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blyxyas 2023-04-17 23:08:44 +02:00 committed by Philipp Krones
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book/src/development/method_checking.md
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@ -4,56 +4,58 @@ In some scenarios we might want to check for methods when developing
a lint. There are two kinds of questions that we might be curious about:
- Invocation: Does an expression call a specific method?
- Definition: Does the type `Ty` of an expression define a method?
- Definition: Does an `impl` define a method?
## Checking if an `expr` is calling a specific method
Suppose we have an `expr`, we can check whether it calls a specific
method, e.g. `our_fancy_method`, by performing a pattern match on
the [ExprKind] that we can access from `expr.kind`:
the [`ExprKind`] that we can access from `expr.kind`:
```rust
use rustc_hir as hir;
use rustc_lint::{LateContext, LateLintPass};
use rustc_span::sym;
use clippy_utils::is_trait_method;
impl<'tcx> LateLintPass<'tcx> for OurFancyMethodLint {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
// Check our expr is calling a method with pattern matching
if let hir::ExprKind::MethodCall(path, _, [_self_arg, ..]) = &expr.kind
if let hir::ExprKind::MethodCall(path, _, [self_arg, ..]) = &expr.kind
// Check if the name of this method is `our_fancy_method`
&& path.ident.name == sym!(our_fancy_method)
// We can check the type of the self argument whenever necessary.
// (It's necessary if we want to check that method is specifically belonging to a specific trait,
// for example, a `map` method could belong to user-defined trait instead of to `Iterator`)
// See the "Type Checking" chapter of the Clippy book for more information.
// (It's necessary if we want to check that method is specifically belonging to a specific trait,
// for example, a `map` method could belong to user-defined trait instead of to `Iterator`)
// See the next section for more information.
&& is_trait_method(cx, self_arg, sym::OurFancyTrait)
{
println!("`expr` is a method call for `our_fancy_method`");
println!("`expr` is a method call for `our_fancy_method`");
}
}
}
```
Take a closer look at the `ExprKind` enum variant [MethodCall] for more
Take a closer look at the `ExprKind` enum variant [`MethodCall`] for more
information on the pattern matching.
As mentioned in [Define Lints](define_lints.md#lint-types),
the `methods` lint type is full of pattern matching with `Methodcall`
in case the reader wishes to explore more.
Additionally, we use the [`clippy_utils::sym!`][sym] macro to conveniently convert
an input `our_fancy_method` into a `Symbol` and compare that symbol to the [ident][Ident]'s name in the [PathSegment]
in the [MethodCall].
an input `our_fancy_method` into a `Symbol` and compare that symbol to the [`ident`][Ident]'s name in the [`PathSegment`]
in the [`MethodCall`].
## Checking if a type defines a specific method
## Checking if a `impl` block implements a method
While sometimes we want to check whether a method is being called or not,
other times we want to know if our type `Ty` defines a method.
other times we want to know if our `Ty` defines a method.
To check if our type defines a method called `our_fancy_method`,
we will utilize the [check_impl_item] method that is available
in our beloved [LateLintPass] (for more information, refer to the
To check if our `impl` block defines a method `our_fancy_method`,
we will utilize the [`check_impl_item`] method that is available
in our beloved [`LateLintPass`] (for more information, refer to the
["Lint Passes"](lint_passes.md) chapter in Clippy book).
This method provides us with an [ImplItem] struct, which represents
This method provides us with an [`ImplItem`] struct, which represents
anything within an `impl` block.
Let us take a look at how we might check for the implementation of
@ -65,7 +67,6 @@ use clippy_utils::return_ty;
use rustc_hir::{ImplItem, ImplItemKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_span::symbol::sym;
impl<'tcx> LateLintPass<'tcx> for MyTypeImpl {
fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx ImplItem<'_>) {
// Check if item is a method/function
@ -83,11 +84,11 @@ impl<'tcx> LateLintPass<'tcx> for MyTypeImpl {
}
```
[check_impl_item]: https://doc.rust-lang.org/stable/nightly-rustc/rustc_lint/trait.LateLintPass.html#method.check_impl_item
[ExprKind]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_hir/hir/enum.ExprKind.html
[`check_impl_item`]: https://doc.rust-lang.org/stable/nightly-rustc/rustc_lint/trait.LateLintPass.html#method.check_impl_item
[`ExprKind`]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_hir/hir/enum.ExprKind.html
[Ident]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_span/symbol/struct.Ident.html
[ImplItem]: https://doc.rust-lang.org/stable/nightly-rustc/rustc_hir/hir/struct.ImplItem.html
[LateLintPass]: https://doc.rust-lang.org/stable/nightly-rustc/rustc_lint/trait.LateLintPass.html
[MethodCall]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_hir/hir/enum.ExprKind.html#variant.MethodCall
[PathSegment]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_hir/hir/struct.PathSegment.html
[`ImplItem`]: https://doc.rust-lang.org/stable/nightly-rustc/rustc_hir/hir/struct.ImplItem.html
[`LateLintPass`]: https://doc.rust-lang.org/stable/nightly-rustc/rustc_lint/trait.LateLintPass.html
[`MethodCall`]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_hir/hir/enum.ExprKind.html#variant.MethodCall
[`PathSegment`]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_hir/hir/struct.PathSegment.html
[sym]: https://doc.rust-lang.org/stable/nightly-rustc/clippy_utils/macro.sym.html