Draft release notes for 1.88.0

[Mark-Simulacrum]

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 1.88.0 (2025-06-26)

Language

• Add invalid_null_arguments lint to prevent invalid usage of null pointers.
  This lint is uplifted from clippy::invalid_null_ptr_usage.
  📝
• Add warn-by-default dangerous_implicit_autorefs lint against implicit autoref of raw pointer dereference.
  The lint may be bumped to deny-by-default in a future version of Rust.
  📝
• Stabilize #![feature(let_chains)] in the 2024 edition.
  This feature allows &&-chaining let statements inside if and while, allowing intermixture with boolean expressions. The patterns inside the let sub-expressions can be irrefutable or refutable.
  📝
• Stabilize #![feature(naked_functions)].
  Naked functions allow writing functions with no compiler-generated epilogue and prologue, allowing full control over the generated assembly for a particular function.
  📝
• Fully de-stabilize the #[bench] attribute. Usage of #[bench] without #![feature(custom_test_frameworks)] already triggered a deny-by-default future-incompatibility lint since Rust 1.77, but will now become a hard error.
  📝
• Change trait impl candidate preference for builtin impls and trivial where-clauses.
  📝
• Stabilize #![feature(cfg_boolean_literals)].
  This allows using boolean literals as cfg predicates, e.g. #[cfg(true)] and #[cfg(false)].
  📝
• Check types of generic const parameter defaults
  📝

Compiler

• Stabilize -Cdwarf-version for selecting the version of DWARF debug information to generate.
  📝

Platform Support

• Demote i686-pc-windows-gnu to Tier 2.
  📝

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

Libraries

• Remove backticks from #[should_panic] test failure message.
  📝
• Guarantee that [T; N]::from_fn is generated in order of increasing indices., for those passing it a stateful closure.
  📝
• The libtest flag --nocapture is deprecated in favor of the more consistent --no-capture flag.
  📝
• Guarantee that {float}::NAN is a quiet NaN.
  📝

Stabilized APIs

• Cell::update
  📝
• impl Default for *const T
• impl Default for *mut T
  📝
• HashMap::extract_if
• HashSet::extract_if
  📝
• proc_macro::Span::line
• proc_macro::Span::column
• proc_macro::Span::start
• proc_macro::Span::end
  📝
• proc_macro::Span::file
• proc_macro::Span::local_file
  📝

These previously stable APIs are now stable in const contexts:

• NonNull<T>::replace
• <*mut T>::replace
  📝
• std::ptr::swap_nonoverlapping
  📝
• Cell::{replace, get, get_mut, from_mut, as_slice_of_cells}
  📝

Cargo

• Stabilize automatic garbage collection.
• use zlib-rs for gzip compression in rust code

Rustdoc

• Doctests can be ignored based on target names using ignore-* attributes.
• Stabilize the --test-runtool and --test-runtool-arg CLI options to specify a program (like qemu) and its arguments to run a doctest.
  📝

Compatibility Notes

• Finish changing the internal representation of pasted tokens. Certain invalid declarative macros that were previously accepted in obscure circumstances are now correctly rejected by the compiler. Use of a tt fragment specifier can often fix these macros.
  📝
• Fully de-stabilize the #[bench] attribute. Usage of #[bench] without #![feature(custom_test_frameworks)] already triggered a deny-by-default future-incompatibility lint since Rust 1.77, but will now become a hard error.
  📝
• Fix borrow checking some always-true patterns.
  The borrow checker was overly permissive in some cases, allowing programs that shouldn't have compiled.
  📝
• Update the minimum external LLVM to 19.
  📝
• Make it a hard error to use a vector type with a non-Rust ABI without enabling the required target feature.
  📝

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.

Other

[Mark-Simulacrum]

@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]

Reordered the lang items according to "excitingness" and added the #[bench] destabilization to the compatibility notes section.

[jieyouxu]

Reordered the lang items according to "excitingness" and added the #[bench] destabilization to the compatibility notes section.

IIRC the summary is tooling-generated, so re-ordering this summary might get lost if it needs to be resync'd by tooling

[BoxyUwU]

Yes, please don't edit the issue manually as those changes will get lost. Instead the relnotes tracking issues should be edited and then the auto generated release notes will reflect the changes.

Unfortunately I don't think we currently have a way to specify a desired ordering so it tends to just happen when the final relnotes are generated and merged

[jieyouxu]

Unfortunately I don't think we currently have a way to specify a desired ordering so it tends to just happen when the final relnotes are generated and merged

For ordering changes, I think it's best deferred to the relnotes blog post 🤔 (Probably logistically the least complicated)

[traviscross]

How are we generating what ends up in the compatibility notes section? (Will that change be overwritten as well?) I don't see, e.g., a label for that.

Regarding ordering, for when it gets overwritten, here is the order I'd suggest for the lang items:

• Stabilize let chains in the 2024 edition
  This allows &&-chaining let statements inside if and while, allowing intermixture with boolean expressions. The patterns inside the let sub-expressions can be irrefutable or refutable.
  📝
• Stabilize naked functions
  Naked functions allow writing functions with no compiler-generated epilogue and prologue, allowing full control over the generated assembly for a particular function.
  📝
• Stabilize cfg_boolean_literals
  📝
• Fully de-stabilize the #[bench] attribute. Usage of #[bench] without #![feature(custom_test_frameworks)] already triggered a deny-by-default future-incompatibility lint since Rust 1.77, but will now become a hard error.
  📝
• Add deny-by-default dangerous_implicit_autorefs lint against implicit autoref of raw pointer dereference
  📝
• Add invalid_null_arguments lint to prevent invalid usage of null pointers
  • Uplifted from clippy::invalid_null_ptr_usage.
    📝
• Changed candidate preference for builtin impls and trivial where-clauses
  📝
• Check types of generic const parameter defaults
  📝

[BoxyUwU]

All entries (including compat notes) are generated from the corresponding relnotes tracking issues. E.g. #140488 has a # Compatibility Notes header

[traviscross]

Got it, thanks. Updated the one for #[bench] accordingly.