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rust-lang
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Description

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

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Clippy

Clippy Test License: MIT OR Apache-2.0

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

There are over 400 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, style, complexity, perf) | warn/deny
clippy::correctness
| code that is outright wrong or very useless | deny
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 might have false positives | 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 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

Below are instructions on how to use Clippy as a subcommand, compiled from source 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. Note that this is still experimental and only supported on the nightly channel:

cargo clippy --fix -Z unstable-options

Running Clippy from the command line without installing it

To have cargo compile your crate with Clippy without Clippy installation in your code, you can use:

cargo run --bin cargo-clippy --manifest-path=path_to_clippys_Cargo.toml

Note: Be sure that Clippy was compiled with the same version of rustc that cargo invokes here!

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.

If you are on nightly, It might happen that Clippy is not available for a certain nightly release. In this case you can try to conditionally install Clippy from the Git repo.

language: rust
rust:
  - nightly
before_script:
   - rustup component add clippy --toolchain=nightly || cargo install --git https://github.com/rust-lang/rust-clippy/ --force clippy
   # 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

Some lints can be configured in a TOML file named

clippy.toml
or
.clippy.toml
. It contains a basic
variable =
value
mapping eg.
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.

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

CLIPPY_DISABLE_DOCS_LINKS
environment variable.

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)]
    )
  • 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:

terminal
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:

terminal
cargo clippy -- -A clippy::all -W clippy::useless_format -W clippy::...
Note that if you've run clippy before, this may only take effect after you've modified a file or ran
cargo clean
.

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"

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

Contributing

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

License

Copyright 2014-2020 The Rust Project Developers

Licensed under the Apache License, Version 2.0 or the MIT license , at your option. Files in the project may not be copied, modified, or distributed except according to those terms.

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