Rust 1.66.0

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> 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