rust-clippy/README.md

# rust-clippy

[![Build Status](https://travis-ci.org/rust-lang-nursery/rust-clippy.svg?branch=master)](https://travis-ci.org/rust-lang-nursery/rust-clippy)
[![Windows build status](https://ci.appveyor.com/api/projects/status/github/rust-lang-nursery/rust-clippy?svg=true)](https://ci.appveyor.com/project/rust-lang-nursery/rust-clippy)
[![Current Version](https://meritbadge.herokuapp.com/clippy)](https://crates.io/crates/clippy)
[![License: MPL-2.0](https://img.shields.io/crates/l/clippy.svg)](#license)

A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.

[There are 268 lints included in this crate!](https://rust-lang-nursery.github.io/rust-clippy/master/index.html)

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](https://github.com/rust-lang-nursery/rust-clippy/issues) if you have ideas!

Table of contents:

*   [Usage instructions](#usage)
*   [Configuration](#configuration)
*   [License](#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. 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](https://rustup.rs/):

```terminal
rustup install nightly
```

### As a cargo subcommand (`cargo clippy`)

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

```terminal
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](rust-update) script or run:

```terminal
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.

```terminal
SYSROOT=/path/to/rustc/sysroot cargo install 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:

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

*[Note](https://github.com/rust-lang-nursery/rust-clippy/wiki#a-word-of-warning):*
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.

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

See the [list of lints](https://rust-lang-nursery.github.io/rust-clippy/master/index.html) 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:

```rust
#[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](rust-update) script to update rustc only if
clippy would also update correctly.

## License

Licensed under [MPL](https://www.mozilla.org/MPL/2.0/).
If you're having issues with the license, let me know and I'll try to change it to something more permissive.