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README.md Copy Chapter

Clippy


A collection of lints to catch common mistakes and improve your Rust code.

There are over 800 lints included in this crate!

Lints are divided into categories, each with a default lint level.
You can choose how much Clippy is supposed to ~~annoy~~ help you by changing the lint level by category.

| 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::restriction | lints which prevent the use of language and library features[^restrict] | 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 if you have ideas!

The restriction category should, emphatically, not be enabled as a whole. The contained
lints may lint against perfectly reasonable code, may not have an alternative suggestion,
and may contradict any other lints (including other categories). Lints should be considered
on a case-by-case basis before enabling.

[^restrict]: Some use cases for restriction lints include:
- Strict coding styles (e.g. [clippy::else_if_without_else]).
- Additional restrictions on CI (e.g. [clippy::todo]).
- Preventing panicking in certain functions (e.g. [clippy::unwrap_used]).
- Running a lint only on a subset of code (e.g. #[forbid(clippy::float_arithmetic)] on a module).

[clippy::else_if_without_else]: https://rust-lang.github.io/rust-clippy/master/index.html#else_if_without_else
[clippy::todo]: https://rust-lang.github.io/rust-clippy/master/index.html#todo
[clippy::unwrap_used]: https://rust-lang.github.io/rust-clippy/master/index.html#unwrap_used

---

Table of contents:

* Usage instructions
* Configuration
* Contributing
* License

Usage Copy Chapter

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) cargo clippy)')" title="Copy section prompt for LLMs"> Copy Section

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

#### Step 1: Install Rustup

You can install Rustup 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:

rustup update

#### Step 2: Install Clippy

Once you have rustup and the latest stable release (at least Rust 1.29) installed, run the following command:

rustup component add clippy

If it says that it can't find the clippy component, please run rustup self update.

#### Step 3: Run Clippy

Now you can run Clippy by invoking the following command:

cargo clippy

#### 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:

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-driver clippy-driver')" title="Copy section prompt for LLMs"> Copy Section

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 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 Copy Section

You can add Clippy to Travis CI in the same way you use it locally:

language: rust
rust:
  - stable
  - beta
before_script:
  - rustup component add clippy
script:
  - cargo clippy
  # if you want the build job to fail when encountering warnings, use
  - cargo clippy -- -D warnings
  # in order to also check tests and non-default crate features, use
  - cargo clippy --all-targets --all-features -- -D warnings
  - cargo test
  # 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
line. (You can swap clippy::all with the specific lint category you are targeting.)

Configuration Copy Chapter

Allowing/denying lints Copy Section

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.

* 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

cargo clippy -- -A clippy::lint_name

And to warn on lint_name, run

cargo clippy -- -W clippy::lint_name

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 warn on
the lint(s) you are interested in:

cargo clippy -- -A clippy::all -W clippy::useless_format -W clippy::...

Configure the behavior of some lints Copy Section

Some lints can be configured in a TOML file named clippy.toml or .clippy.toml. It contains a basic variable =
value mapping e.g.

avoid-breaking-exported-api = false
disallowed-names = ["toto", "tata", "titi"]

The table of configurations
contains all config values, their default, and a list of lints they affect.
Each configurable lint
, also contains information about these values.

For configurations that are a list type with default values such as
disallowed-names,
you can use the unique value ".." to extend the default values instead of replacing them.

default of disallowed-names is ["foo", "baz", "quux"]

disallowed-names = ["bar", ".."] # -> ["bar", "foo", "baz", "quux"]

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.

Specifying the minimum supported Rust version Copy Section

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.

msrv = "1.30.0"

Alternatively, the rust-version field
in the Cargo.toml can be used.

Cargo.toml

rust-version = "1.30"

The MSRV can also be specified as an attribute, like below.

``rust,ignore
#![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: custom_inner_attributes` is an unstable feature, so it has to be enabled explicitly.

Lints that recognize this configuration option can be found here

Contributing Copy Chapter

If you want to contribute to Clippy, you can find more information in CONTRIBUTING.md.

License Copy Chapter

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Copyright (c) The Rust Project Contributors

Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
<LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
option. Files in the project may not be
copied, modified, or distributed except according to those terms.

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