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@@ -73,121 +68,15 @@ an AST expression). `match_def_path()` in Clippy's `utils` module can also be us
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## Writing code
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Clippy depends on the current git master version of rustc, which can change rapidly. Make sure you're
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working near rust-clippy's master, and use the `setup-toolchain.sh` script to configure the appropriate
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toolchain for this directory.
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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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Have a look at the [docs for writing lints](doc/adding_lints.md) for more details. [Llogiq's blog post on lints](https://llogiq.github.io/2015/06/04/workflows.html) is also a nice primer
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to lint-writing, though it does get into advanced stuff and may be a bit
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outdated.
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If you want to add a new lint or change existing ones apart from bugfixing, it's
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also a good idea to give the [stability guarantees][rfc_stability] and
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[lint categories][rfc_lint_cats] sections of the [Clippy 1.0 RFC][clippy_rfc] a
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quick read.
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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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First, create a new UI test file in the `tests/ui/` directory 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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fnmain() {
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#[clippy::author]
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letarr: [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 uitest` to produce
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a `.stdout` 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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ifletExprKind::Array(refelements) =stmt.node;
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ifelements.len() ==1;
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ifletExprKind::Lit(reflit) =elements[0].node;
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ifletLitKind::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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If the command was executed successfully, you can copy the code over to where you are implementing your lint.
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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.github.io/rust-clippy/master/index.html)
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### Running test suite
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Use `cargo test` to run the whole testsuite.
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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:
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 should use `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 the lint you are working on is making use of structured suggestions, the
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test file should include a `// run-rustfix` comment at the top. This will
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additionally run [rustfix](https://github.com/rust-lang-nursery/rustfix) for
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that test. Rustfix will apply the suggestions from the lint to the code of the
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test file and compare that to the contents of a `.fixed` file.
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Use `tests/ui/update-all-references.sh` to automatically generate the
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`.fixed` file after running `cargo test`.
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### Running rustfmt
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[Rustfmt](https://github.com/rust-lang/rustfmt) is a tool for formatting Rust code according
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to style guidelines. The code has to be formatted by `rustfmt` before a PR will be merged.
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It can be installed via `rustup`:
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```bash
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rustup component add rustfmt
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```
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Use `cargo fmt --all` to format the whole codebase.
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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 `env CLIPPY_TESTS=true cargo run --bin clippy-driver -- -L ./target/debug input.rs`
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from the working copy root.
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## How Clippy works
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Clippy is a [rustc compiler plugin][compiler_plugin]. The main entry point is at [`src/lib.rs`][main_entry]. In there, the lint registration is delegated to the [`clippy_lints`][lint_crate] crate.
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