79 lines
3.7 KiB
Markdown
79 lines
3.7 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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All issues on Clippy are mentored, if you want help with a bug just ask @Manishearth or @llogiq.
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Some issues are easier than others. The [E-easy](https://github.com/Manishearth/rust-clippy/labels/E-easy)
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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/Manishearth/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/Manishearth/rust-clippy/labels/T-middle) issues, which involve types
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and resolved paths.
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Issues marked [E-medium](https://github.com/Manishearth/rust-clippy/labels/E-medium) are generally
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pretty easy too, though it's recommended you work on an E-easy issue first.
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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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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](http://manishearth.github.io/rust-internals-docs/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/Manishearth/rust-clippy/blob/de5ccdfab68a5e37689f3c950ed1532ba9d652a0/src/misc.rs#L34).
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T-middle issues can be more involved and require verifying types. The
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[`ty`](http://manishearth.github.io/rust-internals-docs/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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Compiling clippy can take almost a minute or more depending on your machine.
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You can set the environment flag `CARGO_INCREMENTAL=1` to cut down that time to
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almost a third on average, depending on the influence your change has.
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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` and check whether
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the output looks as you expect with `git diff`. Commit all `*.stderr` files, too.
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Also 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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/// ```rust
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/// Insert a short example if you have one.
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/// ```
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```
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Our `util/update_wiki.py` script can then add your lint docs to the wiki.
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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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