Draft release notes for 1.99.0

NOTE: Use the 📝 links to edit those that have a relnotes-tracking-issue,
and they will be updated when we regenerate the notes periodically (manually).

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Version 1.99.0 (2026-10-01)

Language

• Add allow-by-default raw_borrows_via_references lint that checks for references that decay immediately into raw borrows
  📝
• Extend unconditional_panic lint to function calls that panics when the chunks/windows size is zero
  📝
• Stabilize C-variadic function definitions
  📝
• Trait method are now resolved on an adjusted never type (producing a FCW)
  📝
• Coerce from inference variables to trait objects if a subtype or supertype of the inference variable is known to be Sized
  📝
• Stabilize #[my_macro] mod foo;. This allows outlined modules (mod foo;) anywhere in the body of a custom attribute or derive macro.
  📝
• Fix the overflowing_literals lint with repeated negation. For instance, it will now now longer lint on --128_i8, which is already detected by the arithmetic_overflow lint.
  📝
• Add POSIX symbols to the invalid_runtime_symbol_definitions and suspicious_runtime_symbol_definitions lints
  📝
• Lint unused #[path] attributes on inline modules
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• Enable unreachable_cfg_select_predicates lint as part of unused lint group
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• Stabilize passing 128-bit integers via vector registers with asm! on x86
  📝
• Macros that expand to a semicolon now produce a warning lint (semicolon_in_expressions_from_non_local_macros) even when the macro comes from another crate. Previously, such warnings only appeared for macros from the same crate, to avoid showing warnings that can't be fixed locally; however, this masked problems, as integration tests from the crate providing the macro get compiled as a separate crate, so tests often wouldn't reveal this issue. If you encounter a lint like this, please make sure to report it to the crate providing the macro so they can fix it; don't just silence it in your own crate.
  • semicolon_in_expressions_from_macros: Lint on non-local macros too
  • Split non-local semicolon_in_expressions_from_macros into a separate lint
    📝
• Explicitly document that some allocations are allowed to grow in-place (but none are allowed to shrink)
  📝
• The contents of an UnsafeCell can now be accessed without going through get
  • The invalid_reference_casting lint was adjusted accordingly
    📝
• Stabilize the ability to use #[unsafe(naked)] functions to define C-variadic functions (#![feature(c_variadic_naked_functions)]).
  📝
• Warn if an invalid doc attribute is used on a macro invocation
  📝
• Infer anonymous lifetimes in the types of associated consts as 'static
  📝

Compiler

• Convert -Ctarget-cpu into a target-modifier for AVR, AMDGCN and NVPTX
  📝
• Enable static_position_independent_executables on all gnu and musl targets
  📝
• When providing a suggestion about a missing method, rustc now prefers an exactly matching name from a doc alias attribute over a similarity search from other method names. If your new users sometimes expect a method under a different name, adding a doc alias will now help them find it via rustc suggestions, in addition to helping them find it via rustdoc search: When suggesting method names, prefer exact doc aliases over similar names
  📝

Platform Support

• Promote riscv64-unknown-linux-musl to Tier 2 with host tools
  📝

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

Libraries

• Relax transmute_copy to accept ?Sized types)
• Update transmute_copy to use a non-unwinding panic
  📝
• Don't escape U+FF9E and U+FF9F in escape_debug_ext
  📝
• Introduce a PinSafePointer trait that generalizes PinCoerceUnsized
  📝

Stabilized APIs

• Implement IntoIterator for [&[mut]] Box<[T; N], A>
  📝
• VecDeque::retain_back
  📝
• Step::forward_overflowing
• Step::backward_overflowing
  📝
• Box::into_non_null
• Box::from_non_null
• Vec::into_parts
• Vec::from_parts
  📝
• core::mem::size_of_val_raw
• core::mem::align_of_val_raw
• core::alloc::Layout::for_value_raw
  📝
• String::from_utf8_lossy_owned
  📝
• FusedIterator for StepBy<I>
  📝
• std::fs::set_times
• std::fs::set_times_nofollow
  📝

These previously stable APIs are now stable in const contexts:

Cargo

• Stabilize build-dir layout v2
• feat(toml): allow overriding inherited default-features in 2024
• feat(profile): Add built-in profile debug

Rustdoc

• Add new unused_footnote_definition rustdoc lint
  📝
• Smarter filtering of trait impls yields performance improvements of 20% on average and up to 40% on some real-world crates
  📝
  

Compatibility Notes

• fully deprecate the legacy integral modules
  📝
• Upgrade no_mangle_generic_items into hard error
  📝
• Do not promote references to extern statics
  📝
• Ensure inferred let pattern types typecheck
  📝
• hermit/fs: Return unsupported() instead of from_raw_os_error(22)
  📝
• Fixed a bug where #[repr(simd)] was accidentally allowed on macro invocations on stable Rust
  📝
• Abort const-eval when there are generics in the type of the value being produced
  📝
• Box::leak: tell people to avoid unleaking
  📝
• PowerPC inline ASM: Fix scalar floats being in the wrong vector lane on little endian
  📝

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.

Start with the Version 1.99.0 release-note sections in this issue and follow the linked pull requests and 📝 tracking issues to identify entries needing updates. Done means the release notes are complete, consistently formatted, and reflect the linked changes without leaving known tracking items unresolved.