1.66.0 (15 December, 2022) #

Language #

• Permit specifying explicit discriminants on all repr(Int) enums

  #[repr(u8)]
  enum Foo {
      A(u8) = 0,
      B(i8) = 1,
      C(bool) = 42,
  }
  

• Allow transmutes between the same type differing only in lifetimes
• Change constant evaluation errors from a deny-by-default lint to a hard error
• Trigger must_use on impl Trait for supertraits This makes impl ExactSizeIterator respect the existing #[must_use] annotation on Iterator.
• Allow ..=X in patterns
• Uplift clippy::for_loops_over_fallibles lint into rustc
• Stabilize sym operands in inline assembly
• Update to Unicode 15
• Opaque types no longer imply lifetime bounds This is a soundness fix which may break code that was erroneously relying on this behavior.

Compiler #

• Add armv5te-none-eabi and thumbv5te-none-eabi tier 3 targets
  • Refer to Rust’s [platform support page][platform-support-doc] for more information on Rust’s tiered platform support.
• Add support for linking against macOS universal libraries

Libraries #

• Fix #[derive(Default)] on a generic #[default] enum adding unnecessary Default bounds
• Update to Unicode 15

Stabilized APIs #

• proc_macro::Span::source_text
• uX::{checked_add_signed, overflowing_add_signed, saturating_add_signed, wrapping_add_signed}
• iX::{checked_add_unsigned, overflowing_add_unsigned, saturating_add_unsigned, wrapping_add_unsigned}
• iX::{checked_sub_unsigned, overflowing_sub_unsigned, saturating_sub_unsigned, wrapping_sub_unsigned}
• BTreeSet::{first, last, pop_first, pop_last}
• BTreeMap::{first_key_value, last_key_value, first_entry, last_entry, pop_first, pop_last}
• Add AsFd implementations for stdio lock types on WASI.
• impl TryFrom<Vec<T>> for Box<[T; N]>
• core::hint::black_box
• Duration::try_from_secs_{f32,f64}
• Option::unzip
• std::os::fd

Rustdoc #

• Add Rustdoc warning for invalid HTML tags in the documentation

Cargo #

• Added cargo remove to remove dependencies from Cargo.toml
• cargo publish now waits for the new version to be downloadable before exiting

See detailed release notes for more.

Compatibility Notes #

• Only apply ProceduralMasquerade hack to older versions of rental
• Don’t export __heap_base and __data_end on wasm32-wasi.
• Don’t export __wasm_init_memory on WebAssembly.
• Only export __tls_* on wasm32-unknown-unknown.
• Don’t link to libresolv in libstd on Darwin
• Update libstd’s libc to 0.2.135 (to make libstd no longer pull in libiconv.dylib on Darwin)
• Opaque types no longer imply lifetime bounds This is a soundness fix which may break code that was erroneously relying on this behavior.
• Make order_dependent_trait_objects show up in future-breakage reports
• Change std::process::Command spawning to default to inheriting the parent’s signal mask

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.

• Enable BOLT for LLVM compilation
• Enable LTO for rustc_driver.so