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 * [How Clippy works](#how-clippy-works)
23 * [Fixing nightly build failures](#fixing-build-failures-caused-by-rust)
24 * [Issue and PR Triage](#issue-and-pr-triage)
25 * [Bors and Homu](#bors-and-homu)
26 * [Contributions](#contributions)
32 1. Find something to fix/improve
33 2. Change code (likely some file in `clippy_lints/src/`)
34 3. Run `cargo test` in the root directory and wiggle code until it passes
35 4. Open a PR (also can be done between 2. and 3. if you run into problems)
37 ### Finding something to fix/improve
39 All issues on Clippy are mentored, if you want help with a bug just ask @Manishearth, @llogiq, @mcarton or @oli-obk.
41 Some issues are easier than others. The [`good first issue`](https://github.com/rust-lang/rust-clippy/labels/good%20first%20issue)
42 label can be used to find the easy issues. If you want to work on an issue, please leave a comment
43 so that we can assign it to you!
45 There are also some abandoned PRs, marked with
46 [`S-inactive-closed`](https://github.com/rust-lang/rust-clippy/pulls?q=is%3Aclosed+label%3AS-inactive-closed).
47 Pretty often these PRs are nearly completed and just need some extra steps
48 (formatting, addressing review comments, ...) to be merged. If you want to
49 complete such a PR, please leave a comment in the PR and open a new one based
52 Issues marked [`T-AST`](https://github.com/rust-lang/rust-clippy/labels/T-AST) involve simple
53 matching of the syntax tree structure, and are generally easier than
54 [`T-middle`](https://github.com/rust-lang/rust-clippy/labels/T-middle) issues, which involve types
57 [`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
58 how this syntax structure is encoded in the AST, it is recommended to run `rustc -Z ast-json` on an
59 example of the structure and compare with the
60 [nodes in the AST docs](https://doc.rust-lang.org/nightly/nightly-rustc/syntax/ast). Usually
61 the lint will end up to be a nested series of matches and ifs,
62 [like so](https://github.com/rust-lang/rust-clippy/blob/de5ccdfab68a5e37689f3c950ed1532ba9d652a0/src/misc.rs#L34).
64 [`E-medium`](https://github.com/rust-lang/rust-clippy/labels/E-medium) issues are generally
65 pretty easy too, though it's recommended you work on an E-easy issue first. They are mostly classified
66 as `E-medium`, since they might be somewhat involved code wise, but not difficult per-se.
68 [`T-middle`](https://github.com/rust-lang/rust-clippy/labels/T-middle) issues can
69 be more involved and require verifying types. The
70 [`ty`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/ty) module contains a
71 lot of methods that are useful, though one of the most useful would be `expr_ty` (gives the type of
72 an AST expression). `match_def_path()` in Clippy's `utils` module can also be useful.
76 [Llogiq's blog post on lints](https://llogiq.github.io/2015/06/04/workflows.html) is a nice primer
77 to lint-writing, though it does get into advanced stuff. Most lints consist of an implementation of
78 `LintPass` with one or more of its default methods overridden. See the existing lints for examples
81 If you want to add a new lint or change existing ones apart from bugfixing, it's
82 also a good idea to give the [stability guarantees][rfc_stability] and
83 [lint categories][rfc_lint_cats] sections of the [Clippy 1.0 RFC][clippy_rfc] a
88 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.
90 First, create a new UI test file in the `tests/ui/` directory with the pattern you want to match:
93 // ./tests/ui/my_lint.rs
96 let arr: [i32; 1] = [7]; // Replace line with the code you want to match
100 Now you run `TESTNAME=ui/my_lint cargo test --test compile-test` to produce
101 a `.stdout` file with the generated code:
104 // ./tests/ui/my_lint.stdout
107 if let ExprKind::Array(ref elements) = stmt.node;
108 if elements.len() == 1;
109 if let ExprKind::Lit(ref lit) = elements[0].node;
110 if let LitKind::Int(7, _) = lit.node;
112 // report your lint here
117 If the command was executed successfully, you can copy the code over to where you are implementing your lint.
121 Please document your lint with a doc comment akin to the following:
124 /// **What it does:** Checks for ... (describe what the lint matches).
126 /// **Why is this bad?** Supply the reason for linting the code.
128 /// **Known problems:** None. (Or describe where it could go wrong.)
134 /// Insert a short example of code that triggers the lint
137 /// Insert a short example of improved code that doesn't trigger the lint
141 Once your lint is merged it will show up in the [lint list](https://rust-lang.github.io/rust-clippy/master/index.html)
143 ### Running test suite
145 Use `cargo test` to run the whole testsuite.
147 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:
150 TESTNAME=ui/empty_line_after_outer_attr cargo test --test compile-test
153 Clippy uses UI tests. UI tests check that the output of the compiler is exactly as expected.
154 Of course there's little sense in writing the output yourself or copying it around.
155 Therefore you should use `tests/ui/update-all-references.sh` (after running
156 `cargo test`) and check whether the output looks as you expect with `git diff`. Commit all
157 `*.stderr` files, too.
159 If the lint you are working on is making use of structured suggestions, the
160 test file should include a `// run-rustfix` comment at the top. This will
161 additionally run [rustfix](https://github.com/rust-lang-nursery/rustfix) for
162 that test. Rustfix will apply the suggestions from the lint to the code of the
163 test file and compare that to the contents of a `.fixed` file.
165 Use `tests/ui/update-all-references.sh` to automatically generate the
166 `.fixed` file after running `cargo test`.
170 [Rustfmt](https://github.com/rust-lang/rustfmt) is a tool for formatting Rust code according
171 to style guidelines. The code has to be formatted by `rustfmt` before a PR will be merged.
173 It can be installed via `rustup`:
175 rustup component add rustfmt
178 Use `cargo fmt --all` to format the whole codebase.
182 Manually testing against an example file is useful if you have added some
183 `println!`s and test suite output becomes unreadable. To try Clippy with your
184 local modifications, run `env CLIPPY_TESTS=true cargo run --bin clippy-driver -- -L ./target/debug input.rs`
185 from the working copy root.
189 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.
191 [`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:
194 // ./clippy_lints/src/lib.rs
197 pub mod else_if_without_else;
200 pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
202 reg.register_early_lint_pass(box else_if_without_else::ElseIfWithoutElse);
205 reg.register_lint_group("clippy::restriction", vec![
207 else_if_without_else::ELSE_IF_WITHOUT_ELSE,
213 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].
214 Both take an object that implements an [`EarlyLintPass`][early_lint_pass] or [`LateLintPass`][late_lint_pass] respectively. This is done in every single lint.
215 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.
218 // ./clippy_lints/src/else_if_without_else.rs
220 use rustc::lint::{EarlyLintPass, LintArray, LintPass};
224 pub struct ElseIfWithoutElse;
228 impl EarlyLintPass for ElseIfWithoutElse {
229 // ... the functions needed, to make the lint work
233 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.
235 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.
237 ## Fixing build failures caused by Rust
239 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.
241 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].
242 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.
244 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.
246 To check if Clippy is available for a specific target platform, you can check
247 the [rustup component history][rustup_component_history].
249 If you decide to make Clippy work again with a Rust commit that breaks it,
250 you probably want to install the latest Rust from master locally and run Clippy
251 using that version of Rust.
253 You can use [rustup-toolchain-install-master][rtim] to do that:
256 cargo install rustup-toolchain-install-master
257 rustup-toolchain-install-master -n master --force
258 rustup override set master
262 ## Issue and PR triage
264 Clippy is following the [Rust triage procedure][triage] for issues and pull
267 However, we are a smaller project with all contributors being volunteers
268 currently. Between writing new lints, fixing issues, reviewing pull requests and
269 responding to issues there may not always be enough time to stay on top of it
272 Our highest priority is fixing [crashes][l-crash] and [bugs][l-bug]. We don't
273 want Clippy to crash on your code and we want it to be as reliable as the
274 suggestions from Rust compiler errors.
278 We use a bot powered by [Homu][homu] to help automate testing and landing of pull
279 requests in Clippy. The bot's username is @bors.
281 You can find the Clippy bors queue [here][homu_queue].
283 If you have @bors permissions, you can find an overview of the available
284 commands [here][homu_instructions].
289 Contributions to Clippy should be made in the form of GitHub pull requests. Each pull request will
290 be reviewed by a core contributor (someone with permission to land patches) and either landed in the
291 main tree or given feedback for changes that would be required.
293 All code in this repository is under the [Apache-2.0](http://www.apache.org/licenses/LICENSE-2.0>)
294 or the [MIT](http://opensource.org/licenses/MIT) license.
296 <!-- adapted from https://github.com/servo/servo/blob/master/CONTRIBUTING.md -->
298 [main_entry]: https://github.com/rust-lang/rust-clippy/blob/c5b39a5917ffc0f1349b6e414fa3b874fdcf8429/src/lib.rs#L14
299 [lint_crate]: https://github.com/rust-lang/rust-clippy/tree/c5b39a5917ffc0f1349b6e414fa3b874fdcf8429/clippy_lints/src
300 [lint_crate_entry]: https://github.com/rust-lang/rust-clippy/blob/c5b39a5917ffc0f1349b6e414fa3b874fdcf8429/clippy_lints/src/lib.rs
301 [else_if_without_else]: https://github.com/rust-lang/rust-clippy/blob/c5b39a5917ffc0f1349b6e414fa3b874fdcf8429/clippy_lints/src/else_if_without_else.rs
302 [compiler_plugin]: https://doc.rust-lang.org/unstable-book/language-features/plugin.html#lint-plugins
303 [plugin_registry]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_plugin/registry/struct.Registry.html
304 [reg_early_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_plugin/registry/struct.Registry.html#method.register_early_lint_pass
305 [reg_late_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_plugin/registry/struct.Registry.html#method.register_late_lint_pass
306 [early_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc/lint/trait.EarlyLintPass.html
307 [late_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc/lint/trait.LateLintPass.html
308 [toolstate_commit_history]: https://github.com/rust-lang-nursery/rust-toolstate/commits/master
309 [toolstate_commit]: https://github.com/rust-lang-nursery/rust-toolstate/commit/6ce0459f6bfa7c528ae1886492a3e0b5ef0ee547
310 [rtim]: https://github.com/kennytm/rustup-toolchain-install-master
311 [rustup_component_history]: https://mexus.github.io/rustup-components-history
312 [clippy_rfc]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md
313 [rfc_stability]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md#stability-guarantees
314 [rfc_lint_cats]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md#lint-audit-and-categories
315 [triage]: https://forge.rust-lang.org/triage-procedure.html
316 [l-crash]: https://github.com/rust-lang/rust-clippy/labels/L-crash%20%3Aboom%3A
317 [l-bug]: https://github.com/rust-lang/rust-clippy/labels/L-bug%20%3Abeetle%3A
318 [homu]: https://github.com/servo/homu
319 [homu_instructions]: https://buildbot2.rust-lang.org/homu/
320 [homu_queue]: https://buildbot2.rust-lang.org/homu/queue/clippy