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230 lines
8.4 KiB
Markdown
230 lines
8.4 KiB
Markdown
# Clippy
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[](https://github.com/rust-lang/rust-clippy/actions?query=workflow%3A%22Clippy+Test%22+event%3Apush+branch%3Aauto)
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[](#license)
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A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
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[There are over 400 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
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Lints are divided into categories, each with a default [lint level](https://doc.rust-lang.org/rustc/lints/levels.html).
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You can choose how much Clippy is supposed to ~~annoy~~ help you by changing the lint level by category.
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| Category | Description | Default level |
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| --------------------- | ----------------------------------------------------------------------- | ------------- |
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| `clippy::all` | all lints that are on by default (correctness, style, complexity, perf) | **warn/deny** |
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| `clippy::correctness` | code that is outright wrong or very useless | **deny** |
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| `clippy::style` | code that should be written in a more idiomatic way | **warn** |
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| `clippy::complexity` | code that does something simple but in a complex way | **warn** |
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| `clippy::perf` | code that can be written to run faster | **warn** |
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| `clippy::pedantic` | lints which are rather strict or might have false positives | allow |
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| `clippy::nursery` | new lints that are still under development | allow |
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| `clippy::cargo` | lints for the cargo manifest | allow |
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More to come, please [file an issue](https://github.com/rust-lang/rust-clippy/issues) if you have ideas!
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The [lint list](https://rust-lang.github.io/rust-clippy/master/index.html) also contains "restriction lints", which are
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for things which are usually not considered "bad", but may be useful to turn on in specific cases. These should be used
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very selectively, if at all.
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Table of contents:
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* [Usage instructions](#usage)
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* [Configuration](#configuration)
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* [Contributing](#contributing)
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* [License](#license)
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## Usage
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Below are instructions on how to use Clippy as a subcommand, compiled from source
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or in Travis CI.
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### As a cargo subcommand (`cargo clippy`)
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One way to use Clippy is by installing Clippy through rustup as a cargo
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subcommand.
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#### Step 1: Install rustup
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You can install [rustup](https://rustup.rs/) on supported platforms. This will help
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us install Clippy and its dependencies.
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If you already have rustup installed, update to ensure you have the latest
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rustup and compiler:
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```terminal
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rustup update
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```
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#### Step 2: Install Clippy
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Once you have rustup and the latest stable release (at least Rust 1.29) installed, run the following command:
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```terminal
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rustup component add clippy
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```
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If it says that it can't find the `clippy` component, please run `rustup self update`.
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#### Step 3: Run Clippy
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Now you can run Clippy by invoking the following command:
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```terminal
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cargo clippy
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```
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#### Automatically applying Clippy suggestions
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Clippy can automatically apply some lint suggestions.
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Note that this is still experimental and only supported on the nightly channel:
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```terminal
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cargo clippy --fix -Z unstable-options
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```
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#### Workspaces
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All the usual workspace options should work with Clippy. For example the following command
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will run Clippy on the `example` crate:
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```terminal
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cargo clippy -p example
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```
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As with `cargo check`, this includes dependencies that are members of the workspace, like path dependencies.
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If you want to run Clippy **only** on the given crate, use the `--no-deps` option like this:
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```terminal
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cargo clippy -p example -- --no-deps
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```
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### Travis CI
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You can add Clippy to Travis CI in the same way you use it locally:
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```yml
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language: rust
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rust:
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- stable
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- beta
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before_script:
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- rustup component add clippy
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script:
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- cargo clippy
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# if you want the build job to fail when encountering warnings, use
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- cargo clippy -- -D warnings
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# in order to also check tests and non-default crate features, use
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- cargo clippy --all-targets --all-features -- -D warnings
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- cargo test
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# etc.
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```
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Note that adding `-D warnings` will cause your build to fail if **any** warnings are found in your code.
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That includes warnings found by rustc (e.g. `dead_code`, etc.). If you want to avoid this and only cause
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an error for Clippy warnings, use `#![deny(clippy::all)]` in your code or `-D clippy::all` on the command
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line. (You can swap `clippy::all` with the specific lint category you are targeting.)
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## Configuration
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Some lints can be configured in a TOML file named `clippy.toml` or `.clippy.toml`. It contains a basic `variable =
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value` mapping eg.
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```toml
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blacklisted-names = ["toto", "tata", "titi"]
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cognitive-complexity-threshold = 30
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```
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See the [list of lints](https://rust-lang.github.io/rust-clippy/master/index.html) for more information about which
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lints can be configured and the meaning of the variables.
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To deactivate the “for further information visit *lint-link*” message you can
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define the `CLIPPY_DISABLE_DOCS_LINKS` environment variable.
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### Allowing/denying lints
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You can add options to your code to `allow`/`warn`/`deny` Clippy lints:
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* the whole set of `Warn` lints using the `clippy` lint group (`#![deny(clippy::all)]`)
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* all lints using both the `clippy` and `clippy::pedantic` lint groups (`#![deny(clippy::all)]`,
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`#![deny(clippy::pedantic)]`). Note that `clippy::pedantic` contains some very aggressive
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lints prone to false positives.
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* only some lints (`#![deny(clippy::single_match, clippy::box_vec)]`, etc.)
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* `allow`/`warn`/`deny` can be limited to a single function or module using `#[allow(...)]`, etc.
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Note: `allow` means to suppress the lint for your code. With `warn` the lint
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will only emit a warning, while with `deny` the lint will emit an error, when
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triggering for your code. An error causes clippy to exit with an error code, so
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is useful in scripts like CI/CD.
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If you do not want to include your lint levels in your code, you can globally
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enable/disable lints by passing extra flags to Clippy during the run:
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To allow `lint_name`, run
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```terminal
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cargo clippy -- -A clippy::lint_name
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```
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And to warn on `lint_name`, run
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```terminal
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cargo clippy -- -W clippy::lint_name
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```
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This also works with lint groups. For example you
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can run Clippy with warnings for all lints enabled:
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```terminal
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cargo clippy -- -W clippy::pedantic
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```
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If you care only about a single lint, you can allow all others and then explicitly warn on
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the lint(s) you are interested in:
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```terminal
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cargo clippy -- -A clippy::all -W clippy::useless_format -W clippy::...
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```
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Note that if you've run clippy before, this may only take effect after you've modified a file or ran `cargo clean`.
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### Specifying the minimum supported Rust version
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Projects that intend to support old versions of Rust can disable lints pertaining to newer features by
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specifying the minimum supported Rust version (MSRV) in the clippy configuration file.
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```toml
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msrv = "1.30.0"
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```
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The MSRV can also be specified as an inner attribute, like below.
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```rust
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#![feature(custom_inner_attributes)]
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#![clippy::msrv = "1.30.0"]
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fn main() {
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...
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}
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```
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You can also omit the patch version when specifying the MSRV, so `msrv = 1.30`
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is equivalent to `msrv = 1.30.0`.
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Note: `custom_inner_attributes` is an unstable feature so it has to be enabled explicitly.
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Lints that recognize this configuration option can be found [here](https://rust-lang.github.io/rust-clippy/master/index.html#msrv)
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## Contributing
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If you want to contribute to Clippy, you can find more information in [CONTRIBUTING.md](https://github.com/rust-lang/rust-clippy/blob/master/CONTRIBUTING.md).
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## License
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Copyright 2014-2020 The Rust Project Developers
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Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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[https://www.apache.org/licenses/LICENSE-2.0](https://www.apache.org/licenses/LICENSE-2.0)> or the MIT license
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<LICENSE-MIT or [https://opensource.org/licenses/MIT](https://opensource.org/licenses/MIT)>, at your
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option. Files in the project may not be
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copied, modified, or distributed except according to those terms.
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