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Lint #[must_use] attributes applied to methods in trait impls

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The `#[must_use]` attribute has no effect when applied to methods in
trait implementations. This case was not linted before.
This commit is contained in:
Samuel Tardieu 2025-02-12 10:35:32 +01:00
parent 3e66ba73d5
commit e639e886b2
3 changed files with 56 additions and 34 deletions
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49
compiler/rustc_passes/src/check_attr.rs
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@ -1431,37 +1431,48 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
/// Warns against some misuses of `#[must_use]`
fn check_must_use(&self, hir_id: HirId, attr: &Attribute, target: Target) {
if !matches!(
if matches!(
target,
Target::Fn
| Target::Enum
| Target::Struct
| Target::Union
| Target::Method(_)
| Target::Method(MethodKind::Trait { body: false } | MethodKind::Inherent)
| Target::ForeignFn
// `impl Trait` in return position can trip
// `unused_must_use` if `Trait` is marked as
// `#[must_use]`
| Target::Trait
) {
let article = match target {
Target::ExternCrate
| Target::Enum
| Target::Impl
| Target::Expression
| Target::Arm
| Target::AssocConst
| Target::AssocTy => "an",
_ => "a",
};
self.tcx.emit_node_span_lint(
UNUSED_ATTRIBUTES,
hir_id,
attr.span,
errors::MustUseNoEffect { article, target },
);
return;
}
// `#[must_use]` can be applied to a trait method definition with a default body
if let Target::Method(MethodKind::Trait { body: true }) = target
&& let parent_def_id = self.tcx.hir().get_parent_item(hir_id).def_id
&& let containing_item = self.tcx.hir().expect_item(parent_def_id)
&& let hir::ItemKind::Trait(..) = containing_item.kind
{
return;
}
let article = match target {
Target::ExternCrate
| Target::Enum
| Target::Impl
| Target::Expression
| Target::Arm
| Target::AssocConst
| Target::AssocTy => "an",
_ => "a",
};
self.tcx.emit_node_span_lint(
UNUSED_ATTRIBUTES,
hir_id,
attr.span,
errors::MustUseNoEffect { article, target },
);
}
/// Checks if `#[must_not_suspend]` is applied to a struct, enum, union, or trait.