hpb: Introduce CloneMessage with hpb::Arena + Deprecate CloneMessage w/ upb_arena*

PiperOrigin-RevId: 712906220

hpb/hpb.h

@@ -42,6 +42,17 @@ typename T::Proxy CreateMessage(hpb::Arena& arena) {
 }
 
 template <typename T>
+typename T::Proxy CloneMessage(Ptr<T> message, hpb::Arena& arena) {
+  return hpb::internal::PrivateAccess::Proxy<T>(
+      hpb::internal::DeepClone(hpb::interop::upb::GetMessage(message),
+                               T::minitable(), arena.ptr()),
+      arena.ptr());
+}
+
+// Deprecated; do not use. There is one extant caller which we plan to migrate.
+// Tracking deletion TODO: b/385138477
+template <typename T>
+[[deprecated("Use CloneMessage(Ptr<T>, hpb::Arena&) instead.")]]
 typename T::Proxy CloneMessage(Ptr<T> message, upb_Arena* arena) {
   return ::hpb::internal::PrivateAccess::Proxy<T>(
       ::hpb::internal::DeepClone(hpb::interop::upb::GetMessage(message),

hpb_generator/tests/test_generated.cc

@@ -625,6 +625,15 @@ TEST(CppGeneratedCode, ClearConstMessageShouldFailForConstChild) {
   EXPECT_TRUE(CanCallClearMessage<decltype(model.mutable_child_model_1())>());
 }
 
+TEST(CppGeneratedCode, CloneMessage) {
+  hpb::Arena arena;
+  TestModel model;
+  model.set_str1("Hello World");
+  auto ptr = hpb::Ptr<TestModel>(&model);
+  hpb::Ptr<TestModel> cloned_model = hpb::CloneMessage(ptr, arena);
+  EXPECT_EQ(cloned_model->str1(), "Hello World");
+}
+
 TEST(CppGeneratedCode, SetAlias) {
   hpb::Arena arena;
   auto child = hpb::CreateMessage<Child>(arena);