Usage
This chapter describes how to use Clippy to get the most out of it. Clippy can
be used as a cargo
subcommand or, like rustc
, directly with the
clippy-driver
binary.
Note: This chapter assumes that you have Clippy installed already. If you're not sure, take a look at the Installation chapter.
Cargo subcommand
The easiest and most common way to run Clippy is through cargo
. To do that,
just run
cargo clippy
Lint configuration
The above command will run the default set of lints, which are included in the
lint group clippy::all
. You might want to use even more lints, or you may not
agree with every Clippy lint, and for that there are ways to configure lint
levels.
Note: Clippy is meant to be used with a generous sprinkling of
#[allow(..)]
s through your code. So if you disagree with a lint, don't feel bad disabling them for parts of your code or the whole project.
Command line
You can configure lint levels on the command line by adding
-A/W/D clippy::lint_name
like this:
cargo clippy -- -Aclippy::style -Wclippy::double_neg -Dclippy::perf
For CI all warnings can be elevated to errors which will inturn fail
the build and cause Clippy to exit with a code other than 0
.
cargo clippy -- -Dwarnings
Note: 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.).
For more information on configuring lint levels, see the rustc documentation.
Even more lints
Clippy has lint groups which are allow-by-default. This means, that you will have to enable the lints in those groups manually.
For a full list of all lints with their description and examples, please refer to Clippy's lint list. The two most important allow-by-default groups are described below:
clippy::pedantic
The first group is the pedantic
group. This group contains really opinionated
lints, that may have some intentional false positives in order to prevent false
negatives. So while this group is ready to be used in production, you can expect
to sprinkle multiple #[allow(..)]
s in your code. If you find any false
positives, you're still welcome to report them to us for future improvements.
FYI: Clippy uses the whole group to lint itself.
clippy::restriction
The second group is the restriction
group. This group contains lints that
"restrict" the language in some way. For example the clippy::unwrap
lint from
this group won't allow you to use .unwrap()
in your code. You may want to look
through the lints in this group and enable the ones that fit your need.
Note: You shouldn't enable the whole lint group, but cherry-pick lints from this group. Some lints in this group will even contradict other Clippy lints!
Too many lints
The most opinionated warn-by-default group of Clippy is the clippy::style
group. Some people prefer to disable this group completely and then cherry-pick
some lints they like from this group. The same is of course possible with every
other of Clippy's lint groups.
Note: We try to keep the warn-by-default groups free from false positives (FP). If you find that a lint wrongly triggers, please report it in an issue (if there isn't an issue for that FP already)
Source Code
You can configure lint levels in source code the same way you can configure
rustc
lints:
#![allow(clippy::style)]
#[warn(clippy::double_neg)]
fn main() {
let x = 1;
let y = --x;
// ^^ warning: double negation
}
Automatically applying Clippy suggestions
Clippy can automatically apply some lint suggestions, just like the compiler. Note that --fix
implies
--all-targets
, so it can fix as much code as it can.
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 in your workspace:
cargo clippy -p example
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:
cargo clippy -p example -- --no-deps
Using Clippy without cargo
: 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:
clippy-driver --edition 2018 -Cpanic=abort foo.rs
Note:
clippy-driver
is designed for running Clippy and should not be used as a general replacement forrustc
.clippy-driver
may produce artifacts that are not optimized as expected, for example.