# Contributing to rust-clippy Hello fellow Rustacean! Great to see your interest in compiler internals and lints! ## Getting started High level approach: 1. Find something to fix/improve 2. Change code (likely some file in `clippy_lints/src/`) 3. Run `cargo test` in the root directory and wiggle code until it passes 4. Open a PR (also can be done between 2. and 3. if you run into problems) ### Finding something to fix/improve All issues on Clippy are mentored, if you want help with a bug just ask @Manishearth, @llogiq, @mcarton or @oli-obk. Some issues are easier than others. The [`good first issue`](https://github.com/rust-lang-nursery/rust-clippy/labels/good%20first%20issue) label can be used to find the easy issues. If you want to work on an issue, please leave a comment so that we can assign it to you! Issues marked [`T-AST`](https://github.com/rust-lang-nursery/rust-clippy/labels/T-AST) involve simple matching of the syntax tree structure, and are generally easier than [`T-middle`](https://github.com/rust-lang-nursery/rust-clippy/labels/T-middle) issues, which involve types and resolved paths. [`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 how this syntax structure is encoded in the AST, it is recommended to run `rustc -Z ast-json` on an example of the structure and compare with the [nodes in the AST docs](http://manishearth.github.io/rust-internals-docs/syntax/ast/). Usually the lint will end up to be a nested series of matches and ifs, [like so](https://github.com/rust-lang-nursery/rust-clippy/blob/de5ccdfab68a5e37689f3c950ed1532ba9d652a0/src/misc.rs#L34). [`E-medium`](https://github.com/rust-lang-nursery/rust-clippy/labels/E-medium) issues are generally pretty easy too, though it's recommended you work on an E-easy issue first. They are mostly classified as `E-medium`, since they might be somewhat involved code wise, but not difficult per-se. [`T-middle`](https://github.com/rust-lang-nursery/rust-clippy/labels/T-middle) issues can be more involved and require verifying types. The [`ty`](http://manishearth.github.io/rust-internals-docs/rustc/ty) module contains a lot of methods that are useful, though one of the most useful would be `expr_ty` (gives the type of an AST expression). `match_def_path()` in Clippy's `utils` module can also be useful. ### Writing code Compiling clippy from scratch can take almost a minute or more depending on your machine. However, since Rust 1.24.0 incremental compilation is enabled by default and compile times for small changes should be quick. [Llogiq's blog post on lints](https://llogiq.github.io/2015/06/04/workflows.html) is a nice primer to lint-writing, though it does get into advanced stuff. Most lints consist of an implementation of `LintPass` with one or more of its default methods overridden. See the existing lints for examples of this. Please document your lint with a doc comment akin to the following: ```rust /// **What it does:** Checks for ... (describe what the lint matches). /// /// **Why is this bad?** Supply the reason for linting the code. /// /// **Known problems:** None. (Or describe where it could go wrong.) /// /// **Example:** /// /// ```rust /// // Bad /// Insert a short example of code that triggers the lint /// /// // Good /// Insert a short example of improved code that doesn't trigger the lint /// ``` ``` ### Running test suite Clippy uses UI tests. UI tests check that the output of the compiler is exactly as expected. Of course there's little sense in writing the output yourself or copying it around. Therefore you can simply run `tests/ui/update-all-references.sh` (after running `cargo test`) and check whether the output looks as you expect with `git diff`. Commit all `*.stderr` files, too. 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: ```bash TESTNAME=ui/empty_line_after_outer_attr cargo test --test compile-test ``` ### Testing manually Manually testing against an example file is useful if you have added some `println!`s and test suite output becomes unreadable. To try clippy with your local modifications, run `cargo run --bin clippy-driver -- -L ./target/debug input.rs` from the working copy root. Your test file, here `input.rs`, needs to have clippy enabled as a plugin: ```rust #![feature(plugin)] #![plugin(clippy)] ``` ## Contributions Clippy welcomes contributions from everyone. Contributions to Clippy should be made in the form of GitHub pull requests. Each pull request will be reviewed by a core contributor (someone with permission to land patches) and either landed in the main tree or given feedback for changes that would be required. All code in this repository is under the [Mozilla Public License, 2.0](https://www.mozilla.org/MPL/2.0/) ## Conduct We follow the [Rust Code of Conduct](http://www.rust-lang.org/conduct.html).