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 * [Running rustfmt](#running-rustfmt)
21 * [Testing manually](#testing-manually)
22 * [Linting Clippy with your local changes](#linting-clippy-with-your-local-changes)
23 * [How Clippy works](#how-clippy-works)
24 * [Fixing nightly build failures](#fixing-build-failures-caused-by-rust)
25 * [Issue and PR Triage](#issue-and-pr-triage)
26 * [Bors and Homu](#bors-and-homu)
27 * [Contributions](#contributions)
33 1. Find something to fix/improve
34 2. Change code (likely some file in `clippy_lints/src/`)
35 3. Run `cargo test` in the root directory and wiggle code until it passes
36 4. Open a PR (also can be done between 2. and 3. if you run into problems)
38 ### Finding something to fix/improve
40 All issues on Clippy are mentored, if you want help with a bug just ask @Manishearth, @llogiq, @mcarton or @oli-obk.
42 Some issues are easier than others. The [`good first issue`](https://github.com/rust-lang/rust-clippy/labels/good%20first%20issue)
43 label can be used to find the easy issues. If you want to work on an issue, please leave a comment
44 so that we can assign it to you!
46 Issues marked [`T-AST`](https://github.com/rust-lang/rust-clippy/labels/T-AST) involve simple
47 matching of the syntax tree structure, and are generally easier than
48 [`T-middle`](https://github.com/rust-lang/rust-clippy/labels/T-middle) issues, which involve types
51 [`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
52 how this syntax structure is encoded in the AST, it is recommended to run `rustc -Z ast-json` on an
53 example of the structure and compare with the
54 [nodes in the AST docs](https://doc.rust-lang.org/nightly/nightly-rustc/syntax/ast). Usually
55 the lint will end up to be a nested series of matches and ifs,
56 [like so](https://github.com/rust-lang/rust-clippy/blob/de5ccdfab68a5e37689f3c950ed1532ba9d652a0/src/misc.rs#L34).
58 [`E-medium`](https://github.com/rust-lang/rust-clippy/labels/E-medium) issues are generally
59 pretty easy too, though it's recommended you work on an E-easy issue first. They are mostly classified
60 as `E-medium`, since they might be somewhat involved code wise, but not difficult per-se.
62 [`T-middle`](https://github.com/rust-lang/rust-clippy/labels/T-middle) issues can
63 be more involved and require verifying types. The
64 [`ty`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/ty) module contains a
65 lot of methods that are useful, though one of the most useful would be `expr_ty` (gives the type of
66 an AST expression). `match_def_path()` in Clippy's `utils` module can also be useful.
70 [Llogiq's blog post on lints](https://llogiq.github.io/2015/06/04/workflows.html) is a nice primer
71 to lint-writing, though it does get into advanced stuff. Most lints consist of an implementation of
72 `LintPass` with one or more of its default methods overridden. See the existing lints for examples
75 If you want to add a new lint or change existing ones apart from bugfixing, it's
76 also a good idea to give the [stability guaratees][rfc_stability] and
77 [lint categories][rfc_lint_cats] sections of the [Clippy 1.0 RFC][clippy_rfc] a
82 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.
84 First, create a new UI test file in the `tests/ui/` directory with the pattern you want to match:
87 // ./tests/ui/my_lint.rs
90 let arr: [i32; 1] = [7]; // Replace line with the code you want to match
94 Now you run `TESTNAME=ui/my_lint cargo test --test compile-test` to produce
95 a `.stdout` file with the generated code:
98 // ./tests/ui/my_lint.stdout
101 if let ExprKind::Array(ref elements) = stmt.node;
102 if elements.len() == 1;
103 if let ExprKind::Lit(ref lit) = elements[0].node;
104 if let LitKind::Int(7, _) = lit.node;
106 // report your lint here
111 If the command was executed successfully, you can copy the code over to where you are implementing your lint.
115 Please document your lint with a doc comment akin to the following:
118 /// **What it does:** Checks for ... (describe what the lint matches).
120 /// **Why is this bad?** Supply the reason for linting the code.
122 /// **Known problems:** None. (Or describe where it could go wrong.)
128 /// Insert a short example of code that triggers the lint
131 /// Insert a short example of improved code that doesn't trigger the lint
135 Once your lint is merged it will show up in the [lint list](https://rust-lang.github.io/rust-clippy/master/index.html)
137 ### Running test suite
139 Use `cargo test` to run the whole testsuite.
141 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:
144 TESTNAME=ui/empty_line_after_outer_attr cargo test --test compile-test
147 Clippy uses UI tests. UI tests check that the output of the compiler is exactly as expected.
148 Of course there's little sense in writing the output yourself or copying it around.
149 Therefore you should use `tests/ui/update-all-references.sh` (after running
150 `cargo test`) and check whether the output looks as you expect with `git diff`. Commit all
151 `*.stderr` files, too.
155 [Rustfmt](https://github.com/rust-lang/rustfmt) is a tool for formatting Rust code according
156 to style guidelines. The code has to be formatted by `rustfmt` before a PR will be merged.
158 It can be installed via `rustup`:
160 rustup component add rustfmt
163 Use `cargo fmt --all` to format the whole codebase.
167 Manually testing against an example file is useful if you have added some
168 `println!`s and test suite output becomes unreadable. To try Clippy with your
169 local modifications, run `env CLIPPY_TESTS=true cargo run --bin clippy-driver -- -L ./target/debug input.rs`
170 from the working copy root.
174 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.
176 [`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:
179 // ./clippy_lints/src/lib.rs
182 pub mod else_if_without_else;
185 pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
187 reg.register_early_lint_pass(box else_if_without_else::ElseIfWithoutElse);
190 reg.register_lint_group("clippy::restriction", vec![
192 else_if_without_else::ELSE_IF_WITHOUT_ELSE,
198 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].
199 Both take an object that implements an [`EarlyLintPass`][early_lint_pass] or [`LateLintPass`][late_lint_pass] respectively. This is done in every single lint.
200 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.
203 // ./clippy_lints/src/else_if_without_else.rs
205 use rustc::lint::{EarlyLintPass, LintArray, LintPass};
209 pub struct ElseIfWithoutElse;
213 impl EarlyLintPass for ElseIfWithoutElse {
214 // ... the functions needed, to make the lint work
218 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.
220 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.
222 ### Fixing build failures caused by Rust
224 Clippy will sometimes fail to build from source because building it 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.
226 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].
227 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.
229 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.
231 To check if Clippy is available for a specific target platform, you can check
232 the [rustup component history][rustup_component_history].
234 If you decide to make Clippy work again with a Rust commit that breaks it,
235 you probably want to install the latest Rust from master locally and run Clippy
236 using that version of Rust.
238 You can use [rustup-toolchain-install-master][rtim] to do that:
241 cargo install rustup-toolchain-install-master
242 rustup-toolchain-install-master -n master --force
243 rustup override set master
247 ## Issue and PR triage
249 Clippy is following the [Rust triage procedure][triage] for issues and pull
252 However, we are a smaller project with all contributors being volunteers
253 currently. Between writing new lints, fixing issues, reviewing pull requests and
254 responding to issues there may not always be enough time to stay on top of it
257 Our highest priority is fixing [crashes][l-crash] and [bugs][l-bug]. We don't
258 want Clippy to crash on your code and we want it to be as reliable as the
259 suggestions from Rust compiler errors.
263 We use a bot powered by [Homu][homu] to help automate testing and landing of pull
264 requests in Clippy. The bot's username is @bors.
266 You can find the Clippy bors queue [here][homu_queue].
268 If you have @bors permissions, you can find an overview of the available
269 commands [here][homu_instructions].
274 Contributions to Clippy should be made in the form of GitHub pull requests. Each pull request will
275 be reviewed by a core contributor (someone with permission to land patches) and either landed in the
276 main tree or given feedback for changes that would be required.
278 All code in this repository is under the [Apache-2.0](http://www.apache.org/licenses/LICENSE-2.0>)
279 or the [MIT](http://opensource.org/licenses/MIT) license.
281 <!-- adapted from https://github.com/servo/servo/blob/master/CONTRIBUTING.md -->
283 [main_entry]: https://github.com/rust-lang/rust-clippy/blob/c5b39a5917ffc0f1349b6e414fa3b874fdcf8429/src/lib.rs#L14
284 [lint_crate]: https://github.com/rust-lang/rust-clippy/tree/c5b39a5917ffc0f1349b6e414fa3b874fdcf8429/clippy_lints/src
285 [lint_crate_entry]: https://github.com/rust-lang/rust-clippy/blob/c5b39a5917ffc0f1349b6e414fa3b874fdcf8429/clippy_lints/src/lib.rs
286 [else_if_without_else]: https://github.com/rust-lang/rust-clippy/blob/c5b39a5917ffc0f1349b6e414fa3b874fdcf8429/clippy_lints/src/else_if_without_else.rs
287 [compiler_plugin]: https://doc.rust-lang.org/unstable-book/language-features/plugin.html#lint-plugins
288 [plugin_registry]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_plugin/registry/struct.Registry.html
289 [reg_early_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_plugin/registry/struct.Registry.html#method.register_early_lint_pass
290 [reg_late_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_plugin/registry/struct.Registry.html#method.register_late_lint_pass
291 [early_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc/lint/trait.EarlyLintPass.html
292 [late_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc/lint/trait.LateLintPass.html
293 [toolstate_commit_history]: https://github.com/rust-lang-nursery/rust-toolstate/commits/master
294 [toolstate_commit]: https://github.com/rust-lang-nursery/rust-toolstate/commit/6ce0459f6bfa7c528ae1886492a3e0b5ef0ee547
295 [rtim]: https://github.com/kennytm/rustup-toolchain-install-master
296 [rustup_component_history]: https://mexus.github.io/rustup-components-history
297 [clippy_rfc]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md
298 [rfc_stability]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md#stability-guarantees
299 [rfc_lint_cats]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md#lint-audit-and-categories
300 [triage]: https://forge.rust-lang.org/triage-procedure.html
301 [l-crash]: https://github.com/rust-lang/rust-clippy/labels/L-crash%20%3Aboom%3A
302 [l-bug]: https://github.com/rust-lang/rust-clippy/labels/L-bug%20%3Abeetle%3A
303 [homu]: https://github.com/servo/homu
304 [homu_instructions]: https://buildbot2.rust-lang.org/homu/
305 [homu_queue]: https://buildbot2.rust-lang.org/homu/queue/clippy