Rust 1.88: what's new, what was stabilized

• 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](https://github.com/rust-lang/rust/pull/134273). 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.
• 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.

Language

• [Stabilize #![feature(let_chains)] in the 2024 edition.](https://github.com/rust-lang/rust/pull/132833) 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)].](https://github.com/rust-lang/rust/pull/134213) Naked functions allow writing functions with no compiler-generated epilogue and prologue, allowing full control over the generated assembly for a particular function.
• [Stabilize #![feature(cfg_boolean_literals)].](https://github.com/rust-lang/rust/pull/138632) This allows using boolean literals as cfg predicates, e.g. #[cfg(true)] and #[cfg(false)].
• [Fully de-stabilize the #[bench] attribute](https://github.com/rust-lang/rust/pull/134273). 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 warn-by-default dangerous_implicit_autorefs lint against implicit autoref of raw pointer dereference. The lint will be bumped to deny-by-default in the next version of Rust.
• Add invalid_null_arguments lint to prevent invalid usage of null pointers. This lint is uplifted from clippy::invalid_null_ptr_usage.
• Change trait impl candidate preference for builtin impls and trivial where-clauses.
• Check types of generic const parameter defaults

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Compiler

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

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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.

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Libraries

• [Remove backticks from #[should_panic] test failure message.](https://github.com/rust-lang/rust/pull/136160)
• [Guarantee that [T; N]::from_fn is generated in order of increasing indices.](https://github.com/rust-lang/rust/pull/139099), 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.

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Stabilized APIs

• Cell::update
• impl Default for *const T
• impl Default for *mut T
• HashMap::extract_if
• HashSet::extract_if
• hint::select_unpredictable
• 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
• [<[T]>::as_chunks](https://doc.rust-lang.org/stable/std/primitive.slice.html#method.as_chunks)
• [<[T]>::as_chunks_mut](https://doc.rust-lang.org/stable/std/primitive.slice.html#method.as_chunks_mut)
• [<[T]>::as_chunks_unchecked](https://doc.rust-lang.org/stable/std/primitive.slice.html#method.as_chunks_unchecked)
• [<[T]>::as_chunks_unchecked_mut](https://doc.rust-lang.org/stable/std/primitive.slice.html#method.as_chunks_unchecked_mut)
• [<[T]>::as_rchunks](https://doc.rust-lang.org/stable/std/primitive.slice.html#method.as_rchunks)
• [<[T]>::as_rchunks_mut](https://doc.rust-lang.org/stable/std/primitive.slice.html#method.as_rchunks_mut)
• mod ffi::c_str

These previously stable APIs are now stable in const contexts:

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

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Cargo

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

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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.

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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](https://github.com/rust-lang/rust/pull/134273). 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.