Language

• The 2024 Edition is now stable. Seethe edition guide for more details.
• Stabilize async closures SeeRFC 3668 for more details.
• Stabilize#[diagnostic::do_not_recommend]
• Addunpredictable_function_pointer_comparisons lint to warn against function pointer comparisons
• Lint on combining#[no_mangle] and#[export_name] attributes.

Compiler

• The unstable flag-Zpolymorphize has been removed, seerust-lang/compiler-team#810 for some background.

Platform Support

• Promotepowerpc64le-unknown-linux-musl to tier 2 with host tools

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

Libraries

• Panics in the standard library now have a leadinglibrary/ in their path

• std::env::home_dir() on Windows now ignores the non-standard$HOME environment variable

  It will be un-deprecated in a subsequent release.

• AddAsyncFn* to the prelude in all editions.

Stabilized APIs

• BuildHasherDefault::new
• ptr::fn_addr_eq
• io::ErrorKind::QuotaExceeded
• io::ErrorKind::CrossesDevices
• {float}::midpoint
• Unsigned{integer}::midpoint
• NonZeroU*::midpoint
• implstd::iter::Extend for tuples with arity 1 through 12
• FromIterator<(A, ...)> for tuples with arity 1 through 12
• std::task::Waker::noop

These APIs are now stable in const contexts:

• mem::size_of_val
• mem::align_of_val
• Layout::for_value
• Layout::align_to
• Layout::pad_to_align
• Layout::extend
• Layout::array
• std::mem::swap
• std::ptr::swap
• NonNull::new
• HashMap::with_hasher
• HashSet::with_hasher
• BuildHasherDefault::new
• <float>::recip
• <float>::to_degrees
• <float>::to_radians
• <float>::max
• <float>::min
• <float>::clamp
• <float>::abs
• <float>::signum
• <float>::copysign
• MaybeUninit::write

Cargo

• Add future-incompatibility warning against keywords in cfgs and add raw-idents
• Stabilize higher precedence trailing flags
• PassCARGO_CFG_FEATURE to build scripts

Rustdoc

• Doc comment on impl blocks shows the first line, even when the impl block is collapsed

Compatibility Notes

• rustc no longer treats thetest cfg as a well known check-cfg, instead it is up to the build systems and users of--check-cfg[^check-cfg] to set it as a well known cfg using--check-cfg=cfg(test).

  This is done to enable build systems like Cargo to set it conditionally, as not all source files are suitable for unit tests.Cargo (for now) unconditionally sets thetest cfg as a well known cfg. [^check-cfg]:https://doc.rust-lang.org/nightly/rustc/check-cfg.html

• Disable potentially incorrect type inference if there are trivial and non-trivial where-clauses

• std::env::home_dir() has been deprecated for years, because it can give surprising results in some Windows configurations if theHOME environment variable is set (which is not the normal configuration on Windows). We had previously avoided changing its behavior, out of concern for compatibility with code depending on this non-standard configuration. Given how long this function has been deprecated, we're now fixing its behavior as a bugfix. A subsequent release will remove the deprecation for this function.

• Makecore::ffi::c_char signedness more closely match that of the platform-defaultchar

  This changedc_char from ani8 tou8 or vice versa on many Tier 2 and 3 targets (mostly Arm and RISC-V embedded targets). The new definition may result in compilation failures but fixes compatibility issues with C.

  Thelibc crate matches this change as of its 0.2.169 release.

• When compiling a nestedmacro_rules macro from an external crate, the content of the innermacro_rules is now built with the edition of the external crate, not the local crate.

• Increasesparcv9-sun-solaris andx86_64-pc-solaris Solaris baseline to 11.4.

• Showabi_unsupported_vector_types lint in future breakage reports

• Error if multiple super-trait instantiations ofdyn Trait need associated types to be specified but only one is provided

• Changepowerpc64-ibm-aix defaultcodemodel to large

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.

• Buildx86_64-unknown-linux-gnu with LTO for C/C++ code (e.g.,jemalloc)