The Rust team is happy to announce a new version of Rust, 1.55.0. Rust is a programming language empowering everyone to build reliable and efficient software.

If you have a previous version of Rust installed via rustup, getting Rust 1.55.0 is as easy as:

$ rustup update stable

If you don't have it already, you can get rustup from the appropriate page on our website, and check out the detailed release notes for 1.55.0 on GitHub.

What's in 1.55.0 stable

Cargo deduplicates compiler errors

In past releases, when running cargo test, cargo check --all-targets, or similar commands which built the same Rust crate in multiple configurations, errors and warnings could show up duplicated as the rustc's were run in parallel and both showed the same warning.

For example, in 1.54.0, output like this was common:

$ cargo +1.54.0 check --all-targets
    Checking foo v0.1.0
warning: function is never used: `foo`
 --> src/lib.rs:9:4
  |
9 | fn foo() {}
  |    ^^^
  |
  = note: `#[warn(dead_code)]` on by default

warning: 1 warning emitted

warning: function is never used: `foo`
 --> src/lib.rs:9:4
  |
9 | fn foo() {}
  |    ^^^
  |
  = note: `#[warn(dead_code)]` on by default

warning: 1 warning emitted

    Finished dev [unoptimized + debuginfo] target(s) in 0.10s

In 1.55, this behavior has been adjusted to deduplicate and print a report at the end of compilation:

$ cargo +1.55.0 check --all-targets
    Checking foo v0.1.0
warning: function is never used: `foo`
 --> src/lib.rs:9:4
  |
9 | fn foo() {}
  |    ^^^
  |
  = note: `#[warn(dead_code)]` on by default

warning: `foo` (lib) generated 1 warning
warning: `foo` (lib test) generated 1 warning (1 duplicate)
    Finished dev [unoptimized + debuginfo] target(s) in 0.84s

Faster, more correct float parsing

The standard library's implementation of float parsing has been updated to use the Eisel-Lemire algorithm, which brings both speed improvements and improved correctness. In the past, certain edge cases failed to parse, and this has now been fixed.

You can read more details on the new implementation in the pull request description.

std::io::ErrorKind variants updated

std::io::ErrorKind is a #[non_exhaustive] enum that classifies errors into portable categories, such as NotFound or WouldBlock. Rust code that has a std::io::Error can call the kind method to obtain a std::io::ErrorKind and match on that to handle a specific error.

Not all errors are categorized into ErrorKind values; some are left uncategorized and placed in a catch-all variant. In previous versions of Rust, uncategorized errors used ErrorKind::Other; however, user-created std::io::Error values also commonly used ErrorKind::Other. In 1.55, uncategorized errors now use the internal variant ErrorKind::Uncategorized, which we intend to leave hidden and never available for stable Rust code to name explicitly; this leaves ErrorKind::Other exclusively for constructing std::io::Error values that don't come from the standard library. This enforces the #[non_exhaustive] nature of ErrorKind.

Rust code should never match ErrorKind::Other and expect any particular underlying error code; only match ErrorKind::Other if you're catching a constructed std::io::Error that uses that error kind. Rust code matching on std::io::Error should always use _ for any error kinds it doesn't know about, in which case it can match the underlying error code, or report the error, or bubble it up to calling code.

We're making this change to smooth the way for introducing new ErrorKind variants in the future; those new variants will start out nightly-only, and only become stable later. This change ensures that code matching variants it doesn't know about must use a catch-all _ pattern, which will work both with ErrorKind::Uncategorized and with future nightly-only variants.

Open range patterns added

Rust 1.55 stabilized using open ranges in patterns:

match x as u32 {
      0 => println!("zero!"),
      1.. => println!("positive number!"),
}

Read more details here.

Stabilized APIs

The following methods and trait implementations were stabilized.

• Bound::cloned
• Drain::as_str
• IntoInnerError::into_error
• IntoInnerError::into_parts
• MaybeUninit::assume_init_mut
• MaybeUninit::assume_init_ref
• MaybeUninit::write
• array::map
• ops::ControlFlow
• x86::_bittest
• x86::_bittestandcomplement
• x86::_bittestandreset
• x86::_bittestandset
• x86_64::_bittest64
• x86_64::_bittestandcomplement64
• x86_64::_bittestandreset64
• x86_64::_bittestandset64

The following previously stable functions are now const.

• str::from_utf8_unchecked

Other changes

There are other changes in the Rust 1.55.0 release: check out what changed in Rust, Cargo, and Clippy.

Contributors to 1.55.0

Many people came together to create Rust 1.55.0. We couldn't have done it without all of you. Thanks!

Dedication

Anna Harren was a member of the community and contributor to Rust known for coining the term "Turbofish" to describe ::<> syntax. Anna recently passed away after living with cancer. Her contribution will forever be remembered and be part of the language, and we dedicate this release to her memory.