- [Common tools for writing lints](#common-tools-for-writing-lints)
- [Retrieving the type of an expression](#retrieving-the-type-of-an-expression)
+ - [Checking if an expression is calling a specific method](#checking-if-an-expr-is-calling-a-specific-method)
- [Checking if a type implements a specific trait](#checking-if-a-type-implements-a-specific-trait)
+ - [Checking if a type defines a method](#checking-if-a-type-defines-a-method)
- [Dealing with macros](#dealing-with-macros)
Useful Rustc dev guide links:
Sometimes you may want to retrieve the type `Ty` of an expression `Expr`, for example to answer following questions:
- which type does this expression correspond to (using its [`TyKind`][TyKind])?
-- is it a sized type?
+- is it a sized type?
- is it a primitive type?
- does it implement a trait?
-This operation is performed using the [`expr_ty()`][expr_ty] method from the [`TypeckTables`][TypeckTables] struct,
+This operation is performed using the [`expr_ty()`][expr_ty] method from the [`TypeckResults`][TypeckResults] struct,
that gives you access to the underlying structure [`TyS`][TyS].
Example of use:
```rust
-impl LateLintPass<'_, '_> for MyStructLint {
- fn check_expr(&mut self, cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
+impl LateLintPass<'_> for MyStructLint {
+ fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
// Get type of `expr`
- let ty = cx.tables.expr_ty(expr);
+ let ty = cx.typeck_results().expr_ty(expr);
// Match its kind to enter its type
match ty.kind {
ty::Adt(adt_def, _) if adt_def.is_struct() => println!("Our `expr` is a struct!"),
}
```
-Similarly in [`TypeckTables`][TypeckTables] methods, you have the [`pat_ty()`][pat_ty] method
+Similarly in [`TypeckResults`][TypeckResults] methods, you have the [`pat_ty()`][pat_ty] method
to retrieve a type from a pattern.
Two noticeable items here:
-- `cx` is the lint context [`LateContext`][LateContext].
- The two most useful data structures in this context are `tcx` and `tables`,
- allowing us to jump to type definitions and other compilation stages such as HIR.
-- `tables` is [`TypeckTables`][TypeckTables] and is created by type checking step,
- it includes useful information such as types of expressions, ways to resolve methods and so on.
+- `cx` is the lint context [`LateContext`][LateContext]. The two most useful
+ data structures in this context are `tcx` and the `TypeckResults` returned by
+ `LateContext::typeck_results`, allowing us to jump to type definitions and
+ other compilation stages such as HIR.
+- `typeck_results`'s return value is [`TypeckResults`][TypeckResults] and is
+ created by type checking step, it includes useful information such as types
+ of expressions, ways to resolve methods and so on.
+
+# Checking if an expr is calling a specific method
+
+Starting with an `expr`, you can check whether it is calling a specific method `some_method`:
+
+```rust
+impl LateLintPass<'_> for MyStructLint {
+ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
+ if_chain! {
+ // Check our expr is calling a method
+ if let hir::ExprKind::MethodCall(path, _, _args, _) = &expr.kind;
+ // Check the name of this method is `some_method`
+ if path.ident.name == sym!(some_method);
+ then {
+ // ...
+ }
+ }
+ }
+}
+```
# Checking if a type implements a specific trait
```rust
use crate::utils::{implements_trait, match_trait_method, paths};
-impl LateLintPass<'_, '_> for MyStructLint {
- fn check_expr(&mut self, cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
+impl LateLintPass<'_> for MyStructLint {
+ fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
// 1. Using expression and Clippy's convenient method
// we use `match_trait_method` function from Clippy's toolbox
if match_trait_method(cx, expr, &paths::INTO) {
}
// 2. Using type context `TyCtxt`
- let ty = cx.tables.expr_ty(expr);
+ let ty = cx.typeck_results().expr_ty(expr);
if cx.tcx.lang_items()
// we are looking for the `DefId` of `Drop` trait in lang items
.drop_trait()
We access lang items through the type context `tcx`. `tcx` is of type [`TyCtxt`][TyCtxt] and is defined in the `rustc_middle` crate.
+# Checking if a type defines a specific method
+
+To check if our type defines a method called `some_method`:
+
+```rust
+use crate::utils::{is_type_diagnostic_item, return_ty};
+
+impl<'tcx> LateLintPass<'tcx> for MyTypeImpl {
+ fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx ImplItem<'_>) {
+ if_chain! {
+ // Check if item is a method/function
+ if let ImplItemKind::Fn(ref signature, _) = impl_item.kind;
+ // Check the method is named `some_method`
+ if impl_item.ident.name == sym!(some_method);
+ // We can also check it has a parameter `self`
+ if signature.decl.implicit_self.has_implicit_self();
+ // We can go further and even check if its return type is `String`
+ if is_type_diagnostic_item(cx, return_ty(cx, impl_item.hir_id), sym!(string_type));
+ then {
+ // ...
+ }
+ }
+ }
+}
+```
+
# Dealing with macros
There are several helpers in Clippy's utils to deal with macros:
[TyS]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TyS.html
[TyKind]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/enum.TyKind.html
-[TypeckTables]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TypeckTables.html
-[expr_ty]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TypeckTables.html#method.expr_ty
+[TypeckResults]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TypeckResults.html
+[expr_ty]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TypeckResults.html#method.expr_ty
[LateContext]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/struct.LateContext.html
[TyCtxt]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/context/struct.TyCtxt.html
-[pat_ty]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/context/struct.TypeckTables.html#method.pat_ty
+[pat_ty]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/context/struct.TypeckResults.html#method.pat_ty
[paths]: ../clippy_lints/src/utils/paths.rs
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