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Rollup merge of #93926 - PatchMixolydic:bugfix/must_use-on-exprs, r=cjgillot

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Lint against more useless `#[must_use]` attributes

This expands the existing `#[must_use]` check in `unused_attributes` to lint against pretty much everything `#[must_use]` doesn't support.
Fixes #93906.
This commit is contained in:
Dylan DPC 2022-03-01 03:41:49 +01:00 • committed by GitHub
commit daed86445d
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6 changed files with 527 additions and 164 deletions
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35
compiler/rustc_passes/src/check_attr.rs
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@ -1111,7 +1111,7 @@ impl CheckAttrVisitor<'_> {
}
/// Warns against some misuses of `#[must_use]`
fn check_must_use(&self, hir_id: HirId, attr: &Attribute, span: Span, _target: Target) -> bool {
fn check_must_use(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) -> bool {
let node = self.tcx.hir().get(hir_id);
if let Some(fn_node) = node.fn_kind() {
if let rustc_hir::IsAsync::Async = fn_node.asyncness() {
@ -1131,6 +1131,39 @@ impl CheckAttrVisitor<'_> {
}
}
if !matches!(
target,
Target::Fn
| Target::Enum
| Target::Struct
| Target::Union
| Target::Method(_)
| 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::OpaqueTy
| Target::Enum
| Target::Impl
| Target::Expression
| Target::Arm
| Target::AssocConst
| Target::AssocTy => "an",
_ => "a",
};
self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
lint.build(&format!(
"`#[must_use]` has no effect when applied to {article} {target}"
))
.emit();
});
}
// For now, its always valid
true
}