Add InternalVisbility constructors to ImplicitWeakMessage classes

This CLs adds internally visible arena enabled constructors and copy constructors to ImplicitWeakMessage and WeakRepeatedPtrField.

PiperOrigin-RevId: 547544297

src/google/protobuf/implicit_weak_message.h

@@ -57,14 +57,20 @@ namespace internal {
 // message type does not get linked into the binary.
 class PROTOBUF_EXPORT ImplicitWeakMessage : public MessageLite {
  public:
-  ImplicitWeakMessage() : data_(new std::string) {}
+  ImplicitWeakMessage() : ImplicitWeakMessage(nullptr) {}
   explicit constexpr ImplicitWeakMessage(ConstantInitialized)
       : data_(nullptr) {}
-  explicit ImplicitWeakMessage(Arena* arena)
-      : MessageLite(arena), data_(new std::string) {}
   ImplicitWeakMessage(const ImplicitWeakMessage&) = delete;
   ImplicitWeakMessage& operator=(const ImplicitWeakMessage&) = delete;
 
+  // Arena enabled constructors: for internal use only.
+  ImplicitWeakMessage(internal::InternalVisibility, Arena* arena)
+      : ImplicitWeakMessage(arena) {}
+
+  // TODO(b/290091828): make this constructor private
+  explicit ImplicitWeakMessage(Arena* arena)
+      : MessageLite(arena), data_(new std::string) {}
+
   ~ImplicitWeakMessage() override {
     // data_ will be null in the default instance, but we can safely call delete
     // here because the default instance will never be destroyed.
@@ -156,8 +162,21 @@ struct WeakRepeatedPtrField {
   using DestructorSkippable_ = void;
 
   using TypeHandler = internal::ImplicitWeakTypeHandler<T>;
+
   constexpr WeakRepeatedPtrField() : weak() {}
+  WeakRepeatedPtrField(const WeakRepeatedPtrField& rhs)
+      : WeakRepeatedPtrField(nullptr, rhs) {}
+
+  // Arena enabled constructors: for internal use only.
+  WeakRepeatedPtrField(internal::InternalVisibility, Arena* arena)
+      : WeakRepeatedPtrField(arena) {}
+  WeakRepeatedPtrField(internal::InternalVisibility, Arena* arena,
+                       const WeakRepeatedPtrField& rhs)
+      : WeakRepeatedPtrField(arena, rhs) {}
+
+  // TODO(b/290091828): make this constructor private
   explicit WeakRepeatedPtrField(Arena* arena) : weak(arena) {}
+
   ~WeakRepeatedPtrField() { weak.template Destroy<TypeHandler>(); }
 
   typedef internal::RepeatedPtrIterator<MessageLite> iterator;
@@ -208,6 +227,12 @@ struct WeakRepeatedPtrField {
   union {
     RepeatedPtrField<T> weak;
   };
+
+ private:
+  WeakRepeatedPtrField(Arena* arena, const WeakRepeatedPtrField& rhs)
+      : WeakRepeatedPtrField(arena) {
+    MergeFrom(rhs);
+  }
 };
 
 }  // namespace protobuf