rust-clippy/README.md

We are currently in the process of discussing Clippy 1.0 via the RFC process in https://github.com/rust-lang/rfcs/pull/2476 . The RFC's goal is to clarify policies around lint categorizations and the policy around which lints should be in the compiler and which lints should be in Clippy. Please leave your thoughts on the RFC PR.

Clippy

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

There are 273 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_cargo (checks against the cargo manifest)
• 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 instructions
• Configuration
• License

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. These options are detailed below.

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 nightly toolchain

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

To install Rust nightly with rustup:

rustup install nightly

Step 3: Install clippy

Once you have rustup and the nightly toolchain installed, run the following command:

rustup component add clippy-preview --toolchain=nightly

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

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!

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.

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.