Lints

You have noticed that a lot of trivial mistakes exist in the project. You would like to mechanically prevent these from passing code reviews. How can you mechanically detect them?

In programming, linting refers to the process of performing static code analysis on a software project to flag programming errors, bugs, stylistic errors and suspicious constructs. The term originates from an old UNIX tool named lint, which was used to check C programs for common mistakes.

The Rust community has an excellent linting tool named Clippy.

Clippy

The linter that is typically used in Rust is Clippy. It is commonly used in Rust projects to enforce good practises, recognize unsafe or slow code. It is also configurable.

Info

When enforcing coding style, it goes beyond mere aesthetic concerns. Coding style linters can do a lot more:

  • Detect patterns that have cleaner alternatives
  • Detect code that is correct, but slow
  • Disallow writing unsafe code

It usually comes preinstalled when installing Rust through Rustup, or it can be added later by running

rustup component add clippy

What makes Clippy interesting is that it is quite configurable. Lints can be enabled either individually, or in groups. Some default lint groups are enabled by default, but the list[^clippy-lints] can be examined to pick out ones that are relevant for the project.

Example: Overriding Lints in Code

Instead of making sure during code reviews that no unsafe code is written, a Clippy annotation can be added to the crates that should not have unsafe code in them.

#![allow(unused)]
#![deny(clippy::unsafe_code)]
fn main() {
}

Example: Overriding Lints in Cargo.toml

Reading

Static Analysis in Software Engineering at Google

Rust Lints you may not know by Andrew Lilley Brinker