157 lines
6.0 KiB
Markdown
157 lines
6.0 KiB
Markdown
# Contributing to rust-clippy
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Hello fellow Rustacean! Great to see your interest in compiler internals and lints!
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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. Run `cargo test` in the root directory and wiggle code until it passes
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4. Open a PR (also can be done between 2. and 3. 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`](https://github.com/rust-lang-nursery/rust-clippy/labels/good%20first%20issue)
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label can be used to find the easy issues. If you want to work on an issue, please leave a comment
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so that we can assign it to you!
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Issues marked [`T-AST`](https://github.com/rust-lang-nursery/rust-clippy/labels/T-AST) involve simple
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matching of the syntax tree structure, and are generally easier than
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[`T-middle`](https://github.com/rust-lang-nursery/rust-clippy/labels/T-middle) issues, which involve types
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and resolved paths.
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[`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
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how this syntax structure is encoded in the AST, it is recommended to run `rustc -Z ast-json` on an
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example of the structure and compare with the
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[nodes in the AST docs](https://doc.rust-lang.org/nightly/nightly-rustc/syntax/ast). Usually
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the lint will end up to be a nested series of matches and ifs,
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[like so](https://github.com/rust-lang-nursery/rust-clippy/blob/de5ccdfab68a5e37689f3c950ed1532ba9d652a0/src/misc.rs#L34).
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[`E-medium`](https://github.com/rust-lang-nursery/rust-clippy/labels/E-medium) issues are generally
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pretty easy too, though it's recommended you work on an E-easy issue first. They are mostly classified
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as `E-medium`, since they might be somewhat involved code wise, but not difficult per-se.
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[`T-middle`](https://github.com/rust-lang-nursery/rust-clippy/labels/T-middle) issues can
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be more involved and require verifying types. The
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[`ty`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/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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### Writing code
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Compiling clippy from scratch can take almost a minute or more depending on your machine.
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However, since Rust 1.24.0 incremental compilation is enabled by default and compile times for small changes should be quick.
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[Llogiq's blog post on lints](https://llogiq.github.io/2015/06/04/workflows.html) is a nice primer
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to lint-writing, though it does get into advanced stuff. Most lints consist of an implementation of
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`LintPass` with one or more of its default methods overridden. See the existing lints for examples
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of this.
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#### Author lint
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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.
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Create a new UI test with the pattern you want to match:
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```rust
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// ./tests/ui/my_lint.rs
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// The custom_attribute needs to be enabled for the author lint to work
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#![feature(plugin, custom_attribute)]
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fn main() {
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#[clippy(author)]
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let arr: [i32; 1] = [7]; // Replace line with the code you want to match
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}
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```
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Now you run `TESTNAME=ui/my_lint cargo test --test compile-test` to produce
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the file with the generated code:
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```rust
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// ./tests/ui/my_lint.stdout
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if_chain! {
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if let Expr_::ExprArray(ref elements) = stmt.node;
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if elements.len() == 1;
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if let Expr_::ExprLit(ref lit) = elements[0].node;
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if let LitKind::Int(7, _) = lit.node;
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then {
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// report your lint here
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}
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}
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```
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#### Documentation
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Please document your lint with a doc comment akin to the following:
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```rust
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/// **What it does:** Checks for ... (describe what the lint matches).
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///
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/// **Why is this bad?** Supply the reason for linting the code.
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///
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/// **Known problems:** None. (Or describe where it could go wrong.)
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///
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/// **Example:**
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///
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/// ```rust
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/// // Bad
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/// Insert a short example of code that triggers the lint
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///
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/// // Good
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/// Insert a short example of improved code that doesn't trigger the lint
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/// ```
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```
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Once your lint is merged it will show up in the [lint list](https://rust-lang-nursery.github.io/rust-clippy/master/index.html)
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### Running test suite
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Clippy uses UI tests. UI tests check that the output of the compiler is exactly as expected.
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Of course there's little sense in writing the output yourself or copying it around.
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Therefore you can simply run `tests/ui/update-all-references.sh` (after running
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`cargo test`) and check whether the output looks as you expect with `git diff`. Commit all
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`*.stderr` files, too.
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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:
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```bash
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TESTNAME=ui/empty_line_after_outer_attr cargo test --test compile-test
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```
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### Testing manually
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Manually testing against an example file is useful if you have added some
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`println!`s and test suite output becomes unreadable. To try clippy with your
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local modifications, run `cargo run --bin clippy-driver -- -L ./target/debug input.rs` from the
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working copy root. Your test file, here `input.rs`, needs to have clippy
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enabled as a plugin:
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```rust
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#![feature(plugin)]
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#![plugin(clippy)]
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```
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## Contributions
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Clippy welcomes contributions from everyone.
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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 [Mozilla Public License, 2.0](https://www.mozilla.org/MPL/2.0/)
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## Conduct
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We follow the [Rust Code of Conduct](http://www.rust-lang.org/conduct.html).
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<!-- adapted from https://github.com/servo/servo/blob/master/CONTRIBUTING.md -->
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