Change FieldDescriptor::type() to not have the call_once behavior.

This behavior is for lazily build descriptors, and those are for generated code
which always have this field set.
The `type()` function is called extensively in reflection based code and
removing the call_once has significant performance impact.

PiperOrigin-RevId: 625328922

src/google/protobuf/descriptor.cc

@@ -2808,7 +2808,7 @@ bool DescriptorPool::TryFindExtensionInFallbackDatabase(
 // ===================================================================
 
 bool FieldDescriptor::is_map_message_type() const {
-  return type_descriptor_.message_type->options().map_entry();
+  return message_type()->options().map_entry();
 }
 
 std::string FieldDescriptor::DefaultValueAsString(
@@ -6494,12 +6494,8 @@ void DescriptorBuilder::BuildFieldOrExtension(const FieldDescriptorProto& proto,
 
   result->has_json_name_ = proto.has_json_name();
 
-  // Some compilers do not allow static_cast directly between two enum types,
-  // so we must cast to int first.
-  result->type_ = static_cast<FieldDescriptor::Type>(
-      absl::implicit_cast<int>(proto.type()));
-  result->label_ = static_cast<FieldDescriptor::Label>(
-      absl::implicit_cast<int>(proto.label()));
+  result->type_ = proto.type();
+  result->label_ = proto.label();
   result->is_repeated_ = result->label_ == FieldDescriptor::LABEL_REPEATED;
 
   if (result->label() == FieldDescriptor::LABEL_REQUIRED) {
@@ -7379,6 +7375,10 @@ void DescriptorBuilder::CrossLinkField(FieldDescriptor* field,
 
     if (type.IsNull()) {
       if (is_lazy) {
+        ABSL_CHECK(field->type_ == FieldDescriptor::TYPE_MESSAGE ||
+                   field->type_ == FieldDescriptor::TYPE_GROUP ||
+                   field->type_ == FieldDescriptor::TYPE_ENUM)
+            << proto;
         // Save the symbol names for later for lookup, and allocate the once
         // object needed for the accessors.
         const std::string& name = proto.type_name();
@@ -9524,10 +9524,12 @@ void FieldDescriptor::InternalTypeOnceInit() const {
   Symbol result = file()->pool()->CrossLinkOnDemandHelper(
       lazy_type_name, type_ == FieldDescriptor::TYPE_ENUM);
   if (result.type() == Symbol::MESSAGE) {
-    type_ = FieldDescriptor::TYPE_MESSAGE;
+    ABSL_CHECK(type_ == FieldDescriptor::TYPE_MESSAGE ||
+               type_ == FieldDescriptor::TYPE_GROUP)
+        << full_name();
     type_descriptor_.message_type = result.descriptor();
   } else if (result.type() == Symbol::ENUM) {
-    type_ = FieldDescriptor::TYPE_ENUM;
+    ABSL_CHECK_EQ(type_, +FieldDescriptor::TYPE_ENUM);
     enum_type = type_descriptor_.enum_type = result.enum_descriptor();
   }
 
@@ -9566,19 +9568,23 @@ void FieldDescriptor::TypeOnceInit(const FieldDescriptor* to_init) {
 // all share the same absl::call_once init path to do lazy
 // import building and cross linking of a field of a message.
 const Descriptor* FieldDescriptor::message_type() const {
-  if (type_once_) {
-    absl::call_once(*type_once_, FieldDescriptor::TypeOnceInit, this);
+  if (type_ == TYPE_MESSAGE || type_ == TYPE_GROUP) {
+    if (type_once_) {
+      absl::call_once(*type_once_, FieldDescriptor::TypeOnceInit, this);
+    }
+    return type_descriptor_.message_type;
   }
-  return type_ == TYPE_MESSAGE || type_ == TYPE_GROUP
-             ? type_descriptor_.message_type
-             : nullptr;
+  return nullptr;
 }
 
 const EnumDescriptor* FieldDescriptor::enum_type() const {
-  if (type_once_) {
-    absl::call_once(*type_once_, FieldDescriptor::TypeOnceInit, this);
+  if (type_ == TYPE_ENUM) {
+    if (type_once_) {
+      absl::call_once(*type_once_, FieldDescriptor::TypeOnceInit, this);
+    }
+    return type_descriptor_.enum_type;
   }
-  return type_ == TYPE_ENUM ? type_descriptor_.enum_type : nullptr;
+  return nullptr;
 }
 
 const EnumValueDescriptor* FieldDescriptor::default_value_enum() const {

src/google/protobuf/descriptor.h

@@ -1090,7 +1090,7 @@ class PROTOBUF_EXPORT FieldDescriptor : private internal::SymbolBase,
   uint8_t label_ : 2;
 
   // Actually a `Type`, but stored as uint8_t to save space.
-  mutable uint8_t type_;
+  uint8_t type_;
 
   // Logically:
   //   all_names_ = [name, full_name, lower, camel, json]
@@ -2676,9 +2676,6 @@ inline FieldDescriptor::Label FieldDescriptor::label() const {
 }
 
 inline FieldDescriptor::Type FieldDescriptor::type() const {
-  if (type_once_) {
-    absl::call_once(*type_once_, &FieldDescriptor::TypeOnceInit, this);
-  }
   return static_cast<Type>(type_);
 }