diff --git a/doc/adding_lints.md b/doc/adding_lints.md index 1ca93a44e..ea5333260 100644 --- a/doc/adding_lints.md +++ b/doc/adding_lints.md @@ -7,16 +7,25 @@ creating an example lint from scratch. To get started, we will create a lint that detects functions called `foo`, because that's clearly a non-descriptive name. +* [Setup](#Setup) * [Testing](#Testing) +* [Rustfix tests](#Rustfix-tests) * [Lint declaration](#Lint-declaration) * [Lint passes](#Lint-passes) * [Emitting a lint](#Emitting-a-lint) * [Adding the lint logic](#Adding-the-lint-logic) * [Documentation](#Documentation) +* [Running rustfmt](#Running-rustfmt) * [Debugging](#Debugging) * [PR Checklist](#PR-Checklist) * [Cheatsheet](#Cheatsheet) +### Setup + +Clippy depends on the current git master version of rustc, which can change rapidly. Make sure you're +working near rust-clippy's master, and use the `setup-toolchain.sh` script to configure the appropriate +toolchain for this directory. + ### Testing Let's write some tests first that we can execute while we iterate on our lint. @@ -75,7 +84,25 @@ Once you are satisfied with the output, you need to run Running `TESTNAME=ui/foo_functions cargo uitest` should pass then. When you commit your lint, be sure to commit the `*.stderr` files, too. -Let's have a look at implementing our lint now. +### Rustfix tests + +If the lint you are working on is making use of structured suggestions, the +test file should include a `// run-rustfix` comment at the top. This will +additionally run [rustfix](https://github.com/rust-lang-nursery/rustfix) for +that test. Rustfix will apply the suggestions from the lint to the code of the +test file and compare that to the contents of a `.fixed` file. + +Use `tests/ui/update-all-references.sh` to automatically generate the +`.fixed` file after running `cargo test`. + +With tests in place, let's have a look at implementing our lint now. + +### 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 `env CLIPPY_TESTS=true cargo run --bin clippy-driver -- -L ./target/debug input.rs` +from the working copy root. ### Lint declaration @@ -278,7 +305,44 @@ impl LintPass for Pass { /* .. */ } ``` That should be it for the lint implementation. Running `cargo test` should now -pass and we can finish up our work by adding some documentation. +pass. + +### Author lint + +If you have trouble implementing your lint, 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. + +First, create a new UI test file in the `tests/ui/` directory with the pattern +you want to match: + +```rust +// ./tests/ui/my_lint.rs +fn main() { + #[clippy::author] + let arr: [i32; 1] = [7]; // Replace line with the code you want to match +} +``` + +Now you run `TESTNAME=ui/my_lint cargo uitest` to produce a `.stdout` file with +the generated code: + +```rust +// ./tests/ui/my_lint.stdout + +if_chain! { + if let ExprKind::Array(ref elements) = stmt.node; + if elements.len() == 1; + if let ExprKind::Lit(ref lit) = elements[0].node; + if let LitKind::Int(7, _) = lit.node; + then { + // report your lint here + } +} +``` + +If the command was executed successfully, you can copy the code over to where +you are implementing your lint. ### Documentation @@ -309,6 +373,19 @@ declare_clippy_lint! { /* ... */ } Once your lint is merged, this documentation will show up in the [lint list][lint_list]. +### Running rustfmt + +[Rustfmt](https://github.com/rust-lang/rustfmt) is a tool for formatting Rust code according +to style guidelines. Your code has to be formatted by `rustfmt` before a PR can be merged. + +It can be installed via `rustup`: + +```bash +rustup component add rustfmt +``` + +Use `cargo fmt --all` to format the whole codebase. + ### Debugging If you want to debug parts of your lint implementation, you can use the `dbg!` @@ -317,7 +394,7 @@ output in the `stdout` part. ### PR Checklist -TODO: Prose +Before submitting your PR make sure you followed all of the basic requirements: - [ ] Followed [lint naming conventions][lint_naming] - [ ] Added passing UI tests (including committed `.stderr` file) @@ -329,7 +406,7 @@ TODO: Prose Here are some pointers to things you are likely going to need for every lint: * [Clippy utils][utils] - Various helper functions. Maybe the function you need - is already in here. (`implements_trait`, `match_path`, `snippet`, etc) + is already in here (`implements_trait`, `match_path`, `snippet`, etc) * [Clippy diagnostics][diagnostics] * [The `if_chain` macro][if_chain] * [`in_macro`][in_macro] and [`in_external_macro`][in_external_macro]