245 lines
12 KiB
Markdown
245 lines
12 KiB
Markdown
# Contributing to Clippy
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Hello fellow Rustacean! Great to see your interest in compiler internals and lints!
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**First**: if you're unsure or afraid of _anything_, just ask or submit the issue or pull request anyway. You won't be
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yelled at for giving it your best effort. The worst that can happen is that you'll be politely asked to change
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something. We appreciate any sort of contributions, and don't want a wall of rules to get in the way of that.
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Clippy welcomes contributions from everyone. There are many ways to contribute to Clippy and the following document
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explains how you can contribute and how to get started. If you have any questions about contributing or need help with
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anything, feel free to ask questions on issues or visit the `#clippy` on [Discord].
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All contributors are expected to follow the [Rust Code of Conduct].
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* [Getting started](#getting-started)
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* [Finding something to fix/improve](#finding-something-to-fiximprove)
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* [Writing code](#writing-code)
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* [How Clippy works](#how-clippy-works)
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* [Fixing nightly build failures](#fixing-build-failures-caused-by-rust)
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* [Issue and PR Triage](#issue-and-pr-triage)
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* [Bors and Homu](#bors-and-homu)
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* [Contributions](#contributions)
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[Discord]: https://discord.gg/rust-lang
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[Rust Code of Conduct]: https://www.rust-lang.org/policies/code-of-conduct
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## Getting started
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High level approach:
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1. Find something to fix/improve
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2. Change code (likely some file in `clippy_lints/src/`)
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3. Follow the instructions in the [docs for writing lints](doc/adding_lints.md) such as running the `setup-toolchain.sh` script
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4. Run `cargo test` in the root directory and wiggle code until it passes
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5. Open a PR (also can be done after 2. if you run into problems)
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### Finding something to fix/improve
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All issues on Clippy are mentored, if you want help with a bug just ask @Manishearth, @llogiq, @mcarton or @oli-obk.
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Some issues are easier than others. The [`good first issue`] label can be used to find the easy issues.
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If you want to work on an issue, please leave a comment so that we can assign it to you!
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There are also some abandoned PRs, marked with [`S-inactive-closed`].
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Pretty often these PRs are nearly completed and just need some extra steps
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(formatting, addressing review comments, ...) to be merged. If you want to
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complete such a PR, please leave a comment in the PR and open a new one based
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on it.
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Issues marked [`T-AST`] involve simple matching of the syntax tree structure,
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and are generally easier than [`T-middle`] issues, which involve types
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and resolved paths.
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[`T-AST`] issues will generally need you to match against a predefined syntax structure.
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To figure out how this syntax structure is encoded in the AST, it is recommended to run
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`rustc -Z ast-json` on an example of the structure and compare with the [nodes in the AST docs].
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Usually the lint will end up to be a nested series of matches and ifs, [like so][deep-nesting].
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But we can make it nest-less by using [if_chain] macro, [like this][nest-less].
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[`E-medium`] issues are generally pretty easy too, though it's recommended you work on an E-easy issue first.
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They are mostly classified as [`E-medium`], since they might be somewhat involved code wise,
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but not difficult per-se.
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[`T-middle`] issues can be more involved and require verifying types. The [`ty`] module contains a
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lot of methods that are useful, though one of the most useful would be `expr_ty` (gives the type of
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an AST expression). `match_def_path()` in Clippy's `utils` module can also be useful.
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[`good first issue`]: https://github.com/rust-lang/rust-clippy/labels/good%20first%20issue
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[`S-inactive-closed`]: https://github.com/rust-lang/rust-clippy/pulls?q=is%3Aclosed+label%3AS-inactive-closed
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[`T-AST`]: https://github.com/rust-lang/rust-clippy/labels/T-AST
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[`T-middle`]: https://github.com/rust-lang/rust-clippy/labels/T-middle
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[`E-medium`]: https://github.com/rust-lang/rust-clippy/labels/E-medium
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[`ty`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc/ty
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[nodes in the AST docs]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_ast/ast/
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[deep-nesting]: https://github.com/rust-lang/rust-clippy/blob/557f6848bd5b7183f55c1e1522a326e9e1df6030/clippy_lints/src/mem_forget.rs#L29-L43
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[if_chain]: https://docs.rs/if_chain/*/if_chain
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[nest-less]: https://github.com/rust-lang/rust-clippy/blob/557f6848bd5b7183f55c1e1522a326e9e1df6030/clippy_lints/src/bit_mask.rs#L124-L150
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## Writing code
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Have a look at the [docs for writing lints][adding_lints] for more details. [Llogiq's blog post on lints]
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is also a nice primer to lint-writing, though it does get into advanced stuff and may be a bit outdated.
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If you want to add a new lint or change existing ones apart from bugfixing, it's
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also a good idea to give the [stability guarantees][rfc_stability] and
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[lint categories][rfc_lint_cats] sections of the [Clippy 1.0 RFC][clippy_rfc] a
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quick read.
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[adding_lints]: https://github.com/rust-lang/rust-clippy/blob/master/doc/adding_lints.md
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[Llogiq's blog post on lints]: https://llogiq.github.io/2015/06/04/workflows.html
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[clippy_rfc]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md
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[rfc_stability]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md#stability-guarantees
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[rfc_lint_cats]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md#lint-audit-and-categories
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## How Clippy works
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[`clippy_lints/src/lib.rs`][lint_crate_entry] imports all the different lint modules and registers in the [`LintStore`].
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For example, the [`else_if_without_else`][else_if_without_else] lint is registered like this:
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```rust
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// ./clippy_lints/src/lib.rs
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// ...
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pub mod else_if_without_else;
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// ...
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pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: &Conf) {
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// ...
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store.register_early_pass(|| box else_if_without_else::ElseIfWithoutElse);
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// ...
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store.register_group(true, "clippy::restriction", Some("clippy_restriction"), vec![
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// ...
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LintId::of(&else_if_without_else::ELSE_IF_WITHOUT_ELSE),
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// ...
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]);
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}
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```
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The [`rustc_lint::LintStore`][`LintStore`] provides two methods to register lints:
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[register_early_pass][reg_early_pass] and [register_late_pass][reg_late_pass]. Both take an object
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that implements an [`EarlyLintPass`][early_lint_pass] or [`LateLintPass`][late_lint_pass] respectively. This is done in
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every single lint. It's worth noting that the majority of `clippy_lints/src/lib.rs` is autogenerated by `cargo dev
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update_lints`. When you are writing your own lint, you can use that script to save you some time.
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```rust
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// ./clippy_lints/src/else_if_without_else.rs
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use rustc_lint::{EarlyLintPass, EarlyContext};
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// ...
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pub struct ElseIfWithoutElse;
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// ...
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impl EarlyLintPass for ElseIfWithoutElse {
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// ... the functions needed, to make the lint work
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}
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```
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The difference between `EarlyLintPass` and `LateLintPass` is that the methods of the `EarlyLintPass` trait only provide
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AST information. The methods of the `LateLintPass` trait are executed after type checking and contain type information
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via the `LateContext` parameter.
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That's why the `else_if_without_else` example uses the `register_early_pass` function. Because the
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[actual lint logic][else_if_without_else] does not depend on any type information.
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[lint_crate_entry]: https://github.com/rust-lang/rust-clippy/blob/master/clippy_lints/src/lib.rs
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[else_if_without_else]: https://github.com/rust-lang/rust-clippy/blob/4253aa7137cb7378acc96133c787e49a345c2b3c/clippy_lints/src/else_if_without_else.rs
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[`LintStore`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/struct.LintStore.html
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[reg_early_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/struct.LintStore.html#method.register_early_pass
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[reg_late_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/struct.LintStore.html#method.register_late_pass
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[early_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/trait.EarlyLintPass.html
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[late_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/trait.LateLintPass.html
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## Fixing build failures caused by Rust
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Clippy will sometimes fail to build from source because building it depends on unstable internal Rust features. Most of
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the times we have to adapt to the changes and only very rarely there's an actual bug in Rust. Fixing build failures
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caused by Rust updates, can be a good way to learn about Rust internals.
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In order to find out why Clippy does not work properly with a new Rust commit, you can use the [rust-toolstate commit
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history][toolstate_commit_history]. You will then have to look for the last commit that contains
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`test-pass -> build-fail` or `test-pass -> test-fail` for the `clippy-driver` component.
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[Here][toolstate_commit] is an example.
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The commit message contains a link to the PR. The PRs are usually small enough to discover the breaking API change and
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if they are bigger, they likely include some discussion that may help you to fix Clippy.
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To check if Clippy is available for a specific target platform, you can check
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the [rustup component history][rustup_component_history].
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If you decide to make Clippy work again with a Rust commit that breaks it,
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you probably want to install the latest Rust from master locally and run Clippy
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using that version of Rust.
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You can set up the master toolchain by running `./setup-toolchain.sh`. That script will install
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[rustup-toolchain-install-master][rtim] and master toolchain, then run `rustup override set master`.
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After fixing the build failure on this repository, we can submit a pull request
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to [`rust-lang/rust`] to fix the toolstate.
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To submit a pull request, you should follow these steps:
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```bash
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# Assuming you already cloned the rust-lang/rust repo and you're in the correct directory
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git submodule update --remote src/tools/clippy
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cargo update -p clippy
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git add -u
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git commit -m "Update Clippy"
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./x.py test -i --stage 1 src/tools/clippy # This is optional and should succeed anyway
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# Open a PR in rust-lang/rust
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```
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[rustup_component_history]: https://rust-lang.github.io/rustup-components-history
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[toolstate_commit_history]: https://github.com/rust-lang-nursery/rust-toolstate/commits/master
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[toolstate_commit]: https://github.com/rust-lang-nursery/rust-toolstate/commit/aad74d8294e198a7cf8ac81a91aebb7f3bbcf727
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[rtim]: https://github.com/kennytm/rustup-toolchain-install-master
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[`rust-lang/rust`]: https://github.com/rust-lang/rust
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## Issue and PR triage
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Clippy is following the [Rust triage procedure][triage] for issues and pull
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requests.
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However, we are a smaller project with all contributors being volunteers
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currently. Between writing new lints, fixing issues, reviewing pull requests and
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responding to issues there may not always be enough time to stay on top of it
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all.
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Our highest priority is fixing [crashes][l-crash] and [bugs][l-bug]. We don't
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want Clippy to crash on your code and we want it to be as reliable as the
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suggestions from Rust compiler errors.
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## Bors and Homu
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We use a bot powered by [Homu][homu] to help automate testing and landing of pull
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requests in Clippy. The bot's username is @bors.
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You can find the Clippy bors queue [here][homu_queue].
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If you have @bors permissions, you can find an overview of the available
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commands [here][homu_instructions].
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[triage]: https://forge.rust-lang.org/triage-procedure.html
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[l-crash]: https://github.com/rust-lang/rust-clippy/labels/L-crash%20%3Aboom%3A
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[l-bug]: https://github.com/rust-lang/rust-clippy/labels/L-bug%20%3Abeetle%3A
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[homu]: https://github.com/rust-lang/homu
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[homu_instructions]: https://buildbot2.rust-lang.org/homu/
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[homu_queue]: https://buildbot2.rust-lang.org/homu/queue/clippy
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## Contributions
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Contributions to Clippy should be made in the form of GitHub pull requests. Each pull request will
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be reviewed by a core contributor (someone with permission to land patches) and either landed in the
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main tree or given feedback for changes that would be required.
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All code in this repository is under the [Apache-2.0] or the [MIT] license.
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<!-- adapted from https://github.com/servo/servo/blob/master/CONTRIBUTING.md -->
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[Apache-2.0]: https://www.apache.org/licenses/LICENSE-2.0
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[MIT]: https://opensource.org/licenses/MIT
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