Clippy

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

There are over 750 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.

Category	Description	Default level
clippy::all	all lints that are on by default (correctness, suspicious, style, complexity, perf)	warn/deny
clippy::correctness	code that is outright wrong or useless	deny
clippy::suspicious	code that is most likely wrong or useless	warn
clippy::style	code that should be written in a more idiomatic way	warn
clippy::complexity	code that does something simple but in a complex way	warn
clippy::perf	code that can be written to run faster	warn
clippy::pedantic	lints which are rather strict or have occasional false positives	allow
clippy::restriction	lints which prevent the use of language and library features1	allow
clippy::nursery	new lints that are still under development	allow
clippy::cargo	lints for the cargo manifest	allow

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

The restriction category should, emphatically, not be enabled as a whole. The contained lints may lint against perfectly reasonable code, may not have an alternative suggestion, and may contradict any other lints (including other categories). Lints should be considered on a case-by-case basis before enabling.

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Table of contents:

• Usage instructions
• Configuration
• Contributing
• License

Usage

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

As a cargo subcommand (cargo clippy)

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

Step 1: Install Rustup

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

Step 2: Install Clippy

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.

Step 3: Run Clippy

Now you can run Clippy by invoking the following command:

cargo clippy

Automatically applying Clippy suggestions

Clippy can automatically apply some lint suggestions, just like the compiler. Note that --fix implies --all-targets, so it can fix as much code as it can.

cargo clippy --fix

Workspaces

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

Using clippy-driver

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.

Travis CI

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.)

Configuration

Allowing/denying lints

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::...

Configure the behavior of some lints

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
disallowed-names = ["toto", "tata", "titi"]

The table of configurations contains all config values, their default, and a list of lints they affect. Each configurable lint , also contains information about these values.

For configurations that are a list type with default values such as disallowed-names, you can use the unique value ".." to extend the default values instead of replacing them.

# default of disallowed-names is ["foo", "baz", "quux"]
disallowed-names = ["bar", ".."] # -> ["bar", "foo", "baz", "quux"]

Note

clippy.toml or .clippy.toml cannot be used to allow/deny lints.

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

Specifying the minimum supported Rust version

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"

Alternatively, the rust-version field in the Cargo.toml can be used.

# Cargo.toml
rust-version = "1.30"

The MSRV can also be specified as an 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

Contributing

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

License

Copyright 2014-2024 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.

Footnotes

1. Some use cases for restriction lints include:

   • Strict coding styles (e.g. clippy::else_if_without_else).
   • Additional restrictions on CI (e.g. clippy::todo).
   • Preventing panicking in certain functions (e.g. clippy::unwrap_used).
   • Running a lint only on a subset of code (e.g. #[forbid(clippy::float_arithmetic)] on a module).
   ↩