Stop inlining ClassDataLite::type_name[] to make

sizeof(ClassDataFull) == sizeof(ClassDataLite) #ifdef PROTOBUF_MESSAGE_GLOBALS.

This allows embedding ClassData(Lite|Full) under a common type (GlobalsBase)
to access default instances with known offset.

PiperOrigin-RevId: 866629828

Author: protobuf-github-bot

src/google/protobuf/compiler/cpp/helpers.cc

@@ -624,8 +624,7 @@ std::string ClassDataType(const Descriptor* descriptor,
                  // via options.
                  IsBootstrapProto(options, descriptor->file())
              ? "ClassDataFull"
-             : absl::StrFormat("ClassDataLite<%d>",
-                               descriptor->full_name().size() + 1);
+             : "ClassDataLite";
 }
 
 std::string DescriptorTableName(const FileDescriptor* file,

src/google/protobuf/compiler/cpp/message.cc

@@ -4123,14 +4123,13 @@ void MessageGenerator::GenerateClassData(io::Printer* p) {
   } else {
     p->Emit(
         {
-            {"type_size", descriptor_->full_name().size() + 1},
             {"is_initialized", is_initialized},
             {"custom_vtable_methods", custom_vtable_methods},
             {"v2_data", emit_v2_data},
         },
         R"cc(
           constexpr auto $classname$::InternalGenerateClassData_() {
-            return $pbi$::ClassDataLite<$type_size$>{
+            return $pbi$::ClassDataLite{
                 {
                     $default_instance$,
                     &_table_.header,
@@ -4151,7 +4150,7 @@ void MessageGenerator::GenerateClassData(io::Printer* p) {
 
           PROTOBUF_CONSTINIT
           PROTOBUF_ATTRIBUTE_INIT_PRIORITY1
-          const $pbi$::ClassDataLite<$type_size$> $classname$_class_data_ =
+          const $pbi$::ClassDataLite $classname$_class_data_ =
               $classname$::InternalGenerateClassData_();
 
           //~ This function needs to be marked as weak to avoid significantly

src/google/protobuf/implicit_weak_message.cc

@@ -62,7 +62,7 @@ const TcParseTable<0> ImplicitWeakMessage::table_ =
     internal::CreateStubTcParseTable<ImplicitWeakMessage, ParseImpl>(
         class_data_.base());
 
-constexpr ClassDataLite<1> ImplicitWeakMessage::class_data_ = {
+constexpr ClassDataLite ImplicitWeakMessage::class_data_ = {
     {
         &implicit_weak_message_default_instance.instance,
         &table_.header,

src/google/protobuf/implicit_weak_message.h

@@ -85,7 +85,7 @@ class PROTOBUF_EXPORT ImplicitWeakMessage final : public MessageLite {
 
  private:
   static const TcParseTable<0> table_;
-  static const ClassDataLite<1> class_data_;
+  static const ClassDataLite class_data_;
 
   static void MergeImpl(MessageLite&, const MessageLite&);
 

src/google/protobuf/message_lite.cc

@@ -114,8 +114,8 @@ absl::string_view TypeId::name() const {
     return data_->full().descriptor_methods()->get_type_name(data_);
   }
 
-  // For LITE messages, the type name is a char[] just beyond ClassData.
-  return reinterpret_cast<const char*>(data_) + sizeof(internal::ClassData);
+  // For LITE messages, the type name is accessed via ClassDataLite.
+  return static_cast<const internal::ClassDataLite*>(data_)->type_name;
 }
 
 std::string MessageLite::InitializationErrorString() const {

src/google/protobuf/message_lite.h

@@ -464,12 +464,13 @@ struct PROTOBUF_EXPORT ClassData {
   uint8_t alignment() const { return message_creator.alignment(); }
 };
 
-template <size_t N>
-struct ClassDataLite {
-  ClassData header;
-  const char type_name[N];
+struct ClassDataLite : ClassData {
+  constexpr ClassDataLite(ClassData base, const char* type_name)
+      : ClassData(base), type_name(type_name) {}
 
-  constexpr const ClassData* base() const { return &header; }
+  const char* type_name;
+
+  constexpr const ClassData* base() const { return this; }
 };
 
 // We use a secondary vtable for descriptor based methods. This way ClassData