Rust 1.67: what's new, what was stabilized

• [The layout of repr(Rust) types now groups m\*2^n-sized fields with
• 0.5 now rounds to 0 when formatted to 0 decimal places.
• [Chains of && and || will now drop temporaries from their sub-expressions in
• Underscore suffixes on string literals are now a hard error.
• Stop passing -export-dynamic to wasm-ld.
• main is now mangled as __main_void on wasm32-wasi.
• [Cargo now emits an error if there are multiple registries in the configuration

Language

• Make Sized predicates coinductive, allowing cycles.
• [#[must_use] annotations on async fn also affect the Future::Output.](https://github.com/rust-lang/rust/pull/100633/)
• Elaborate supertrait obligations when deducing closure signatures.
• Invalid literals are no longer an error under cfg(FALSE).
• Unreserve braced enum variants in value namespace.

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Compiler

• Enable varargs support for calling conventions other than C or cdecl.
• Add new MIR constant propagation based on dataflow analysis.
• Optimize field ordering by grouping m\*2^n-sized fields with equivalently aligned ones.
• Stabilize native library modifier verbatim.

Added, updated, and removed targets:

• Add a tier 3 target for PowerPC on AIX, powerpc64-ibm-aix.
• Add a tier 3 target for the Sony PlayStation 1, mipsel-sony-psx.
• Add tier 3 no_std targets for the QNX Neutrino RTOS, aarch64-unknown-nto-qnx710 and x86_64-pc-nto-qnx710.
• Promote UEFI targets to tier 2, aarch64-unknown-uefi, i686-unknown-uefi, and x86_64-unknown-uefi.
• Remove tier 3 linuxkernel targets (not used by the actual kernel).

Refer to Rust's [platform support page][platform-support-doc] for more information on Rust's tiered platform support.

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Libraries

• Merge crossbeam-channel into std::sync::mpsc.
• Fix inconsistent rounding of 0.5 when formatted to 0 decimal places.
• Derive Eq and Hash for ControlFlow.
• Don't build compiler_builtins with -C panic=abort.

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Stabilized APIs

• {integer}::checked_ilog
• {integer}::checked_ilog2
• {integer}::checked_ilog10
• {integer}::ilog
• {integer}::ilog2
• {integer}::ilog10
• NonZeroU*::ilog2
• NonZeroU*::ilog10
• NonZero*::BITS

These APIs are now stable in const contexts:

• char::from_u32
• char::from_digit
• char::to_digit
• core::char::from_u32
• core::char::from_digit

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Compatibility Notes

• The layout of repr(Rust) types now groups m\*2^n-sized fields with equivalently aligned ones. This is intended to be an optimization, but it is also known to increase type sizes in a few cases for the placement of enum tags. As a reminder, the layout of repr(Rust) types is an implementation detail, subject to change.
• 0.5 now rounds to 0 when formatted to 0 decimal places. This makes it consistent with the rest of floating point formatting that rounds ties toward even digits.
• Chains of && and || will now drop temporaries from their sub-expressions in evaluation order, left-to-right. Previously, it was "twisted" such that the _first_ expression dropped its temporaries _last_, after all of the other expressions dropped in order.
• Underscore suffixes on string literals are now a hard error. This has been a future-compatibility warning since 1.20.0.
• Stop passing -export-dynamic to wasm-ld.
• main is now mangled as __main_void on wasm32-wasi.
• Cargo now emits an error if there are multiple registries in the configuration with the same index URL.

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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.

• Rewrite LLVM's archive writer in Rust.

1.67.1 (Feb 9, 2023)

• Fix interoperability with thin archives.
• Fix an internal error in the compiler build process.
• Downgrade clippy::uninlined_format_args to pedantic.