================
@@ -1632,21 +1632,34 @@ QualType CallExpr::getCallReturnType(const ASTContext
&Ctx) const {
std::pair<const NamedDecl *, const WarnUnusedResultAttr *>
Expr::getUnusedResultAttrImpl(const Decl *Callee, QualType ReturnType) {
- // If the callee is marked nodiscard, return that attribute
- if (Callee != nullptr)
+ // If the callee is marked nodiscard, return that attribute for the
+ // diagnostic. If the callee is marked candiscard, do not diagnose.
+ // If seen on the same level, candiscard beats nodiscard.
+ if (Callee != nullptr) {
+ if (const auto *A = Callee->getAttr<CanDiscardAttr>())
+ return {nullptr, nullptr};
if (const auto *A = Callee->getAttr<WarnUnusedResultAttr>())
return {nullptr, A};
+ }
- // If the return type is a struct, union, or enum that is marked nodiscard,
- // then return the return type attribute.
- if (const TagDecl *TD = ReturnType->getAsTagDecl())
- if (const auto *A = TD->getAttr<WarnUnusedResultAttr>())
- return {TD, A};
-
+ // Walk the return type's (chain of) type aliases. The first alias
+ // that is marked either nodiscard or candiscard ends the walk.
for (const auto *TD = ReturnType->getAs<TypedefType>(); TD;
- TD = TD->desugar()->getAs<TypedefType>())
+ TD = TD->desugar()->getAs<TypedefType>()) {
----------------
halbi2 wrote:
Bug #68456 prevents these attributes from working on alias templates
https://github.com/llvm/llvm-project/pull/154943
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