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blyxyas 2023-04-18 20:50:41 +02:00
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book/src/development/trait_checking.md
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@ -11,10 +11,6 @@ that we want to examine has a [diagnostic item][diagnostic_items],
As explained in the [Rust Compiler Development Guide][rustc_dev_guide], diagnostic items As explained in the [Rust Compiler Development Guide][rustc_dev_guide], diagnostic items
are introduced for identifying types via [Symbols][symbol]. are introduced for identifying types via [Symbols][symbol].
While the Rust Compiler Development Guide has [a section][using_diagnostic_items] on
how to check for a specific trait on a type `Ty`, Clippy provides
a helper function `is_trait_method`, which simplifies the process for us.
For instance, if we want to examine whether an expression implements For instance, if we want to examine whether an expression implements
the `Iterator` trait, we could simply write the following code, the `Iterator` trait, we could simply write the following code,
providing the `LateContext` (`cx`), our expression at hand, and providing the `LateContext` (`cx`), our expression at hand, and
@ -28,9 +24,13 @@ use rustc_span::symbol::sym;
impl LateLintPass<'_> for CheckIteratorTraitLint { impl LateLintPass<'_> for CheckIteratorTraitLint {
fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) { fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
if is_trait_method(cx, expr, sym::Iterator) { let implements_iterator = cx.tcx.get_diagnostic_item(sym::Iterator).map_or(false, |id| {
println!("This expression implements `Iterator` trait!"); implements_trait(cx, cx.typeck_results().expr_ty(arg), id, &[])
} });
if implements_iterator {
// [...]
}
} }
} }
``` ```
@ -40,9 +40,8 @@ impl LateLintPass<'_> for CheckIteratorTraitLint {
## Using Lang Items ## Using Lang Items
Besides diagnostic items, we can also use [`lang_items`][lang_items]. Besides diagnostic items, we can also use [`lang_items`][lang_items].
Take a look at the documentation and we find that `LanguageItems` contains Take a look at the documentation to find that `LanguageItems` contains
all language items both from the current crate or its all language items defined in the compiler.
dependencies.
Using one of its `*_trait` method, we could obtain the [DefId] of any Using one of its `*_trait` method, we could obtain the [DefId] of any
specific item, such as `Clone`, `Copy`, `Drop`, `Eq`, which are familiar specific item, such as `Clone`, `Copy`, `Drop`, `Eq`, which are familiar
@ -73,11 +72,11 @@ impl LateLintPass<'_> for CheckDropTraitLint {
## Using Type Path ## Using Type Path
If neither diagnostic item or lang item is available, we can use If neither diagnostic item nor a language item is available, we can use
[`clippy_utils::paths`][paths] with the `match_trait_method` to determine trait [`clippy_utils::paths`][paths] with the `match_trait_method` to determine trait
implementation. implementation.
> **Note**: This approach should be avoided if possible. > **Note**: This approach should be avoided if possible, the best thing to do would be to make a PR to [`rust-lang/rust`][rust].
Below, we check if the given `expr` implements `tokio`'s Below, we check if the given `expr` implements `tokio`'s
[`AsyncReadExt`][AsyncReadExt] trait: [`AsyncReadExt`][AsyncReadExt] trait:
@ -89,17 +88,13 @@ use rustc_lint::{LateContext, LateLintPass};
impl LateLintPass<'_> for CheckTokioAsyncReadExtTrait { impl LateLintPass<'_> for CheckTokioAsyncReadExtTrait {
fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) { fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
if match_trait_method(cx, expr, &paths::TOKIO_IO_ASYNCREADEXT) { if match_trait_method(cx, expr, &paths::CORE_ITER_CLONED) {
println!("`expr` implements `TOKIO_IO_ASYNCREADEXT` trait!"); println!("`expr` implements `CORE_ITER_CLONED` trait!");
} }
} }
} }
``` ```
> **Note**: Even though all the `clippy_utils` methods we have seen in this
> chapter takes `expr` as a parameter, these methods are actually using
> each expression's `HirId` under the hood.
[AsyncReadExt]: https://docs.rs/tokio/latest/tokio/io/trait.AsyncReadExt.html [AsyncReadExt]: https://docs.rs/tokio/latest/tokio/io/trait.AsyncReadExt.html
[DefId]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/def_id/struct.DefId.html [DefId]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/def_id/struct.DefId.html
[diagnostic_items]: https://rustc-dev-guide.rust-lang.org/diagnostics/diagnostic-items.html [diagnostic_items]: https://rustc-dev-guide.rust-lang.org/diagnostics/diagnostic-items.html
@ -110,3 +105,4 @@ impl LateLintPass<'_> for CheckTokioAsyncReadExtTrait {
[symbol_index]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_span/symbol/sym/index.html [symbol_index]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_span/symbol/sym/index.html
[TyCtxt]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/context/struct.TyCtxt.html [TyCtxt]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/context/struct.TyCtxt.html
[using_diagnostic_items]: https://rustc-dev-guide.rust-lang.org/diagnostics/diagnostic-items.html#using-diagnostic-items [using_diagnostic_items]: https://rustc-dev-guide.rust-lang.org/diagnostics/diagnostic-items.html#using-diagnostic-items
[rust]: https://github.com/rust-lang/rust