[clang] [Bounds-Safety] Add sized_by, counted_by_or_null & sized_by_or_null (PR #93231)

[Henrik G. Olsson via cfe-commits]

================
@@ -8641,22 +8641,33 @@ enum class CountedByInvalidPointeeTypeKind {
   VALID,
 };
 
-static bool CheckCountedByAttrOnField(
-    Sema &S, FieldDecl *FD, Expr *E,
-    llvm::SmallVectorImpl<TypeCoupledDeclRefInfo> &Decls) {
+static bool
+CheckCountedByAttrOnField(Sema &S, FieldDecl *FD, Expr *E,
+                          llvm::SmallVectorImpl<TypeCoupledDeclRefInfo> &Decls,
+                          bool CountInBytes, bool OrNull) {
   // Check the context the attribute is used in
 
+  unsigned Kind = CountInBytes;
+  if (OrNull)
+    Kind += 2;
+
   if (FD->getParent()->isUnion()) {
     S.Diag(FD->getBeginLoc(), diag::err_counted_by_attr_in_union)
-        << FD->getSourceRange();
+        << Kind << FD->getSourceRange();
     return true;
   }
 
   const auto FieldTy = FD->getType();
+  if (FieldTy->isArrayType() && (CountInBytes || OrNull)) {
+    S.Diag(FD->getBeginLoc(),
+           diag::err_counted_by_attr_not_on_ptr_or_flexible_array_member)
----------------
hnrklssn wrote:

> The OrNull case probably deserves its own special diagnostic because in that case the diagnostic should explain that they cannot use the attribute on arrays and that they need to use __counted_by instead.

That is also true for `CountInBytes`. But I agree that it would be good for the diagnostic to suggest `counted_by`.

https://github.com/llvm/llvm-project/pull/93231