Rust 1.23: what's new, what was stabilized

Short answerRust 1.23 was released on Jan 4, 2018: 4 compatibility notes that can affect existing code.

Jan 4, 2018release date

0language stabilizations

0APIs stabilized

-new edition

← Rust 1.22 All versions Rust 1.24 →

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:

[Changes have been made to type equality to make it more correct,
[char::escape_debug now uses Unicode 10 over 9.][45571]
[Upgraded Android SDK to 27, and NDK to r15c.][45580] This drops support for
[Bumped the minimum LLVM to 3.9][45326]

Use it

rustup update stable        # get the newest release
rustup install 1.23          # or exactly this one
rustup override set 1.23     # pin a project to it

To require at least this version from users of your crate, set rust-version = "1.23" 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

[Arbitrary auto traits are now permitted in trait objects.][45772]
[rustc now uses subtyping on the left hand side of binary operations.][45435] Which should fix some confusing errors in some operations.

Compiler

[Enabled TrapUnreachable in LLVM which should mitigate the impact of undefined behavior.][45920]
[rustc now suggests renaming import if names clash.][45660]
[Display errors/warnings correctly when there are zero-width or wide characters.][45711]
[rustc now avoids unnecessary copies of arguments that are simple bindings][45380] This should improve memory usage on average by 5-10%.
[Updated musl used to build musl rustc to 1.1.17][45393]

Libraries

[Allow a trailing comma in assert_eq/ne macro][45887]
[Implement Hash for raw pointers to unsized types][45483]
[impl From<*mut T> for AtomicPtr<T>][45610]
[impl From<usize/isize> for AtomicUsize/AtomicIsize.][45610]
[Removed the T: Sync requirement for RwLock<T>: Send][45267]
[Removed T: Sized requirement for {<*const T>, <*mut T>}::as_ref and <*mut T>::as_mut][44932]
[Optimized Thread::{park, unpark} implementation][45524]
[Improved SliceExt::binary_search performance.][45333]
[impl FromIterator<()> for ()][45379]
[Copied AsciiExt trait methods to primitive types.][44042] Use of AsciiExt is now deprecated.

Cargo

[Cargo now supports uninstallation of multiple packages][cargo/4561] eg. cargo uninstall foo bar uninstalls foo and bar.
[Added unit test checking to cargo check][cargo/4592]
[Cargo now lets you install a specific version using cargo install --version][cargo/4637]

Misc

[Releases now ship with the Cargo book documentation.][45692]
[rustdoc now prints rendering warnings on every run.][45324]

Compatibility Notes

Changes have been made to type equality to make it more correct, in rare cases this could break some code. Tracking issue for further information
char::escape_debug now uses Unicode 10 over 9.
Upgraded Android SDK to 27, and NDK to r15c. This drops support for Android 9, the minimum supported version is Android 14.
Bumped the minimum LLVM to 3.9

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

← Rust 1.22 All versions Rust 1.24 →

Up next

Next releaseRust 1.24Released Feb 15, 2018.Read it next →

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