[clang] [Clang] handle [[warn_unused]] attribute for unused private fields (PR #120734)

[Oleksandr T. via cfe-commits]

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@@ -3307,6 +3307,29 @@ void Sema::CheckShadowInheritedFields(const SourceLocation &Loc,
   }
 }
 
+template <typename AttrType>
+inline static bool HasAttribute(const QualType &T) {
+  if (const TagDecl *TD = T->getAsTagDecl())
+    return TD->hasAttr<AttrType>();
+  if (const TypedefType *TDT = T->getAs<TypedefType>())
+    return TDT->getDecl()->hasAttr<AttrType>();
+  return false;
+}
+
+inline static bool IsUnusedPrivateField(FieldDecl *FD) {
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a-tarasyuk wrote:

@erichkeane I was thinking of using `IsPrivateFieldWithoutSideEffects` to proceed with adding it to `UnusedPrivateFields`, however, decided to match with `UnusedPrivateFields`...  What do you think about this?

https://github.com/llvm/llvm-project/pull/120734