[clang] [clang] Improve diagnostic on [[nodiscard]] attribute (PR #112521)

[Shafik Yaghmour via cfe-commits]

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@@ -1615,22 +1615,24 @@ QualType CallExpr::getCallReturnType(const ASTContext &Ctx) const {
   return FnType->getReturnType();
 }
 
-const Attr *CallExpr::getUnusedResultAttr(const ASTContext &Ctx) const {
+std::pair<const NamedDecl *, const Attr *>
+CallExpr::getUnusedResultAttr(const ASTContext &Ctx) const {
+  // If the callee is marked nodiscard, return that attribute
+  const Decl *D = getCalleeDecl();
+  if (const auto *A = D->getAttr<WarnUnusedResultAttr>())
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shafik wrote:

This looks like an unconditional access of `D` but it is not obvious this is a correct assumption

https://github.com/llvm/llvm-project/pull/112521