Rust release · Aug 27, 2020

Rust 1.46: what's new, what was stabilized

Short answerRust 1.46 was released on Aug 27, 2020: 2 newly stable APIs (Option::zip, vec::Drain::as_slice); 11 compatibility notes that can affect existing code.

Aug 27, 2020release date

0language stabilizations

2APIs stabilized

-new edition

← Rust 1.45 All versions Rust 1.47 →

2 APIs stabilized

Option::zip, vec::Drain::as_slice

Can it break my build?

The release lists these compatibility notes. Most only affect rare code, but read them before you raise your toolchain in CI:

[The target configuration option abi_blacklist has been renamed
[Rustc will now warn if you cast a C-like enum that implements Drop.][72331]
[Rustc will fail to compile if you have a struct with
[Tokens passed to macro_rules! are now always captured.][73293] This helps
[The InnoSetup installer for Windows is no longer available.][72569] This was
[{f32, f64}::asinh now returns the correct values for negative numbers.][72486]
[Rustc will no longer accept overlapping trait implementations that only
[Rustc now correctly relates the lifetime of an existential associated
[Rustc now dynamically links to libz (also called zlib) on Linux.][74420]
[Tests annotated with #[should_panic] are broken on ARMv7 while running
[Pretty printing of some tokens in procedural macros changed.][75453] The

Use it

rustup update stable        # get the newest release
rustup install 1.46          # or exactly this one
rustup override set 1.46     # pin a project to it

To require at least this version from users of your crate, set rust-version = "1.46" under [package] in Cargo.toml. Cargo then refuses to build it on older compilers with a clear message, and with resolver 3 (the default on the 2024 edition, Rust 1.85+) it also prefers dependency versions that support it.

Full release notes

Language

[if, match, and loop expressions can now be used in const functions.][72437]
[Additionally you are now also able to coerce and cast to slices (&[T]) in const functions.][73862]
[The #[track_caller] attribute can now be added to functions to use the function's caller's location information for panic messages.][72445]
[Recursively indexing into tuples no longer needs parentheses.][71322] E.g. x.0.0 over (x.0).0.
[mem::transmute can now be used in statics and constants.][72920] **Note** You currently can't use mem::transmute in constant functions.

Compiler

[You can now use the cdylib target on Apple iOS and tvOS platforms.][73516]
[Enabled static "Position Independent Executables" by default for x86_64-unknown-linux-musl.][70740]

Libraries

[mem::forget is now a const fn.][73887]
[String now implements From<char>.][73466]
[The leading_ones, and trailing_ones methods have been stabilised for all integer types.][73032]
[vec::IntoIter<T> now implements AsRef<[T]>.][72583]
[All non-zero integer types (NonZeroU8) now implement TryFrom for their zero-able equivalent (e.g. TryFrom<u8>).][72717]
[&[T] and &mut [T] now implement PartialEq<Vec<T>>.][71660]
[(String, u16) now implements ToSocketAddrs.][73007]
[vec::Drain<'_, T> now implements AsRef<[T]>.][72584]

Stabilized APIs

[Option::zip]
[vec::Drain::as_slice]

Cargo

Added a number of new environment variables that are now available when compiling your crate.

[CARGO_BIN_NAME and CARGO_CRATE_NAME][cargo/8270] Providing the name of the specific binary being compiled and the name of the crate.
[CARGO_PKG_LICENSE][cargo/8325] The license from the manifest of the package.
[CARGO_PKG_LICENSE_FILE][cargo/8387] The path to the license file.

Compatibility Notes

The target configuration option abi_blacklist has been renamed to unsupported_abis. The old name will still continue to work.
Rustc will now warn if you cast a C-like enum that implements Drop. This was previously accepted but will become a hard error in a future release.
[Rustc will fail to compile if you have a struct with #[repr(i128)] or #[repr(u128)].]74109 This representation is currently only allowed on enums.
Tokens passed to macro_rules! are now always captured. This helps ensure that spans have the correct information, and may cause breakage if you were relying on receiving spans with dummy information.
The InnoSetup installer for Windows is no longer available. This was a legacy installer that was replaced by a MSI installer a few years ago but was still being built.
{f32, f64}::asinh now returns the correct values for negative numbers.
Rustc will no longer accept overlapping trait implementations that only differ in how the lifetime was bound.
Rustc now correctly relates the lifetime of an existential associated type. This fixes some edge cases where rustc would erroneously allow you to pass a shorter lifetime than expected.
Rustc now dynamically links to libz (also called zlib) on Linux. The library will need to be installed for rustc to work, even though we expect it to be already available on most systems.
[Tests annotated with #[should_panic] are broken on ARMv7 while running under QEMU.]74820
Pretty printing of some tokens in procedural macros changed. The exact output returned by rustc's pretty printing is an unstable implementation detail: we recommend any macro relying on it to switch to a more robust parsing system.

Release notes from the Rust project's RELEASES.md (MIT or Apache-2.0); summaries above are ours.