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)
# 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 clippy_utils::{implements_trait, match_trait_method, paths};
+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 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
+ // 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`
+ // 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
.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