Draft release notes for 1.89.0

[cuviper]

NOTE: We are trying this issue as a new way to work on the draft release notes.
Use the 📝 links to edit those that have a relnotes-tracking-issue,
and they will be updated when we regenerate the notes periodically.

cc @rust-lang/release

---

Version 1.89.0 (2025-08-07)

Language

• Lint on function pointers comparisons in external macros
  📝
• Stabilize x86 keylocker target feature
  📝
• Partially stabilize LoongArch target features
  📝
• Remove i128 and u128 from improper_ctypes_definitions
  📝
• Stabilize repr128
  📝
• 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.
  📝
• Stabilize the avx512 target features
  📝
• Allow #![doc(test(attr(..)))] everywhere
  📝
• Extend temporary lifetime extension to also go through tuple struct and tuple variant constructors
  📝
• Stabilize kl and widekl target features for x86
  📝
• Stabilize sha512, sm3 and sm4 target features for x86
  📝
• Stabilize feature(generic_arg_infer)
  📝
• Make the dangerous_implicit_autorefs lint deny-by-default
  📝

Compiler

• aarch64-linux: Default to FramePointer::NonLeaf
  📝
• Enable non-leaf Frame Pointers for Arm64EC Windows
  📝
• compiler: set Apple frame pointers by architecture
  📝

Platform Support

• Add new Tier-3 targets loongarch32-unknown-none and loongarch32-unknown-none-softfloat
  📝

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

Libraries

• Specify the base path for file!
  📝
• Implement std::io::Seek for std::io::Take
  📝
• add CStr::display
• Allow storing format_args!() in variable
  📝
• Add #[must_use] to [T; N]::map.
  📝

Stabilized APIs

• AVX512 intrinsics
  📝
• Stabilize x86 SHA512, SM3 and SM4 intrinsics
  📝
• Stabilize std::os::linux::net::TcpStreamExt::{set_}quickack
  📝
• Implement DerefMut for Lazy[Cell/Lock]
  📝
• Stabilize core::ptr::NonNull::{from_ref,from_mut}
  📝
• Stabilize {str,[u8]}::eq_ignore_ascii_case
  📝
• Stabilize x86 keylocker intrinsics (kl, widekl)
  📝
• NonNull::without_provenance
• NonNull::from_exposed_provenance
• NonNull::expose_provenance
  📝
• Stabilize {OsString,PathBuf}::leak
  📝
• Added Clone implementation for ChunkBy
  📝
• Allow NonZero<char>
  📝
• Stabilize Result::flatten
  📝
• impl Default for array::IntoIter
  📝

These previously stable APIs are now stable in const contexts:

• NonNull::without_provenance
  📝
• Stabilize <[T; N]>::as_mut_slice as const
  📝

Cargo

• fix: default to all targets when using --edition and --edition-idioms in cargo fix
• Stabilize doctest-xcompile

Rustdoc

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

Compatibility Notes

• Optimize Seek::stream_len impl for File
  📝
• 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 builtin 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 copy* intrinsics also perform the static self-init checks
  📝

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
  📝

Other

[cuviper]

@rustbot ping relnotes-interest-group

[rustbot]

Hi relnotes-interest-group, this issue/PR could use some help in reviewing /
adjusting release notes. Could you take a look if available? Thanks <3

cc @alex-semenyuk @jieyouxu @joshtriplett @Kobzol @lcnr @traviscross

[traviscross]

Let's double-check how well we did in having Reference updates for all changes to the language. We had Reference updates for each of these:

• Partially stabilize LoongArch target features
  • Doc: Add the LoongArch stabilized target features reference#1707
• Stabilize the avx512 target features
  • Add doc for avx512 target features reference#1778
• Extend temporary lifetime extension to also go through tuple struct and tuple variant constructors
  • Add new temporary lifetime extension rule reference#1813
• Stabilize kl and widekl target features for x86
  • Add doc for keylocker target features reference#1829
• Stabilize sha512, sm3 and sm4 target features for x86
  • Add doc for sha512, sm3 and sm4 target features reference#1830
• Stabilize feature(generic_arg_infer)
  • Document inferred const args (feature(generic_arg_infer)) reference#1835

The Reference was already correct for this one:

• Stabilize repr128
  • Primitive representations don't allow 128-bit types reference#1368

We don't document lints, so there were no updates for lint changes:

• Lint on function pointers comparisons in external macros
• Add a warn-by-default mismatched_lifetime_syntaxes lint.
• Remove i128 and u128 from improper_ctypes_definitions
• Make the dangerous_implicit_autorefs lint deny-by-default

And one was a change to an attribute we may have delegated to the rustdoc team:

• Allow #![doc(test(attr(..)))] everywhere

The details of this attribute aren't documented in the Reference. The update to the rustdoc book was made.

cc @ehuss @tomassedovic

[djc]

• Remove i128 and u128 from improper_ctypes_definitions
  📝
• Stabilize repr128
  📝

Should these be combined to have a single item?

• Stabilize {str,[u8]}::eq_ignore_ascii_case
  📝

I think this is only the constification.

[traviscross]

• Remove i128 and u128 from improper_ctypes_definitions
  📝
• Stabilize repr128
  📝

Should these be combined to have a single item?

No, they're distinct.