diff --git a/book/src/SUMMARY.md b/book/src/SUMMARY.md index 22fbdce75e8f..f6378b1fb90f 100644 --- a/book/src/SUMMARY.md +++ b/book/src/SUMMARY.md @@ -13,6 +13,7 @@ - [Development](development/README.md) - [Basics](development/basics.md) - [Adding Lints](development/adding_lints.md) + - [Defining Lints](development/defining_lints.md) - [Lint Passes](development/lint_passes.md) - [Type Checking](development/type_checking.md) - [Macro Expansions](development/macro_expansions.md) diff --git a/book/src/development/defining_lints.md b/book/src/development/defining_lints.md new file mode 100644 index 000000000000..7c4aa5d45239 --- /dev/null +++ b/book/src/development/defining_lints.md @@ -0,0 +1,205 @@ +# Define New Lints + +The first step in the journey of a new lint is the definition +and registration of the lint in Clippy's codebase. +We can use the Clippy dev tools to handle this step since setting up the +lint involves some boilerplate code. + +#### Lint types + +A lint type is the category of items and expressions in which your lint focuses on. + +As of the writing of this documentation update, there are 12 _types_ of lints +besides the numerous standalone lints living under `clippy_lints/src/`: + +- `cargo` +- `casts` +- `functions` +- `loops` +- `matches` +- `methods` +- `misc_early` +- `operators` +- `transmute` +- `types` +- `unit_types` +- `utils / internal` (Clippy internal lints) + +These types group together lints that share some common behaviors. For instance, +`functions` groups together lints that deal with some aspects of functions in +Rust, like definitions, signatures and attributes. + +For more information, feel free to compare the lint files under any category +with [All Clippy lints][all_lints] or ask one of the maintainers. + +## Lint name + +A good lint name is important, make sure to check the [lint naming +guidelines][lint_naming]. Don't worry, if the lint name doesn't fit, a Clippy +team member will alert you in the PR process. + +--- + +We'll name our example lint that detects functions named "foo" `foo_functions`. +Check the [lint naming guidelines][lint_naming] to see why this name makes +sense. + +## Add and Register the Lint + +Now that a name is chosen, we shall register `foo_functions` as a lint to the +codebase. There are two ways to register a lint. + +### Standalone + +If you believe that this new lint is a standalone lint (that doesn't belong to +any specific [type](#lint-types) like `functions` or `loops`), you can run the +following command in your Clippy project: + +```sh +$ cargo dev new_lint --name=lint_name --pass=late --category=pedantic +``` + +There are two things to note here: + +1. `--pass`: We set `--pass=late` in this command to do a late lint pass. The + alternative is an `early` lint pass. We will discuss this difference in a + later chapter. + +2. `--category`: If not provided, the `category` of this new lint will default + to `nursery`. + +The `cargo dev new_lint` command will create a new file: +`clippy_lints/src/foo_functions.rs` as well as [register the +lint](#lint-registration). + +Overall, you should notice that the following files are modified or created: + +```sh +$ git status +On branch foo_functions +Changes not staged for commit: + (use "git add ..." to update what will be committed) + (use "git restore ..." to discard changes in working directory) + modified: CHANGELOG.md + modified: clippy_lints/src/lib.register_lints.rs + modified: clippy_lints/src/lib.register_pedantic.rs + modified: clippy_lints/src/lib.rs + +Untracked files: + (use "git add ..." to include in what will be committed) + clippy_lints/src/foo_functions.rs + tests/ui/foo_functions.rs +``` + + +### Specific Type + +> **Note**: Lint types are listed in the ["Lint types"](#lint-types) section + +If you believe that this new lint belongs to a specific type of lints, +you can run `cargo dev new_lint` with a `--type` option. + +Since our `foo_functions` lint is related to function calls, one could +argue that we should put it into a group of lints that detect some behaviors +of functions, we can put it in the `functions` group. + +Let's run the following command in your Clippy project: + +```sh +$ cargo dev new_lint --name=foo_functions --type=functions --category=pedantic +``` + +This command will create, among other things, a new file: +`clippy_lints/src/{type}/foo_functions.rs`. +In our case, the path will be `clippy_lints/src/functions/foo_functions.rs`. + +Notice how this command has a `--type` flag instead of `--pass`. Unlike a standalone +definition, this lint won't be registered in the traditional sense. Instead, you will +call your lint from within the type's lint pass, found in `clippy_lints/src/{type}/mod.rs`. + +A _type_ is just the name of a directory in `clippy_lints/src`, like `functions` in +the example command. Clippy groups together some lints that share common behaviors, +so if your lint falls into one, it would be best to add it to that type. + +Overall, you should notice that the following files are modified or created: + +```sh +$ git status +On branch foo_functions +Changes not staged for commit: + (use "git add ..." to update what will be committed) + (use "git restore ..." to discard changes in working directory) + modified: CHANGELOG.md + modified: clippy_lints/src/declared_lints.rs + modified: clippy_lints/src/functions/mod.rs + +Untracked files: + (use "git add ..." to include in what will be committed) + clippy_lints/src/functions/foo_functions.rs + tests/ui/foo_functions.rs +``` + + +## The `define_clippy_lints` macro + +After `cargo dev new_lint`, you should see a macro with the name +`define_clippy_lints`. It will be in the same file if you defined a standalone +lint, and it will be in `mod.rs` if you defined a type-specific lint. + +The macro looks something like this: + +```rust +declare_clippy_lint! { + /// ### What it does + /// + /// // Describe here what does the lint do. + /// + /// Triggers when detects... + /// + /// ### Why is this bad? + /// + /// // Describe why this pattern would be bad + /// + /// It can lead to... + /// + /// ### Example + /// ```rust + /// // example code where clippy issues a warning + /// ``` + /// Use instead: + /// ```rust + /// // example code which does not raise clippy warning + /// ``` + #[clippy::version = "1.70.0"] // <- In which version was this implemented, keep it up to date! + pub LINT_NAME, // <- The lint name IN_ALL_CAPS + pedantic, // <- The lint group + "default lint description" // <- A lint description, e.g. "A function has an unit return type." +} +``` + +## Lint registration + +If we run the `cargo dev new_lint` command for a new lint, the lint will be +automatically registered and there is nothing more to do. + +However, sometimes we might want to declare a new lint by hand. In this case, +we'd use `cargo dev update_lints` command afterwards. + +When a lint is manually declared, we might need to register the lint pass +manually in the `register_plugins` function in `clippy_lints/src/lib.rs`: + +```rust +store.register_late_pass(|_| Box::new(foo_functions::FooFunctions)); +``` + +As you might have guessed, where there's something late, there is something +early: in Clippy there is a `register_early_pass` method as well. More on early +vs. late passes in a later chapter. + + +Without a call to one of `register_early_pass` or `register_late_pass`, the lint +pass in question will not be run. + + +[all_lints]: https://rust-lang.github.io/rust-clippy/master/ +[lint_naming]: https://rust-lang.github.io/rfcs/0344-conventions-galore.html#lints