Rust 1.38 release: Pipelined compilation for Cargo & more

According to GitHub, Rust is the 5th fastest growing programming language. More and more developers are coding in Rust, submitting PRs, contributing to open source, and creating new projects.

Rust-lang v1.38.0 stable arrived on September 26, 2019. Check out what’s new in the programming language, including pipelined compilation and a few library changes.

Feature highlight: Pipelined compilation

With this new release, Cargo will now automatically begin building dependent crates as soon as the metadata is ready.

Since you don’t need to wait for the dependencies to be fully built when compiling a crate, this may help improve some compilation speeds.

According to the announcement blog, this will likely not have a major effect on builds for single creates. However, Rust found an increase of 10-20% compilation speed for some crate graphs. Click here to find out more about testing pipelined rustc compilation out.

Check out this tool created for exploring crate graph build times. Be sure to have a look at the PR for enabling pipelined compilation by default.

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New lints for incorrect uses of mem::{uninitialized, zeroed}

We’re happy to announce the release of Rust 1.38.0, featuring pipelined compilation! Check out all the new features in our blog post:https://t.co/UN5NN4beju

— Rust Language (@rustlang) September 26, 2019

In a future release, mem::uninitializedwill be deprecated. Although not deprecated yet, this release limits some of its incorrect uses in order to prevent unsafe usage. Incorrect usage will result in a warning in order to help identify incorrect code.

However, this update does not include every unsound usage. Thus, in order to play it safe, users should move their code to  MaybeUninit instead.

#[deprecated] attribute change

Now, the #[deprecated] attribute can be used on macros.

Check out the PR.

#[global_allocator] attribute change

The #[global_allocator] attribute can now be used in submodules.

See the PR.

Library changes

This version includes a variety of changes made to the library. Taken from the release notes on GitHub, these changes include:

• ascii::EscapeDefault now implements Clone and Display.
• Derive macros for prelude traits (e.g. Clone, Debug, Hash) are now available at the same path as the trait. (e.g. The Clone derive macro is available at std::clone::Clone). This also makes all built-in macros available in std/core root. e.g. std::include_bytes!.
• str::Chars now implements Debug.
• slice::{concat, connect, join} now accepts &[T] in addition to &T.
• *const T and *mut T now implement marker::Unpin.
• Arc<[T]> and Rc<[T]> now implement FromIterator<T>.
• Added euclidean remainder and division operations (div_euclid, rem_euclid) to all numeric primitives. Additionally checked, overflowing, and wrapping versions are available for all integer primitives.
• thread::AccessError now implements Clone, Copy, Eq, Error, and PartialEq.
• iter::{StepBy, Peekable, Take} now implement DoubleEndedIterator.

What features or changes do you want to see in future releases?

For more information about the newest update and a full list of changes, view the Rust 1.38.0 blog post, or browse the release notes on GitHub.