1 # Contributing to Clippy
3 Hello fellow Rustacean! Great to see your interest in compiler internals and lints!
5 **First**: if you're unsure or afraid of _anything_, just ask or submit the issue or pull request anyway. You won't be yelled at for giving it your best effort. The worst that can happen is that you'll be politely asked to change something. We appreciate any sort of contributions, and don't want a wall of rules to get in the way of that.
7 Clippy welcomes contributions from everyone. There are many ways to contribute to Clippy and the following document explains how
8 you can contribute and how to get started.
9 If you have any questions about contributing or need help with anything, feel free to ask questions on issues or
10 visit the `#clippy` IRC channel on `irc.mozilla.org` or meet us in `#wg-clippy` on [Discord](https://discord.gg/rust-lang).
12 All contributors are expected to follow the [Rust Code of Conduct](http://www.rust-lang.org/conduct.html).
14 * [Getting started](#getting-started)
15 * [Finding something to fix/improve](#finding-something-to-fiximprove)
16 * [Writing code](#writing-code)
17 * [Author lint](#author-lint)
18 * [Documentation](#documentation)
19 * [Running test suite](#running-test-suite)
20 * [Testing manually](#testing-manually)
21 * [How Clippy works](#how-clippy-works)
22 * [Fixing nightly build failures](#fixing-build-failures-caused-by-rust)
23 * [Contributions](#contributions)
29 1. Find something to fix/improve
30 2. Change code (likely some file in `clippy_lints/src/`)
31 3. Run `cargo test` in the root directory and wiggle code until it passes
32 4. Open a PR (also can be done between 2. and 3. if you run into problems)
34 ### Finding something to fix/improve
36 All issues on Clippy are mentored, if you want help with a bug just ask @Manishearth, @llogiq, @mcarton or @oli-obk.
38 Some issues are easier than others. The [`good first issue`](https://github.com/rust-lang/rust-clippy/labels/good%20first%20issue)
39 label can be used to find the easy issues. If you want to work on an issue, please leave a comment
40 so that we can assign it to you!
42 Issues marked [`T-AST`](https://github.com/rust-lang/rust-clippy/labels/T-AST) involve simple
43 matching of the syntax tree structure, and are generally easier than
44 [`T-middle`](https://github.com/rust-lang/rust-clippy/labels/T-middle) issues, which involve types
47 [`T-AST`](https://github.com/rust-lang/rust-clippy/labels/T-AST) issues will generally need you to match against a predefined syntax structure. To figure out
48 how this syntax structure is encoded in the AST, it is recommended to run `rustc -Z ast-json` on an
49 example of the structure and compare with the
50 [nodes in the AST docs](https://doc.rust-lang.org/nightly/nightly-rustc/syntax/ast). Usually
51 the lint will end up to be a nested series of matches and ifs,
52 [like so](https://github.com/rust-lang/rust-clippy/blob/de5ccdfab68a5e37689f3c950ed1532ba9d652a0/src/misc.rs#L34).
54 [`E-medium`](https://github.com/rust-lang/rust-clippy/labels/E-medium) issues are generally
55 pretty easy too, though it's recommended you work on an E-easy issue first. They are mostly classified
56 as `E-medium`, since they might be somewhat involved code wise, but not difficult per-se.
58 [`T-middle`](https://github.com/rust-lang/rust-clippy/labels/T-middle) issues can
59 be more involved and require verifying types. The
60 [`ty`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/ty) module contains a
61 lot of methods that are useful, though one of the most useful would be `expr_ty` (gives the type of
62 an AST expression). `match_def_path()` in Clippy's `utils` module can also be useful.
66 [Llogiq's blog post on lints](https://llogiq.github.io/2015/06/04/workflows.html) is a nice primer
67 to lint-writing, though it does get into advanced stuff. Most lints consist of an implementation of
68 `LintPass` with one or more of its default methods overridden. See the existing lints for examples
71 If want to add a new lint or change existing ones apart from bugfixing, it's
72 also a good idea to give the [stability guaratees][rfc_stability] and
73 [lint categories][rfc_lint_cats] sections of the [Clippy 1.0 RFC][clippy_rfc] a
78 There is also the internal `author` lint to generate Clippy code that detects the offending pattern. It does not work for all of the Rust syntax, but can give a good starting point.
80 First, create a new UI test file in the `tests/ui/` directory with the pattern you want to match:
83 // ./tests/ui/my_lint.rs
86 let arr: [i32; 1] = [7]; // Replace line with the code you want to match
90 Now you run `TESTNAME=ui/my_lint cargo test --test compile-test` to produce
91 a `.stdout` file with the generated code:
94 // ./tests/ui/my_lint.stdout
97 if let ExprKind::Array(ref elements) = stmt.node;
98 if elements.len() == 1;
99 if let ExprKind::Lit(ref lit) = elements[0].node;
100 if let LitKind::Int(7, _) = lit.node;
102 // report your lint here
107 If the command was executed successfully, you can copy the code over to where you are implementing your lint.
111 Please document your lint with a doc comment akin to the following:
114 /// **What it does:** Checks for ... (describe what the lint matches).
116 /// **Why is this bad?** Supply the reason for linting the code.
118 /// **Known problems:** None. (Or describe where it could go wrong.)
124 /// Insert a short example of code that triggers the lint
127 /// Insert a short example of improved code that doesn't trigger the lint
131 Once your lint is merged it will show up in the [lint list](https://rust-lang-nursery.github.io/rust-clippy/master/index.html)
133 ### Running test suite
135 Use `cargo test` to run the whole testsuite.
137 If you don't want to wait for all tests to finish, you can also execute a single test file by using `TESTNAME` to specify the test to run:
140 TESTNAME=ui/empty_line_after_outer_attr cargo test --test compile-test
143 Clippy uses UI tests. UI tests check that the output of the compiler is exactly as expected.
144 Of course there's little sense in writing the output yourself or copying it around.
145 Therefore you should use `tests/ui/update-all-references.sh` (after running
146 `cargo test`) and check whether the output looks as you expect with `git diff`. Commit all
147 `*.stderr` files, too.
151 Manually testing against an example file is useful if you have added some
152 `println!`s and test suite output becomes unreadable. To try Clippy with your
153 local modifications, run `env CLIPPY_TESTS=true cargo run --bin clippy-driver -- -L ./target/debug input.rs`
154 from the working copy root.
156 ### Linting Clippy with your changes locally
158 Clippy CI only passes if all lints defined in the version of the Clippy being
159 tested pass (that is, don’t report any suggestions). You can avoid prolonging
160 the CI feedback cycle for PRs you submit by running these lints yourself ahead
161 of time and addressing any issues found:
165 `pwd`/target/debug/cargo-clippy clippy --all-targets --all-features -- -D clippy::all -D clippy::internal -D clippy::pedantic
170 Clippy is a [rustc compiler plugin][compiler_plugin]. The main entry point is at [`src/lib.rs`][main_entry]. In there, the lint registration is delegated to the [`clippy_lints`][lint_crate] crate.
172 [`clippy_lints/src/lib.rs`][lint_crate_entry] imports all the different lint modules and registers them with the rustc plugin registry. For example, the [`else_if_without_else`][else_if_without_else] lint is registered like this:
175 // ./clippy_lints/src/lib.rs
178 pub mod else_if_without_else;
181 pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
183 reg.register_early_lint_pass(box else_if_without_else::ElseIfWithoutElse);
186 reg.register_lint_group("clippy::restriction", vec![
188 else_if_without_else::ELSE_IF_WITHOUT_ELSE,
194 The [`rustc_plugin::PluginRegistry`][plugin_registry] provides two methods to register lints: [register_early_lint_pass][reg_early_lint_pass] and [register_late_lint_pass][reg_late_lint_pass].
195 Both take an object that implements an [`EarlyLintPass`][early_lint_pass] or [`LateLintPass`][late_lint_pass] respectively. This is done in every single lint.
196 It's worth noting that the majority of `clippy_lints/src/lib.rs` is autogenerated by `util/dev update_lints` and you don't have to add anything by hand. When you are writing your own lint, you can use that script to save you some time.
199 // ./clippy_lints/src/else_if_without_else.rs
201 use rustc::lint::{EarlyLintPass, LintArray, LintPass};
205 pub struct ElseIfWithoutElse;
209 impl EarlyLintPass for ElseIfWithoutElse {
210 // ... the functions needed, to make the lint work
214 The difference between `EarlyLintPass` and `LateLintPass` is that the methods of the `EarlyLintPass` trait only provide AST information. The methods of the `LateLintPass` trait are executed after type checking and contain type information via the `LateContext` parameter.
216 That's why the `else_if_without_else` example uses the `register_early_lint_pass` function. Because the [actual lint logic][else_if_without_else] does not depend on any type information.
218 ### Fixing build failures caused by Rust
220 Clippy will sometimes break because it still depends on unstable internal Rust features. Most of the times we have to adapt to the changes and only very rarely there's an actual bug in Rust. Fixing build failures caused by Rust updates, can be a good way to learn about Rust internals.
222 In order to find out why Clippy does not work properly with a new Rust commit, you can use the [rust-toolstate commit history][toolstate_commit_history].
223 You will then have to look for the last commit that contains `test-pass -> build-fail` or `test-pass` -> `test-fail` for the `clippy-driver` component. [Here][toolstate_commit] is an example.
225 The commit message contains a link to the PR. The PRs are usually small enough to discover the breaking API change and if they are bigger, they likely include some discussion that may help you to fix Clippy.
227 To check if Clippy is available for a specific target platform, you can check
228 the [rustup component history][rustup_component_history].
230 If you decide to make Clippy work again with a Rust commit that breaks it,
231 you probably want to install the latest Rust from master locally and run Clippy
232 using that version of Rust.
234 You can use [rustup-toolchain-install-master][rtim] to do that:
237 cargo install rustup-toolchain-install-master
238 rustup-toolchain-install-master -n master --force
239 rustup override set master
245 Contributions to Clippy should be made in the form of GitHub pull requests. Each pull request will
246 be reviewed by a core contributor (someone with permission to land patches) and either landed in the
247 main tree or given feedback for changes that would be required.
249 All code in this repository is under the [Mozilla Public License, 2.0](https://www.mozilla.org/MPL/2.0/)
251 <!-- adapted from https://github.com/servo/servo/blob/master/CONTRIBUTING.md -->
253 [main_entry]: https://github.com/rust-lang/rust-clippy/blob/c5b39a5917ffc0f1349b6e414fa3b874fdcf8429/src/lib.rs#L14
254 [lint_crate]: https://github.com/rust-lang/rust-clippy/tree/c5b39a5917ffc0f1349b6e414fa3b874fdcf8429/clippy_lints/src
255 [lint_crate_entry]: https://github.com/rust-lang/rust-clippy/blob/c5b39a5917ffc0f1349b6e414fa3b874fdcf8429/clippy_lints/src/lib.rs
256 [else_if_without_else]: https://github.com/rust-lang/rust-clippy/blob/c5b39a5917ffc0f1349b6e414fa3b874fdcf8429/clippy_lints/src/else_if_without_else.rs
257 [compiler_plugin]: https://doc.rust-lang.org/unstable-book/language-features/plugin.html#lint-plugins
258 [plugin_registry]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_plugin/registry/struct.Registry.html
259 [reg_early_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_plugin/registry/struct.Registry.html#method.register_early_lint_pass
260 [reg_late_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_plugin/registry/struct.Registry.html#method.register_late_lint_pass
261 [early_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc/lint/trait.EarlyLintPass.html
262 [late_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc/lint/trait.LateLintPass.html
263 [toolstate_commit_history]: https://github.com/rust-lang-nursery/rust-toolstate/commits/master
264 [toolstate_commit]: https://github.com/rust-lang-nursery/rust-toolstate/commit/6ce0459f6bfa7c528ae1886492a3e0b5ef0ee547
265 [rtim]: https://github.com/kennytm/rustup-toolchain-install-master
266 [rustup_component_history]: https://mexus.github.io/rustup-components-history
267 [clippy_rfc]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md
268 [rfc_stability]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md#stability-guarantees
269 [rfc_lint_cats]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md#lint-audit-and-categories