Google's Rust Style Guide

What Google published

Google wrote a style guide for Rust code used across its many products. The guide covers more than formatting. It also gives advice on how to design APIs (the ways that code parts connect to each other) and how to build the code inside.

Where Rust is used at Google

Rust is used in many Google projects, including google3, Android, ChromeOS, Fuchsia, and Chrome. Google wants Rust code to look the same inside one project and across projects. Consistent code also helps set a standard of quality.

Why the rules exist

Google says the rules serve a few goals. The code will be used for a long time, so extra care while writing is worth it if it makes the code easier to read. The rules also make Large-Scale Changes (LSCs), which are big updates to many files at once, easier to do with tools. Google also follows the public Rust style rules wherever it can, so new engineers do not have to learn something completely different.

Key points for readers

• Library code must follow the API design rules. Application code should follow them as a strong suggestion.
• Application code should favor simple, direct solutions over code made for many uses too early.
• In Chromium, Google prefers small crates (units of compilation), ideally one file each.
• Where the Google guide and the public Rust rules conflict, the Google guide wins.