Rust release · Feb 11, 2021

Rust 1.50: what's new, what was stabilized

Short answerRust 1.50 was released on Feb 11, 2021: 37 newly stable APIs (bool::then, btree_map::Entry::or_insert_with_key, f32::clamp, f64::clamp, ...); 6 compatibility notes that can affect existing code.

Feb 11, 2021release date

0language stabilizations

37APIs stabilized

-new edition

← Rust 1.49 All versions Rust 1.51 →

37 APIs stabilized

bool::then, btree_map::Entry::or_insert_with_key, f32::clamp, f64::clamp, hash_map::Entry::or_insert_with_key, Ord::clamp, RefCell::take, slice::fill, UnsafeCell::get_mut, IpAddr::is_ipv4, IpAddr::is_ipv6, IpAddr::is_unspecified, IpAddr::is_loopback, IpAddr::is_multicast, Ipv4Addr::octets, Ipv4Addr::is_loopback, Ipv4Addr::is_private, Ipv4Addr::is_link_local, Ipv4Addr::is_multicast, Ipv4Addr::is_broadcast, Ipv4Addr::is_documentation, Ipv4Addr::to_ipv6_compatible, Ipv4Addr::to_ipv6_mapped, Ipv6Addr::segments, Ipv6Addr::is_unspecified, Ipv6Addr::is_loopback, Ipv6Addr::is_multicast, Ipv6Addr::to_ipv4, Layout::size, Layout::align, Layout::from_size_align, pow, checked_pow, saturating_pow, wrapping_pow, next_power_of_two, checked_next_power_of_two

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 compare_and_swap method on atomics has been deprecated.][79261] It's
[Changes in how TokenStreams are checked have fixed some cases where you could write
[#![test] as an inner attribute is now considered unstable like other inner macro
[Overriding a forbid lint at the same level that it was set is now a hard error.][78864]
[You can no longer intercept panic! calls by supplying your own macro.][78343] It's
[Semi-colons after item statements (e.g. struct Foo {};) now produce a warning.][78296]

Use it

rustup update stable        # get the newest release
rustup install 1.50          # or exactly this one
rustup override set 1.50     # pin a project to it

To require at least this version from users of your crate, set rust-version = "1.50" 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

[You can now use const values for x in [x; N] array expressions.][79270] This has been technically possible since 1.38.0, as it was unintentionally stabilized.
[Assignments to ManuallyDrop<T> union fields are now considered safe.][78068]

Compiler

[Added tier 3\* support for the armv5te-unknown-linux-uclibceabi target.][78142]
[Added tier 3 support for the aarch64-apple-ios-macabi target.][77484]
[The x86_64-unknown-freebsd is now built with the full toolset.][79484]
[Dropped support for all cloudabi targets.][78439]

\* Refer to Rust's [platform support page][platform-support-doc] for more information on Rust's tiered platform support.

Libraries

[proc_macro::Punct now implements PartialEq<char>.][78636]
[ops::{Index, IndexMut} are now implemented for fixed sized arrays of any length.][74989]
[On Unix platforms, the std::fs::File type now has a "niche" of -1.][74699] This value cannot be a valid file descriptor, and now means Option<File> takes up the same amount of space as File.

Stabilized APIs

[bool::then]
[btree_map::Entry::or_insert_with_key]
[f32::clamp]
[f64::clamp]
[hash_map::Entry::or_insert_with_key]
[Ord::clamp]
[RefCell::take]
[slice::fill]
[UnsafeCell::get_mut]

The following previously stable methods are now const.

[IpAddr::is_ipv4]
[IpAddr::is_ipv6]
[IpAddr::is_unspecified]
[IpAddr::is_loopback]
[IpAddr::is_multicast]
[Ipv4Addr::octets]
[Ipv4Addr::is_loopback]
[Ipv4Addr::is_private]
[Ipv4Addr::is_link_local]
[Ipv4Addr::is_multicast]
[Ipv4Addr::is_broadcast]
[Ipv4Addr::is_documentation]
[Ipv4Addr::to_ipv6_compatible]
[Ipv4Addr::to_ipv6_mapped]
[Ipv6Addr::segments]
[Ipv6Addr::is_unspecified]
[Ipv6Addr::is_loopback]
[Ipv6Addr::is_multicast]
[Ipv6Addr::to_ipv4]
[Layout::size]
[Layout::align]
[Layout::from_size_align]
pow for all integer types.
checked_pow for all integer types.
saturating_pow for all integer types.
wrapping_pow for all integer types.
next_power_of_two for all unsigned integer types.
checked_next_power_of_two for all unsigned integer types.

Cargo

[Added the [build.rustc-workspace-wrapper] option.][cargo/8976] This option sets a wrapper to execute instead of rustc, for workspace members only.
[cargo:rerun-if-changed will now, if provided a directory, scan the entire contents of that directory for changes.][cargo/8973]
[Added the --workspace flag to the cargo update command.][cargo/8725]

Misc

[The search results tab and the help button are focusable with keyboard in rustdoc.][79896]
[Running tests will now print the total time taken to execute.][75752]

Compatibility Notes

The compare_and_swap method on atomics has been deprecated. It's recommended to use the compare_exchange and compare_exchange_weak methods instead.
Changes in how TokenStreams are checked have fixed some cases where you could write unhygenic macro_rules! macros.
[#![test] as an inner attribute is now considered unstable like other inner macro attributes, and reports an error by default through the soft_unstable lint.]79003
Overriding a forbid lint at the same level that it was set is now a hard error.
You can no longer intercept panic! calls by supplying your own macro. It's recommended to use the #[panic_handler] attribute to provide your own implementation.
Semi-colons after item statements (e.g. struct Foo {};) now produce a warning.

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