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 [Zulip].
13 All contributors are expected to follow the [Rust Code of Conduct].
15 - [Contributing to Clippy](#contributing-to-clippy)
16 - [Getting started](#getting-started)
17 - [High level approach](#high-level-approach)
18 - [Finding something to fix/improve](#finding-something-to-fiximprove)
19 - [Writing code](#writing-code)
20 - [Getting code-completion for rustc internals to work](#getting-code-completion-for-rustc-internals-to-work)
21 - [How Clippy works](#how-clippy-works)
22 - [Fixing build failures caused by Rust](#fixing-build-failures-caused-by-rust)
23 - [Patching git-subtree to work with big repos](#patching-git-subtree-to-work-with-big-repos)
24 - [Performing the sync](#performing-the-sync)
25 - [Syncing back changes in Clippy to [`rust-lang/rust`]](#syncing-back-changes-in-clippy-to-rust-langrust)
26 - [Defining remotes](#defining-remotes)
27 - [Issue and PR triage](#issue-and-pr-triage)
28 - [Bors and Homu](#bors-and-homu)
29 - [Contributions](#contributions)
31 [Zulip]: https://rust-lang.zulipchat.com/#narrow/stream/clippy
32 [Rust Code of Conduct]: https://www.rust-lang.org/policies/code-of-conduct
36 **Note: If this is your first time contributing to Clippy, you should
37 first read the [Basics docs](doc/basics.md).**
39 ### High level approach
41 1. Find something to fix/improve
42 2. Change code (likely some file in `clippy_lints/src/`)
43 3. Follow the instructions in the [Basics docs](doc/basics.md) to get set up
44 4. Run `cargo test` in the root directory and wiggle code until it passes
45 5. Open a PR (also can be done after 2. if you run into problems)
47 ### Finding something to fix/improve
49 All issues on Clippy are mentored, if you want help with a bug just ask
50 @Manishearth, @flip1995, @phansch or @yaahc.
52 Some issues are easier than others. The [`good first issue`] label can be used to find the easy issues.
53 If you want to work on an issue, please leave a comment so that we can assign it to you!
55 There are also some abandoned PRs, marked with [`S-inactive-closed`].
56 Pretty often these PRs are nearly completed and just need some extra steps
57 (formatting, addressing review comments, ...) to be merged. If you want to
58 complete such a PR, please leave a comment in the PR and open a new one based
61 Issues marked [`T-AST`] involve simple matching of the syntax tree structure,
62 and are generally easier than [`T-middle`] issues, which involve types
65 [`T-AST`] issues will generally need you to match against a predefined syntax structure.
66 To figure out how this syntax structure is encoded in the AST, it is recommended to run
67 `rustc -Z ast-json` on an example of the structure and compare with the [nodes in the AST docs].
68 Usually the lint will end up to be a nested series of matches and ifs, [like so][deep-nesting].
69 But we can make it nest-less by using [if_chain] macro, [like this][nest-less].
71 [`E-medium`] issues are generally pretty easy too, though it's recommended you work on an [`good first issue`]
72 first. Sometimes they are only somewhat involved code wise, but not difficult per-se.
73 Note that [`E-medium`] issues may require some knowledge of Clippy internals or some
74 debugging to find the actual problem behind the issue.
76 [`T-middle`] issues can be more involved and require verifying types. The [`ty`] module contains a
77 lot of methods that are useful, though one of the most useful would be `expr_ty` (gives the type of
78 an AST expression). `match_def_path()` in Clippy's `utils` module can also be useful.
80 [`good first issue`]: https://github.com/rust-lang/rust-clippy/labels/good%20first%20issue
81 [`S-inactive-closed`]: https://github.com/rust-lang/rust-clippy/pulls?q=is%3Aclosed+label%3AS-inactive-closed
82 [`T-AST`]: https://github.com/rust-lang/rust-clippy/labels/T-AST
83 [`T-middle`]: https://github.com/rust-lang/rust-clippy/labels/T-middle
84 [`E-medium`]: https://github.com/rust-lang/rust-clippy/labels/E-medium
85 [`ty`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty
86 [nodes in the AST docs]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_ast/ast/
87 [deep-nesting]: https://github.com/rust-lang/rust-clippy/blob/557f6848bd5b7183f55c1e1522a326e9e1df6030/clippy_lints/src/mem_forget.rs#L29-L43
88 [if_chain]: https://docs.rs/if_chain/*/if_chain
89 [nest-less]: https://github.com/rust-lang/rust-clippy/blob/557f6848bd5b7183f55c1e1522a326e9e1df6030/clippy_lints/src/bit_mask.rs#L124-L150
93 Have a look at the [docs for writing lints][adding_lints] for more details.
95 If you want to add a new lint or change existing ones apart from bugfixing, it's
96 also a good idea to give the [stability guarantees][rfc_stability] and
97 [lint categories][rfc_lint_cats] sections of the [Clippy 1.0 RFC][clippy_rfc] a
100 [adding_lints]: https://github.com/rust-lang/rust-clippy/blob/master/doc/adding_lints.md
101 [clippy_rfc]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md
102 [rfc_stability]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md#stability-guarantees
103 [rfc_lint_cats]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md#lint-audit-and-categories
105 ## Getting code-completion for rustc internals to work
107 Unfortunately, [`rust-analyzer`][ra_homepage] does not (yet?) understand how Clippy uses compiler-internals
108 using `extern crate` and it also needs to be able to read the source files of the rustc-compiler which are not
109 available via a `rustup` component at the time of writing.
110 To work around this, you need to have a copy of the [rustc-repo][rustc_repo] available which can be obtained via
111 `git clone https://github.com/rust-lang/rust/`.
112 Then you can run a `cargo dev` command to automatically make Clippy use the rustc-repo via path-dependencies
113 which rust-analyzer will be able to understand.
114 Run `cargo dev ra-setup --repo-path <repo-path>` where `<repo-path>` is an absolute path to the rustc repo
116 The command will add path-dependencies pointing towards rustc-crates inside the rustc repo to
117 Clippys `Cargo.toml`s and should allow rust-analyzer to understand most of the types that Clippy uses.
118 Just make sure to remove the dependencies again before finally making a pull request!
120 [ra_homepage]: https://rust-analyzer.github.io/
121 [rustc_repo]: https://github.com/rust-lang/rust/
125 [`clippy_lints/src/lib.rs`][lint_crate_entry] imports all the different lint modules and registers in the [`LintStore`].
126 For example, the [`else_if_without_else`][else_if_without_else] lint is registered like this:
129 // ./clippy_lints/src/lib.rs
132 pub mod else_if_without_else;
135 pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: &Conf) {
137 store.register_early_pass(|| box else_if_without_else::ElseIfWithoutElse);
140 store.register_group(true, "clippy::restriction", Some("clippy_restriction"), vec![
142 LintId::of(&else_if_without_else::ELSE_IF_WITHOUT_ELSE),
148 The [`rustc_lint::LintStore`][`LintStore`] provides two methods to register lints:
149 [register_early_pass][reg_early_pass] and [register_late_pass][reg_late_pass]. Both take an object
150 that implements an [`EarlyLintPass`][early_lint_pass] or [`LateLintPass`][late_lint_pass] respectively. This is done in
151 every single lint. It's worth noting that the majority of `clippy_lints/src/lib.rs` is autogenerated by `cargo dev
152 update_lints`. When you are writing your own lint, you can use that script to save you some time.
155 // ./clippy_lints/src/else_if_without_else.rs
157 use rustc_lint::{EarlyLintPass, EarlyContext};
161 pub struct ElseIfWithoutElse;
165 impl EarlyLintPass for ElseIfWithoutElse {
166 // ... the functions needed, to make the lint work
170 The difference between `EarlyLintPass` and `LateLintPass` is that the methods of the `EarlyLintPass` trait only provide
171 AST information. The methods of the `LateLintPass` trait are executed after type checking and contain type information
172 via the `LateContext` parameter.
174 That's why the `else_if_without_else` example uses the `register_early_pass` function. Because the
175 [actual lint logic][else_if_without_else] does not depend on any type information.
177 [lint_crate_entry]: https://github.com/rust-lang/rust-clippy/blob/master/clippy_lints/src/lib.rs
178 [else_if_without_else]: https://github.com/rust-lang/rust-clippy/blob/4253aa7137cb7378acc96133c787e49a345c2b3c/clippy_lints/src/else_if_without_else.rs
179 [`LintStore`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/struct.LintStore.html
180 [reg_early_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/struct.LintStore.html#method.register_early_pass
181 [reg_late_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/struct.LintStore.html#method.register_late_pass
182 [early_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/trait.EarlyLintPass.html
183 [late_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/trait.LateLintPass.html
185 ## Syncing changes between Clippy and [`rust-lang/rust`]
187 Clippy currently gets built with a pinned nightly version.
189 In the `rust-lang/rust` repository, where rustc resides, there's a copy of Clippy
190 that compiler hackers modify from time to time to adapt to changes in the unstable
193 We need to sync these changes back to this repository periodically, and the changes
194 made to this repository in the meantime also need to be synced to the `rust-lang/rust` repository.
196 To avoid flooding the `rust-lang/rust` PR queue, this two-way sync process is done
197 in a bi-weekly basis if there's no urgent changes. This is done starting on the day of
198 the Rust stable release and then every other week. That way we guarantee that we keep
199 this repo up to date with the latest compiler API, and every feature in Clippy is available
200 for 2 weeks in nightly, before it can get to beta. For reference, the first sync
201 following this cadence was performed the 2020-08-27.
203 This process is described in detail in the following sections. For general information
204 about `subtree`s in the Rust repository see [Rust's `CONTRIBUTING.md`][subtree].
206 ### Patching git-subtree to work with big repos
208 Currently there's a bug in `git-subtree` that prevents it from working properly
209 with the [`rust-lang/rust`] repo. There's an open PR to fix that, but it's stale.
210 Before continuing with the following steps, we need to manually apply that fix to
211 our local copy of `git-subtree`.
213 You can get the patched version of `git-subtree` from [here][gitgitgadget-pr].
214 Put this file under `/usr/lib/git-core` (taking a backup of the previous file)
215 and make sure it has the proper permissions:
218 sudo cp --backup /path/to/patched/git-subtree.sh /usr/lib/git-core/git-subtree
219 sudo chmod --reference=/usr/lib/git-core/git-subtree~ /usr/lib/git-core/git-subtree
220 sudo chown --reference=/usr/lib/git-core/git-subtree~ /usr/lib/git-core/git-subtree
223 _Note:_ The first time running `git subtree push` a cache has to be built. This
224 involves going through the complete Clippy history once. For this you have to
225 increase the stack limit though, which you can do with `ulimit -s 60000`.
226 Make sure to run the `ulimit` command from the same session you call git subtree.
228 _Note:_ If you are a Debian user, `dash` is the shell used by default for scripts instead of `sh`.
229 This shell has a hardcoded recursion limit set to 1000. In order to make this process work,
230 you need to force the script to run `bash` instead. You can do this by editing the first
231 line of the `git-subtree` script and changing `sh` to `bash`.
233 ### Performing the sync from [`rust-lang/rust`] to Clippy
235 Here is a TL;DR version of the sync process (all of the following commands have
236 to be run inside the `rust` directory):
238 1. Clone the [`rust-lang/rust`] repository or make sure it is up to date.
239 2. Checkout the commit from the latest available nightly. You can get it using `rustup check`.
240 3. Sync the changes to the rust-copy of Clippy to your Clippy fork:
242 # Make sure to change `your-github-name` to your github name in the following command
243 git subtree push -P src/tools/clippy git@github.com:your-github-name/rust-clippy sync-from-rust
246 _Note:_ This will directly push to the remote repository. You can also push
247 to your local copy by replacing the remote address with `/path/to/rust-clippy`
250 _Note:_ Most of the time you have to create a merge commit in the
251 `rust-clippy` repo (this has to be done in the Clippy repo, not in the
252 rust-copy of Clippy):
254 git fetch origin && git fetch upstream
255 git checkout sync-from-rust
256 git merge upstream/master
258 4. Open a PR to `rust-lang/rust-clippy` and wait for it to get merged (to
259 accelerate the process ping the `@rust-lang/clippy` team in your PR and/or
260 ~~annoy~~ ask them in the [Zulip] stream.)
262 ### Performing the sync from Clippy to [`rust-lang/rust`]
264 All of the following commands have to be run inside the `rust` directory.
266 1. Make sure Clippy itself is up-to-date by following the steps outlined in the previous
267 section if necessary.
269 2. Sync the `rust-lang/rust-clippy` master to the rust-copy of Clippy:
271 git checkout -b sync-from-clippy
272 git subtree pull -P src/tools/clippy https://github.com/rust-lang/rust-clippy master
274 3. Open a PR to [`rust-lang/rust`]
278 You may want to define remotes, so you don't have to type out the remote
279 addresses on every sync. You can do this with the following commands (these
280 commands still have to be run inside the `rust` directory):
283 # Set clippy-upstream remote for pulls
284 $ git remote add clippy-upstream https://github.com/rust-lang/rust-clippy
285 # Make sure to not push to the upstream repo
286 $ git remote set-url --push clippy-upstream DISABLED
287 # Set clippy-origin remote to your fork for pushes
288 $ git remote add clippy-origin git@github.com:your-github-name/rust-clippy
290 $ git remote add clippy-local /path/to/rust-clippy
293 You can then sync with the remote names from above, e.g.:
296 $ git subtree push -P src/tools/clippy clippy-local sync-from-rust
299 [gitgitgadget-pr]: https://github.com/gitgitgadget/git/pull/493
300 [subtree]: https://rustc-dev-guide.rust-lang.org/contributing.html#external-dependencies-subtree
301 [`rust-lang/rust`]: https://github.com/rust-lang/rust
303 ## Issue and PR triage
305 Clippy is following the [Rust triage procedure][triage] for issues and pull
308 However, we are a smaller project with all contributors being volunteers
309 currently. Between writing new lints, fixing issues, reviewing pull requests and
310 responding to issues there may not always be enough time to stay on top of it
313 Our highest priority is fixing [crashes][l-crash] and [bugs][l-bug]. We don't
314 want Clippy to crash on your code and we want it to be as reliable as the
315 suggestions from Rust compiler errors.
319 We use a bot powered by [Homu][homu] to help automate testing and landing of pull
320 requests in Clippy. The bot's username is @bors.
322 You can find the Clippy bors queue [here][homu_queue].
324 If you have @bors permissions, you can find an overview of the available
325 commands [here][homu_instructions].
327 [triage]: https://forge.rust-lang.org/release/triage-procedure.html
328 [l-crash]: https://github.com/rust-lang/rust-clippy/labels/L-crash
329 [l-bug]: https://github.com/rust-lang/rust-clippy/labels/L-bug
330 [homu]: https://github.com/rust-lang/homu
331 [homu_instructions]: https://bors.rust-lang.org/
332 [homu_queue]: https://bors.rust-lang.org/queue/clippy
336 Contributions to Clippy should be made in the form of GitHub pull requests. Each pull request will
337 be reviewed by a core contributor (someone with permission to land patches) and either landed in the
338 main tree or given feedback for changes that would be required.
340 All code in this repository is under the [Apache-2.0] or the [MIT] license.
342 <!-- adapted from https://github.com/servo/servo/blob/master/CONTRIBUTING.md -->
344 [Apache-2.0]: https://www.apache.org/licenses/LICENSE-2.0
345 [MIT]: https://opensource.org/licenses/MIT