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152 lines
4.9 KiB
Markdown
152 lines
4.9 KiB
Markdown
# Usage
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This chapter describes how to use Clippy to get the most out of it. Clippy can
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be used as a `cargo` subcommand or, like `rustc`, directly with the
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`clippy-driver` binary.
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> _Note:_ This chapter assumes that you have Clippy installed already. If you're
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> not sure, take a look at the [Installation] chapter.
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## Cargo subcommand
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The easiest and most common way to run Clippy is through `cargo`. To do that,
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just run
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```bash
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cargo clippy
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```
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### Lint configuration
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The above command will run the default set of lints, which are included in the
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lint group `clippy::all`. You might want to use even more lints, or you may not
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agree with every Clippy lint, and for that there are ways to configure lint
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levels.
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> _Note:_ Clippy is meant to be used with a generous sprinkling of
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> `#[allow(..)]`s through your code. So if you disagree with a lint, don't feel
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> bad disabling them for parts of your code or the whole project.
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#### Command line
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You can configure lint levels on the command line by adding
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`-A/W/D clippy::lint_name` like this:
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```bash
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cargo clippy -- -Aclippy::style -Wclippy::double_neg -Dclippy::perf
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```
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For [CI] all warnings can be elevated to errors which will in turn fail
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the build and cause Clippy to exit with a code other than `0`.
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```
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cargo clippy -- -Dwarnings
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```
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> _Note:_ Adding `-D warnings` will cause your build to fail if **any** warnings
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> are found in your code. That includes warnings found by rustc (e.g.
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> `dead_code`, etc.).
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For more information on configuring lint levels, see the [rustc documentation].
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[rustc documentation]: https://doc.rust-lang.org/rustc/lints/levels.html#configuring-warning-levels
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#### Even more lints
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Clippy has lint groups which are allow-by-default. This means, that you will
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have to enable the lints in those groups manually.
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For a full list of all lints with their description and examples, please refer
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to [Clippy's lint list]. The two most important allow-by-default groups are
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described below:
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[Clippy's lint list]: https://rust-lang.github.io/rust-clippy/master/index.html
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##### `clippy::pedantic`
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The first group is the `pedantic` group. This group contains really opinionated
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lints, that may have some intentional false positives in order to prevent false
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negatives. So while this group is ready to be used in production, you can expect
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to sprinkle multiple `#[allow(..)]`s in your code. If you find any false
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positives, you're still welcome to report them to us for future improvements.
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> FYI: Clippy uses the whole group to lint itself.
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##### `clippy::restriction`
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The second group is the `restriction` group. This group contains lints that
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"restrict" the language in some way. For example the `clippy::unwrap` lint from
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this group won't allow you to use `.unwrap()` in your code. You may want to look
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through the lints in this group and enable the ones that fit your need.
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> _Note:_ You shouldn't enable the whole lint group, but cherry-pick lints from
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> this group. Some lints in this group will even contradict other Clippy lints!
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#### Too many lints
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The most opinionated warn-by-default group of Clippy is the `clippy::style`
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group. Some people prefer to disable this group completely and then cherry-pick
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some lints they like from this group. The same is of course possible with every
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other of Clippy's lint groups.
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> _Note:_ We try to keep the warn-by-default groups free from false positives
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> (FP). If you find that a lint wrongly triggers, please report it in an issue
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> (if there isn't an issue for that FP already)
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#### Source Code
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You can configure lint levels in source code the same way you can configure
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`rustc` lints:
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```rust,ignore
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#![allow(clippy::style)]
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#[warn(clippy::double_neg)]
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fn main() {
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let x = 1;
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let y = --x;
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// ^^ warning: double negation
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}
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```
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### Automatically applying Clippy suggestions
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Clippy can automatically apply some lint suggestions, just like the compiler. Note that `--fix` implies
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`--all-targets`, so it can fix as much code as it can.
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```terminal
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cargo clippy --fix
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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
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following command will run Clippy on the `example` crate in your workspace:
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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
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workspace, like path dependencies. If you want to run Clippy **only** on the
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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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## Using Clippy without `cargo`: `clippy-driver`
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Clippy can also be used in projects that do not use cargo. To do so, run
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`clippy-driver` with the same arguments you use for `rustc`. For example:
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```terminal
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clippy-driver --edition 2018 -Cpanic=abort foo.rs
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```
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> _Note:_ `clippy-driver` is designed for running Clippy and should not be used
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> as a general replacement for `rustc`. `clippy-driver` may produce artifacts
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> that are not optimized as expected, for example.
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[Installation]: installation.md
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[CI]: continuous_integration/index.md
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