# Clippy
-[](https://github.com/rust-lang/rust-clippy/actions?query=workflow%3A%22Clippy+Test%22+event%3Apush+branch%3Aauto)
+[/badge.svg?branch=auto&event=push)](https://github.com/rust-lang/rust-clippy/actions?query=workflow%3A%22Clippy+Test+(bors)%22+event%3Apush+branch%3Aauto)
[](#license)
A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
-[There are over 350 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
+[There are over 550 lints included in this crate!](https://rust-lang.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:
+Lints are divided into categories, each with a default [lint level](https://doc.rust-lang.org/rustc/lints/levels.html).
+You can choose how much Clippy is supposed to ~~annoy~~ help you by changing the lint level by category.
-* `clippy::all` (everything that is on by default: all the categories below except for `nursery`, `pedantic`, and `cargo`)
-* `clippy::correctness` (code that is just **outright wrong** or **very very useless**, causes hard errors by default)
-* `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::pedantic` (lints which are rather strict, off by default)
-* `clippy::nursery` (new lints that aren't quite ready yet, off by default)
-* `clippy::cargo` (checks against the cargo manifest, off by default)
+| 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::nursery` | new lints that are still under development | allow |
+| `clippy::cargo` | lints for the cargo manifest | allow |
More to come, please [file an issue](https://github.com/rust-lang/rust-clippy/issues) if you have ideas!
-Only the following of those categories are enabled by default:
-
-* `clippy::style`
-* `clippy::correctness`
-* `clippy::complexity`
-* `clippy::perf`
-
-Other categories need to be enabled in order for their lints to be executed.
-
The [lint list](https://rust-lang.github.io/rust-clippy/master/index.html) 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.
## 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.
+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
+#### Step 1: Install Rustup
-You can install [rustup](https://rustup.rs/) on supported platforms. This will help
+You can install [Rustup](https://rustup.rs/) 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:
+If you already have Rustup installed, update to ensure you have the latest
+Rustup and compiler:
```terminal
rustup update
#### Automatically applying Clippy suggestions
-Clippy can automatically apply some lint suggestions.
-Note that this is still experimental and only supported on the nightly channel:
+Clippy can automatically apply some lint suggestions, just like the compiler.
+
+```terminal
+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:
```terminal
-cargo clippy --fix -Z unstable-options
+cargo clippy -p example
```
-### Running Clippy from the command line without installing it
+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:
-To have cargo compile your crate with Clippy without Clippy installation
-in your code, you can use:
+```terminal
+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:
```terminal
-cargo run --bin cargo-clippy --manifest-path=path_to_clippys_Cargo.toml
+clippy-driver --edition 2018 -Cpanic=abort foo.rs
```
-*Note:* Be sure that Clippy was compiled with the same version of rustc that cargo invokes here!
+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
# 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.
-
-```yaml
-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
## 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](https://doc.rust-lang.org/rustc/lints/groups.html).
+
+* 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
+
+```terminal
+cargo clippy -- -A clippy::lint_name
+```
+
+And to warn on `lint_name`, run
+
+```terminal
+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::...
+```
+
+### 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 eg.
+value` mapping e.g.
```toml
-blacklisted-names = ["toto", "tata", "titi"]
+avoid-breaking-exported-api = false
+disallowed-names = ["toto", "tata", "titi"]
cognitive-complexity-threshold = 30
```
-See the [list of lints](https://rust-lang.github.io/rust-clippy/master/index.html) for more information about which
-lints can be configured and the meaning of the variables.
+See the [list of configurable lints](https://rust-lang.github.io/rust-clippy/master/index.html#Configuration),
+the lint descriptions contain the names and meanings of these configuration variables.
+
+> **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.
-### Allowing/denying lints
+### Specifying the minimum supported Rust version
-You can add options to your code to `allow`/`warn`/`deny` Clippy lints:
+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.
-* the whole set of `Warn` lints using the `clippy` lint group (`#![deny(clippy::all)]`)
+```toml
+msrv = "1.30.0"
+```
-* 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.
+Alternatively, the [`rust-version` field](https://doc.rust-lang.org/cargo/reference/manifest.html#the-rust-version-field)
+in the `Cargo.toml` can be used.
-* only some lints (`#![deny(clippy::single_match, clippy::box_vec)]`, etc.)
+```toml
+# Cargo.toml
+rust-version = "1.30"
+```
-* `allow`/`warn`/`deny` can be limited to a single function or module using `#[allow(...)]`, etc.
+The MSRV can also be specified as an attribute, like below.
+
+```rust
+#![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: `deny` produces errors instead of warnings.
+Note: `custom_inner_attributes` is an unstable feature, so it has to be enabled explicitly.
-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: `cargo clippy -- -A clippy::lint_name` will run Clippy with `lint_name` disabled and
-`cargo clippy -- -W clippy::lint_name` will run it with that enabled. 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 reenable
-the lint(s) you are interested in: `cargo clippy -- -Aclippy::all -Wclippy::useless_format -Wclippy::...`
+Lints that recognize this configuration option can be found [here](https://rust-lang.github.io/rust-clippy/master/index.html#msrv)
## Contributing
## License
-Copyright 2014-2020 The Rust Project Developers
+Copyright 2014-2022 The Rust Project Developers
Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
[https://www.apache.org/licenses/LICENSE-2.0](https://www.apache.org/licenses/LICENSE-2.0)> or the MIT license
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