Rust 1.89: what's new, what was stabilized

• Make missing_fragment_specifier an unconditional error
• Enabling the neon target feature on aarch64-unknown-none-softfloat causes a warning because mixing code with and without that target feature is not properly supported by LLVM
• Sized Hierarchy: Part I
• The warn-by-default elided_named_lifetimes lint is superseded by the warn-by-default mismatched_lifetime_syntaxes lint.
• Error on recursive opaque types earlier in the type checker
• Type inference side effects from requiring element types of array repeat expressions are Copy are now only available at the end of type checking
• The deprecated accidentally-stable std::intrinsics::{copy,copy_nonoverlapping,write_bytes} are now proper intrinsics. There are no debug assertions guarding against UB, and they cannot be coerced to function pointers.
• Remove long-deprecated std::intrinsics::drop_in_place
• Make well-formedness predicates no longer coinductive
• Remove hack when checking impl method compatibility
• Remove unnecessary type inference due to built-in trait object impls
• Lint against "stdcall", "fastcall", and "cdecl" on non-x86-32 targets
• Future incompatibility warnings relating to the never type (!) are now reported in dependencies
• Ensure std::ptr::copy_* intrinsics also perform the static self-init checks
• extern "C" functions on the wasm32-unknown-unknown target now have a standards compliant ABI

Language

• Stabilize explicitly inferred const arguments (feature(generic_arg_infer))
• Add a warn-by-default mismatched_lifetime_syntaxes lint. This lint detects when the same lifetime is referred to by different syntax categories between function arguments and return values, which can be confusing to read, especially in unsafe code. This lint supersedes the warn-by-default elided_named_lifetimes lint.
• Expand unpredictable_function_pointer_comparisons to also lint on function pointer comparisons in external macros
• Make the dangerous_implicit_autorefs lint deny-by-default
• Stabilize the avx512 target features
• Stabilize kl and widekl target features for x86
• Stabilize sha512, sm3 and sm4 target features for x86
• Stabilize LoongArch target features f, d, frecipe, lasx, lbt, lsx, and lvz
• Remove i128 and u128 from improper_ctypes_definitions
• [Stabilize repr128 (#[repr(u128)], #[repr(i128)])](https://github.com/rust-lang/rust/pull/138285)
• [Allow #![doc(test(attr(..)))] everywhere](https://github.com/rust-lang/rust/pull/140560)
• Extend temporary lifetime extension to also go through tuple struct and tuple variant constructors
• extern "C" functions on the wasm32-unknown-unknown target now have a standards compliant ABI

<a id="1.89.0-Compiler"></a>

Compiler

• Default to non-leaf frame pointers on aarch64-linux
• Enable non-leaf frame pointers for Arm64EC Windows
• Set Apple frame pointers by architecture

<a id="1.89.0-Platform-Support"></a>

Platform Support

• Add new Tier-3 targets loongarch32-unknown-none and loongarch32-unknown-none-softfloat
• x86_64-apple-darwin is in the process of being demoted to Tier 2 with host tools

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

<a id="1.89.0-Libraries"></a>

Libraries

• Specify the base path for file!
• Allow storing format_args!() in a variable
• [Add #[must_use] to [T; N]::map](https://github.com/rust-lang/rust/pull/140957)
• Implement DerefMut for Lazy{Cell,Lock}
• Implement Default for array::IntoIter
• Implement Clone for slice::ChunkBy
• Implement io::Seek for io::Take

<a id="1.89.0-Stabilized-APIs"></a>

Stabilized APIs

• NonZero<char>
• Many intrinsics for x86, not enumerated here
• AVX512 intrinsics
• SHA512, SM3 and SM4 intrinsics
• File::lock
• File::lock_shared
• File::try_lock
• File::try_lock_shared
• File::unlock
• NonNull::from_ref
• NonNull::from_mut
• NonNull::without_provenance
• NonNull::with_exposed_provenance
• NonNull::expose_provenance
• OsString::leak
• PathBuf::leak
• Result::flatten
• std::os::linux::net::TcpStreamExt::quickack
• std::os::linux::net::TcpStreamExt::set_quickack

These previously stable APIs are now stable in const contexts:

• [<[T; N]>::as_mut_slice](https://doc.rust-lang.org/stable/std/primitive.array.html#method.as_mut_slice)
• [<[u8]>::eq_ignore_ascii_case](https://doc.rust-lang.org/stable/std/primitive.slice.html#impl-%5Bu8%5D/method.eq_ignore_ascii_case)
• str::eq_ignore_ascii_case

<a id="1.89.0-Cargo"></a>

Cargo

• cargo fix and cargo clippy --fix now default to the same Cargo target selection as other build commands. Previously it would apply to all targets (like binaries, examples, tests, etc.). The --edition flag still applies to all targets.
• Stabilize doctest-xcompile. Doctests are now tested when cross-compiling. Just like other tests, it will use the runner setting to run the tests. If you need to disable tests for a target, you can use the ignore doctest attribute to specify the targets to ignore.

<a id="1.89.0-Rustdoc"></a>

Rustdoc

• On mobile, make the sidebar full width and linewrap. This makes long section and item names much easier to deal with on mobile.

<a id="1.89.0-Compatibility-Notes"></a>

Compatibility Notes

• Make missing_fragment_specifier an unconditional error
• Enabling the neon target feature on aarch64-unknown-none-softfloat causes a warning because mixing code with and without that target feature is not properly supported by LLVM
• Sized Hierarchy: Part I
• Introduces a small breaking change affecting ?Sized bounds on impls on recursive types which contain associated type projections. It is not expected to affect any existing published crates. Can be fixed by refactoring the involved types or opting into the sized_hierarchy unstable feature. See the FCP report for a code example.
• The warn-by-default elided_named_lifetimes lint is superseded by the warn-by-default mismatched_lifetime_syntaxes lint.
• Error on recursive opaque types earlier in the type checker
• Type inference side effects from requiring element types of array repeat expressions are Copy are now only available at the end of type checking
• The deprecated accidentally-stable std::intrinsics::{copy,copy_nonoverlapping,write_bytes} are now proper intrinsics. There are no debug assertions guarding against UB, and they cannot be coerced to function pointers.
• Remove long-deprecated std::intrinsics::drop_in_place
• Make well-formedness predicates no longer coinductive
• Remove hack when checking impl method compatibility
• Remove unnecessary type inference due to built-in trait object impls
• Lint against "stdcall", "fastcall", and "cdecl" on non-x86-32 targets
• Future incompatibility warnings relating to the never type (!) are now reported in dependencies
• Ensure std::ptr::copy_* intrinsics also perform the static self-init checks
• extern "C" functions on the wasm32-unknown-unknown target now have a standards compliant ABI

<a id="1.89.0-Internal-Changes"></a>

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.

• Correctly un-remap compiler sources paths with the rustc-dev component