A collection of lints to catch common mistakes and improve your Rust code.

There are over 500 lints included in this crate!

Lints are divided into categories, each with a default lint level. You can choose how much Clippy is supposed to annoy help you by changing the lint level by category.

More to come, please file an issue if you have ideas!

The lint list also contains "restriction lints", which are for things which are usually not considered "bad", but may be useful to turn on in specific cases. These should be used very selectively, if at all.

Table of contents:

• Usage instructions
• Configuration
• Contributing
• License

Below are instructions on how to use Clippy as a cargo subcommand, in projects that do not use cargo, or in Travis CI.

One way to use Clippy is by installing Clippy through rustup as a cargo subcommand.

You can install Rustup on supported platforms. This will help us install Clippy and its dependencies.

If you already have Rustup installed, update to ensure you have the latest Rustup and compiler:

rustup update 

Once you have rustup and the latest stable release (at least Rust 1.29) installed, run the following command:

rustup component add clippy 

If it says that it can't find the clippy component, please run rustup self update.

Now you can run Clippy by invoking the following command:

cargo clippy 

Clippy can automatically apply some lint suggestions, just like the compiler.

cargo clippy --fix 

All the usual workspace options should work with Clippy. For example the following command will run Clippy on the example crate:

cargo clippy -p example 

As with cargo check, this includes dependencies that are members of the workspace, like path dependencies. If you want to run Clippy only on the given crate, use the --no-deps option like this:

cargo clippy -p example -- --no-deps 

Clippy can also be used in projects that do not use cargo. To do so, run clippy-driver with the same arguments you use for rustc. For example:

clippy-driver --edition 2018 -Cpanic=abort foo.rs 

Note that clippy-driver is designed for running Clippy only and should not be used as a general replacement for rustc. clippy-driver may produce artifacts that are not optimized as expected, for example.

You can add Clippy to Travis CI in the same way you use it locally:

language: rust rust: - stable - beta before_script: - rustup component add clippy script: - cargo clippy # if you want the build job to fail when encountering warnings, use - cargo clippy -- -D warnings # in order to also check tests and non-default crate features, use - cargo clippy --all-targets --all-features -- -D warnings - cargo test # etc.

Note that adding -D warnings will cause your build to fail if any warnings are found in your code. That includes warnings found by rustc (e.g. dead_code, etc.). If you want to avoid this and only cause an error for Clippy warnings, use #![deny(clippy::all)] in your code or -D clippy::all on the command line. (You can swap clippy::all with the specific lint category you are targeting.)

Some lints can be configured in a TOML file named clippy.toml or .clippy.toml. It contains a basic variable = value mapping e.g.

avoid-breaking-exported-api = false blacklisted-names = ["toto", "tata", "titi"] cognitive-complexity-threshold = 30

See the list of lints for more information about which lints can be configured and the meaning of the variables.

Note that configuration changes will not apply for code that has already been compiled and cached under ./target/; for example, adding a new string to doc-valid-idents may still result in Clippy flagging that string. To be sure that any configuration changes are applied, you may want to run cargo clean and re-compile your crate from scratch.

To deactivate the “for further information visit lint-link” message you can define the CLIPPY_DISABLE_DOCS_LINKS environment variable.

You can add options to your code to allow/warn/deny Clippy lints:

• the whole set of Warn lints using the clippy lint group (#![deny(clippy::all)]). Note that rustc has additional lint groups.

• all lints using both the clippy and clippy::pedantic lint groups (#![deny(clippy::all)], #![deny(clippy::pedantic)]). Note that clippy::pedantic contains some very aggressive lints prone to false positives.

• only some lints (#![deny(clippy::single_match, clippy::box_vec)], etc.)

• allow/warn/deny can be limited to a single function or module using #[allow(...)], etc.

Note: allow means to suppress the lint for your code. With warn the lint will only emit a warning, while with deny the lint will emit an error, when triggering for your code. An error causes clippy to exit with an error code, so is useful in scripts like CI/CD.

If you do not want to include your lint levels in your code, you can globally enable/disable lints by passing extra flags to Clippy during the run:

To allow lint_name, run

cargo clippy -- -A clippy::lint_name 

And to warn on lint_name, run

cargo clippy -- -W clippy::lint_name 

This also works with lint groups. For example, you can run Clippy with warnings for all lints enabled:

cargo clippy -- -W clippy::pedantic 

If you care only about a single lint, you can allow all others and then explicitly warn on the lint(s) you are interested in:

cargo clippy -- -A clippy::all -W clippy::useless_format -W clippy::... 

Projects that intend to support old versions of Rust can disable lints pertaining to newer features by specifying the minimum supported Rust version (MSRV) in the clippy configuration file.

msrv = "1.30.0"

The MSRV can also be specified as an inner attribute, like below.

#![feature(custom_inner_attributes)] #![clippy::msrv = "1.30.0"] fn main() { ... }

You can also omit the patch version when specifying the MSRV, so msrv = 1.30 is equivalent to msrv = 1.30.0.

Note: custom_inner_attributes is an unstable feature, so it has to be enabled explicitly.

Lints that recognize this configuration option can be found here

If you want to contribute to Clippy, you can find more information in CONTRIBUTING.md.

Copyright 2014-2022 The Rust Project Developers

Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option. Files in the project may not be copied, modified, or distributed except according to those terms.