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)
-* [Edition 2018 tests](#Edition-2018-tests)
-* [Lint declaration](#Lint-declaration)
-* [Lint passes](#Lint-passes)
-* [Emitting a lint](#Emitting-a-lint)
-* [Adding the lint logic](#Adding-the-lint-logic)
-* [Author lint](#Author-lint)
-* [Documentation](#Documentation)
-* [Running rustfmt](#Running-rustfmt)
-* [Debugging](#Debugging)
-* [PR Checklist](#PR-Checklist)
-* [Cheatsheet](#Cheatsheet)
+- [Adding a new lint](#adding-a-new-lint)
+ - [Setup](#setup)
+ - [Getting Started](#getting-started)
+ - [Testing](#testing)
+ - [Rustfix tests](#rustfix-tests)
+ - [Edition 2018 tests](#edition-2018-tests)
+ - [Testing manually](#testing-manually)
+ - [Lint declaration](#lint-declaration)
+ - [Lint passes](#lint-passes)
+ - [Emitting a lint](#emitting-a-lint)
+ - [Adding the lint logic](#adding-the-lint-logic)
+ - [Author lint](#author-lint)
+ - [Documentation](#documentation)
+ - [Running rustfmt](#running-rustfmt)
+ - [Debugging](#debugging)
+ - [PR Checklist](#pr-checklist)
+ - [Cheatsheet](#cheatsheet)
### Setup
and use the `setup-toolchain.sh` script to configure the appropriate toolchain
for the Clippy directory.
+### Getting Started
+
+There is a bit of boilerplate code that needs to be set up when creating a new
+lint. Fortunately, you can use the clippy dev tools to handle this for you. We
+are naming our new lint `foo_functions` (lints are generally written in snake
+case), and we don't need type information so it will have an early pass type
+(more on this later on). To get started on this lint you can run
+`cargo dev new_lint --name=foo_functions --pass=early --category=pedantic`
+(category will default to nursery if not provided). This command will create
+two files: `tests/ui/foo_functions.rs` and `clippy_lints/src/foo_functions.rs`,
+as well as run `cargo dev update_lints` to register the new lint. Next, we'll
+open up these files and add our lint!
+
### Testing
Let's write some tests first that we can execute while we iterate on our lint.
Note that you don't have to create this file yourself, we'll get to
generating the `.stderr` files further down.
-We start by creating the test file at `tests/ui/foo_functions.rs`. It doesn't
-really matter what the file is called, but it's a good convention to name it
-after the lint it is testing, so `foo_functions.rs` it is.
+We start by opening the test file created at `tests/ui/foo_functions.rs`.
-Inside the file we put some examples to get started:
+Update the file with some examples to get started:
```rust
#![warn(clippy::foo_functions)]
```
-Now we can run the test with `TESTNAME=ui/foo_functions cargo uitest`.
+Now we can run the test with `TESTNAME=foo_functions cargo uitest`.
Currently this test will fail. If you go through the output you will see that we
are told that `clippy::foo_functions` is an unknown lint, which is expected.
Once we are satisfied with the output, we need to run
`tests/ui/update-all-references.sh` to update the `.stderr` file for our lint.
-Running `TESTNAME=ui/foo_functions cargo uitest` should pass then. When we
-commit our lint, we need to commit the generated `.stderr` files, too.
+Please note that, we should run `TESTNAME=foo_functions cargo uitest`
+every time before running `tests/ui/update-all-references.sh`.
+Running `TESTNAME=foo_functions cargo uitest` should pass then. When we commit
+our lint, we need to commit the generated `.stderr` files, too.
### Rustfix tests
Use `tests/ui/update-all-references.sh` to automatically generate the
`.fixed` file after running the tests.
-With tests in place, let's have a look at implementing our lint now.
-
### Edition 2018 tests
Some features require the 2018 edition to work (e.g. `async_await`), but
your local modifications, run `env CLIPPY_TESTS=true cargo run --bin
clippy-driver -- -L ./target/debug input.rs` from the working copy root.
+With tests in place, let's have a look at implementing our lint now.
+
### Lint declaration
-We start by creating a new file in the `clippy_lints` crate. That's the crate
-where all the lint code is. We are going to call the file
-`clippy_lints/src/foo_functions.rs` and import some initial things we need:
+Let's start by opening the new file created in the `clippy_lints` crate
+at `clippy_lints/src/foo_functions.rs`. That's the crate where all the
+lint code is. This file has already imported some initial things we will need:
```rust
-use rustc::lint::{LintArray, LintPass, EarlyLintPass};
-use rustc::{declare_lint_pass, declare_tool_lint};
+use rustc_lint::{EarlyLintPass, EarlyContext};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use syntax::ast::*;
```
-The next step is to provide a lint declaration. Lints are declared using the
-[`declare_clippy_lint!`][declare_clippy_lint] macro:
+The next step is to update the lint declaration. Lints are declared using the
+[`declare_clippy_lint!`][declare_clippy_lint] macro, and we just need to update
+the auto-generated lint declaration to have a real description, something like this:
```rust
declare_clippy_lint! {
+ /// **What it does:**
+ ///
+ /// **Why is this bad?**
+ ///
+ /// **Known problems:** None.
+ ///
+ /// **Example:**
+ ///
+ /// ```rust
+ /// // example code
+ /// ```
pub FOO_FUNCTIONS,
pedantic,
"function named `foo`, which is not a descriptive name"
}
```
+* The section of lines prefixed with `///` constitutes the lint documentation
+section. This is the default documentation style and will be displayed at
+https://rust-lang.github.io/rust-clippy/master/index.html.
* `FOO_FUNCTIONS` is the name of our lint. Be sure to follow the [lint naming
guidelines][lint_naming] here when naming your lint. In short, the name should
state the thing that is being checked for and read well when used with
* The last part should be a text that explains what exactly is wrong with the
code
-With our lint declaration done, we will now make sure that it is assigned to a
-lint pass:
+The rest of this file contains an empty implementation for our lint pass,
+which in this case is `EarlyLintPass` and should look like this:
```rust
// clippy_lints/src/foo_functions.rs
Don't worry about the `name` method here. As long as it includes the name of the
lint pass it should be fine.
-Next we need to run `util/dev update_lints` to register the lint in various
-places, mainly in `clippy_lints/src/lib.rs`.
-
-While `update_lints` automates some things, it doesn't automate everything. We
-will have to register our lint pass manually in the `register_plugins` function
-in `clippy_lints/src/lib.rs`:
+The new lint automation runs `update_lints`, which automates some things, but it
+doesn't automate everything. We will have to register our lint pass manually in
+the `register_plugins` function in `clippy_lints/src/lib.rs`:
```rust
reg.register_early_lint_pass(box foo_functions::FooFunctions);
`EarlyLintPass`. The `EarlyLintPass` is also faster. However linting speed
hasn't really been a concern with Clippy so far.
-Since we don't need type information for checking the function name, we are
-going to use the `EarlyLintPass`. It has to be imported as well, changing our
-imports to:
-
-```rust
-use rustc::lint::{LintArray, LintPass, EarlyLintPass, EarlyContext};
-use rustc::{declare_tool_lint, lint_array};
-```
+Since we don't need type information for checking the function name, we used
+`--pass=early` when running the new lint automation and all the imports were
+added accordingly.
### Emitting a lint
variety of lint emission functions. They can all be found in
[`clippy_lints/src/utils/diagnostics.rs`][diagnostics].
-`span_help_and_lint` seems most appropriate in this case. It allows us to
+`span_lint_and_help` seems most appropriate in this case. It allows us to
provide an extra help message and we can't really suggest a better name
automatically. This is how it looks:
```rust
impl EarlyLintPass for FooFunctions {
fn check_fn(&mut self, cx: &EarlyContext<'_>, _: FnKind<'_>, _: &FnDecl, span: Span, _: NodeId) {
- span_help_and_lint(
+ span_lint_and_help(
cx,
FOO_FUNCTIONS,
span,
impl EarlyLintPass for FooFunctions {
fn check_fn(&mut self, cx: &EarlyContext<'_>, fn_kind: FnKind<'_>, _: &FnDecl, span: Span, _: NodeId) {
if is_foo_fn(fn_kind) {
- span_help_and_lint(
+ span_lint_and_help(
cx,
FOO_FUNCTIONS,
span,
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.
-The quickest way to use it, is the [Rust playground][play].rust-lang.org).
+The quickest way to use it, is the [Rust playground: play.rust-lang.org][Play].
Put the code you want to lint into the editor and add the `#[clippy::author]`
attribute above the item. Then run Clippy via `Tools -> Clippy` and you should
see the generated code in the output below.
rustup component add rustfmt --toolchain=nightly
```
-Use `./util/dev fmt` to format the whole codebase. Make sure that `rustfmt` is
+Use `cargo dev fmt` to format the whole codebase. Make sure that `rustfmt` is
installed for the nightly toolchain.
### Debugging
- [ ] Followed [lint naming conventions][lint_naming]
- [ ] Added passing UI tests (including committed `.stderr` file)
- [ ] `cargo test` passes locally
-- [ ] Executed `./util/dev update_lints`
+- [ ] Executed `cargo dev update_lints`
- [ ] Added lint documentation
-- [ ] Run `./util/dev fmt`
+- [ ] Run `cargo dev fmt`
### Cheatsheet
[diagnostics]: https://github.com/rust-lang/rust-clippy/blob/master/clippy_lints/src/utils/diagnostics.rs
[utils]: https://github.com/rust-lang/rust-clippy/blob/master/clippy_lints/src/utils/mod.rs
[ident]: https://doc.rust-lang.org/nightly/nightly-rustc/syntax/source_map/symbol/struct.Ident.html
-[span]: https://doc.rust-lang.org/nightly/nightly-rustc/syntax_pos/struct.Span.html
+[span]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_span/struct.Span.html
[applicability]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/enum.Applicability.html
-[if_chain]: https://docs.rs/if_chain/0.1.2/if_chain/
+[if_chain]: https://docs.rs/if_chain/*/if_chain/
[ty]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc/ty/sty/index.html
[ast]: https://doc.rust-lang.org/nightly/nightly-rustc/syntax/ast/index.html
-[from_expansion]: https://doc.rust-lang.org/nightly/nightly-rustc/syntax_pos/struct.Span.html#method.from_expansion
+[from_expansion]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_span/struct.Span.html#method.from_expansion
[in_external_macro]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc/lint/fn.in_external_macro.html
[play]: https://play.rust-lang.org
[author_example]: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=f093b986e80ad62f3b67a1f24f5e66e2
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