Rust release · Aug 2, 2018

Rust 1.28: what's new, what was stabilized

Short answerRust 1.28 was released on Aug 2, 2018: 29 newly stable APIs (Iterator::step_by, Path::ancestors, SystemTime::UNIX_EPOCH, alloc::GlobalAlloc, ...); 1 compatibility note that can affect existing code.

Aug 2, 2018release date

0language stabilizations

29APIs stabilized

-new edition

← Rust 1.27 All versions Rust 1.29 →

29 APIs stabilized

Iterator::step_by, Path::ancestors, SystemTime::UNIX_EPOCH, alloc::GlobalAlloc, alloc::Layout, alloc::LayoutErr, alloc::System, alloc::alloc, alloc::alloc_zeroed, alloc::dealloc, alloc::realloc, alloc::handle_alloc_error, btree_map::Entry::or_default, fmt::Alignment, hash_map::Entry::or_default, iter::repeat_with, num::NonZeroUsize, num::NonZeroU128, num::NonZeroU16, num::NonZeroU32, num::NonZeroU64, num::NonZeroU8, ops::RangeBounds, slice::SliceIndex, slice::from_mut, slice::from_ref, {Any + Send + Sync}::downcast_mut, {Any + Send + Sync}::downcast_ref, {Any + Send + Sync}::is

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:

[Rust will consider trait objects with duplicated constraints to be the same

Use it

rustup update stable        # get the newest release
rustup install 1.28          # or exactly this one
rustup override set 1.28     # pin a project to it

To require at least this version from users of your crate, set rust-version = "1.28" 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

[The #[repr(transparent)] attribute is now stable.][51562] This attribute allows a Rust newtype wrapper (struct NewType<T>(T);) to be represented as the inner type across Foreign Function Interface (FFI) boundaries.
[The keywords pure, sizeof, alignof, and offsetof have been unreserved and can now be used as identifiers.][51196]
[The GlobalAlloc trait and #[global_allocator] attribute are now stable.][51241] This will allow users to specify a global allocator for their program.
[Unit test functions marked with the #[test] attribute can now return Result<(), E: Debug> in addition to ().][51298]
[The lifetime specifier for macro_rules! is now stable.][50385] This allows macros to easily target lifetimes.

Compiler

[The s and z optimisation levels are now stable.][50265] These optimisations prioritise making smaller binary sizes. z is the same as s with the exception that it does not vectorise loops, which typically results in an even smaller binary.
[The short error format is now stable.][49546] Specified with --error-format=short this option will provide a more compressed output of rust error messages.
[Added a lint warning when you have duplicated macro_exports.][50143]
[Reduced the number of allocations in the macro parser.][50855] This can improve compile times of macro heavy crates on average by 5%.

Libraries

[Implemented Default for &mut str.][51306]
[Implemented From<bool> for all integer and unsigned number types.][50554]
[Implemented Extend for ().][50234]
[The Debug implementation of time::Duration should now be more easily human readable.][50364] Previously a Duration of one second would printed as Duration { secs: 1, nanos: 0 } and will now be printed as 1s.
[Implemented From<&String> for Cow<str>, From<&Vec<T>> for Cow<[T]>, From<Cow<CStr>> for CString, From<CString>, From<CStr>, From<&CString> for Cow<CStr>, From<OsString>, From<OsStr>, From<&OsString> for Cow<OsStr>, From<&PathBuf> for Cow<Path>, and From<Cow<Path>> for PathBuf.][50170]
[Implemented Shl and Shr for Wrapping<u128> and Wrapping<i128>.][50465]
[DirEntry::metadata now uses fstatat instead of lstat when possible.][51050] This can provide up to a 40% speed increase.
[Improved error messages when using format!.][50610]

Stabilized APIs

[Iterator::step_by]
[Path::ancestors]
[SystemTime::UNIX_EPOCH]
[alloc::GlobalAlloc]
[alloc::Layout]
[alloc::LayoutErr]
[alloc::System]
[alloc::alloc]
[alloc::alloc_zeroed]
[alloc::dealloc]
[alloc::realloc]
[alloc::handle_alloc_error]
[btree_map::Entry::or_default]
[fmt::Alignment]
[hash_map::Entry::or_default]
[iter::repeat_with]
[num::NonZeroUsize]
[num::NonZeroU128]
[num::NonZeroU16]
[num::NonZeroU32]
[num::NonZeroU64]
[num::NonZeroU8]
[ops::RangeBounds]
[slice::SliceIndex]
[slice::from_mut]
[slice::from_ref]
[{Any + Send + Sync}::downcast_mut]
[{Any + Send + Sync}::downcast_ref]
[{Any + Send + Sync}::is]

Cargo

[Cargo will now no longer allow you to publish crates with build scripts that modify the src directory.][cargo/5584] The src directory in a crate should be considered to be immutable.

Misc

[The suggestion_applicability field in rustc's json output is now stable.][50486] This will allow dev tools to check whether a code suggestion would apply to them.

Compatibility Notes

Rust will consider trait objects with duplicated constraints to be the same type as without the duplicated constraint. For example the below code will now fail to compile. ```rust trait Trait {}

impl Trait + Send { fn test(&self) { println!("one"); } //~ ERROR duplicate definitions with name test }

impl Trait + Send + Send { fn test(&self) { println!("two"); } } ```

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