[clang] [clang] Diagnose [[nodiscard]] return types in Objective-C++ (PR #142541)

[Erich Keane via cfe-commits]

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@@ -272,6 +273,26 @@ QualType ObjCMessageExpr::getCallReturnType(ASTContext &Ctx) const {
   return Ctx.getReferenceQualifiedType(this);
 }
 
+std::pair<const NamedDecl *, const Attr *>
+ObjCMessageExpr::getUnusedResultAttr(ASTContext &Ctx) const {
+  // If the callee is marked nodiscard, return that attribute
+  if (const ObjCMethodDecl *MD = getMethodDecl())
+    if (const auto *A = MD->getAttr<WarnUnusedResultAttr>())
+      return {nullptr, A};
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erichkeane wrote:

Can you better explain that?  What happens if this DOES set the `MD` correctly?  Do we have a test that shows the behavior change?

https://github.com/llvm/llvm-project/pull/142541