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
6 yelled at for giving it your best effort. The worst that can happen is that you'll be politely asked to change
7 something. We appreciate any sort of contributions, and don't want a wall of rules to get in the way of that.
9 Clippy welcomes contributions from everyone. There are many ways to contribute to Clippy and the following document
10 explains how you can contribute and how to get started. If you have any questions about contributing or need help with
11 anything, feel free to ask questions on issues or visit the `#clippy` on [Discord].
13 All contributors are expected to follow the [Rust Code of Conduct].
15 * [Getting started](#getting-started)
16 * [Finding something to fix/improve](#finding-something-to-fiximprove)
17 * [Writing code](#writing-code)
18 * [How Clippy works](#how-clippy-works)
19 * [Fixing nightly build failures](#fixing-build-failures-caused-by-rust)
20 * [Issue and PR Triage](#issue-and-pr-triage)
21 * [Bors and Homu](#bors-and-homu)
22 * [Contributions](#contributions)
24 [Discord]: https://discord.gg/rust-lang
25 [Rust Code of Conduct]: https://www.rust-lang.org/policies/code-of-conduct
31 1. Find something to fix/improve
32 2. Change code (likely some file in `clippy_lints/src/`)
33 3. Follow the instructions in the [docs for writing lints](doc/adding_lints.md) such as running the `setup-toolchain.sh` script
34 4. Run `cargo test` in the root directory and wiggle code until it passes
35 5. Open a PR (also can be done after 2. 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`] label can be used to find the easy issues.
42 If you want to work on an issue, please leave a comment so that we can assign it to you!
44 There are also some abandoned PRs, marked with [`S-inactive-closed`].
45 Pretty often these PRs are nearly completed and just need some extra steps
46 (formatting, addressing review comments, ...) to be merged. If you want to
47 complete such a PR, please leave a comment in the PR and open a new one based
50 Issues marked [`T-AST`] involve simple matching of the syntax tree structure,
51 and are generally easier than [`T-middle`] issues, which involve types
54 [`T-AST`] issues will generally need you to match against a predefined syntax structure.
55 To figure out how this syntax structure is encoded in the AST, it is recommended to run
56 `rustc -Z ast-json` on an example of the structure and compare with the [nodes in the AST docs].
57 Usually the lint will end up to be a nested series of matches and ifs, [like so][deep-nesting].
58 But we can make it nest-less by using [if_chain] macro, [like this][nest-less].
60 [`E-medium`] issues are generally pretty easy too, though it's recommended you work on an E-easy issue first.
61 They are mostly classified as [`E-medium`], since they might be somewhat involved code wise,
62 but not difficult per-se.
64 [`T-middle`] issues can be more involved and require verifying types. The [`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.
68 [`good first issue`]: https://github.com/rust-lang/rust-clippy/labels/good%20first%20issue
69 [`S-inactive-closed`]: https://github.com/rust-lang/rust-clippy/pulls?q=is%3Aclosed+label%3AS-inactive-closed
70 [`T-AST`]: https://github.com/rust-lang/rust-clippy/labels/T-AST
71 [`T-middle`]: https://github.com/rust-lang/rust-clippy/labels/T-middle
72 [`E-medium`]: https://github.com/rust-lang/rust-clippy/labels/E-medium
73 [`ty`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty
74 [nodes in the AST docs]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_ast/ast/
75 [deep-nesting]: https://github.com/rust-lang/rust-clippy/blob/557f6848bd5b7183f55c1e1522a326e9e1df6030/clippy_lints/src/mem_forget.rs#L29-L43
76 [if_chain]: https://docs.rs/if_chain/*/if_chain
77 [nest-less]: https://github.com/rust-lang/rust-clippy/blob/557f6848bd5b7183f55c1e1522a326e9e1df6030/clippy_lints/src/bit_mask.rs#L124-L150
81 Have a look at the [docs for writing lints][adding_lints] for more details. [Llogiq's blog post on lints]
82 is also a nice primer to lint-writing, though it does get into advanced stuff and may be a bit outdated.
84 If you want to add a new lint or change existing ones apart from bugfixing, it's
85 also a good idea to give the [stability guarantees][rfc_stability] and
86 [lint categories][rfc_lint_cats] sections of the [Clippy 1.0 RFC][clippy_rfc] a
89 [adding_lints]: https://github.com/rust-lang/rust-clippy/blob/master/doc/adding_lints.md
90 [Llogiq's blog post on lints]: https://llogiq.github.io/2015/06/04/workflows.html
91 [clippy_rfc]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md
92 [rfc_stability]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md#stability-guarantees
93 [rfc_lint_cats]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md#lint-audit-and-categories
97 [`clippy_lints/src/lib.rs`][lint_crate_entry] imports all the different lint modules and registers in the [`LintStore`].
98 For example, the [`else_if_without_else`][else_if_without_else] lint is registered like this:
101 // ./clippy_lints/src/lib.rs
104 pub mod else_if_without_else;
107 pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: &Conf) {
109 store.register_early_pass(|| box else_if_without_else::ElseIfWithoutElse);
112 store.register_group(true, "clippy::restriction", Some("clippy_restriction"), vec![
114 LintId::of(&else_if_without_else::ELSE_IF_WITHOUT_ELSE),
120 The [`rustc_lint::LintStore`][`LintStore`] provides two methods to register lints:
121 [register_early_pass][reg_early_pass] and [register_late_pass][reg_late_pass]. Both take an object
122 that implements an [`EarlyLintPass`][early_lint_pass] or [`LateLintPass`][late_lint_pass] respectively. This is done in
123 every single lint. It's worth noting that the majority of `clippy_lints/src/lib.rs` is autogenerated by `cargo dev
124 update_lints`. When you are writing your own lint, you can use that script to save you some time.
127 // ./clippy_lints/src/else_if_without_else.rs
129 use rustc_lint::{EarlyLintPass, EarlyContext};
133 pub struct ElseIfWithoutElse;
137 impl EarlyLintPass for ElseIfWithoutElse {
138 // ... the functions needed, to make the lint work
142 The difference between `EarlyLintPass` and `LateLintPass` is that the methods of the `EarlyLintPass` trait only provide
143 AST information. The methods of the `LateLintPass` trait are executed after type checking and contain type information
144 via the `LateContext` parameter.
146 That's why the `else_if_without_else` example uses the `register_early_pass` function. Because the
147 [actual lint logic][else_if_without_else] does not depend on any type information.
149 [lint_crate_entry]: https://github.com/rust-lang/rust-clippy/blob/master/clippy_lints/src/lib.rs
150 [else_if_without_else]: https://github.com/rust-lang/rust-clippy/blob/4253aa7137cb7378acc96133c787e49a345c2b3c/clippy_lints/src/else_if_without_else.rs
151 [`LintStore`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/struct.LintStore.html
152 [reg_early_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/struct.LintStore.html#method.register_early_pass
153 [reg_late_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/struct.LintStore.html#method.register_late_pass
154 [early_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/trait.EarlyLintPass.html
155 [late_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/trait.LateLintPass.html
157 ## Fixing build failures caused by Rust
159 Clippy will sometimes fail to build from source because building it depends on unstable internal Rust features. Most of
160 the times we have to adapt to the changes and only very rarely there's an actual bug in Rust. Fixing build failures
161 caused by Rust updates, can be a good way to learn about Rust internals.
163 In order to find out why Clippy does not work properly with a new Rust commit, you can use the [rust-toolstate commit
164 history][toolstate_commit_history]. You will then have to look for the last commit that contains
165 `test-pass -> build-fail` or `test-pass -> test-fail` for the `clippy-driver` component.
166 [Here][toolstate_commit] is an example.
168 The commit message contains a link to the PR. The PRs are usually small enough to discover the breaking API change and
169 if they are bigger, they likely include some discussion that may help you to fix Clippy.
171 To check if Clippy is available for a specific target platform, you can check
172 the [rustup component history][rustup_component_history].
174 If you decide to make Clippy work again with a Rust commit that breaks it,
175 you probably want to install the latest Rust from master locally and run Clippy
176 using that version of Rust.
178 You can set up the master toolchain by running `./setup-toolchain.sh`. That script will install
179 [rustup-toolchain-install-master][rtim] and master toolchain, then run `rustup override set master`.
181 After fixing the build failure on this repository, we can submit a pull request
182 to [`rust-lang/rust`] to fix the toolstate.
184 To submit a pull request, you should follow these steps:
187 # Assuming you already cloned the rust-lang/rust repo and you're in the correct directory
188 git submodule update --remote src/tools/clippy
189 cargo update -p clippy
191 git commit -m "Update Clippy"
192 ./x.py test -i --stage 1 src/tools/clippy # This is optional and should succeed anyway
193 # Open a PR in rust-lang/rust
196 [rustup_component_history]: https://rust-lang.github.io/rustup-components-history
197 [toolstate_commit_history]: https://github.com/rust-lang-nursery/rust-toolstate/commits/master
198 [toolstate_commit]: https://github.com/rust-lang-nursery/rust-toolstate/commit/aad74d8294e198a7cf8ac81a91aebb7f3bbcf727
199 [rtim]: https://github.com/kennytm/rustup-toolchain-install-master
200 [`rust-lang/rust`]: https://github.com/rust-lang/rust
202 ## Issue and PR triage
204 Clippy is following the [Rust triage procedure][triage] for issues and pull
207 However, we are a smaller project with all contributors being volunteers
208 currently. Between writing new lints, fixing issues, reviewing pull requests and
209 responding to issues there may not always be enough time to stay on top of it
212 Our highest priority is fixing [crashes][l-crash] and [bugs][l-bug]. We don't
213 want Clippy to crash on your code and we want it to be as reliable as the
214 suggestions from Rust compiler errors.
218 We use a bot powered by [Homu][homu] to help automate testing and landing of pull
219 requests in Clippy. The bot's username is @bors.
221 You can find the Clippy bors queue [here][homu_queue].
223 If you have @bors permissions, you can find an overview of the available
224 commands [here][homu_instructions].
226 [triage]: https://forge.rust-lang.org/triage-procedure.html
227 [l-crash]: https://github.com/rust-lang/rust-clippy/labels/L-crash%20%3Aboom%3A
228 [l-bug]: https://github.com/rust-lang/rust-clippy/labels/L-bug%20%3Abeetle%3A
229 [homu]: https://github.com/rust-lang/homu
230 [homu_instructions]: https://buildbot2.rust-lang.org/homu/
231 [homu_queue]: https://buildbot2.rust-lang.org/homu/queue/clippy
235 Contributions to Clippy should be made in the form of GitHub pull requests. Each pull request will
236 be reviewed by a core contributor (someone with permission to land patches) and either landed in the
237 main tree or given feedback for changes that would be required.
239 All code in this repository is under the [Apache-2.0] or the [MIT] license.
241 <!-- adapted from https://github.com/servo/servo/blob/master/CONTRIBUTING.md -->
243 [Apache-2.0]: https://www.apache.org/licenses/LICENSE-2.0
244 [MIT]: https://opensource.org/licenses/MIT