Rust release · Oct 8, 2020

Rust 1.47: what's new, what was stabilized

Short answerRust 1.47 was released on Oct 8, 2020: 13 newly stable APIs (Ident::new_raw, Range::is_empty, RangeInclusive::is_empty, Result::as_deref, ...); 6 compatibility notes that can affect existing code.

Oct 8, 2020release date

0language stabilizations

13APIs stabilized

-new edition

← Rust 1.46 All versions Rust 1.48 →

13 APIs stabilized

Ident::new_raw, Range::is_empty, RangeInclusive::is_empty, Result::as_deref, Result::as_deref_mut, Vec::leak, pointer::offset_from, f32::TAU, f64::TAU, new, checked_add, checked_abs, is_ascii_alphabetic

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:

[Bumped the minimum supported Emscripten version to 1.39.20.][75716]
[Fixed a regression parsing {} && false in tail expressions.][74650]
[Added changes to how proc-macros are expanded in macro_rules! that should
[Moved support for the CloudABI target to tier 3.][75568]
[linux-gnu targets now require minimum kernel 2.6.32 and glibc 2.11.][74163]
[Added the rustc-docs component.][75560] This allows you to install

Use it

rustup update stable        # get the newest release
rustup install 1.47          # or exactly this one
rustup override set 1.47     # pin a project to it

To require at least this version from users of your crate, set rust-version = "1.47" 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

[Closures will now warn when not used.][74869]

Compiler

[Stabilized the -C control-flow-guard codegen option][73893], which enables [Control Flow Guard][1.47.0-cfg] for Windows platforms, and is ignored on other platforms.
[Upgraded to LLVM 11.][73526]
[Added tier 3\* support for the thumbv4t-none-eabi target.][74419]
[Upgrade the FreeBSD toolchain to version 11.4][75204]
[RUST_BACKTRACE's output is now more compact.][75048]

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

Libraries

[CStr now implements Index<RangeFrom<usize>>.][74021]
[Traits in std/core are now implemented for arrays of any length, not just those of length less than 33.][74060]
[ops::RangeFull and ops::Range now implement Default.][73197]
[panic::Location now implements Copy, Clone, Eq, Hash, Ord, PartialEq, and PartialOrd.][73583]

Stabilized APIs

[Ident::new_raw]
[Range::is_empty]
[RangeInclusive::is_empty]
[Result::as_deref]
[Result::as_deref_mut]
[Vec::leak]
[pointer::offset_from]
[f32::TAU]
[f64::TAU]

The following previously stable APIs have now been made const.

[The new method for all NonZero integers.][73858]
[The checked_add,checked_sub,checked_mul,checked_neg, checked_shl, checked_shr, saturating_add, saturating_sub, and saturating_mul methods for all integers.][73858]
[The checked_abs, saturating_abs, saturating_neg, and signum for all signed integers.][73858]
[The is_ascii_alphabetic, is_ascii_uppercase, is_ascii_lowercase, is_ascii_alphanumeric, is_ascii_digit, is_ascii_hexdigit, is_ascii_punctuation, is_ascii_graphic, is_ascii_whitespace, and is_ascii_control methods for char and u8.][73858]

Cargo

[build-dependencies are now built with opt-level 0 by default.][cargo/8500] You can override this by setting the following in your Cargo.toml. ``toml [profile.release.build-override] opt-level = 3 ``
[cargo-help will now display man pages for commands rather just the --help text.][cargo/8456]
[cargo-metadata now emits a test field indicating if a target has tests enabled.][cargo/8478]
[workspace.default-members now respects workspace.exclude.][cargo/8485]
[cargo-publish will now use an alternative registry by default if it's the only registry specified in package.publish.][cargo/8571]

Misc

[Added a help button beside Rustdoc's searchbar that explains rustdoc's type based search.][75366]
[Added the Ayu theme to rustdoc.][71237]

Compatibility Notes

[Bumped the minimum supported Emscripten version to 1.39.20.][75716]
[Fixed a regression parsing {} && false in tail expressions.][74650]
[Added changes to how proc-macros are expanded in macro_rules! that should help to preserve more span information.][73084] These changes may cause compilation errors if your macro was unhygenic or didn't correctly handle Delimiter::None.
[Moved support for the CloudABI target to tier 3.][75568]
[linux-gnu targets now require minimum kernel 2.6.32 and glibc 2.11.][74163]
[Added the rustc-docs component.][75560] This allows you to install and read the documentation for the compiler internal APIs. (Currently only available for x86_64-unknown-linux-gnu.)

Internal Only

Improved default settings for bootstrapping in x.py. You can read details about this change in the "Changes to x.py defaults" post on the Inside Rust blog.

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