[clang] [clang] Generate note on declaration for nodiscard-related attributes (PR #112289)

[Erich Keane via cfe-commits]

================
@@ -204,23 +205,29 @@ static bool DiagnoseUnusedComparison(Sema &S, const Expr *E) {
   return true;
 }
 
-static bool DiagnoseNoDiscard(Sema &S, const WarnUnusedResultAttr *A,
-                              SourceLocation Loc, SourceRange R1,
-                              SourceRange R2, bool IsCtor) {
+static bool DiagnoseNoDiscard(Sema &S, const NamedDecl *OffendingDecl,
+                              const WarnUnusedResultAttr *A, SourceLocation Loc,
+                              SourceRange R1, SourceRange R2, bool IsCtor) {
   if (!A)
     return false;
   StringRef Msg = A->getMessage();
 
+  bool result;
   if (Msg.empty()) {
     if (IsCtor)
-      return S.Diag(Loc, diag::warn_unused_constructor) << A << R1 << R2;
-    return S.Diag(Loc, diag::warn_unused_result) << A << R1 << R2;
-  }
+      result = S.Diag(Loc, diag::warn_unused_constructor) << A << R1 << R2;
+    else
+      result = S.Diag(Loc, diag::warn_unused_result) << A << R1 << R2;
+  } else if (IsCtor)
+    result = S.Diag(Loc, diag::warn_unused_constructor_msg)
+             << A << Msg << R1 << R2;
+  else
+    result = S.Diag(Loc, diag::warn_unused_result_msg) << A << Msg << R1 << R2;
 
-  if (IsCtor)
-    return S.Diag(Loc, diag::warn_unused_constructor_msg) << A << Msg << R1
-                                                          << R2;
-  return S.Diag(Loc, diag::warn_unused_result_msg) << A << Msg << R1 << R2;
+  if (OffendingDecl)
----------------
erichkeane wrote:

I can't imagine anything that would not be a `NamedDecl` that one could put the `nodiscard` on.  Also though, WHY dose it have to be a `NamedDecl`?  We only need the location for the diagnostic anyway, so having `getUnusedResultAttr` return just a `Decl` is probably sufficient.

https://github.com/llvm/llvm-project/pull/112289