rust-clippy/CONTRIBUTING.md

# Contributing to rust-clippy

Hello fellow Rustacean! Great to see your interest in compiler internals and lints!

## Getting started

All issues on Clippy are mentored, if you want help with a bug just ask @Manishearth or @llogiq.

Some issues are easier than others. The [E-easy](https://github.com/Manishearth/rust-clippy/labels/E-easy)
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/Manishearth/rust-clippy/labels/T-AST) involve simple
matching of the syntax tree structure, and are generally easier than
[T-middle](https://github.com/Manishearth/rust-clippy/labels/T-middle) issues, which involve types
and resolved paths.

Issues marked [E-medium](https://github.com/Manishearth/rust-clippy/labels/E-medium) are generally
pretty easy too, though it's recommended you work on an E-easy issue first.

[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.

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/Manishearth/rust-clippy/blob/de5ccdfab68a5e37689f3c950ed1532ba9d652a0/src/misc.rs#L34)

T-middle issues can be more involved and require verifying types. The
[`middle::ty`](http://manishearth.github.io/rust-internals-docs/rustc/middle/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.

## 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.

## Conduct

We follow the [Rust Code of Conduct](http://www.rust-lang.org/conduct.html).


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