Rust style editions

The default Rust style evolves over time, as Rust does. However, to avoid breaking established code style, and CI jobs checking code style, changes to the default Rust style only appear in style editions.

Code written in a given Rust edition uses the corresponding Rust style edition by default. To make it easier to migrate code style separately from the semantic changes between Rust editions, formatting tools such as rustfmt allow updating the style edition separately from the Rust edition.

The current version of the style guide describes the latest Rust style edition. Each distinct past style will have a corresponding archived version of the style guide.

Note that archived versions of the style guide do not document formatting for newer Rust constructs that did not exist at the time that version of the style guide was archived. However, each style edition will still format all constructs valid in that Rust edition, with the style of newer constructs coming from the first subsequent style edition providing formatting rules for that construct (without any of the systematic/global changes from that style edition).

Not all Rust editions have corresponding changes to the Rust style. For instance, Rust 2015, Rust 2018, and Rust 2021 all use the same style edition.

Rust 2024 style edition

This style guide describes the Rust 2024 style edition. The Rust 2024 style edition is currently nightly-only and may change before the release of Rust 2024.

For a full history of changes in the Rust 2024 style edition, see the git history of the style guide. Notable changes in the Rust 2024 style edition include:

• #114764 As the last member of a delimited expression, delimited expressions are generally combinable, regardless of the number of members. Previously only applied with exactly one member (except for closures with explicit blocks).
• When line-breaking an assignment operator, if the left-hand side spans multiple lines, use the base indentation of the last line of the left-hand side to indent the right-hand side.
• Miscellaneous rustfmt bugfixes.
• Use version-sort (sort x8, x16, x32, x64, x128 in that order).
• Change "ASCIIbetical" sort to Unicode-aware "non-lowercase before lowercase".
• Format single associated type where clauses on the same line if they fit.

Rust 2015/2018/2021 style edition

The archived version of the style guide at https://github.com/rust-lang/rust/tree/37343f4a4d4ed7ad0891cb79e8eb25acf43fb821/src/doc/style-guide/src describes the style edition corresponding to Rust 2015, Rust 2018, and Rust 2021.