destructors

• Speed up str::contains on aarch64 targets with neon target feature enabled by default

Stabilized APIs¶

• MaybeUninit<[T; N]>: From<[MaybeUninit<T>; N]>

• MaybeUninit<[T; N]>: AsRef<[MaybeUninit<T>; N]>

• MaybeUninit<[T; N]>: AsRef<[MaybeUninit<T>]>

• MaybeUninit<[T; N]>: AsMut<[MaybeUninit<T>; N]>

• MaybeUninit<[T; N]>: AsMut<[MaybeUninit<T>]>

• [MaybeUninit<T>; N]: From<MaybeUninit<[T; N]>>

• Cell<[T; N]>: AsRef<[Cell<T>; N]>

• Cell<[T; N]>: AsRef<[Cell<T>]>

• Cell<[T]>: AsRef<[Cell<T>]>

• bool: TryFrom<{integer}>

• AtomicPtr::update

• AtomicPtr::try_update

• AtomicBool::update

• AtomicBool::try_update

• AtomicIn::update

• AtomicIn::try_update

• AtomicUn::update

• AtomicUn::try_update

• cfg_select!

• mod core::range

• core::range::RangeInclusive

• core::range::RangeInclusiveIter

• core::hint::cold_path

• <*const T>::as_ref_unchecked

• <*mut T>::as_ref_unchecked

• <*mut T>::as_mut_unchecked

• Vec::push_mut

• Vec::insert_mut

• VecDeque::push_front_mut

• VecDeque::push_back_mut

• VecDeque::insert_mut

• LinkedList::push_front_mut

• LinkedList::push_back_mut

• Layout::dangling_ptr

• Layout::repeat

• Layout::repeat_packed

• Layout::extend_packed

These previously stable APIs are now stable in const contexts:

• fmt::from_fn

• ControlFlow::is_break

• ControlFlow::is_continue

Rustdoc¶

• In search results, rank unstable items lower

• Add new “hide deprecated items” setting in rustdoc

Compatibility Notes¶

• Array coercions may now result in less inference constraints than before

• Importing $crate without renaming, i.e. use $crate::{self};, is now no longer permitted due to stricter error checking for self imports.

• const-eval: be more consistent in the behavior of padding during typed copies. In very rare cases, this may cause compilation errors due to bytes from parts of a pointer ending up in the padding bytes of a const or static.

• A future-incompatibility warning lint ambiguous_glob_imported_traits is now reported when using an ambiguously glob imported trait

• Check lifetime bounds of types mentioning only type parameters

• Report more visibility-related ambiguous import errors

• Deprecate Eq::assert_receiver_is_total_eq and emit future compatibility warnings on manual impls

• powerpc64: Use the ELF ABI version set in target spec instead of guessing (fixes the ELF ABI used by the OpenBSD target)

• Matching on a #[non_exhaustive] enum now reads the discriminant, even if the enum has only one variant. This can cause closures to capture values that they previously wouldn’t.

• mut ref and mut ref mut patterns, part of the unstable Match Ergonomics 2024 RFC, were accidentally allowed on stable within struct pattern field shorthand. These patterns are now correctly feature-gated as unstable in this position.

• Add future-compatibility warning for derive helper attributes which conflict with built-in attributes

• JSON target specs have been destabilized and now require -Z unstable-options to use. Previously, they could not be used without the standard library, which has no stable build mechanism. In preparation for the build-std project adding that support, JSON target specs are being proactively gated to ensure they remain unstable even if build-std is stabilized. Cargo now includes the -Z json-target-spec CLI flag to automatically pass -Z unstable-options to the compiler when needed. See #150151, #151534, and rust-lang/cargo#16557.

• The arguments of #[feature] attributes on invalid targets are now checked

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 22