rust-clippy/book/src/lints.md

Clippy's Lints

Clippy offers a bunch of additional lints, to help its users write more correct and idiomatic Rust code. A full list of all lints, that can be filtered by category, lint level or keywords, can be found in the Clippy lint documentation.

This chapter will give an overview of the different lint categories, which kind of lints they offer and recommended actions when you should see a lint out of that category. For examples, see the Clippy lint documentation and filter by category.

The different lint groups were defined in the Clippy 1.0 RFC.

Correctness

The clippy::correctness group is the only lint group in Clippy which lints are deny-by-default and abort the compilation when triggered. This is for good reason: If you see a correctness lint, it means that your code is outright wrong or useless, and you should try to fix it.

Lints in this category are carefully picked and should be free of false positives. So just #[allow]ing those lints is not recommended.

Suspicious

The clippy::suspicious group is similar to the correctness lints in that it contains lints that trigger on code that is really sus and should be fixed. As opposed to correctness lints, it might be possible that the linted code is intentionally written like it is.

It is still recommended to fix code that is linted by lints out of this group instead of #[allow]ing the lint. In case you intentionally have written code that offends the lint you should specifically and locally #[allow] the lint and add give a reason why the code is correct as written.

Complexity

The clippy::complexity group offers lints that give you suggestions on how to simplify your code. It mostly focuses on code that can be written in a shorter and more readable way, while preserving the semantics.

If you should see a complexity lint, it usually means that you can remove or replace some code, and it is recommended to do so. However, if you need the more complex code for some expressiveness reason, it is recommended to allow complexity lints on a case-by-case basis.

Perf

The clippy::perf group gives you suggestions on how you can increase the performance of your code. Those lints are mostly about code that the compiler can't trivially optimize, but has to be written in a slightly different way to make the optimizer job easier.

Perf lints are usually easy to apply, and it is recommended to do so.

Style

The clippy::style group is mostly about writing idiomatic code. Because style is subjective, this lint group is the most opinionated warn-by-default group in Clippy.

If you see a style lint, applying the suggestion usually makes your code more readable and idiomatic. But because we know that this is opinionated, feel free to sprinkle #[allow]s for style lints in your code or #![allow] a style lint on your whole crate if you disagree with the suggested style completely.

Pedantic

The clippy::pedantic group makes Clippy even more pedantic. You can enable the whole group with #![warn(clippy::pedantic)] in the lib.rs/main.rs of your crate. This lint group is for Clippy power users that want an in depth check of their code.

Note: Instead of enabling the whole group (like Clippy itself does), you may want to cherry-pick lints out of the pedantic group.

If you enable this group, expect to also use #[allow] attributes generously throughout your code. Lints in this group are designed to be pedantic and false positives sometimes are intentional in order to prevent false negatives.

Restriction

The clippy::restriction group contains lints that will restrict you from using certain parts of the Rust language. It is not recommended to enable the whole group, but rather cherry-pick lints that are useful for your code base and your use case.

Note: Clippy will produce a warning if it finds a #![warn(clippy::restriction)] attribute in your code!

Lints from this group will restrict you in some way. If you enable a restriction lint for your crate it is recommended to also fix code that this lint triggers on. However, those lints are really strict by design, and you might want to #[allow] them in some special cases, with a comment justifying that.

Cargo

The clippy::cargo group gives you suggestions on how to improve your Cargo.toml file. This might be especially interesting if you want to publish your crate and are not sure if you have all useful information in your Cargo.toml.