- [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)
+ - [Checking if a type defines a specific method](#checking-if-a-type-defines-a-specific-method)
- [Dealing with macros](#dealing-with-macros)
Useful Rustc dev guide links:
- [Stages of compilation](https://rustc-dev-guide.rust-lang.org/compiler-src.html#the-main-stages-of-compilation)
+- [Diagnostic items](https://rustc-dev-guide.rust-lang.org/diagnostics/diagnostic-items.html)
- [Type checking](https://rustc-dev-guide.rust-lang.org/type-checking.html)
- [Ty module](https://rustc-dev-guide.rust-lang.org/ty.html)
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<'a, 'tcx>, expr: &'tcx hir::Expr<'_>) {
+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;
+ 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
-There are two ways to do this, depending if the target trait is part of lang items.
+There are three ways to do this, depending on if the target trait has a diagnostic item, lang item or neither.
```rust
-use crate::utils::{implements_trait, match_trait_method, paths};
-
-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) {
- // `expr` implements `Into` trait
+use clippy_utils::{implements_trait, is_trait_method, match_trait_method, paths};
+use rustc_span::symbol::sym;
+
+impl LateLintPass<'_> for MyStructLint {
+ fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
+ // 1. Using diagnostic items with the expression
+ // we use `is_trait_method` function from Clippy's utils
+ if is_trait_method(cx, expr, sym::Iterator) {
+ // method call in `expr` belongs to `Iterator` trait
}
- // 2. Using type context `TyCtxt`
- let ty = cx.tables.expr_ty(expr);
+ // 2. Using lang items with the expression type
+ 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()
.map_or(false, |id| implements_trait(cx, ty, id, &[])) {
// `expr` implements `Drop` trait
}
+
+ // 3. Using the type path with the expression
+ // we use `match_trait_method` function from Clippy's utils
+ if match_trait_method(cx, expr, &paths::INTO) {
+ // `expr` implements `Into` trait
+ }
}
}
```
-> Prefer using lang items, if the target trait is available there.
-
-A list of defined paths for Clippy can be found in [paths.rs][paths]
+> Prefer using diagnostic and lang items, if the target trait has one.
We access lang items through the type context `tcx`. `tcx` is of type [`TyCtxt`][TyCtxt] and is defined in the `rustc_middle` crate.
+A list of defined paths for Clippy can be found in [paths.rs][paths]
# 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};
+use clippy_utils::{is_type_diagnostic_item, return_ty};
-impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MyTypeImpl {
- fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, impl_item: &'tcx ImplItem<'_>) {
+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;
# Dealing with macros
-There are several helpers in Clippy's utils to deal with macros:
+There are several helpers in [`clippy_utils`][utils] to deal with macros:
- `in_macro()`: detect if the given span is expanded by a macro
[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
-[paths]: ../clippy_lints/src/utils/paths.rs
+[pat_ty]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/context/struct.TypeckResults.html#method.pat_ty
+[paths]: ../clippy_utils/src/paths.rs
+[utils]: https://github.com/rust-lang/rust-clippy/blob/master/clippy_utils/src/lib.rs
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