1 # Contributing to rust-clippy
3 Hello fellow Rustacean! Great to see your interest in compiler internals and lints!
5 Clippy welcomes contributions from everyone. There are many ways to contribute to Clippy and the following document explains how
6 you can contribute and how to get started.
7 If you have any questions about contributing or need help with anything, feel free to ask questions on issues or
8 visit the `#clippy` IRC channel on `irc.mozilla.org`.
10 All contributors are expected to follow the [Rust Code of Conduct](http://www.rust-lang.org/conduct.html).
12 * [Getting started](#getting-started)
13 * [Finding something to fix/improve](#finding-something-to-fiximprove)
14 * [Writing code](#writing-code)
15 * [Author lint](#author-lint)
16 * [Documentation](#documentation)
17 * [Running test suite](#running-test-suite)
18 * [Testing manually](#testing-manually)
19 * [How Clippy works](#how-clippy-works)
20 * [Contributions](#contributions)
26 1. Find something to fix/improve
27 2. Change code (likely some file in `clippy_lints/src/`)
28 3. Run `cargo test` in the root directory and wiggle code until it passes
29 4. Open a PR (also can be done between 2. and 3. if you run into problems)
31 ### Finding something to fix/improve
33 All issues on Clippy are mentored, if you want help with a bug just ask @Manishearth, @llogiq, @mcarton or @oli-obk.
35 Some issues are easier than others. The [`good first issue`](https://github.com/rust-lang-nursery/rust-clippy/labels/good%20first%20issue)
36 label can be used to find the easy issues. If you want to work on an issue, please leave a comment
37 so that we can assign it to you!
39 Issues marked [`T-AST`](https://github.com/rust-lang-nursery/rust-clippy/labels/T-AST) involve simple
40 matching of the syntax tree structure, and are generally easier than
41 [`T-middle`](https://github.com/rust-lang-nursery/rust-clippy/labels/T-middle) issues, which involve types
44 [`T-AST`](https://github.com/rust-lang-nursery/rust-clippy/labels/T-AST) issues will generally need you to match against a predefined syntax structure. To figure out
45 how this syntax structure is encoded in the AST, it is recommended to run `rustc -Z ast-json` on an
46 example of the structure and compare with the
47 [nodes in the AST docs](https://doc.rust-lang.org/nightly/nightly-rustc/syntax/ast). Usually
48 the lint will end up to be a nested series of matches and ifs,
49 [like so](https://github.com/rust-lang-nursery/rust-clippy/blob/de5ccdfab68a5e37689f3c950ed1532ba9d652a0/src/misc.rs#L34).
51 [`E-medium`](https://github.com/rust-lang-nursery/rust-clippy/labels/E-medium) issues are generally
52 pretty easy too, though it's recommended you work on an E-easy issue first. They are mostly classified
53 as `E-medium`, since they might be somewhat involved code wise, but not difficult per-se.
55 [`T-middle`](https://github.com/rust-lang-nursery/rust-clippy/labels/T-middle) issues can
56 be more involved and require verifying types. The
57 [`ty`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/ty) module contains a
58 lot of methods that are useful, though one of the most useful would be `expr_ty` (gives the type of
59 an AST expression). `match_def_path()` in Clippy's `utils` module can also be useful.
63 Compiling clippy from scratch can take almost a minute or more depending on your machine.
64 However, since Rust 1.24.0 incremental compilation is enabled by default and compile times for small changes should be quick.
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
74 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.
76 First, create a new UI test file in the `tests/ui/` directory with the pattern you want to match:
79 // ./tests/ui/my_lint.rs
81 // The custom_attribute needs to be enabled for the author lint to work
82 #![feature(plugin, custom_attribute)]
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 Expr_::ExprArray(ref elements) = stmt.node;
98 if elements.len() == 1;
99 if let Expr_::ExprLit(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 `cargo run --bin clippy-driver -- -L ./target/debug input.rs` from the
154 working copy root. Your test file, here `input.rs`, needs to have clippy
164 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.
166 [`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:
169 // ./clippy_lints/src/lib.rs
172 pub mod else_if_without_else;
175 pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
177 reg.register_early_lint_pass(box else_if_without_else::ElseIfWithoutElse);
180 reg.register_lint_group("clippy_restriction", vec![
182 else_if_without_else::ELSE_IF_WITHOUT_ELSE,
188 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].
189 Both take an object that implements an [`EarlyLintPass`][early_lint_pass] or [`LateLintPass`][late_lint_pass] respectively. This is done in every single lint.
190 It's worth noting that the majority of `clippy_lints/src/lib.rs` is autogenerated by `util/update_lints.py` 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.
193 // ./clippy_lints/src/else_if_without_else.rs
199 pub struct ElseIfWithoutElse;
203 impl EarlyLintPass for ElseIfWithoutElse {
204 // ... the functions needed, to make the lint work
208 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.
210 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.
214 Contributions to Clippy should be made in the form of GitHub pull requests. Each pull request will
215 be reviewed by a core contributor (someone with permission to land patches) and either landed in the
216 main tree or given feedback for changes that would be required.
218 All code in this repository is under the [Mozilla Public License, 2.0](https://www.mozilla.org/MPL/2.0/)
220 <!-- adapted from https://github.com/servo/servo/blob/master/CONTRIBUTING.md -->
222 [main_entry]: https://github.com/rust-lang-nursery/rust-clippy/blob/c5b39a5917ffc0f1349b6e414fa3b874fdcf8429/src/lib.rs#L14
223 [lint_crate]: https://github.com/rust-lang-nursery/rust-clippy/tree/c5b39a5917ffc0f1349b6e414fa3b874fdcf8429/clippy_lints/src
224 [lint_crate_entry]: https://github.com/rust-lang-nursery/rust-clippy/blob/c5b39a5917ffc0f1349b6e414fa3b874fdcf8429/clippy_lints/src/lib.rs
225 [else_if_without_else]: https://github.com/rust-lang-nursery/rust-clippy/blob/c5b39a5917ffc0f1349b6e414fa3b874fdcf8429/clippy_lints/src/else_if_without_else.rs
226 [compiler_plugin]: https://doc.rust-lang.org/unstable-book/language-features/plugin.html#lint-plugins
227 [plugin_registry]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_plugin/registry/struct.Registry.html
228 [reg_early_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_plugin/registry/struct.Registry.html#method.register_early_lint_pass
229 [reg_late_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_plugin/registry/struct.Registry.html#method.register_late_lint_pass
230 [early_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc/lint/trait.EarlyLintPass.html
231 [late_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc/lint/trait.LateLintPass.html