A bunch of helpful lints to avoid common pitfalls in Rust


Keywords
plugin, lint, clippy
License
MPL-2.0

Documentation

rust-clippy

Build Status Windows build status Current Version License: MPL-2.0

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

There are 253 lints included in this crate!

We have a bunch of lint categories to allow you to choose how much clippy is supposed to annoy help you:

  • clippy (everything that has no false positives)
  • clippy_pedantic (everything)
  • clippy_nursery (new lints that aren't quite ready yet)
  • clippy_style (code that should be written in a more idiomatic way)
  • clippy_complexity (code that does something simple but in a complex way)
  • clippy_perf (code that can be written in a faster way)
  • clippy_correctness (code that is just outright wrong or very very useless)

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

Table of contents:

Usage

Since this is a tool for helping the developer of a library or application write better code, it is recommended not to include clippy as a hard dependency. Options include using it as an optional dependency, as a cargo subcommand, or as an included feature during build. All of these options are detailed below.

As a general rule clippy will only work with the latest Rust nightly for now.

To install Rust nightly, the recommended way is to use rustup:

rustup install nightly

As a cargo subcommand (cargo clippy)

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

cargo +nightly install clippy

(The +nightly is not necessary if your default rustup install is nightly)

Now you can run clippy by invoking cargo +nightly clippy.

To update the subcommand together with the latest nightly use the rust-update script or run:

rustup update nightly
cargo +nightly install --force clippy

In case you are not using rustup, you need to set the environment flag SYSROOT during installation so clippy knows where to find librustc and similar crates.

SYSROOT=/path/to/rustc/sysroot cargo install clippy

Optional dependency

In some cases you might want to include clippy in your project directly, as an optional dependency. To do this, just modify Cargo.toml:

[dependencies]
clippy = { version = "*", optional = true }

And, in your main.rs or lib.rs, add these lines:

#![cfg_attr(feature="clippy", feature(plugin))]
#![cfg_attr(feature="clippy", plugin(clippy))]

Then build by enabling the feature: cargo +nightly build --features "clippy".

Instead of adding the cfg_attr attributes you can also run clippy on demand: cargo rustc --features clippy -- -Z no-trans -Z extra-plugins=clippy (the -Z no trans, while not necessary, will stop the compilation process after typechecking (and lints) have completed, which can significantly reduce the runtime).

Alternatively, to only run clippy when testing:

[dev-dependencies]
clippy = { version = "*" }

and add to main.rs or lib.rs:

#![cfg_attr(test, feature(plugin))]
#![cfg_attr(test, plugin(clippy))]

Running clippy from the command line without installing it

To have cargo compile your crate with clippy without clippy installation and without needing #![plugin(clippy)] 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!

As a Compiler Plugin

Note: This is not a recommended installation method.

Since stable Rust is backwards compatible, you should be able to compile your stable programs with nightly Rust with clippy plugged in to circumvent this.

Add in your Cargo.toml:

[dependencies]
clippy = "*"

You then need to add #![feature(plugin)] and #![plugin(clippy)] to the top of your crate entry point (main.rs or lib.rs).

Sample main.rs:

#![feature(plugin)]

#![plugin(clippy)]


fn main(){
    let x = Some(1u8);
    match x {
        Some(y) => println!("{:?}", y),
        _ => ()
    }
}

Produces this warning:

src/main.rs:8:5: 11:6 warning: you seem to be trying to use match for destructuring a single type. Consider using `if let`, #[warn(single_match)] on by default
src/main.rs:8     match x {
src/main.rs:9         Some(y) => println!("{:?}", y),
src/main.rs:10         _ => ()
src/main.rs:11     }
src/main.rs:8:5: 11:6 help: Try
if let Some(y) = x { println!("{:?}", y) }

Configuration

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

blacklisted-names = ["toto", "tata", "titi"]
cyclomatic-complexity-threshold = 30

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

You can also specify the path to the configuration file with:

#![plugin(clippy(conf_file="path/to/clippy's/configuration"))]

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 allow/warn/deny:

  • the whole set of Warn lints using the clippy lint group (#![deny(clippy)])

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

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

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

Note: deny produces errors instead of warnings.

For convenience, cargo clippy automatically defines a cargo-clippy feature. This lets you set lint levels and compile with or without clippy transparently:

#[cfg_attr(feature = "cargo-clippy", allow(needless_lifetimes))]

Updating rustc

Sometimes, rustc moves forward without clippy catching up. Therefore updating rustc may leave clippy a non-functional state until we fix the resulting breakage.

You can use the rust-update script to update rustc only if clippy would also update correctly.

License

Licensed under MPL. If you're having issues with the license, let me know and I'll try to change it to something more permissive.