Re-enable separation of protobufs for Python 2 and Python 3

Это откат коммита https://a.yandex-team.ru/arcadia/commit/rXXXXXX
И соответственно возврат коммитов https://a.yandex-team.ru/arcadia/commit/rXXXXXX и https://a.yandex-team.ru/arcadia/commit/rXXXXXX

Починка причины отката влилась здесь: https://a.yandex-team.ru/arcadia/commit/rXXXXXX
ae529e54d3ef7992b0e9f152373bc300061c1293

1 files changed, 2255 insertions, 0 deletions

diff --git a/contrib/libs/protobuf_old/src/google/protobuf/extension_set.cc b/contrib/libs/protobuf_old/src/google/protobuf/extension_set.cc
new file mode 100644
index 0000000000..af851b2a45
--- /dev/null
+++ b/contrib/libs/protobuf_old/src/google/protobuf/extension_set.cc
@@ -0,0 +1,2255 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Author: kenton@google.com (Kenton Varda)
+//  Based on original Protocol Buffers design by
+//  Sanjay Ghemawat, Jeff Dean, and others.
+
+#include <google/protobuf/extension_set.h>
+
+#include <tuple>
+#include <unordered_set>
+#include <utility>
+
+#include <google/protobuf/stubs/common.h>
+#include <google/protobuf/extension_set_inl.h>
+#include <google/protobuf/parse_context.h>
+#include <google/protobuf/io/coded_stream.h>
+#include <google/protobuf/io/zero_copy_stream_impl_lite.h>
+#include <google/protobuf/arena.h>
+#include <google/protobuf/message_lite.h>
+#include <google/protobuf/metadata_lite.h>
+#include <google/protobuf/repeated_field.h>
+#include <google/protobuf/stubs/map_util.h>
+#include <google/protobuf/stubs/hash.h>
+
+// clang-format off
+#include <google/protobuf/port_def.inc>  // must be last.
+// clang-format on
+namespace google {
+namespace protobuf {
+namespace internal {
+
+namespace {
+
+inline WireFormatLite::FieldType real_type(FieldType type) {
+  GOOGLE_DCHECK(type > 0 && type <= WireFormatLite::MAX_FIELD_TYPE);
+  return static_cast<WireFormatLite::FieldType>(type);
+}
+
+inline WireFormatLite::CppType cpp_type(FieldType type) {
+  return WireFormatLite::FieldTypeToCppType(real_type(type));
+}
+
+inline bool is_packable(WireFormatLite::WireType type) {
+  switch (type) {
+    case WireFormatLite::WIRETYPE_VARINT:
+    case WireFormatLite::WIRETYPE_FIXED64:
+    case WireFormatLite::WIRETYPE_FIXED32:
+      return true;
+    case WireFormatLite::WIRETYPE_LENGTH_DELIMITED:
+    case WireFormatLite::WIRETYPE_START_GROUP:
+    case WireFormatLite::WIRETYPE_END_GROUP:
+      return false;
+
+      // Do not add a default statement. Let the compiler complain when someone
+      // adds a new wire type.
+  }
+  GOOGLE_LOG(FATAL) << "can't reach here.";
+  return false;
+}
+
+// Registry stuff.
+
+// Note that we cannot use hetererogeneous lookup for std containers since we
+// need to support C++11.
+struct ExtensionEq {
+  bool operator()(const ExtensionInfo& lhs, const ExtensionInfo& rhs) const {
+    return lhs.message == rhs.message && lhs.number == rhs.number;
+  }
+};
+
+struct ExtensionHasher {
+  std::size_t operator()(const ExtensionInfo& info) const {
+    return std::hash<const MessageLite*>{}(info.message) ^
+           std::hash<int>{}(info.number);
+  }
+};
+
+using ExtensionRegistry =
+    std::unordered_set<ExtensionInfo, ExtensionHasher, ExtensionEq>;
+
+static const ExtensionRegistry* global_registry = nullptr;
+
+// This function is only called at startup, so there is no need for thread-
+// safety.
+void Register(const ExtensionInfo& info) {
+  static auto local_static_registry = OnShutdownDelete(new ExtensionRegistry);
+  global_registry = local_static_registry;
+  if (!InsertIfNotPresent(local_static_registry, info)) {
+    GOOGLE_LOG(FATAL) << "Multiple extension registrations for type \""
+               << info.message->GetTypeName() << "\", field number "
+               << info.number << ".";
+  }
+}
+
+const ExtensionInfo* FindRegisteredExtension(const MessageLite* extendee,
+                                             int number) {
+  if (!global_registry) return nullptr;
+
+  ExtensionInfo info;
+  info.message = extendee;
+  info.number = number;
+
+  auto it = global_registry->find(info);
+  if (it == global_registry->end()) {
+    return nullptr;
+  } else {
+    return &*it;
+  }
+}
+
+}  // namespace
+
+ExtensionFinder::~ExtensionFinder() {}
+
+bool GeneratedExtensionFinder::Find(int number, ExtensionInfo* output) {
+  const ExtensionInfo* extension = FindRegisteredExtension(extendee_, number);
+  if (extension == nullptr) {
+    return false;
+  } else {
+    *output = *extension;
+    return true;
+  }
+}
+
+void ExtensionSet::RegisterExtension(const MessageLite* extendee, int number,
+                                     FieldType type, bool is_repeated,
+                                     bool is_packed) {
+  GOOGLE_CHECK_NE(type, WireFormatLite::TYPE_ENUM);
+  GOOGLE_CHECK_NE(type, WireFormatLite::TYPE_MESSAGE);
+  GOOGLE_CHECK_NE(type, WireFormatLite::TYPE_GROUP);
+  ExtensionInfo info(extendee, number, type, is_repeated, is_packed);
+  Register(info);
+}
+
+static bool CallNoArgValidityFunc(const void* arg, int number) {
+  // Note:  Must use C-style cast here rather than reinterpret_cast because
+  //   the C++ standard at one point did not allow casts between function and
+  //   data pointers and some compilers enforce this for C++-style casts.  No
+  //   compiler enforces it for C-style casts since lots of C-style code has
+  //   relied on these kinds of casts for a long time, despite being
+  //   technically undefined.  See:
+  //     http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#195
+  // Also note:  Some compilers do not allow function pointers to be "const".
+  //   Which makes sense, I suppose, because it's meaningless.
+  return ((EnumValidityFunc*)arg)(number);
+}
+
+void ExtensionSet::RegisterEnumExtension(const MessageLite* extendee,
+                                         int number, FieldType type,
+                                         bool is_repeated, bool is_packed,
+                                         EnumValidityFunc* is_valid) {
+  GOOGLE_CHECK_EQ(type, WireFormatLite::TYPE_ENUM);
+  ExtensionInfo info(extendee, number, type, is_repeated, is_packed);
+  info.enum_validity_check.func = CallNoArgValidityFunc;
+  // See comment in CallNoArgValidityFunc() about why we use a c-style cast.
+  info.enum_validity_check.arg = (void*)is_valid;
+  Register(info);
+}
+
+void ExtensionSet::RegisterMessageExtension(const MessageLite* extendee,
+                                            int number, FieldType type,
+                                            bool is_repeated, bool is_packed,
+                                            const MessageLite* prototype) {
+  GOOGLE_CHECK(type == WireFormatLite::TYPE_MESSAGE ||
+        type == WireFormatLite::TYPE_GROUP);
+  ExtensionInfo info(extendee, number, type, is_repeated, is_packed);
+  info.message_info = {prototype};
+  Register(info);
+}
+
+// ===================================================================
+// Constructors and basic methods.
+
+ExtensionSet::ExtensionSet(Arena* arena)
+    : arena_(arena),
+      flat_capacity_(0),
+      flat_size_(0),
+      map_{flat_capacity_ == 0
+               ? nullptr
+               : Arena::CreateArray<KeyValue>(arena_, flat_capacity_)} {}
+
+ExtensionSet::~ExtensionSet() {
+  // Deletes all allocated extensions.
+  if (arena_ == nullptr) {
+    ForEach([](int /* number */, Extension& ext) { ext.Free(); });
+    if (PROTOBUF_PREDICT_FALSE(is_large())) {
+      delete map_.large;
+    } else {
+      DeleteFlatMap(map_.flat, flat_capacity_);
+    }
+  }
+}
+
+void ExtensionSet::DeleteFlatMap(const ExtensionSet::KeyValue* flat,
+                                 uint16_t flat_capacity) {
+#ifdef __cpp_sized_deallocation
+  // Arena::CreateArray already requires a trivially destructible type, but
+  // ensure this constraint is not violated in the future.
+  static_assert(std::is_trivially_destructible<KeyValue>::value,
+                "CreateArray requires a trivially destructible type");
+  // A const-cast is needed, but this is safe as we are about to deallocate the
+  // array.
+  ::operator delete[](const_cast<ExtensionSet::KeyValue*>(flat),
+                      sizeof(*flat) * flat_capacity);
+#else   // !__cpp_sized_deallocation
+  delete[] flat;
+#endif  // !__cpp_sized_deallocation
+}
+
+// Defined in extension_set_heavy.cc.
+// void ExtensionSet::AppendToList(const Descriptor* extendee,
+//                                 const DescriptorPool* pool,
+//                                 vector<const FieldDescriptor*>* output) const
+
+bool ExtensionSet::Has(int number) const {
+  const Extension* ext = FindOrNull(number);
+  if (ext == nullptr) return false;
+  GOOGLE_DCHECK(!ext->is_repeated);
+  return !ext->is_cleared;
+}
+
+bool ExtensionSet::HasLazy(int number) const {
+  return Has(number) && FindOrNull(number)->is_lazy;
+}
+
+int ExtensionSet::NumExtensions() const {
+  int result = 0;
+  ForEach([&result](int /* number */, const Extension& ext) {
+    if (!ext.is_cleared) {
+      ++result;
+    }
+  });
+  return result;
+}
+
+int ExtensionSet::ExtensionSize(int number) const {
+  const Extension* ext = FindOrNull(number);
+  return ext == nullptr ? 0 : ext->GetSize();
+}
+
+FieldType ExtensionSet::ExtensionType(int number) const {
+  const Extension* ext = FindOrNull(number);
+  if (ext == nullptr) {
+    GOOGLE_LOG(DFATAL) << "Don't lookup extension types if they aren't present (1). ";
+    return 0;
+  }
+  if (ext->is_cleared) {
+    GOOGLE_LOG(DFATAL) << "Don't lookup extension types if they aren't present (2). ";
+  }
+  return ext->type;
+}
+
+void ExtensionSet::ClearExtension(int number) {
+  Extension* ext = FindOrNull(number);
+  if (ext == nullptr) return;
+  ext->Clear();
+}
+
+// ===================================================================
+// Field accessors
+
+namespace {
+
+enum { REPEATED_FIELD, OPTIONAL_FIELD };
+
+}  // namespace
+
+#define GOOGLE_DCHECK_TYPE(EXTENSION, LABEL, CPPTYPE)                                 \
+  GOOGLE_DCHECK_EQ((EXTENSION).is_repeated ? REPEATED_FIELD : OPTIONAL_FIELD, LABEL); \
+  GOOGLE_DCHECK_EQ(cpp_type((EXTENSION).type), WireFormatLite::CPPTYPE_##CPPTYPE)
+
+// -------------------------------------------------------------------
+// Primitives
+
+#define PRIMITIVE_ACCESSORS(UPPERCASE, LOWERCASE, CAMELCASE)                  \
+                                                                              \
+  LOWERCASE ExtensionSet::Get##CAMELCASE(int number, LOWERCASE default_value) \
+      const {                                                                 \
+    const Extension* extension = FindOrNull(number);                          \
+    if (extension == nullptr || extension->is_cleared) {                      \
+      return default_value;                                                   \
+    } else {                                                                  \
+      GOOGLE_DCHECK_TYPE(*extension, OPTIONAL_FIELD, UPPERCASE);                     \
+      return extension->LOWERCASE##_value;                                    \
+    }                                                                         \
+  }                                                                           \
+                                                                              \
+  const LOWERCASE& ExtensionSet::GetRef##CAMELCASE(                           \
+      int number, const LOWERCASE& default_value) const {                     \
+    const Extension* extension = FindOrNull(number);                          \
+    if (extension == nullptr || extension->is_cleared) {                      \
+      return default_value;                                                   \
+    } else {                                                                  \
+      GOOGLE_DCHECK_TYPE(*extension, OPTIONAL_FIELD, UPPERCASE);                     \
+      return extension->LOWERCASE##_value;                                    \
+    }                                                                         \
+  }                                                                           \
+                                                                              \
+  void ExtensionSet::Set##CAMELCASE(int number, FieldType type,               \
+                                    LOWERCASE value,                          \
+                                    const FieldDescriptor* descriptor) {      \
+    Extension* extension;                                                     \
+    if (MaybeNewExtension(number, descriptor, &extension)) {                  \
+      extension->type = type;                                                 \
+      GOOGLE_DCHECK_EQ(cpp_type(extension->type),                                    \
+                WireFormatLite::CPPTYPE_##UPPERCASE);                         \
+      extension->is_repeated = false;                                         \
+    } else {                                                                  \
+      GOOGLE_DCHECK_TYPE(*extension, OPTIONAL_FIELD, UPPERCASE);                     \
+    }                                                                         \
+    extension->is_cleared = false;                                            \
+    extension->LOWERCASE##_value = value;                                     \
+  }                                                                           \
+                                                                              \
+  LOWERCASE ExtensionSet::GetRepeated##CAMELCASE(int number, int index)       \
+      const {                                                                 \
+    const Extension* extension = FindOrNull(number);                          \
+    GOOGLE_CHECK(extension != nullptr) << "Index out-of-bounds (field is empty).";   \
+    GOOGLE_DCHECK_TYPE(*extension, REPEATED_FIELD, UPPERCASE);                       \
+    return extension->repeated_##LOWERCASE##_value->Get(index);               \
+  }                                                                           \
+                                                                              \
+  const LOWERCASE& ExtensionSet::GetRefRepeated##CAMELCASE(int number,        \
+                                                           int index) const { \
+    const Extension* extension = FindOrNull(number);                          \
+    GOOGLE_CHECK(extension != nullptr) << "Index out-of-bounds (field is empty).";   \
+    GOOGLE_DCHECK_TYPE(*extension, REPEATED_FIELD, UPPERCASE);                       \
+    return extension->repeated_##LOWERCASE##_value->Get(index);               \
+  }                                                                           \
+                                                                              \
+  void ExtensionSet::SetRepeated##CAMELCASE(int number, int index,            \
+                                            LOWERCASE value) {                \
+    Extension* extension = FindOrNull(number);                                \
+    GOOGLE_CHECK(extension != nullptr) << "Index out-of-bounds (field is empty).";   \
+    GOOGLE_DCHECK_TYPE(*extension, REPEATED_FIELD, UPPERCASE);                       \
+    extension->repeated_##LOWERCASE##_value->Set(index, value);               \
+  }                                                                           \
+                                                                              \
+  void ExtensionSet::Add##CAMELCASE(int number, FieldType type, bool packed,  \
+                                    LOWERCASE value,                          \
+                                    const FieldDescriptor* descriptor) {      \
+    Extension* extension;                                                     \
+    if (MaybeNewExtension(number, descriptor, &extension)) {                  \
+      extension->type = type;                                                 \
+      GOOGLE_DCHECK_EQ(cpp_type(extension->type),                                    \
+                WireFormatLite::CPPTYPE_##UPPERCASE);                         \
+      extension->is_repeated = true;                                          \
+      extension->is_packed = packed;                                          \
+      extension->repeated_##LOWERCASE##_value =                               \
+          Arena::CreateMessage<RepeatedField<LOWERCASE>>(arena_);             \
+    } else {                                                                  \
+      GOOGLE_DCHECK_TYPE(*extension, REPEATED_FIELD, UPPERCASE);                     \
+      GOOGLE_DCHECK_EQ(extension->is_packed, packed);                                \
+    }                                                                         \
+    extension->repeated_##LOWERCASE##_value->Add(value);                      \
+  }
+
+PRIMITIVE_ACCESSORS(INT32, arc_i32, Int32)
+PRIMITIVE_ACCESSORS(INT64, arc_i64, Int64)
+PRIMITIVE_ACCESSORS(UINT32, arc_ui32, UInt32)
+PRIMITIVE_ACCESSORS(UINT64, arc_ui64, UInt64)
+PRIMITIVE_ACCESSORS(FLOAT, float, Float)
+PRIMITIVE_ACCESSORS(DOUBLE, double, Double)
+PRIMITIVE_ACCESSORS(BOOL, bool, Bool)
+
+#undef PRIMITIVE_ACCESSORS
+
+const void* ExtensionSet::GetRawRepeatedField(int number,
+                                              const void* default_value) const {
+  const Extension* extension = FindOrNull(number);
+  if (extension == nullptr) {
+    return default_value;
+  }
+  // We assume that all the RepeatedField<>* pointers have the same
+  // size and alignment within the anonymous union in Extension.
+  return extension->repeated_arc_i32_value;
+}
+
+void* ExtensionSet::MutableRawRepeatedField(int number, FieldType field_type,
+                                            bool packed,
+                                            const FieldDescriptor* desc) {
+  Extension* extension;
+
+  // We instantiate an empty Repeated{,Ptr}Field if one doesn't exist for this
+  // extension.
+  if (MaybeNewExtension(number, desc, &extension)) {
+    extension->is_repeated = true;
+    extension->type = field_type;
+    extension->is_packed = packed;
+
+    switch (WireFormatLite::FieldTypeToCppType(
+        static_cast<WireFormatLite::FieldType>(field_type))) {
+      case WireFormatLite::CPPTYPE_INT32:
+        extension->repeated_arc_i32_value =
+            Arena::CreateMessage<RepeatedField<arc_i32>>(arena_);
+        break;
+      case WireFormatLite::CPPTYPE_INT64:
+        extension->repeated_arc_i64_value =
+            Arena::CreateMessage<RepeatedField<arc_i64>>(arena_);
+        break;
+      case WireFormatLite::CPPTYPE_UINT32:
+        extension->repeated_arc_ui32_value =
+            Arena::CreateMessage<RepeatedField<arc_ui32>>(arena_);
+        break;
+      case WireFormatLite::CPPTYPE_UINT64:
+        extension->repeated_arc_ui64_value =
+            Arena::CreateMessage<RepeatedField<arc_ui64>>(arena_);
+        break;
+      case WireFormatLite::CPPTYPE_DOUBLE:
+        extension->repeated_double_value =
+            Arena::CreateMessage<RepeatedField<double>>(arena_);
+        break;
+      case WireFormatLite::CPPTYPE_FLOAT:
+        extension->repeated_float_value =
+            Arena::CreateMessage<RepeatedField<float>>(arena_);
+        break;
+      case WireFormatLite::CPPTYPE_BOOL:
+        extension->repeated_bool_value =
+            Arena::CreateMessage<RepeatedField<bool>>(arena_);
+        break;
+      case WireFormatLite::CPPTYPE_ENUM:
+        extension->repeated_enum_value =
+            Arena::CreateMessage<RepeatedField<int>>(arena_);
+        break;
+      case WireFormatLite::CPPTYPE_STRING:
+        extension->repeated_string_value =
+            Arena::CreateMessage<RepeatedPtrField<TProtoStringType>>(arena_);
+        break;
+      case WireFormatLite::CPPTYPE_MESSAGE:
+        extension->repeated_message_value =
+            Arena::CreateMessage<RepeatedPtrField<MessageLite>>(arena_);
+        break;
+    }
+  }
+
+  // We assume that all the RepeatedField<>* pointers have the same
+  // size and alignment within the anonymous union in Extension.
+  return extension->repeated_arc_i32_value;
+}
+
+// Compatible version using old call signature. Does not create extensions when
+// the don't already exist; instead, just GOOGLE_CHECK-fails.
+void* ExtensionSet::MutableRawRepeatedField(int number) {
+  Extension* extension = FindOrNull(number);
+  GOOGLE_CHECK(extension != nullptr) << "Extension not found.";
+  // We assume that all the RepeatedField<>* pointers have the same
+  // size and alignment within the anonymous union in Extension.
+  return extension->repeated_arc_i32_value;
+}
+
+// -------------------------------------------------------------------
+// Enums
+
+int ExtensionSet::GetEnum(int number, int default_value) const {
+  const Extension* extension = FindOrNull(number);
+  if (extension == nullptr || extension->is_cleared) {
+    // Not present.  Return the default value.
+    return default_value;
+  } else {
+    GOOGLE_DCHECK_TYPE(*extension, OPTIONAL_FIELD, ENUM);
+    return extension->enum_value;
+  }
+}
+
+const int& ExtensionSet::GetRefEnum(int number,
+                                    const int& default_value) const {
+  const Extension* extension = FindOrNull(number);
+  if (extension == nullptr || extension->is_cleared) {
+    // Not present.  Return the default value.
+    return default_value;
+  } else {
+    GOOGLE_DCHECK_TYPE(*extension, OPTIONAL_FIELD, ENUM);
+    return extension->enum_value;
+  }
+}
+
+void ExtensionSet::SetEnum(int number, FieldType type, int value,
+                           const FieldDescriptor* descriptor) {
+  Extension* extension;
+  if (MaybeNewExtension(number, descriptor, &extension)) {
+    extension->type = type;
+    GOOGLE_DCHECK_EQ(cpp_type(extension->type), WireFormatLite::CPPTYPE_ENUM);
+    extension->is_repeated = false;
+  } else {
+    GOOGLE_DCHECK_TYPE(*extension, OPTIONAL_FIELD, ENUM);
+  }
+  extension->is_cleared = false;
+  extension->enum_value = value;
+}
+
+int ExtensionSet::GetRepeatedEnum(int number, int index) const {
+  const Extension* extension = FindOrNull(number);
+  GOOGLE_CHECK(extension != nullptr) << "Index out-of-bounds (field is empty).";
+  GOOGLE_DCHECK_TYPE(*extension, REPEATED_FIELD, ENUM);
+  return extension->repeated_enum_value->Get(index);
+}
+
+const int& ExtensionSet::GetRefRepeatedEnum(int number, int index) const {
+  const Extension* extension = FindOrNull(number);
+  GOOGLE_CHECK(extension != nullptr) << "Index out-of-bounds (field is empty).";
+  GOOGLE_DCHECK_TYPE(*extension, REPEATED_FIELD, ENUM);
+  return extension->repeated_enum_value->Get(index);
+}
+
+void ExtensionSet::SetRepeatedEnum(int number, int index, int value) {
+  Extension* extension = FindOrNull(number);
+  GOOGLE_CHECK(extension != nullptr) << "Index out-of-bounds (field is empty).";
+  GOOGLE_DCHECK_TYPE(*extension, REPEATED_FIELD, ENUM);
+  extension->repeated_enum_value->Set(index, value);
+}
+
+void ExtensionSet::AddEnum(int number, FieldType type, bool packed, int value,
+                           const FieldDescriptor* descriptor) {
+  Extension* extension;
+  if (MaybeNewExtension(number, descriptor, &extension)) {
+    extension->type = type;
+    GOOGLE_DCHECK_EQ(cpp_type(extension->type), WireFormatLite::CPPTYPE_ENUM);
+    extension->is_repeated = true;
+    extension->is_packed = packed;
+    extension->repeated_enum_value =
+        Arena::CreateMessage<RepeatedField<int>>(arena_);
+  } else {
+    GOOGLE_DCHECK_TYPE(*extension, REPEATED_FIELD, ENUM);
+    GOOGLE_DCHECK_EQ(extension->is_packed, packed);
+  }
+  extension->repeated_enum_value->Add(value);
+}
+
+// -------------------------------------------------------------------
+// Strings
+
+const TProtoStringType& ExtensionSet::GetString(
+    int number, const TProtoStringType& default_value) const {
+  const Extension* extension = FindOrNull(number);
+  if (extension == nullptr || extension->is_cleared) {
+    // Not present.  Return the default value.
+    return default_value;
+  } else {
+    GOOGLE_DCHECK_TYPE(*extension, OPTIONAL_FIELD, STRING);
+    return *extension->string_value;
+  }
+}
+
+TProtoStringType* ExtensionSet::MutableString(int number, FieldType type,
+                                         const FieldDescriptor* descriptor) {
+  Extension* extension;
+  if (MaybeNewExtension(number, descriptor, &extension)) {
+    extension->type = type;
+    GOOGLE_DCHECK_EQ(cpp_type(extension->type), WireFormatLite::CPPTYPE_STRING);
+    extension->is_repeated = false;
+    extension->string_value = Arena::Create<TProtoStringType>(arena_);
+  } else {
+    GOOGLE_DCHECK_TYPE(*extension, OPTIONAL_FIELD, STRING);
+  }
+  extension->is_cleared = false;
+  return extension->string_value;
+}
+
+const TProtoStringType& ExtensionSet::GetRepeatedString(int number,
+                                                   int index) const {
+  const Extension* extension = FindOrNull(number);
+  GOOGLE_CHECK(extension != nullptr) << "Index out-of-bounds (field is empty).";
+  GOOGLE_DCHECK_TYPE(*extension, REPEATED_FIELD, STRING);
+  return extension->repeated_string_value->Get(index);
+}
+
+TProtoStringType* ExtensionSet::MutableRepeatedString(int number, int index) {
+  Extension* extension = FindOrNull(number);
+  GOOGLE_CHECK(extension != nullptr) << "Index out-of-bounds (field is empty).";
+  GOOGLE_DCHECK_TYPE(*extension, REPEATED_FIELD, STRING);
+  return extension->repeated_string_value->Mutable(index);
+}
+
+TProtoStringType* ExtensionSet::AddString(int number, FieldType type,
+                                     const FieldDescriptor* descriptor) {
+  Extension* extension;
+  if (MaybeNewExtension(number, descriptor, &extension)) {
+    extension->type = type;
+    GOOGLE_DCHECK_EQ(cpp_type(extension->type), WireFormatLite::CPPTYPE_STRING);
+    extension->is_repeated = true;
+    extension->is_packed = false;
+    extension->repeated_string_value =
+        Arena::CreateMessage<RepeatedPtrField<TProtoStringType>>(arena_);
+  } else {
+    GOOGLE_DCHECK_TYPE(*extension, REPEATED_FIELD, STRING);
+  }
+  return extension->repeated_string_value->Add();
+}
+
+// -------------------------------------------------------------------
+// Messages
+
+const MessageLite& ExtensionSet::GetMessage(
+    int number, const MessageLite& default_value) const {
+  const Extension* extension = FindOrNull(number);
+  if (extension == nullptr) {
+    // Not present.  Return the default value.
+    return default_value;
+  } else {
+    GOOGLE_DCHECK_TYPE(*extension, OPTIONAL_FIELD, MESSAGE);
+    if (extension->is_lazy) {
+      return extension->lazymessage_value->GetMessage(default_value, arena_);
+    } else {
+      return *extension->message_value;
+    }
+  }
+}
+
+// Defined in extension_set_heavy.cc.
+// const MessageLite& ExtensionSet::GetMessage(int number,
+//                                             const Descriptor* message_type,
+//                                             MessageFactory* factory) const
+
+MessageLite* ExtensionSet::MutableMessage(int number, FieldType type,
+                                          const MessageLite& prototype,
+                                          const FieldDescriptor* descriptor) {
+  Extension* extension;
+  if (MaybeNewExtension(number, descriptor, &extension)) {
+    extension->type = type;
+    GOOGLE_DCHECK_EQ(cpp_type(extension->type), WireFormatLite::CPPTYPE_MESSAGE);
+    extension->is_repeated = false;
+    extension->is_lazy = false;
+    extension->message_value = prototype.New(arena_);
+    extension->is_cleared = false;
+    return extension->message_value;
+  } else {
+    GOOGLE_DCHECK_TYPE(*extension, OPTIONAL_FIELD, MESSAGE);
+    extension->is_cleared = false;
+    if (extension->is_lazy) {
+      return extension->lazymessage_value->MutableMessage(prototype, arena_);
+    } else {
+      return extension->message_value;
+    }
+  }
+}
+
+// Defined in extension_set_heavy.cc.
+// MessageLite* ExtensionSet::MutableMessage(int number, FieldType type,
+//                                           const Descriptor* message_type,
+//                                           MessageFactory* factory)
+
+void ExtensionSet::SetAllocatedMessage(int number, FieldType type,
+                                       const FieldDescriptor* descriptor,
+                                       MessageLite* message) {
+  if (message == nullptr) {
+    ClearExtension(number);
+    return;
+  }
+  GOOGLE_DCHECK(message->GetOwningArena() == nullptr ||
+         message->GetOwningArena() == arena_);
+  Arena* message_arena = message->GetOwningArena();
+  Extension* extension;
+  if (MaybeNewExtension(number, descriptor, &extension)) {
+    extension->type = type;
+    GOOGLE_DCHECK_EQ(cpp_type(extension->type), WireFormatLite::CPPTYPE_MESSAGE);
+    extension->is_repeated = false;
+    extension->is_lazy = false;
+    if (message_arena == arena_) {
+      extension->message_value = message;
+    } else if (message_arena == nullptr) {
+      extension->message_value = message;
+      arena_->Own(message);  // not nullptr because not equal to message_arena
+    } else {
+      extension->message_value = message->New(arena_);
+      extension->message_value->CheckTypeAndMergeFrom(*message);
+    }
+  } else {
+    GOOGLE_DCHECK_TYPE(*extension, OPTIONAL_FIELD, MESSAGE);
+    if (extension->is_lazy) {
+      extension->lazymessage_value->SetAllocatedMessage(message, arena_);
+    } else {
+      if (arena_ == nullptr) {
+        delete extension->message_value;
+      }
+      if (message_arena == arena_) {
+        extension->message_value = message;
+      } else if (message_arena == nullptr) {
+        extension->message_value = message;
+        arena_->Own(message);  // not nullptr because not equal to message_arena
+      } else {
+        extension->message_value = message->New(arena_);
+        extension->message_value->CheckTypeAndMergeFrom(*message);
+      }
+    }
+  }
+  extension->is_cleared = false;
+}
+
+void ExtensionSet::UnsafeArenaSetAllocatedMessage(
+    int number, FieldType type, const FieldDescriptor* descriptor,
+    MessageLite* message) {
+  if (message == nullptr) {
+    ClearExtension(number);
+    return;
+  }
+  Extension* extension;
+  if (MaybeNewExtension(number, descriptor, &extension)) {
+    extension->type = type;
+    GOOGLE_DCHECK_EQ(cpp_type(extension->type), WireFormatLite::CPPTYPE_MESSAGE);
+    extension->is_repeated = false;
+    extension->is_lazy = false;
+    extension->message_value = message;
+  } else {
+    GOOGLE_DCHECK_TYPE(*extension, OPTIONAL_FIELD, MESSAGE);
+    if (extension->is_lazy) {
+      extension->lazymessage_value->UnsafeArenaSetAllocatedMessage(message,
+                                                                   arena_);
+    } else {
+      if (arena_ == nullptr) {
+        delete extension->message_value;
+      }
+      extension->message_value = message;
+    }
+  }
+  extension->is_cleared = false;
+}
+
+MessageLite* ExtensionSet::ReleaseMessage(int number,
+                                          const MessageLite& prototype) {
+  Extension* extension = FindOrNull(number);
+  if (extension == nullptr) {
+    // Not present.  Return nullptr.
+    return nullptr;
+  } else {
+    GOOGLE_DCHECK_TYPE(*extension, OPTIONAL_FIELD, MESSAGE);
+    MessageLite* ret = nullptr;
+    if (extension->is_lazy) {
+      ret = extension->lazymessage_value->ReleaseMessage(prototype, arena_);
+      if (arena_ == nullptr) {
+        delete extension->lazymessage_value;
+      }
+    } else {
+      if (arena_ == nullptr) {
+        ret = extension->message_value;
+      } else {
+        // ReleaseMessage() always returns a heap-allocated message, and we are
+        // on an arena, so we need to make a copy of this message to return.
+        ret = extension->message_value->New();
+        ret->CheckTypeAndMergeFrom(*extension->message_value);
+      }
+    }
+    Erase(number);
+    return ret;
+  }
+}
+
+MessageLite* ExtensionSet::UnsafeArenaReleaseMessage(
+    int number, const MessageLite& prototype) {
+  Extension* extension = FindOrNull(number);
+  if (extension == nullptr) {
+    // Not present.  Return nullptr.
+    return nullptr;
+  } else {
+    GOOGLE_DCHECK_TYPE(*extension, OPTIONAL_FIELD, MESSAGE);
+    MessageLite* ret = nullptr;
+    if (extension->is_lazy) {
+      ret = extension->lazymessage_value->UnsafeArenaReleaseMessage(prototype,
+                                                                    arena_);
+      if (arena_ == nullptr) {
+        delete extension->lazymessage_value;
+      }
+    } else {
+      ret = extension->message_value;
+    }
+    Erase(number);
+    return ret;
+  }
+}
+
+// Defined in extension_set_heavy.cc.
+// MessageLite* ExtensionSet::ReleaseMessage(const FieldDescriptor* descriptor,
+//                                           MessageFactory* factory);
+
+const MessageLite& ExtensionSet::GetRepeatedMessage(int number,
+                                                    int index) const {
+  const Extension* extension = FindOrNull(number);
+  GOOGLE_CHECK(extension != nullptr) << "Index out-of-bounds (field is empty).";
+  GOOGLE_DCHECK_TYPE(*extension, REPEATED_FIELD, MESSAGE);
+  return extension->repeated_message_value->Get(index);
+}
+
+MessageLite* ExtensionSet::MutableRepeatedMessage(int number, int index) {
+  Extension* extension = FindOrNull(number);
+  GOOGLE_CHECK(extension != nullptr) << "Index out-of-bounds (field is empty).";
+  GOOGLE_DCHECK_TYPE(*extension, REPEATED_FIELD, MESSAGE);
+  return extension->repeated_message_value->Mutable(index);
+}
+
+MessageLite* ExtensionSet::AddMessage(int number, FieldType type,
+                                      const MessageLite& prototype,
+                                      const FieldDescriptor* descriptor) {
+  Extension* extension;
+  if (MaybeNewExtension(number, descriptor, &extension)) {
+    extension->type = type;
+    GOOGLE_DCHECK_EQ(cpp_type(extension->type), WireFormatLite::CPPTYPE_MESSAGE);
+    extension->is_repeated = true;
+    extension->repeated_message_value =
+        Arena::CreateMessage<RepeatedPtrField<MessageLite>>(arena_);
+  } else {
+    GOOGLE_DCHECK_TYPE(*extension, REPEATED_FIELD, MESSAGE);
+  }
+
+  // RepeatedPtrField<MessageLite> does not know how to Add() since it cannot
+  // allocate an abstract object, so we have to be tricky.
+  MessageLite* result = reinterpret_cast<internal::RepeatedPtrFieldBase*>(
+                            extension->repeated_message_value)
+                            ->AddFromCleared<GenericTypeHandler<MessageLite>>();
+  if (result == nullptr) {
+    result = prototype.New(arena_);
+    extension->repeated_message_value->AddAllocated(result);
+  }
+  return result;
+}
+
+// Defined in extension_set_heavy.cc.
+// MessageLite* ExtensionSet::AddMessage(int number, FieldType type,
+//                                       const Descriptor* message_type,
+//                                       MessageFactory* factory)
+
+#undef GOOGLE_DCHECK_TYPE
+
+void ExtensionSet::RemoveLast(int number) {
+  Extension* extension = FindOrNull(number);
+  GOOGLE_CHECK(extension != nullptr) << "Index out-of-bounds (field is empty).";
+  GOOGLE_DCHECK(extension->is_repeated);
+
+  switch (cpp_type(extension->type)) {
+    case WireFormatLite::CPPTYPE_INT32:
+      extension->repeated_arc_i32_value->RemoveLast();
+      break;
+    case WireFormatLite::CPPTYPE_INT64:
+      extension->repeated_arc_i64_value->RemoveLast();
+      break;
+    case WireFormatLite::CPPTYPE_UINT32:
+      extension->repeated_arc_ui32_value->RemoveLast();
+      break;
+    case WireFormatLite::CPPTYPE_UINT64:
+      extension->repeated_arc_ui64_value->RemoveLast();
+      break;
+    case WireFormatLite::CPPTYPE_FLOAT:
+      extension->repeated_float_value->RemoveLast();
+      break;
+    case WireFormatLite::CPPTYPE_DOUBLE:
+      extension->repeated_double_value->RemoveLast();
+      break;
+    case WireFormatLite::CPPTYPE_BOOL:
+      extension->repeated_bool_value->RemoveLast();
+      break;
+    case WireFormatLite::CPPTYPE_ENUM:
+      extension->repeated_enum_value->RemoveLast();
+      break;
+    case WireFormatLite::CPPTYPE_STRING:
+      extension->repeated_string_value->RemoveLast();
+      break;
+    case WireFormatLite::CPPTYPE_MESSAGE:
+      extension->repeated_message_value->RemoveLast();
+      break;
+  }
+}
+
+MessageLite* ExtensionSet::ReleaseLast(int number) {
+  Extension* extension = FindOrNull(number);
+  GOOGLE_CHECK(extension != nullptr) << "Index out-of-bounds (field is empty).";
+  GOOGLE_DCHECK(extension->is_repeated);
+  GOOGLE_DCHECK(cpp_type(extension->type) == WireFormatLite::CPPTYPE_MESSAGE);
+  return extension->repeated_message_value->ReleaseLast();
+}
+
+MessageLite* ExtensionSet::UnsafeArenaReleaseLast(int number) {
+  Extension* extension = FindOrNull(number);
+  GOOGLE_CHECK(extension != nullptr) << "Index out-of-bounds (field is empty).";
+  GOOGLE_DCHECK(extension->is_repeated);
+  GOOGLE_DCHECK(cpp_type(extension->type) == WireFormatLite::CPPTYPE_MESSAGE);
+  return extension->repeated_message_value->UnsafeArenaReleaseLast();
+}
+
+void ExtensionSet::SwapElements(int number, int index1, int index2) {
+  Extension* extension = FindOrNull(number);
+  GOOGLE_CHECK(extension != nullptr) << "Index out-of-bounds (field is empty).";
+  GOOGLE_DCHECK(extension->is_repeated);
+
+  switch (cpp_type(extension->type)) {
+    case WireFormatLite::CPPTYPE_INT32:
+      extension->repeated_arc_i32_value->SwapElements(index1, index2);
+      break;
+    case WireFormatLite::CPPTYPE_INT64:
+      extension->repeated_arc_i64_value->SwapElements(index1, index2);
+      break;
+    case WireFormatLite::CPPTYPE_UINT32:
+      extension->repeated_arc_ui32_value->SwapElements(index1, index2);
+      break;
+    case WireFormatLite::CPPTYPE_UINT64:
+      extension->repeated_arc_ui64_value->SwapElements(index1, index2);
+      break;
+    case WireFormatLite::CPPTYPE_FLOAT:
+      extension->repeated_float_value->SwapElements(index1, index2);
+      break;
+    case WireFormatLite::CPPTYPE_DOUBLE:
+      extension->repeated_double_value->SwapElements(index1, index2);
+      break;
+    case WireFormatLite::CPPTYPE_BOOL:
+      extension->repeated_bool_value->SwapElements(index1, index2);
+      break;
+    case WireFormatLite::CPPTYPE_ENUM:
+      extension->repeated_enum_value->SwapElements(index1, index2);
+      break;
+    case WireFormatLite::CPPTYPE_STRING:
+      extension->repeated_string_value->SwapElements(index1, index2);
+      break;
+    case WireFormatLite::CPPTYPE_MESSAGE:
+      extension->repeated_message_value->SwapElements(index1, index2);
+      break;
+  }
+}
+
+// ===================================================================
+
+void ExtensionSet::Clear() {
+  ForEach([](int /* number */, Extension& ext) { ext.Clear(); });
+}
+
+namespace {
+// Computes the size of a std::set_union without constructing the union.
+template <typename ItX, typename ItY>
+size_t SizeOfUnion(ItX it_xs, ItX end_xs, ItY it_ys, ItY end_ys) {
+  size_t result = 0;
+  while (it_xs != end_xs && it_ys != end_ys) {
+    ++result;
+    if (it_xs->first < it_ys->first) {
+      ++it_xs;
+    } else if (it_xs->first == it_ys->first) {
+      ++it_xs;
+      ++it_ys;
+    } else {
+      ++it_ys;
+    }
+  }
+  result += std::distance(it_xs, end_xs);
+  result += std::distance(it_ys, end_ys);
+  return result;
+}
+}  // namespace
+
+void ExtensionSet::MergeFrom(const MessageLite* extendee,
+                             const ExtensionSet& other) {
+  if (PROTOBUF_PREDICT_TRUE(!is_large())) {
+    if (PROTOBUF_PREDICT_TRUE(!other.is_large())) {
+      GrowCapacity(SizeOfUnion(flat_begin(), flat_end(), other.flat_begin(),
+                               other.flat_end()));
+    } else {
+      GrowCapacity(SizeOfUnion(flat_begin(), flat_end(),
+                               other.map_.large->begin(),
+                               other.map_.large->end()));
+    }
+  }
+  other.ForEach([extendee, this, &other](int number, const Extension& ext) {
+    this->InternalExtensionMergeFrom(extendee, number, ext, other.arena_);
+  });
+}
+
+void ExtensionSet::InternalExtensionMergeFrom(const MessageLite* extendee,
+                                              int number,
+                                              const Extension& other_extension,
+                                              Arena* other_arena) {
+  if (other_extension.is_repeated) {
+    Extension* extension;
+    bool is_new =
+        MaybeNewExtension(number, other_extension.descriptor, &extension);
+    if (is_new) {
+      // Extension did not already exist in set.
+      extension->type = other_extension.type;
+      extension->is_packed = other_extension.is_packed;
+      extension->is_repeated = true;
+    } else {
+      GOOGLE_DCHECK_EQ(extension->type, other_extension.type);
+      GOOGLE_DCHECK_EQ(extension->is_packed, other_extension.is_packed);
+      GOOGLE_DCHECK(extension->is_repeated);
+    }
+
+    switch (cpp_type(other_extension.type)) {
+#define HANDLE_TYPE(UPPERCASE, LOWERCASE, REPEATED_TYPE) \
+  case WireFormatLite::CPPTYPE_##UPPERCASE:              \
+    if (is_new) {                                        \
+      extension->repeated_##LOWERCASE##_value =          \
+          Arena::CreateMessage<REPEATED_TYPE>(arena_);   \
+    }                                                    \
+    extension->repeated_##LOWERCASE##_value->MergeFrom(  \
+        *other_extension.repeated_##LOWERCASE##_value);  \
+    break;
+
+      HANDLE_TYPE(INT32, arc_i32, RepeatedField<arc_i32>);
+      HANDLE_TYPE(INT64, arc_i64, RepeatedField<arc_i64>);
+      HANDLE_TYPE(UINT32, arc_ui32, RepeatedField<arc_ui32>);
+      HANDLE_TYPE(UINT64, arc_ui64, RepeatedField<arc_ui64>);
+      HANDLE_TYPE(FLOAT, float, RepeatedField<float>);
+      HANDLE_TYPE(DOUBLE, double, RepeatedField<double>);
+      HANDLE_TYPE(BOOL, bool, RepeatedField<bool>);
+      HANDLE_TYPE(ENUM, enum, RepeatedField<int>);
+      HANDLE_TYPE(STRING, string, RepeatedPtrField<TProtoStringType>);
+#undef HANDLE_TYPE
+
+      case WireFormatLite::CPPTYPE_MESSAGE:
+        if (is_new) {
+          extension->repeated_message_value =
+              Arena::CreateMessage<RepeatedPtrField<MessageLite>>(arena_);
+        }
+        // We can't call RepeatedPtrField<MessageLite>::MergeFrom() because
+        // it would attempt to allocate new objects.
+        RepeatedPtrField<MessageLite>* other_repeated_message =
+            other_extension.repeated_message_value;
+        for (int i = 0; i < other_repeated_message->size(); i++) {
+          const MessageLite& other_message = other_repeated_message->Get(i);
+          MessageLite* target =
+              reinterpret_cast<internal::RepeatedPtrFieldBase*>(
+                  extension->repeated_message_value)
+                  ->AddFromCleared<GenericTypeHandler<MessageLite>>();
+          if (target == nullptr) {
+            target = other_message.New(arena_);
+            extension->repeated_message_value->AddAllocated(target);
+          }
+          target->CheckTypeAndMergeFrom(other_message);
+        }
+        break;
+    }
+  } else {
+    if (!other_extension.is_cleared) {
+      switch (cpp_type(other_extension.type)) {
+#define HANDLE_TYPE(UPPERCASE, LOWERCASE, CAMELCASE)  \
+  case WireFormatLite::CPPTYPE_##UPPERCASE:           \
+    Set##CAMELCASE(number, other_extension.type,      \
+                   other_extension.LOWERCASE##_value, \
+                   other_extension.descriptor);       \
+    break;
+
+        HANDLE_TYPE(INT32, arc_i32, Int32);
+        HANDLE_TYPE(INT64, arc_i64, Int64);
+        HANDLE_TYPE(UINT32, arc_ui32, UInt32);
+        HANDLE_TYPE(UINT64, arc_ui64, UInt64);
+        HANDLE_TYPE(FLOAT, float, Float);
+        HANDLE_TYPE(DOUBLE, double, Double);
+        HANDLE_TYPE(BOOL, bool, Bool);
+        HANDLE_TYPE(ENUM, enum, Enum);
+#undef HANDLE_TYPE
+        case WireFormatLite::CPPTYPE_STRING:
+          SetString(number, other_extension.type, *other_extension.string_value,
+                    other_extension.descriptor);
+          break;
+        case WireFormatLite::CPPTYPE_MESSAGE: {
+          Extension* extension;
+          bool is_new =
+              MaybeNewExtension(number, other_extension.descriptor, &extension);
+          if (is_new) {
+            extension->type = other_extension.type;
+            extension->is_packed = other_extension.is_packed;
+            extension->is_repeated = false;
+            if (other_extension.is_lazy) {
+              extension->is_lazy = true;
+              extension->lazymessage_value =
+                  other_extension.lazymessage_value->New(arena_);
+              extension->lazymessage_value->MergeFrom(
+                  GetPrototypeForLazyMessage(extendee, number),
+                  *other_extension.lazymessage_value, arena_);
+            } else {
+              extension->is_lazy = false;
+              extension->message_value =
+                  other_extension.message_value->New(arena_);
+              extension->message_value->CheckTypeAndMergeFrom(
+                  *other_extension.message_value);
+            }
+          } else {
+            GOOGLE_DCHECK_EQ(extension->type, other_extension.type);
+            GOOGLE_DCHECK_EQ(extension->is_packed, other_extension.is_packed);
+            GOOGLE_DCHECK(!extension->is_repeated);
+            if (other_extension.is_lazy) {
+              if (extension->is_lazy) {
+                extension->lazymessage_value->MergeFrom(
+                    GetPrototypeForLazyMessage(extendee, number),
+                    *other_extension.lazymessage_value, arena_);
+              } else {
+                extension->message_value->CheckTypeAndMergeFrom(
+                    other_extension.lazymessage_value->GetMessage(
+                        *extension->message_value, other_arena));
+              }
+            } else {
+              if (extension->is_lazy) {
+                extension->lazymessage_value
+                    ->MutableMessage(*other_extension.message_value, arena_)
+                    ->CheckTypeAndMergeFrom(*other_extension.message_value);
+              } else {
+                extension->message_value->CheckTypeAndMergeFrom(
+                    *other_extension.message_value);
+              }
+            }
+          }
+          extension->is_cleared = false;
+          break;
+        }
+      }
+    }
+  }
+}
+
+void ExtensionSet::Swap(const MessageLite* extendee, ExtensionSet* other) {
+#ifdef PROTOBUF_FORCE_COPY_IN_SWAP
+  if (GetArena() != nullptr && GetArena() == other->GetArena()) {
+#else   // PROTOBUF_FORCE_COPY_IN_SWAP
+  if (GetArena() == other->GetArena()) {
+#endif  // !PROTOBUF_FORCE_COPY_IN_SWAP
+    InternalSwap(other);
+  } else {
+    // TODO(cfallin, rohananil): We maybe able to optimize a case where we are
+    // swapping from heap to arena-allocated extension set, by just Own()'ing
+    // the extensions.
+    ExtensionSet extension_set;
+    extension_set.MergeFrom(extendee, *other);
+    other->Clear();
+    other->MergeFrom(extendee, *this);
+    Clear();
+    MergeFrom(extendee, extension_set);
+  }
+}
+
+void ExtensionSet::InternalSwap(ExtensionSet* other) {
+  using std::swap;
+  swap(arena_, other->arena_);
+  swap(flat_capacity_, other->flat_capacity_);
+  swap(flat_size_, other->flat_size_);
+  swap(map_, other->map_);
+}
+
+void ExtensionSet::SwapExtension(const MessageLite* extendee,
+                                 ExtensionSet* other, int number) {
+  if (this == other) return;
+
+  if (GetArena() == other->GetArena()) {
+    UnsafeShallowSwapExtension(other, number);
+    return;
+  }
+
+  Extension* this_ext = FindOrNull(number);
+  Extension* other_ext = other->FindOrNull(number);
+
+  if (this_ext == other_ext) return;
+
+  if (this_ext != nullptr && other_ext != nullptr) {
+    // TODO(cfallin, rohananil): We could further optimize these cases,
+    // especially avoid creation of ExtensionSet, and move MergeFrom logic
+    // into Extensions itself (which takes arena as an argument).
+    // We do it this way to reuse the copy-across-arenas logic already
+    // implemented in ExtensionSet's MergeFrom.
+    ExtensionSet temp;
+    temp.InternalExtensionMergeFrom(extendee, number, *other_ext,
+                                    other->GetArena());
+    Extension* temp_ext = temp.FindOrNull(number);
+
+    other_ext->Clear();
+    other->InternalExtensionMergeFrom(extendee, number, *this_ext,
+                                      this->GetArena());
+    this_ext->Clear();
+    InternalExtensionMergeFrom(extendee, number, *temp_ext, temp.GetArena());
+  } else if (this_ext == nullptr) {
+    InternalExtensionMergeFrom(extendee, number, *other_ext, other->GetArena());
+    if (other->GetArena() == nullptr) other_ext->Free();
+    other->Erase(number);
+  } else {
+    other->InternalExtensionMergeFrom(extendee, number, *this_ext,
+                                      this->GetArena());
+    if (GetArena() == nullptr) this_ext->Free();
+    Erase(number);
+  }
+}
+
+void ExtensionSet::UnsafeShallowSwapExtension(ExtensionSet* other, int number) {
+  if (this == other) return;
+
+  Extension* this_ext = FindOrNull(number);
+  Extension* other_ext = other->FindOrNull(number);
+
+  if (this_ext == other_ext) return;
+
+  GOOGLE_DCHECK_EQ(GetArena(), other->GetArena());
+
+  if (this_ext != nullptr && other_ext != nullptr) {
+    std::swap(*this_ext, *other_ext);
+  } else if (this_ext == nullptr) {
+    *Insert(number).first = *other_ext;
+    other->Erase(number);
+  } else {
+    *other->Insert(number).first = *this_ext;
+    Erase(number);
+  }
+}
+
+bool ExtensionSet::IsInitialized() const {
+  // Extensions are never required.  However, we need to check that all
+  // embedded messages are initialized.
+  if (PROTOBUF_PREDICT_FALSE(is_large())) {
+    for (const auto& kv : *map_.large) {
+      if (!kv.second.IsInitialized()) return false;
+    }
+    return true;
+  }
+  for (const KeyValue* it = flat_begin(); it != flat_end(); ++it) {
+    if (!it->second.IsInitialized()) return false;
+  }
+  return true;
+}
+
+bool ExtensionSet::FindExtensionInfoFromTag(arc_ui32 tag,
+                                            ExtensionFinder* extension_finder,
+                                            int* field_number,
+                                            ExtensionInfo* extension,
+                                            bool* was_packed_on_wire) {
+  *field_number = WireFormatLite::GetTagFieldNumber(tag);
+  WireFormatLite::WireType wire_type = WireFormatLite::GetTagWireType(tag);
+  return FindExtensionInfoFromFieldNumber(wire_type, *field_number,
+                                          extension_finder, extension,
+                                          was_packed_on_wire);
+}
+
+bool ExtensionSet::FindExtensionInfoFromFieldNumber(
+    int wire_type, int field_number, ExtensionFinder* extension_finder,
+    ExtensionInfo* extension, bool* was_packed_on_wire) const {
+  if (!extension_finder->Find(field_number, extension)) {
+    return false;
+  }
+
+  WireFormatLite::WireType expected_wire_type =
+      WireFormatLite::WireTypeForFieldType(real_type(extension->type));
+
+  // Check if this is a packed field.
+  *was_packed_on_wire = false;
+  if (extension->is_repeated &&
+      wire_type == WireFormatLite::WIRETYPE_LENGTH_DELIMITED &&
+      is_packable(expected_wire_type)) {
+    *was_packed_on_wire = true;
+    return true;
+  }
+  // Otherwise the wire type must match.
+  return expected_wire_type == wire_type;
+}
+
+bool ExtensionSet::ParseField(arc_ui32 tag, io::CodedInputStream* input,
+                              ExtensionFinder* extension_finder,
+                              FieldSkipper* field_skipper) {
+  int number;
+  bool was_packed_on_wire;
+  ExtensionInfo extension;
+  if (!FindExtensionInfoFromTag(tag, extension_finder, &number, &extension,
+                                &was_packed_on_wire)) {
+    return field_skipper->SkipField(input, tag);
+  } else {
+    return ParseFieldWithExtensionInfo(number, was_packed_on_wire, extension,
+                                       input, field_skipper);
+  }
+}
+
+const char* ExtensionSet::ParseField(arc_ui64 tag, const char* ptr,
+                                     const MessageLite* extendee,
+                                     internal::InternalMetadata* metadata,
+                                     internal::ParseContext* ctx) {
+  GeneratedExtensionFinder finder(extendee);
+  int number = tag >> 3;
+  bool was_packed_on_wire;
+  ExtensionInfo extension;
+  if (!FindExtensionInfoFromFieldNumber(tag & 7, number, &finder, &extension,
+                                        &was_packed_on_wire)) {
+    return UnknownFieldParse(
+        tag, metadata->mutable_unknown_fields<TProtoStringType>(), ptr, ctx);
+  }
+  return ParseFieldWithExtensionInfo<TProtoStringType>(
+      number, was_packed_on_wire, extension, metadata, ptr, ctx);
+}
+
+const char* ExtensionSet::ParseMessageSetItem(
+    const char* ptr, const MessageLite* extendee,
+    internal::InternalMetadata* metadata, internal::ParseContext* ctx) {
+  return ParseMessageSetItemTmpl<MessageLite, TProtoStringType>(ptr, extendee,
+                                                           metadata, ctx);
+}
+
+bool ExtensionSet::ParseFieldWithExtensionInfo(int number,
+                                               bool was_packed_on_wire,
+                                               const ExtensionInfo& extension,
+                                               io::CodedInputStream* input,
+                                               FieldSkipper* field_skipper) {
+  // Explicitly not read extension.is_packed, instead check whether the field
+  // was encoded in packed form on the wire.
+  if (was_packed_on_wire) {
+    arc_ui32 size;
+    if (!input->ReadVarint32(&size)) return false;
+    io::CodedInputStream::Limit limit = input->PushLimit(size);
+
+    switch (extension.type) {
+#define HANDLE_TYPE(UPPERCASE, CPP_CAMELCASE, CPP_LOWERCASE)                \
+  case WireFormatLite::TYPE_##UPPERCASE:                                    \
+    while (input->BytesUntilLimit() > 0) {                                  \
+      CPP_LOWERCASE value;                                                  \
+      if (!WireFormatLite::ReadPrimitive<CPP_LOWERCASE,                     \
+                                         WireFormatLite::TYPE_##UPPERCASE>( \
+              input, &value))                                               \
+        return false;                                                       \
+      Add##CPP_CAMELCASE(number, WireFormatLite::TYPE_##UPPERCASE,          \
+                         extension.is_packed, value, extension.descriptor); \
+    }                                                                       \
+    break
+
+      HANDLE_TYPE(INT32, Int32, arc_i32);
+      HANDLE_TYPE(INT64, Int64, arc_i64);
+      HANDLE_TYPE(UINT32, UInt32, arc_ui32);
+      HANDLE_TYPE(UINT64, UInt64, arc_ui64);
+      HANDLE_TYPE(SINT32, Int32, arc_i32);
+      HANDLE_TYPE(SINT64, Int64, arc_i64);
+      HANDLE_TYPE(FIXED32, UInt32, arc_ui32);
+      HANDLE_TYPE(FIXED64, UInt64, arc_ui64);
+      HANDLE_TYPE(SFIXED32, Int32, arc_i32);
+      HANDLE_TYPE(SFIXED64, Int64, arc_i64);
+      HANDLE_TYPE(FLOAT, Float, float);
+      HANDLE_TYPE(DOUBLE, Double, double);
+      HANDLE_TYPE(BOOL, Bool, bool);
+#undef HANDLE_TYPE
+
+      case WireFormatLite::TYPE_ENUM:
+        while (input->BytesUntilLimit() > 0) {
+          int value;
+          if (!WireFormatLite::ReadPrimitive<int, WireFormatLite::TYPE_ENUM>(
+                  input, &value))
+            return false;
+          if (extension.enum_validity_check.func(
+                  extension.enum_validity_check.arg, value)) {
+            AddEnum(number, WireFormatLite::TYPE_ENUM, extension.is_packed,
+                    value, extension.descriptor);
+          } else {
+            // Invalid value.  Treat as unknown.
+            field_skipper->SkipUnknownEnum(number, value);
+          }
+        }
+        break;
+
+      case WireFormatLite::TYPE_STRING:
+      case WireFormatLite::TYPE_BYTES:
+      case WireFormatLite::TYPE_GROUP:
+      case WireFormatLite::TYPE_MESSAGE:
+        GOOGLE_LOG(FATAL) << "Non-primitive types can't be packed.";
+        break;
+    }
+
+    input->PopLimit(limit);
+  } else {
+    switch (extension.type) {
+#define HANDLE_TYPE(UPPERCASE, CPP_CAMELCASE, CPP_LOWERCASE)                \
+  case WireFormatLite::TYPE_##UPPERCASE: {                                  \
+    CPP_LOWERCASE value;                                                    \
+    if (!WireFormatLite::ReadPrimitive<CPP_LOWERCASE,                       \
+                                       WireFormatLite::TYPE_##UPPERCASE>(   \
+            input, &value))                                                 \
+      return false;                                                         \
+    if (extension.is_repeated) {                                            \
+      Add##CPP_CAMELCASE(number, WireFormatLite::TYPE_##UPPERCASE,          \
+                         extension.is_packed, value, extension.descriptor); \
+    } else {                                                                \
+      Set##CPP_CAMELCASE(number, WireFormatLite::TYPE_##UPPERCASE, value,   \
+                         extension.descriptor);                             \
+    }                                                                       \
+  } break
+
+      HANDLE_TYPE(INT32, Int32, arc_i32);
+      HANDLE_TYPE(INT64, Int64, arc_i64);
+      HANDLE_TYPE(UINT32, UInt32, arc_ui32);
+      HANDLE_TYPE(UINT64, UInt64, arc_ui64);
+      HANDLE_TYPE(SINT32, Int32, arc_i32);
+      HANDLE_TYPE(SINT64, Int64, arc_i64);
+      HANDLE_TYPE(FIXED32, UInt32, arc_ui32);
+      HANDLE_TYPE(FIXED64, UInt64, arc_ui64);
+      HANDLE_TYPE(SFIXED32, Int32, arc_i32);
+      HANDLE_TYPE(SFIXED64, Int64, arc_i64);
+      HANDLE_TYPE(FLOAT, Float, float);
+      HANDLE_TYPE(DOUBLE, Double, double);
+      HANDLE_TYPE(BOOL, Bool, bool);
+#undef HANDLE_TYPE
+
+      case WireFormatLite::TYPE_ENUM: {
+        int value;
+        if (!WireFormatLite::ReadPrimitive<int, WireFormatLite::TYPE_ENUM>(
+                input, &value))
+          return false;
+
+        if (!extension.enum_validity_check.func(
+                extension.enum_validity_check.arg, value)) {
+          // Invalid value.  Treat as unknown.
+          field_skipper->SkipUnknownEnum(number, value);
+        } else if (extension.is_repeated) {
+          AddEnum(number, WireFormatLite::TYPE_ENUM, extension.is_packed, value,
+                  extension.descriptor);
+        } else {
+          SetEnum(number, WireFormatLite::TYPE_ENUM, value,
+                  extension.descriptor);
+        }
+        break;
+      }
+
+      case WireFormatLite::TYPE_STRING: {
+        TProtoStringType* value =
+            extension.is_repeated
+                ? AddString(number, WireFormatLite::TYPE_STRING,
+                            extension.descriptor)
+                : MutableString(number, WireFormatLite::TYPE_STRING,
+                                extension.descriptor);
+        if (!WireFormatLite::ReadString(input, value)) return false;
+        break;
+      }
+
+      case WireFormatLite::TYPE_BYTES: {
+        TProtoStringType* value =
+            extension.is_repeated
+                ? AddString(number, WireFormatLite::TYPE_BYTES,
+                            extension.descriptor)
+                : MutableString(number, WireFormatLite::TYPE_BYTES,
+                                extension.descriptor);
+        if (!WireFormatLite::ReadBytes(input, value)) return false;
+        break;
+      }
+
+      case WireFormatLite::TYPE_GROUP: {
+        MessageLite* value =
+            extension.is_repeated
+                ? AddMessage(number, WireFormatLite::TYPE_GROUP,
+                             *extension.message_info.prototype,
+                             extension.descriptor)
+                : MutableMessage(number, WireFormatLite::TYPE_GROUP,
+                                 *extension.message_info.prototype,
+                                 extension.descriptor);
+        if (!WireFormatLite::ReadGroup(number, input, value)) return false;
+        break;
+      }
+
+      case WireFormatLite::TYPE_MESSAGE: {
+        MessageLite* value =
+            extension.is_repeated
+                ? AddMessage(number, WireFormatLite::TYPE_MESSAGE,
+                             *extension.message_info.prototype,
+                             extension.descriptor)
+                : MutableMessage(number, WireFormatLite::TYPE_MESSAGE,
+                                 *extension.message_info.prototype,
+                                 extension.descriptor);
+        if (!WireFormatLite::ReadMessage(input, value)) return false;
+        break;
+      }
+    }
+  }
+
+  return true;
+}
+
+bool ExtensionSet::ParseField(arc_ui32 tag, io::CodedInputStream* input,
+                              const MessageLite* extendee) {
+  FieldSkipper skipper;
+  GeneratedExtensionFinder finder(extendee);
+  return ParseField(tag, input, &finder, &skipper);
+}
+
+bool ExtensionSet::ParseField(arc_ui32 tag, io::CodedInputStream* input,
+                              const MessageLite* extendee,
+                              io::CodedOutputStream* unknown_fields) {
+  CodedOutputStreamFieldSkipper skipper(unknown_fields);
+  GeneratedExtensionFinder finder(extendee);
+  return ParseField(tag, input, &finder, &skipper);
+}
+
+bool ExtensionSet::ParseMessageSetLite(io::CodedInputStream* input,
+                                       ExtensionFinder* extension_finder,
+                                       FieldSkipper* field_skipper) {
+  while (true) {
+    const arc_ui32 tag = input->ReadTag();
+    switch (tag) {
+      case 0:
+        return true;
+      case WireFormatLite::kMessageSetItemStartTag:
+        if (!ParseMessageSetItemLite(input, extension_finder, field_skipper)) {
+          return false;
+        }
+        break;
+      default:
+        if (!ParseField(tag, input, extension_finder, field_skipper)) {
+          return false;
+        }
+        break;
+    }
+  }
+}
+
+bool ExtensionSet::ParseMessageSetItemLite(io::CodedInputStream* input,
+                                           ExtensionFinder* extension_finder,
+                                           FieldSkipper* field_skipper) {
+  struct MSLite {
+    bool ParseField(int type_id, io::CodedInputStream* input) {
+      return me->ParseField(
+          WireFormatLite::WIRETYPE_LENGTH_DELIMITED + 8 * type_id, input,
+          extension_finder, field_skipper);
+    }
+
+    bool SkipField(arc_ui32 tag, io::CodedInputStream* input) {
+      return field_skipper->SkipField(input, tag);
+    }
+
+    ExtensionSet* me;
+    ExtensionFinder* extension_finder;
+    FieldSkipper* field_skipper;
+  };
+
+  return ParseMessageSetItemImpl(input,
+                                 MSLite{this, extension_finder, field_skipper});
+}
+
+bool ExtensionSet::ParseMessageSet(io::CodedInputStream* input,
+                                   const MessageLite* extendee,
+                                   TProtoStringType* unknown_fields) {
+  io::StringOutputStream zcis(unknown_fields);
+  io::CodedOutputStream output(&zcis);
+  CodedOutputStreamFieldSkipper skipper(&output);
+  GeneratedExtensionFinder finder(extendee);
+  return ParseMessageSetLite(input, &finder, &skipper);
+}
+
+uint8_t* ExtensionSet::_InternalSerializeImpl(
+    const MessageLite* extendee, int start_field_number, int end_field_number,
+    uint8_t* target, io::EpsCopyOutputStream* stream) const {
+  if (PROTOBUF_PREDICT_FALSE(is_large())) {
+    const auto& end = map_.large->end();
+    for (auto it = map_.large->lower_bound(start_field_number);
+         it != end && it->first < end_field_number; ++it) {
+      target = it->second.InternalSerializeFieldWithCachedSizesToArray(
+          extendee, this, it->first, target, stream);
+    }
+    return target;
+  }
+  const KeyValue* end = flat_end();
+  for (const KeyValue* it = std::lower_bound(
+           flat_begin(), end, start_field_number, KeyValue::FirstComparator());
+       it != end && it->first < end_field_number; ++it) {
+    target = it->second.InternalSerializeFieldWithCachedSizesToArray(
+        extendee, this, it->first, target, stream);
+  }
+  return target;
+}
+
+uint8_t* ExtensionSet::InternalSerializeMessageSetWithCachedSizesToArray(
+    const MessageLite* extendee, uint8_t* target,
+    io::EpsCopyOutputStream* stream) const {
+  const ExtensionSet* extension_set = this;
+  ForEach([&target, extendee, stream, extension_set](int number,
+                                                     const Extension& ext) {
+    target = ext.InternalSerializeMessageSetItemWithCachedSizesToArray(
+        extendee, extension_set, number, target, stream);
+  });
+  return target;
+}
+
+size_t ExtensionSet::ByteSize() const {
+  size_t total_size = 0;
+  ForEach([&total_size](int number, const Extension& ext) {
+    total_size += ext.ByteSize(number);
+  });
+  return total_size;
+}
+
+// Defined in extension_set_heavy.cc.
+// int ExtensionSet::SpaceUsedExcludingSelf() const
+
+bool ExtensionSet::MaybeNewExtension(int number,
+                                     const FieldDescriptor* descriptor,
+                                     Extension** result) {
+  bool extension_is_new = false;
+  std::tie(*result, extension_is_new) = Insert(number);
+  (*result)->descriptor = descriptor;
+  return extension_is_new;
+}
+
+// ===================================================================
+// Methods of ExtensionSet::Extension
+
+void ExtensionSet::Extension::Clear() {
+  if (is_repeated) {
+    switch (cpp_type(type)) {
+#define HANDLE_TYPE(UPPERCASE, LOWERCASE)   \
+  case WireFormatLite::CPPTYPE_##UPPERCASE: \
+    repeated_##LOWERCASE##_value->Clear();  \
+    break
+
+      HANDLE_TYPE(INT32, arc_i32);
+      HANDLE_TYPE(INT64, arc_i64);
+      HANDLE_TYPE(UINT32, arc_ui32);
+      HANDLE_TYPE(UINT64, arc_ui64);
+      HANDLE_TYPE(FLOAT, float);
+      HANDLE_TYPE(DOUBLE, double);
+      HANDLE_TYPE(BOOL, bool);
+      HANDLE_TYPE(ENUM, enum);
+      HANDLE_TYPE(STRING, string);
+      HANDLE_TYPE(MESSAGE, message);
+#undef HANDLE_TYPE
+    }
+  } else {
+    if (!is_cleared) {
+      switch (cpp_type(type)) {
+        case WireFormatLite::CPPTYPE_STRING:
+          string_value->clear();
+          break;
+        case WireFormatLite::CPPTYPE_MESSAGE:
+          if (is_lazy) {
+            lazymessage_value->Clear();
+          } else {
+            message_value->Clear();
+          }
+          break;
+        default:
+          // No need to do anything.  Get*() will return the default value
+          // as long as is_cleared is true and Set*() will overwrite the
+          // previous value.
+          break;
+      }
+
+      is_cleared = true;
+    }
+  }
+}
+
+size_t ExtensionSet::Extension::ByteSize(int number) const {
+  size_t result = 0;
+
+  if (is_repeated) {
+    if (is_packed) {
+      switch (real_type(type)) {
+#define HANDLE_TYPE(UPPERCASE, CAMELCASE, LOWERCASE)                 \
+  case WireFormatLite::TYPE_##UPPERCASE:                             \
+    for (int i = 0; i < repeated_##LOWERCASE##_value->size(); i++) { \
+      result += WireFormatLite::CAMELCASE##Size(                     \
+          repeated_##LOWERCASE##_value->Get(i));                     \
+    }                                                                \
+    break
+
+        HANDLE_TYPE(INT32, Int32, arc_i32);
+        HANDLE_TYPE(INT64, Int64, arc_i64);
+        HANDLE_TYPE(UINT32, UInt32, arc_ui32);
+        HANDLE_TYPE(UINT64, UInt64, arc_ui64);
+        HANDLE_TYPE(SINT32, SInt32, arc_i32);
+        HANDLE_TYPE(SINT64, SInt64, arc_i64);
+        HANDLE_TYPE(ENUM, Enum, enum);
+#undef HANDLE_TYPE
+
+        // Stuff with fixed size.
+#define HANDLE_TYPE(UPPERCASE, CAMELCASE, LOWERCASE)             \
+  case WireFormatLite::TYPE_##UPPERCASE:                         \
+    result += WireFormatLite::k##CAMELCASE##Size *               \
+              FromIntSize(repeated_##LOWERCASE##_value->size()); \
+    break
+        HANDLE_TYPE(FIXED32, Fixed32, arc_ui32);
+        HANDLE_TYPE(FIXED64, Fixed64, arc_ui64);
+        HANDLE_TYPE(SFIXED32, SFixed32, arc_i32);
+        HANDLE_TYPE(SFIXED64, SFixed64, arc_i64);
+        HANDLE_TYPE(FLOAT, Float, float);
+        HANDLE_TYPE(DOUBLE, Double, double);
+        HANDLE_TYPE(BOOL, Bool, bool);
+#undef HANDLE_TYPE
+
+        case WireFormatLite::TYPE_STRING:
+        case WireFormatLite::TYPE_BYTES:
+        case WireFormatLite::TYPE_GROUP:
+        case WireFormatLite::TYPE_MESSAGE:
+          GOOGLE_LOG(FATAL) << "Non-primitive types can't be packed.";
+          break;
+      }
+
+      cached_size = ToCachedSize(result);
+      if (result > 0) {
+        result += io::CodedOutputStream::VarintSize32(result);
+        result += io::CodedOutputStream::VarintSize32(WireFormatLite::MakeTag(
+            number, WireFormatLite::WIRETYPE_LENGTH_DELIMITED));
+      }
+    } else {
+      size_t tag_size = WireFormatLite::TagSize(number, real_type(type));
+
+      switch (real_type(type)) {
+#define HANDLE_TYPE(UPPERCASE, CAMELCASE, LOWERCASE)                        \
+  case WireFormatLite::TYPE_##UPPERCASE:                                    \
+    result += tag_size * FromIntSize(repeated_##LOWERCASE##_value->size()); \
+    for (int i = 0; i < repeated_##LOWERCASE##_value->size(); i++) {        \
+      result += WireFormatLite::CAMELCASE##Size(                            \
+          repeated_##LOWERCASE##_value->Get(i));                            \
+    }                                                                       \
+    break
+
+        HANDLE_TYPE(INT32, Int32, arc_i32);
+        HANDLE_TYPE(INT64, Int64, arc_i64);
+        HANDLE_TYPE(UINT32, UInt32, arc_ui32);
+        HANDLE_TYPE(UINT64, UInt64, arc_ui64);
+        HANDLE_TYPE(SINT32, SInt32, arc_i32);
+        HANDLE_TYPE(SINT64, SInt64, arc_i64);
+        HANDLE_TYPE(STRING, String, string);
+        HANDLE_TYPE(BYTES, Bytes, string);
+        HANDLE_TYPE(ENUM, Enum, enum);
+        HANDLE_TYPE(GROUP, Group, message);
+        HANDLE_TYPE(MESSAGE, Message, message);
+#undef HANDLE_TYPE
+
+        // Stuff with fixed size.
+#define HANDLE_TYPE(UPPERCASE, CAMELCASE, LOWERCASE)             \
+  case WireFormatLite::TYPE_##UPPERCASE:                         \
+    result += (tag_size + WireFormatLite::k##CAMELCASE##Size) *  \
+              FromIntSize(repeated_##LOWERCASE##_value->size()); \
+    break
+        HANDLE_TYPE(FIXED32, Fixed32, arc_ui32);
+        HANDLE_TYPE(FIXED64, Fixed64, arc_ui64);
+        HANDLE_TYPE(SFIXED32, SFixed32, arc_i32);
+        HANDLE_TYPE(SFIXED64, SFixed64, arc_i64);
+        HANDLE_TYPE(FLOAT, Float, float);
+        HANDLE_TYPE(DOUBLE, Double, double);
+        HANDLE_TYPE(BOOL, Bool, bool);
+#undef HANDLE_TYPE
+      }
+    }
+  } else if (!is_cleared) {
+    result += WireFormatLite::TagSize(number, real_type(type));
+    switch (real_type(type)) {
+#define HANDLE_TYPE(UPPERCASE, CAMELCASE, LOWERCASE)      \
+  case WireFormatLite::TYPE_##UPPERCASE:                  \
+    result += WireFormatLite::CAMELCASE##Size(LOWERCASE); \
+    break
+
+      HANDLE_TYPE(INT32, Int32, arc_i32_value);
+      HANDLE_TYPE(INT64, Int64, arc_i64_value);
+      HANDLE_TYPE(UINT32, UInt32, arc_ui32_value);
+      HANDLE_TYPE(UINT64, UInt64, arc_ui64_value);
+      HANDLE_TYPE(SINT32, SInt32, arc_i32_value);
+      HANDLE_TYPE(SINT64, SInt64, arc_i64_value);
+      HANDLE_TYPE(STRING, String, *string_value);
+      HANDLE_TYPE(BYTES, Bytes, *string_value);
+      HANDLE_TYPE(ENUM, Enum, enum_value);
+      HANDLE_TYPE(GROUP, Group, *message_value);
+#undef HANDLE_TYPE
+      case WireFormatLite::TYPE_MESSAGE: {
+        if (is_lazy) {
+          size_t size = lazymessage_value->ByteSizeLong();
+          result += io::CodedOutputStream::VarintSize32(size) + size;
+        } else {
+          result += WireFormatLite::MessageSize(*message_value);
+        }
+        break;
+      }
+
+      // Stuff with fixed size.
+#define HANDLE_TYPE(UPPERCASE, CAMELCASE)         \
+  case WireFormatLite::TYPE_##UPPERCASE:          \
+    result += WireFormatLite::k##CAMELCASE##Size; \
+    break
+        HANDLE_TYPE(FIXED32, Fixed32);
+        HANDLE_TYPE(FIXED64, Fixed64);
+        HANDLE_TYPE(SFIXED32, SFixed32);
+        HANDLE_TYPE(SFIXED64, SFixed64);
+        HANDLE_TYPE(FLOAT, Float);
+        HANDLE_TYPE(DOUBLE, Double);
+        HANDLE_TYPE(BOOL, Bool);
+#undef HANDLE_TYPE
+    }
+  }
+
+  return result;
+}
+
+int ExtensionSet::Extension::GetSize() const {
+  GOOGLE_DCHECK(is_repeated);
+  switch (cpp_type(type)) {
+#define HANDLE_TYPE(UPPERCASE, LOWERCASE)   \
+  case WireFormatLite::CPPTYPE_##UPPERCASE: \
+    return repeated_##LOWERCASE##_value->size()
+
+    HANDLE_TYPE(INT32, arc_i32);
+    HANDLE_TYPE(INT64, arc_i64);
+    HANDLE_TYPE(UINT32, arc_ui32);
+    HANDLE_TYPE(UINT64, arc_ui64);
+    HANDLE_TYPE(FLOAT, float);
+    HANDLE_TYPE(DOUBLE, double);
+    HANDLE_TYPE(BOOL, bool);
+    HANDLE_TYPE(ENUM, enum);
+    HANDLE_TYPE(STRING, string);
+    HANDLE_TYPE(MESSAGE, message);
+#undef HANDLE_TYPE
+  }
+
+  GOOGLE_LOG(FATAL) << "Can't get here.";
+  return 0;
+}
+
+// This function deletes all allocated objects. This function should be only
+// called if the Extension was created without an arena.
+void ExtensionSet::Extension::Free() {
+  if (is_repeated) {
+    switch (cpp_type(type)) {
+#define HANDLE_TYPE(UPPERCASE, LOWERCASE)   \
+  case WireFormatLite::CPPTYPE_##UPPERCASE: \
+    delete repeated_##LOWERCASE##_value;    \
+    break
+
+      HANDLE_TYPE(INT32, arc_i32);
+      HANDLE_TYPE(INT64, arc_i64);
+      HANDLE_TYPE(UINT32, arc_ui32);
+      HANDLE_TYPE(UINT64, arc_ui64);
+      HANDLE_TYPE(FLOAT, float);
+      HANDLE_TYPE(DOUBLE, double);
+      HANDLE_TYPE(BOOL, bool);
+      HANDLE_TYPE(ENUM, enum);
+      HANDLE_TYPE(STRING, string);
+      HANDLE_TYPE(MESSAGE, message);
+#undef HANDLE_TYPE
+    }
+  } else {
+    switch (cpp_type(type)) {
+      case WireFormatLite::CPPTYPE_STRING:
+        delete string_value;
+        break;
+      case WireFormatLite::CPPTYPE_MESSAGE:
+        if (is_lazy) {
+          delete lazymessage_value;
+        } else {
+          delete message_value;
+        }
+        break;
+      default:
+        break;
+    }
+  }
+}
+
+// Defined in extension_set_heavy.cc.
+// int ExtensionSet::Extension::SpaceUsedExcludingSelf() const
+
+bool ExtensionSet::Extension::IsInitialized() const {
+  if (cpp_type(type) == WireFormatLite::CPPTYPE_MESSAGE) {
+    if (is_repeated) {
+      for (int i = 0; i < repeated_message_value->size(); i++) {
+        if (!repeated_message_value->Get(i).IsInitialized()) {
+          return false;
+        }
+      }
+    } else {
+      if (!is_cleared) {
+        if (is_lazy) {
+          if (!lazymessage_value->IsInitialized()) return false;
+        } else {
+          if (!message_value->IsInitialized()) return false;
+        }
+      }
+    }
+  }
+  return true;
+}
+
+// Dummy key method to avoid weak vtable.
+void ExtensionSet::LazyMessageExtension::UnusedKeyMethod() {}
+
+const ExtensionSet::Extension* ExtensionSet::FindOrNull(int key) const {
+  if (flat_size_ == 0) {
+    return nullptr;
+  } else if (PROTOBUF_PREDICT_TRUE(!is_large())) {
+    auto it = std::lower_bound(flat_begin(), flat_end() - 1, key,
+                               KeyValue::FirstComparator());
+    return it->first == key ? &it->second : nullptr;
+  } else {
+    return FindOrNullInLargeMap(key);
+  }
+}
+
+const ExtensionSet::Extension* ExtensionSet::FindOrNullInLargeMap(
+    int key) const {
+  assert(is_large());
+  LargeMap::const_iterator it = map_.large->find(key);
+  if (it != map_.large->end()) {
+    return &it->second;
+  }
+  return nullptr;
+}
+
+ExtensionSet::Extension* ExtensionSet::FindOrNull(int key) {
+  const auto* const_this = this;
+  return const_cast<ExtensionSet::Extension*>(const_this->FindOrNull(key));
+}
+
+ExtensionSet::Extension* ExtensionSet::FindOrNullInLargeMap(int key) {
+  const auto* const_this = this;
+  return const_cast<ExtensionSet::Extension*>(
+      const_this->FindOrNullInLargeMap(key));
+}
+
+std::pair<ExtensionSet::Extension*, bool> ExtensionSet::Insert(int key) {
+  if (PROTOBUF_PREDICT_FALSE(is_large())) {
+    auto maybe = map_.large->insert({key, Extension()});
+    return {&maybe.first->second, maybe.second};
+  }
+  KeyValue* end = flat_end();
+  KeyValue* it =
+      std::lower_bound(flat_begin(), end, key, KeyValue::FirstComparator());
+  if (it != end && it->first == key) {
+    return {&it->second, false};
+  }
+  if (flat_size_ < flat_capacity_) {
+    std::copy_backward(it, end, end + 1);
+    ++flat_size_;
+    it->first = key;
+    it->second = Extension();
+    return {&it->second, true};
+  }
+  GrowCapacity(flat_size_ + 1);
+  return Insert(key);
+}
+
+void ExtensionSet::GrowCapacity(size_t minimum_new_capacity) {
+  if (PROTOBUF_PREDICT_FALSE(is_large())) {
+    return;  // LargeMap does not have a "reserve" method.
+  }
+  if (flat_capacity_ >= minimum_new_capacity) {
+    return;
+  }
+
+  auto new_flat_capacity = flat_capacity_;
+  do {
+    new_flat_capacity = new_flat_capacity == 0 ? 1 : new_flat_capacity * 4;
+  } while (new_flat_capacity < minimum_new_capacity);
+
+  const KeyValue* begin = flat_begin();
+  const KeyValue* end = flat_end();
+  AllocatedData new_map;
+  if (new_flat_capacity > kMaximumFlatCapacity) {
+    new_map.large = Arena::Create<LargeMap>(arena_);
+    LargeMap::iterator hint = new_map.large->begin();
+    for (const KeyValue* it = begin; it != end; ++it) {
+      hint = new_map.large->insert(hint, {it->first, it->second});
+    }
+    flat_size_ = static_cast<uint16_t>(-1);
+    GOOGLE_DCHECK(is_large());
+  } else {
+    new_map.flat = Arena::CreateArray<KeyValue>(arena_, new_flat_capacity);
+    std::copy(begin, end, new_map.flat);
+  }
+
+  if (arena_ == nullptr) {
+    DeleteFlatMap(begin, flat_capacity_);
+  }
+  flat_capacity_ = new_flat_capacity;
+  map_ = new_map;
+}
+
+#if (__cplusplus < 201703) && \
+    (!defined(_MSC_VER) || (_MSC_VER >= 1900 && _MSC_VER < 1912))
+// static
+constexpr uint16_t ExtensionSet::kMaximumFlatCapacity;
+#endif  //  (__cplusplus < 201703) && (!defined(_MSC_VER) || (_MSC_VER >= 1900
+        //  && _MSC_VER < 1912))
+
+void ExtensionSet::Erase(int key) {
+  if (PROTOBUF_PREDICT_FALSE(is_large())) {
+    map_.large->erase(key);
+    return;
+  }
+  KeyValue* end = flat_end();
+  KeyValue* it =
+      std::lower_bound(flat_begin(), end, key, KeyValue::FirstComparator());
+  if (it != end && it->first == key) {
+    std::copy(it + 1, end, it);
+    --flat_size_;
+  }
+}
+
+// ==================================================================
+// Default repeated field instances for iterator-compatible accessors
+
+const RepeatedPrimitiveDefaults* RepeatedPrimitiveDefaults::default_instance() {
+  static auto instance = OnShutdownDelete(new RepeatedPrimitiveDefaults);
+  return instance;
+}
+
+const RepeatedStringTypeTraits::RepeatedFieldType*
+RepeatedStringTypeTraits::GetDefaultRepeatedField() {
+  static auto instance = OnShutdownDelete(new RepeatedFieldType);
+  return instance;
+}
+
+uint8_t* ExtensionSet::Extension::InternalSerializeFieldWithCachedSizesToArray(
+    const MessageLite* extendee, const ExtensionSet* extension_set, int number,
+    uint8_t* target, io::EpsCopyOutputStream* stream) const {
+  if (is_repeated) {
+    if (is_packed) {
+      if (cached_size == 0) return target;
+
+      target = stream->EnsureSpace(target);
+      target = WireFormatLite::WriteTagToArray(
+          number, WireFormatLite::WIRETYPE_LENGTH_DELIMITED, target);
+      target = WireFormatLite::WriteInt32NoTagToArray(cached_size, target);
+
+      switch (real_type(type)) {
+#define HANDLE_TYPE(UPPERCASE, CAMELCASE, LOWERCASE)                 \
+  case WireFormatLite::TYPE_##UPPERCASE:                             \
+    for (int i = 0; i < repeated_##LOWERCASE##_value->size(); i++) { \
+      target = stream->EnsureSpace(target);                          \
+      target = WireFormatLite::Write##CAMELCASE##NoTagToArray(       \
+          repeated_##LOWERCASE##_value->Get(i), target);             \
+    }                                                                \
+    break
+
+        HANDLE_TYPE(INT32, Int32, arc_i32);
+        HANDLE_TYPE(INT64, Int64, arc_i64);
+        HANDLE_TYPE(UINT32, UInt32, arc_ui32);
+        HANDLE_TYPE(UINT64, UInt64, arc_ui64);
+        HANDLE_TYPE(SINT32, SInt32, arc_i32);
+        HANDLE_TYPE(SINT64, SInt64, arc_i64);
+        HANDLE_TYPE(FIXED32, Fixed32, arc_ui32);
+        HANDLE_TYPE(FIXED64, Fixed64, arc_ui64);
+        HANDLE_TYPE(SFIXED32, SFixed32, arc_i32);
+        HANDLE_TYPE(SFIXED64, SFixed64, arc_i64);
+        HANDLE_TYPE(FLOAT, Float, float);
+        HANDLE_TYPE(DOUBLE, Double, double);
+        HANDLE_TYPE(BOOL, Bool, bool);
+        HANDLE_TYPE(ENUM, Enum, enum);
+#undef HANDLE_TYPE
+
+        case WireFormatLite::TYPE_STRING:
+        case WireFormatLite::TYPE_BYTES:
+        case WireFormatLite::TYPE_GROUP:
+        case WireFormatLite::TYPE_MESSAGE:
+          GOOGLE_LOG(FATAL) << "Non-primitive types can't be packed.";
+          break;
+      }
+    } else {
+      switch (real_type(type)) {
+#define HANDLE_TYPE(UPPERCASE, CAMELCASE, LOWERCASE)                 \
+  case WireFormatLite::TYPE_##UPPERCASE:                             \
+    for (int i = 0; i < repeated_##LOWERCASE##_value->size(); i++) { \
+      target = stream->EnsureSpace(target);                          \
+      target = WireFormatLite::Write##CAMELCASE##ToArray(            \
+          number, repeated_##LOWERCASE##_value->Get(i), target);     \
+    }                                                                \
+    break
+
+        HANDLE_TYPE(INT32, Int32, arc_i32);
+        HANDLE_TYPE(INT64, Int64, arc_i64);
+        HANDLE_TYPE(UINT32, UInt32, arc_ui32);
+        HANDLE_TYPE(UINT64, UInt64, arc_ui64);
+        HANDLE_TYPE(SINT32, SInt32, arc_i32);
+        HANDLE_TYPE(SINT64, SInt64, arc_i64);
+        HANDLE_TYPE(FIXED32, Fixed32, arc_ui32);
+        HANDLE_TYPE(FIXED64, Fixed64, arc_ui64);
+        HANDLE_TYPE(SFIXED32, SFixed32, arc_i32);
+        HANDLE_TYPE(SFIXED64, SFixed64, arc_i64);
+        HANDLE_TYPE(FLOAT, Float, float);
+        HANDLE_TYPE(DOUBLE, Double, double);
+        HANDLE_TYPE(BOOL, Bool, bool);
+        HANDLE_TYPE(ENUM, Enum, enum);
+#undef HANDLE_TYPE
+#define HANDLE_TYPE(UPPERCASE, CAMELCASE, LOWERCASE)                 \
+  case WireFormatLite::TYPE_##UPPERCASE:                             \
+    for (int i = 0; i < repeated_##LOWERCASE##_value->size(); i++) { \
+      target = stream->EnsureSpace(target);                          \
+      target = stream->WriteString(                                  \
+          number, repeated_##LOWERCASE##_value->Get(i), target);     \
+    }                                                                \
+    break
+        HANDLE_TYPE(STRING, String, string);
+        HANDLE_TYPE(BYTES, Bytes, string);
+#undef HANDLE_TYPE
+#define HANDLE_TYPE(UPPERCASE, CAMELCASE, LOWERCASE)                     \
+  case WireFormatLite::TYPE_##UPPERCASE:                                 \
+    for (int i = 0; i < repeated_##LOWERCASE##_value->size(); i++) {     \
+      target = stream->EnsureSpace(target);                              \
+      target = WireFormatLite::InternalWrite##CAMELCASE(                 \
+          number, repeated_##LOWERCASE##_value->Get(i), target, stream); \
+    }                                                                    \
+    break
+
+        HANDLE_TYPE(GROUP, Group, message);
+        HANDLE_TYPE(MESSAGE, Message, message);
+#undef HANDLE_TYPE
+      }
+    }
+  } else if (!is_cleared) {
+    switch (real_type(type)) {
+#define HANDLE_TYPE(UPPERCASE, CAMELCASE, VALUE)                               \
+  case WireFormatLite::TYPE_##UPPERCASE:                                       \
+    target = stream->EnsureSpace(target);                                      \
+    target = WireFormatLite::Write##CAMELCASE##ToArray(number, VALUE, target); \
+    break
+
+      HANDLE_TYPE(INT32, Int32, arc_i32_value);
+      HANDLE_TYPE(INT64, Int64, arc_i64_value);
+      HANDLE_TYPE(UINT32, UInt32, arc_ui32_value);
+      HANDLE_TYPE(UINT64, UInt64, arc_ui64_value);
+      HANDLE_TYPE(SINT32, SInt32, arc_i32_value);
+      HANDLE_TYPE(SINT64, SInt64, arc_i64_value);
+      HANDLE_TYPE(FIXED32, Fixed32, arc_ui32_value);
+      HANDLE_TYPE(FIXED64, Fixed64, arc_ui64_value);
+      HANDLE_TYPE(SFIXED32, SFixed32, arc_i32_value);
+      HANDLE_TYPE(SFIXED64, SFixed64, arc_i64_value);
+      HANDLE_TYPE(FLOAT, Float, float_value);
+      HANDLE_TYPE(DOUBLE, Double, double_value);
+      HANDLE_TYPE(BOOL, Bool, bool_value);
+      HANDLE_TYPE(ENUM, Enum, enum_value);
+#undef HANDLE_TYPE
+#define HANDLE_TYPE(UPPERCASE, CAMELCASE, VALUE)         \
+  case WireFormatLite::TYPE_##UPPERCASE:                 \
+    target = stream->EnsureSpace(target);                \
+    target = stream->WriteString(number, VALUE, target); \
+    break
+      HANDLE_TYPE(STRING, String, *string_value);
+      HANDLE_TYPE(BYTES, Bytes, *string_value);
+#undef HANDLE_TYPE
+      case WireFormatLite::TYPE_GROUP:
+        target = stream->EnsureSpace(target);
+        target = WireFormatLite::InternalWriteGroup(number, *message_value,
+                                                    target, stream);
+        break;
+      case WireFormatLite::TYPE_MESSAGE:
+        if (is_lazy) {
+          const auto* prototype =
+              extension_set->GetPrototypeForLazyMessage(extendee, number);
+          target = lazymessage_value->WriteMessageToArray(prototype, number,
+                                                          target, stream);
+        } else {
+          target = stream->EnsureSpace(target);
+          target = WireFormatLite::InternalWriteMessage(number, *message_value,
+                                                        target, stream);
+        }
+        break;
+    }
+  }
+  return target;
+}
+
+const MessageLite* ExtensionSet::GetPrototypeForLazyMessage(
+    const MessageLite* extendee, int number) const {
+  GeneratedExtensionFinder finder(extendee);
+  bool was_packed_on_wire = false;
+  ExtensionInfo extension_info;
+  if (!FindExtensionInfoFromFieldNumber(
+          WireFormatLite::WireType::WIRETYPE_LENGTH_DELIMITED, number, &finder,
+          &extension_info, &was_packed_on_wire)) {
+    return nullptr;
+  }
+  return extension_info.message_info.prototype;
+}
+
+uint8_t*
+ExtensionSet::Extension::InternalSerializeMessageSetItemWithCachedSizesToArray(
+    const MessageLite* extendee, const ExtensionSet* extension_set, int number,
+    uint8_t* target, io::EpsCopyOutputStream* stream) const {
+  if (type != WireFormatLite::TYPE_MESSAGE || is_repeated) {
+    // Not a valid MessageSet extension, but serialize it the normal way.
+    GOOGLE_LOG(WARNING) << "Invalid message set extension.";
+    return InternalSerializeFieldWithCachedSizesToArray(extendee, extension_set,
+                                                        number, target, stream);
+  }
+
+  if (is_cleared) return target;
+
+  target = stream->EnsureSpace(target);
+  // Start group.
+  target = io::CodedOutputStream::WriteTagToArray(
+      WireFormatLite::kMessageSetItemStartTag, target);
+  // Write type ID.
+  target = WireFormatLite::WriteUInt32ToArray(
+      WireFormatLite::kMessageSetTypeIdNumber, number, target);
+  // Write message.
+  if (is_lazy) {
+    const auto* prototype =
+        extension_set->GetPrototypeForLazyMessage(extendee, number);
+    target = lazymessage_value->WriteMessageToArray(
+        prototype, WireFormatLite::kMessageSetMessageNumber, target, stream);
+  } else {
+    target = WireFormatLite::InternalWriteMessage(
+        WireFormatLite::kMessageSetMessageNumber, *message_value, target,
+        stream);
+  }
+  // End group.
+  target = stream->EnsureSpace(target);
+  target = io::CodedOutputStream::WriteTagToArray(
+      WireFormatLite::kMessageSetItemEndTag, target);
+  return target;
+}
+
+size_t ExtensionSet::Extension::MessageSetItemByteSize(int number) const {
+  if (type != WireFormatLite::TYPE_MESSAGE || is_repeated) {
+    // Not a valid MessageSet extension, but compute the byte size for it the
+    // normal way.
+    return ByteSize(number);
+  }
+
+  if (is_cleared) return 0;
+
+  size_t our_size = WireFormatLite::kMessageSetItemTagsSize;
+
+  // type_id
+  our_size += io::CodedOutputStream::VarintSize32(number);
+
+  // message
+  size_t message_size = 0;
+  if (is_lazy) {
+    message_size = lazymessage_value->ByteSizeLong();
+  } else {
+    message_size = message_value->ByteSizeLong();
+  }
+
+  our_size += io::CodedOutputStream::VarintSize32(message_size);
+  our_size += message_size;
+
+  return our_size;
+}
+
+size_t ExtensionSet::MessageSetByteSize() const {
+  size_t total_size = 0;
+  ForEach([&total_size](int number, const Extension& ext) {
+    total_size += ext.MessageSetItemByteSize(number);
+  });
+  return total_size;
+}
+
+
+}  // namespace internal
+}  // namespace protobuf
+}  // namespace google
+
+#include <google/protobuf/port_undef.inc>