src/google/protobuf/message_lite.h

// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd

// Authors: wink@google.com (Wink Saville),
//          kenton@google.com (Kenton Varda)
//  Based on original Protocol Buffers design by
//  Sanjay Ghemawat, Jeff Dean, and others.
//
// Defines MessageLite, the abstract interface implemented by all (lite
// and non-lite) protocol message objects.
//
// This is only intended to be extended by protoc created gencode or types
// defined in the Protobuf runtime. It is not intended or supported for
// application code to extend this class, and any protected methods may be
// removed without being it being considered a breaking change as long as the
// corresponding gencode does not use it.

#ifndef GOOGLE_PROTOBUF_MESSAGE_LITE_H__
#define GOOGLE_PROTOBUF_MESSAGE_LITE_H__

#include <atomic>
#include <climits>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <iosfwd>
#include <memory>
#include <new>
#include <string>
#include <type_traits>
#include <utility>
#include <variant>

#include "absl/base/attributes.h"
#include "absl/base/macros.h"
#include "absl/log/absl_check.h"
#include "absl/strings/cord.h"
#include "absl/strings/string_view.h"
#include "google/protobuf/arena.h"
#include "google/protobuf/class_data.h"
#include "google/protobuf/internal_visibility.h"
#include "google/protobuf/io/coded_stream.h"
#include "google/protobuf/message_traits.h"
#include "google/protobuf/metadata_lite.h"
#include "google/protobuf/port.h"
#include "google/protobuf/type_id.h"


// clang-format off
#include "google/protobuf/port_def.inc"
// clang-format on

#ifdef SWIG
#error "You cannot SWIG proto headers"
#endif

namespace google {
namespace protobuf {

class FastReflectionMessageMutator;
class FastReflectionStringSetter;
class Reflection;
class Descriptor;
class AssignDescriptorsHelper;
class MessageLite;

namespace io {

class CodedInputStream;
class CodedOutputStream;
class ZeroCopyInputStream;
class ZeroCopyOutputStream;

}  // namespace io

namespace compiler {
namespace cpp {
class MessageTableTester;
}  // namespace cpp
}  // namespace compiler

// Type trait to check if a type T is a concrete proto message.
template <typename T>
struct is_concrete_proto_message
    : std::integral_constant<bool, std::is_base_of_v<MessageLite, T> &&
                                       !std::is_same_v<T, MessageLite> &&
                                       !std::is_same_v<T, Message>> {};
template <typename T>
inline constexpr bool is_concrete_proto_message_v =
    is_concrete_proto_message<T>::value;

namespace internal {

struct PrivateAccess;

// Allow easy change to regular int on platforms where the atomic might have a
// perf impact.
//
// CachedSize is like std::atomic<int> but with some important changes:
//
// 1) CachedSize uses Get / Set rather than load / store.
// 2) CachedSize always uses relaxed ordering.
// 3) CachedSize is assignable and copy-constructible.
// 4) CachedSize has a constexpr default constructor, and a constexpr
//    constructor that takes an int argument.
// 5) If the compiler supports the __atomic_load_n / __atomic_store_n builtins,
//    then CachedSize is trivially copyable.
//
// Developed at https://godbolt.org/z/vYcx7zYs1 ; supports gcc, clang, MSVC.
class PROTOBUF_EXPORT CachedSize {
 private:
  using Scalar = int;

 public:
  constexpr CachedSize() noexcept : atom_(Scalar{}) {}

  void Set(Scalar desired) const noexcept {
    // Avoid writing the value when it is zero. This prevents writing to global
    // default instances, which might be in readonly memory.
    if (ABSL_PREDICT_FALSE(desired == 0)) {
      if (Get() == 0) return;
    }
    SetImpl(desired);
  }

  void SetNonZero(Scalar desired) const noexcept {
    ABSL_DCHECK_NE(desired, 0);
    SetImpl(desired);
  }

#ifdef PROTOBUF_BUILTIN_ATOMIC
  constexpr CachedSize(const CachedSize& other) = default;
  CachedSize& operator=(const CachedSize& other) = default;

  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD Scalar Get() const noexcept {
    return __atomic_load_n(&atom_, __ATOMIC_RELAXED);
  }

 private:
  void SetImpl(Scalar desired) const noexcept {
    __atomic_store_n(&atom_, desired, __ATOMIC_RELAXED);
  }

  mutable Scalar atom_;
#else
  CachedSize(const CachedSize& other) noexcept : atom_(other.Get()) {}
  CachedSize& operator=(const CachedSize& other) noexcept {
    Set(other.Get());
    return *this;
  }

  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD Scalar Get() const noexcept {  //
    return atom_.load(std::memory_order_relaxed);
  }

 private:
  void SetImpl(Scalar desired) const noexcept {
    atom_.store(desired, std::memory_order_relaxed);
  }
  mutable std::atomic<Scalar> atom_;
#endif
};

template <const uint32_t* kValidationData>
struct EnumTraitsT {
  static constexpr const uint32_t* validation_data() { return kValidationData; }
};

struct EnumTraitsImpl {
  struct Undefined;
  // We use an incomplete type to cause a compiler error if something tries to
  // instantiate `value<T>` with a `T` that had no specialization.
  // The `enable_if` is there to workaround some compilers/tools that complain
  // on the declaration even with no instantiations.
  template <typename T>
  static std::enable_if_t<sizeof(T) != 0, Undefined> value;
};
template <typename T>
using EnumTraits = decltype(EnumTraitsImpl::value<T>);

template <typename T>
struct LiteEnumFuncs {
  static constexpr bool kIsDefined = false;
  // Lite enums will specialize this struct to allow templates to parse/unparse
  // enums.
  // The declarations will be like:
  // static constexpr bool kIsDefined = true;
  // static constexpr auto kParseFunc = ...
  // static constexpr auto kNameFunc = ...
};

class SwapFieldHelper;

// See parse_context.h for explanation
class ParseContext;

struct DescriptorTable;
class DescriptorPoolExtensionFinder;
class ExtensionSet;
class HasBitsTestPeer;
class InternalMetadataOffset;
template <typename T, size_t kFieldOffset>
struct InternalMetadataOffsetHelper;
class LazyField;
class RepeatedPtrFieldBase;
class TcParser;
struct TcParseTableBase;
class WireFormatLite;
class WeakFieldMap;
class RustMapHelper;

// We compute sizes as size_t but cache them as int.  This function converts a
// computed size to a cached size.  Since we don't proceed with serialization
// if the total size was > INT_MAX, it is not important what this function
// returns for inputs > INT_MAX.  However this case should not error or
// ABSL_CHECK-fail, because the full size_t resolution is still returned from
// ByteSizeLong() and checked against INT_MAX; we can catch the overflow
// there.
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD
inline int ToCachedSize(size_t size) { return static_cast<int>(size); }

// We mainly calculate sizes in terms of size_t, but some functions that
// compute sizes return "int".  These int sizes are expected to always be
// positive. This function is more efficient than casting an int to size_t
// directly on 64-bit platforms because it avoids making the compiler emit a
// sign extending instruction, which we don't want and don't want to pay for.
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD
inline size_t FromIntSize(int size) {
  // Convert to unsigned before widening so sign extension is not necessary.
  return static_cast<unsigned int>(size);
}

// For cases where a legacy function returns an integer size.  We ABSL_DCHECK()
// that the conversion will fit within an integer; if this is false then we
// are losing information.
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD
inline int ToIntSize(size_t size) {
  ABSL_DCHECK_LE(size, static_cast<size_t>(INT_MAX));
  return static_cast<int>(size);
}


PROTOBUF_EXPORT inline const std::string& GetEmptyStringAlreadyInited() {
  return fixed_address_empty_string.get();
}

#ifndef PROTOBUF_MESSAGE_GLOBALS
struct MessageGlobalsBase {
  template <typename T = MessageLite>
  static const T* ToDefaultInstance(const void* globals) {
    return reinterpret_cast<const T*>(globals);
  }

  static const MessageGlobalsBase* FromDefaultInstance(
      const void* default_instance) {
    return reinterpret_cast<const MessageGlobalsBase*>(default_instance);
  }
};

template <const auto* kDefault, const auto* kClassData>
struct GeneratedMessageTraitsT {
  static constexpr const void* default_instance() { return kDefault; }
  static constexpr const auto* class_data() { return kClassData->base(); }
  static constexpr const auto* tc_table() { return class_data()->tc_table; }
  static constexpr auto StrongPointer() { return default_instance(); }
};
#else
struct MessageGlobalsBase {
  template <size_t R, size_t KnownAlignment = 0>
  static constexpr size_t RoundUpTo(size_t n) {
    static_assert(absl::has_single_bit(R), "Must be power of two");
    if constexpr (KnownAlignment != 0) {
      assert(n % KnownAlignment == 0);
    }
    if constexpr (KnownAlignment >= R) {
      return n;
    } else {
      return (n + (R - 1)) & ~(R - 1);
    }
  }

  static constexpr size_t OffsetToDefault() {
    return RoundUpTo<kMaxMessageAlignment>(sizeof(MessageGlobalsBase));
  }
  template <typename T = MessageLite>
  static const T* ToDefaultInstance(const void* globals) {
    return reinterpret_cast<const T*>(reinterpret_cast<const char*>(globals) +
                                      OffsetToDefault());
  }

  static const MessageGlobalsBase* FromDefaultInstance(
      const void* default_instance) {
    return reinterpret_cast<const MessageGlobalsBase*>(
        reinterpret_cast<const char*>(default_instance) - OffsetToDefault());
  }

  static constexpr const ClassData* GetClassData(const void* globals) {
    return static_cast<const MessageGlobalsBase*>(globals)->class_data.base();
  }
  constexpr const ClassData* GetClassData() const { return class_data.base(); }

  explicit constexpr MessageGlobalsBase(ClassDataFull class_data)
      : class_data(class_data) {}

  static const TcParseTableBase* ToParseTableBase(const void* g) {
    const auto* globals = static_cast<const MessageGlobalsBase*>(g);
    ABSL_DCHECK_NE(globals, nullptr);
    ABSL_DCHECK(!globals->class_data.is_dynamic);
    return reinterpret_cast<const TcParseTableBase*>(
        ToDefaultInstance<char>(g) +
        RoundUpTo<8, alignof(void*)>(globals->class_data.allocation_size()));
  }

  // It also aliases to ClassDataLite.
  ClassDataFull class_data;
};

template <const auto* kGlobals>
struct GeneratedMessageTraitsT {
  static const void* default_instance() {
    return MessageGlobalsBase::ToDefaultInstance(kGlobals);
  }
  static const auto* class_data() {
    return MessageGlobalsBase::GetClassData(kGlobals);
  }
  static const auto* tc_table() {
    return MessageGlobalsBase::ToParseTableBase(kGlobals);
  }
  static constexpr const auto* globals() { return kGlobals; }
  static constexpr auto StrongPointer() { return kGlobals; }
};

inline const MessageLite* ClassData::default_instance() const {
  static_assert(PROTOBUF_FIELD_OFFSET(MessageGlobalsBase, class_data) == 0);
  return MessageGlobalsBase::ToDefaultInstance(this);
}

#endif  // PROTOBUF_MESSAGE_GLOBALS

inline const TcParseTableBase* ClassData::GetTcParseTable() const {
#ifdef PROTOBUF_MESSAGE_GLOBALS
  if (ABSL_PREDICT_FALSE(is_dynamic)) {
#else
  if (ABSL_PREDICT_FALSE(tc_table == nullptr)) {
#endif
    ABSL_DCHECK(!is_lite);
    return full().descriptor_methods()->get_tc_table(this);
  }
#ifdef PROTOBUF_MESSAGE_GLOBALS
  return MessageGlobalsBase::ToParseTableBase(this);
#else
  return tc_table;
#endif
}

}  // namespace internal

// Interface to light weight protocol messages.
//
// This interface is implemented by all protocol message objects.  Non-lite
// messages additionally implement the Message interface, which is a
// subclass of MessageLite.  Use MessageLite instead when you only need
// the subset of features which it supports -- namely, nothing that uses
// descriptors or reflection.  You can instruct the protocol compiler
// to generate classes which implement only MessageLite, not the full
// Message interface, by adding the following line to the .proto file:
//
//   option optimize_for = LITE_RUNTIME;
//
// This is particularly useful on resource-constrained systems where
// the full protocol buffers runtime library is too big.
//
// Note that on non-constrained systems (e.g. servers) when you need
// to link in lots of protocol definitions, a better way to reduce
// total code footprint is to use optimize_for = CODE_SIZE.  This
// will make the generated code smaller while still supporting all the
// same features (at the expense of speed).  optimize_for = LITE_RUNTIME
// is best when you only have a small number of message types linked
// into your binary, in which case the size of the protocol buffers
// runtime itself is the biggest problem.
//
// Users must not derive from this class. Only the protocol compiler and
// the internal library are allowed to create subclasses.
class PROTOBUF_EXPORT MessageLite {
 public:
  MessageLite(const MessageLite&) = delete;
  MessageLite& operator=(const MessageLite&) = delete;
#if !defined(PROTOBUF_PROTECTED_MESSAGE_BASE_DESTRUCTOR)
  PROTOBUF_VIRTUAL ~MessageLite() = default;
#endif  // !PROTOBUF_PROTECTED_MESSAGE_BASE_DESTRUCTOR

  // Basic Operations ------------------------------------------------

  // Get the name of this message type, e.g. "foo.bar.BazProto".
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD absl::string_view GetTypeName() const;

  // Construct a new instance of the same type.  Ownership is passed to the
  // caller.
  [[nodiscard]] MessageLite* New() const { return New(nullptr); }

  // Construct a new instance on the arena. Ownership is passed to the caller
  // if arena is a nullptr.
  [[nodiscard]] MessageLite* New(Arena* arena) const;

  // Returns the arena, if any, that directly owns this message and its internal
  // memory (Arena::Own is different in that the arena doesn't directly own the
  // internal memory). This method is used in proto's implementation for
  // swapping, moving and setting allocated, for deciding whether the ownership
  // of this message or its internal memory could be changed.
  [[nodiscard]] Arena* GetArena() const { return _internal_metadata_.arena(); }

  // Clear all fields of the message and set them to their default values.
  // Clear() assumes that any memory allocated to hold parts of the message
  // will likely be needed again, so the memory used may not be freed.
  // To ensure that all memory used by a Message is freed, you must delete it.
#if defined(PROTOBUF_CUSTOM_VTABLE)
  void Clear() { this->class_data()->clear(*this); }
#else
  virtual void Clear() = 0;
#endif  // PROTOBUF_CUSTOM_VTABLE

  // Quickly check if all required fields have values set.
  [[nodiscard]] bool IsInitialized() const;

  // This is not implemented for Lite messages -- it just returns "(cannot
  // determine missing fields for lite message)".  However, it is implemented
  // for full messages.  See message.h.
  [[nodiscard]] std::string InitializationErrorString() const;

  // If |other| is the exact same class as this, calls MergeFrom(). Otherwise,
  // results are undefined (probably crash).
  void CheckTypeAndMergeFrom(const MessageLite& other);

  // These methods return a human-readable summary of the message. Note that
  // since the MessageLite interface does not support reflection, there is very
  // little information that these methods can provide. They are shadowed by
  // methods of the same name on the Message interface which provide much more
  // information. The methods here are intended primarily to facilitate code
  // reuse for logic that needs to interoperate with both full and lite protos.
  //
  // The format of the returned string is subject to change, so please do not
  // assume it will remain stable over time.
  [[nodiscard]] std::string DebugString() const;
  [[nodiscard]] std::string ShortDebugString() const { return DebugString(); }
  // MessageLite::DebugString is already Utf8 Safe. This is to add compatibility
  // with Message.
  [[nodiscard]] std::string Utf8DebugString() const { return DebugString(); }

  // Implementation of the `AbslStringify` interface. This adds `DebugString()`
  // to the sink. Do not rely on exact format.
  template <typename Sink>
  friend void AbslStringify(Sink& sink, const google::protobuf::MessageLite& msg) {
    sink.Append(msg.DebugString());
  }

  // Parsing ---------------------------------------------------------
  // Methods for parsing in protocol buffer format.  Most of these are
  // just simple wrappers around MergeFromCodedStream().  Clear() will be
  // called before merging the input.
  //
  // If parsing fails (returns false), the message is left in an arbitrary
  // but valid state. The guarantees are similar to those of a moved-from
  // state: the message is safe to destroy or Clear(), but its contents are
  // otherwise unspecified.

  // Fill the message with a protocol buffer parsed from the given input
  // stream. Returns false on a read error or if the input is in the wrong
  // format.  A successful return does not indicate the entire input is
  // consumed, ensure you call ConsumedEntireMessage() to check that if
  // applicable.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParseFromCodedStream(io::CodedInputStream* input);
  // Like ParseFromCodedStream(), but accepts messages that are missing
  // required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParsePartialFromCodedStream(io::CodedInputStream* input);
  // Read a protocol buffer from the given zero-copy input stream.  If
  // successful, the entire input will be consumed.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParseFromZeroCopyStream(io::ZeroCopyInputStream* input);
  // Like ParseFromZeroCopyStream(), but accepts messages that are missing
  // required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParsePartialFromZeroCopyStream(io::ZeroCopyInputStream* input);
  // Parse a protocol buffer from a file descriptor.  If successful, the entire
  // input will be consumed.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParseFromFileDescriptor(int file_descriptor);
  // Like ParseFromFileDescriptor(), but accepts messages that are missing
  // required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParsePartialFromFileDescriptor(int file_descriptor);
  // Parse a protocol buffer from a C++ istream.  If successful, the entire
  // input will be consumed.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParseFromIstream(std::istream* input);
  // Like ParseFromIstream(), but accepts messages that are missing
  // required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParsePartialFromIstream(std::istream* input);
  // Read a protocol buffer from the given zero-copy input stream, expecting
  // the message to be exactly "size" bytes long.  If successful, exactly
  // this many bytes will have been consumed from the input.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool
  MergePartialFromBoundedZeroCopyStream(io::ZeroCopyInputStream* input,
                                        int size);
  // Like ParseFromBoundedZeroCopyStream(), but accepts messages that are
  // missing required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool MergeFromBoundedZeroCopyStream(
      io::ZeroCopyInputStream* input, int size);
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParseFromBoundedZeroCopyStream(io::ZeroCopyInputStream* input, int size);
  // Like ParseFromBoundedZeroCopyStream(), but accepts messages that are
  // missing required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParsePartialFromBoundedZeroCopyStream(io::ZeroCopyInputStream* input,
                                        int size);
  // Parses a protocol buffer contained in a string or Cord. Returns true on
  // success. This function takes a string in the (non-human-readable) binary
  // wire format, matching the encoding output by
  // MessageLite::SerializeToString(). If you'd like to convert a human-readable
  // string into a protocol buffer object, see
  // google::protobuf::TextFormat::ParseFromString().
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParseFromString(absl::string_view data);
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParseFromString(const absl::Cord& data);
  // Like ParseFromString(), but accepts messages that are missing
  // required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParsePartialFromString(absl::string_view data);
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParsePartialFromString(const absl::Cord& data);
  // Parse a protocol buffer contained in an array of bytes.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParseFromArray(const void* data, int size);
  // Like ParseFromArray(), but accepts messages that are missing
  // required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParsePartialFromArray(const void* data, int size);


  // Reads a protocol buffer from the stream and merges it into this
  // Message.  Singular fields read from the what is
  // already in the Message and repeated fields are appended to those
  // already present.
  //
  // It is the responsibility of the caller to call input->LastTagWas()
  // (for groups) or input->ConsumedEntireMessage() (for non-groups) after
  // this returns to verify that the message's end was delimited correctly.
  //
  // ParseFromCodedStream() is implemented as Clear() followed by
  // MergeFromCodedStream().
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool MergeFromCodedStream(
      io::CodedInputStream* input);

  // Like MergeFromCodedStream(), but succeeds even if required fields are
  // missing in the input.
  //
  // MergeFromCodedStream() is just implemented as MergePartialFromCodedStream()
  // followed by IsInitialized().
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool MergePartialFromCodedStream(
      io::CodedInputStream* input);

  // Merge a protocol buffer contained in a string.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool MergeFromString(
      absl::string_view data);
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool MergeFromString(
      const absl::Cord& data);

  // Like MergeFromString(), but accepts messages that are missing required
  // fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool MergePartialFromString(
      absl::string_view data);
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool MergePartialFromString(
      const absl::Cord& data);

  // Serialization ---------------------------------------------------
  // Methods for serializing in protocol buffer format.  Most of these
  // are just simple wrappers around ByteSize() and SerializeWithCachedSizes().

  // Write a protocol buffer of this message to the given output.  Returns
  // false on a write error.  If the message is missing required fields,
  // this may ABSL_CHECK-fail.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool SerializeToCodedStream(
      io::CodedOutputStream* output) const;
  // Like SerializeToCodedStream(), but allows missing required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool SerializePartialToCodedStream(
      io::CodedOutputStream* output) const;
  // Write the message to the given zero-copy output stream.  All required
  // fields must be set.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool SerializeToZeroCopyStream(
      io::ZeroCopyOutputStream* output) const;
  // Like SerializeToZeroCopyStream(), but allows missing required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool SerializePartialToZeroCopyStream(
      io::ZeroCopyOutputStream* output) const;
  // Serialize the message and store it in the given string.  All required
  // fields must be set.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool SerializeToString(
      std::string* output) const;
  // Serialize the message and store it in the given Cord.  All required
  // fields must be set.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool SerializeToString(
      absl::Cord* output) const;
  // Like SerializeToString(), but allows missing required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool SerializePartialToString(
      std::string* output) const;
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool SerializePartialToString(
      absl::Cord* output) const;
  // Serialize the message and store it in the given byte array.  All required
  // fields must be set.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool SerializeToArray(void* data,
                                                            int size) const;
  // Like SerializeToArray(), but allows missing required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool SerializePartialToArray(
      void* data, int size) const;

  // Make a string encoding the message. Is equivalent to calling
  // SerializeToString() on a string and using that.  Returns the empty
  // string if SerializeToString() would have returned an error.
  // Note: If you intend to generate many such strings, you may
  // reduce heap fragmentation by instead re-using the same string
  // object with calls to SerializeToString().
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD std::string SerializeAsString() const;
  // Like SerializeAsString(), but allows missing required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD std::string SerializePartialAsString()
      const;

  // Serialize the message and write it to the given file descriptor.  All
  // required fields must be set.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool SerializeToFileDescriptor(
      int file_descriptor) const;
  // Like SerializeToFileDescriptor(), but allows missing required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool SerializePartialToFileDescriptor(
      int file_descriptor) const;
  // Serialize the message and write it to the given C++ ostream.  All
  // required fields must be set.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool SerializeToOstream(
      std::ostream* output) const;
  // Like SerializeToOstream(), but allows missing required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool SerializePartialToOstream(
      std::ostream* output) const;

  // Like SerializeToString(), but appends to the data to the string's
  // existing contents.  All required fields must be set.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool AppendToString(
      std::string* output) const;
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool AppendToString(
      absl::Cord* output) const;
  // Like AppendToString(), but allows missing required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool AppendPartialToString(
      std::string* output) const;
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool AppendPartialToString(
      absl::Cord* output) const;

  // Reads a protocol buffer from a Cord and merges it into this message.
  PROTOBUF_DEPRECATE_AND_INLINE()
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD
  bool MergeFromCord(const absl::Cord& data) { return MergeFromString(data); }
  // Like MergeFromCord(), but accepts messages that are missing
  // required fields.
  PROTOBUF_DEPRECATE_AND_INLINE()
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool MergePartialFromCord(
      const absl::Cord& data) {
    return MergePartialFromString(data);
  }
  // Parse a protocol buffer contained in a Cord.
  PROTOBUF_DEPRECATE_AND_INLINE()
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParseFromCord(const absl::Cord& data) {
    return ParseFromString(data);
  }
  // Like ParseFromCord(), but accepts messages that are missing
  // required fields.
  PROTOBUF_DEPRECATE_AND_INLINE()
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD ABSL_ATTRIBUTE_REINITIALIZES bool
  ParsePartialFromCord(const absl::Cord& data) {
    return ParsePartialFromString(data);
  }

  // Serialize the message and store it in the given Cord.  All required
  // fields must be set.
  PROTOBUF_DEPRECATE_AND_INLINE()
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool SerializeToCord(
      absl::Cord* output) const {
    return SerializeToString(output);
  }
  // Like SerializeToCord(), but allows missing required fields.
  PROTOBUF_DEPRECATE_AND_INLINE()
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool SerializePartialToCord(
      absl::Cord* output) const {
    return SerializePartialToString(output);
  }

  // Make a Cord encoding the message. Is equivalent to calling
  // SerializeToCord() on a Cord and using that.  Returns an empty
  // Cord if SerializeToCord() would have returned an error.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD absl::Cord SerializeAsCord() const;
  // Like SerializeAsCord(), but allows missing required fields.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD absl::Cord SerializePartialAsCord() const;

  // Like SerializeToCord(), but appends to the data to the Cord's existing
  // contents.  All required fields must be set.
  PROTOBUF_DEPRECATE_AND_INLINE()
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD
  bool AppendToCord(absl::Cord* output) const { return AppendToString(output); }
  // Like AppendToCord(), but allows missing required fields.
  PROTOBUF_DEPRECATE_AND_INLINE()
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool AppendPartialToCord(
      absl::Cord* output) const {
    return AppendPartialToString(output);
  }

  // Computes the serialized size of the message.  This recursively calls
  // ByteSizeLong() on all embedded messages.
  //
  // ByteSizeLong() is generally linear in the number of fields defined for the
  // proto.
#if defined(PROTOBUF_CUSTOM_VTABLE)
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD size_t ByteSizeLong() const {
    return class_data()->byte_size_long(*this);
  }
#else
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD virtual size_t ByteSizeLong() const = 0;
#endif  // PROTOBUF_CUSTOM_VTABLE

  // Legacy ByteSize() API.
  [[deprecated(
      "Please use ByteSizeLong() "
      "instead")]] PROTOBUF_FUTURE_ADD_EARLY_NODISCARD int
  ByteSize() const {
    return internal::ToIntSize(ByteSizeLong());
  }

  // Serializes the message without recomputing the size.  The message must not
  // have changed since the last call to ByteSize(), and the value returned by
  // ByteSize must be non-negative.  Otherwise the results are undefined.
  void SerializeWithCachedSizes(io::CodedOutputStream* output) const {
    output->SetCur(_InternalSerialize(output->Cur(), output->EpsCopy()));
  }

  // Functions below here are not part of the public interface.  It isn't
  // enforced, but they should be treated as private, and will be private
  // at some future time.  Unfortunately the implementation of the "friend"
  // keyword in GCC is broken at the moment, but we expect it will be fixed.

  // Like SerializeWithCachedSizes, but writes directly to *target, returning
  // a pointer to the byte immediately after the last byte written.  "target"
  // must point at a byte array of at least ByteSize() bytes.  Whether to use
  // deterministic serialization, e.g., maps in sorted order, is determined by
  // CodedOutputStream::IsDefaultSerializationDeterministic().
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD uint8_t* SerializeWithCachedSizesToArray(
      uint8_t* target) const;

  // Returns the result of the last call to ByteSize().  An embedded message's
  // size is needed both to serialize it (only true for length-prefixed
  // submessages) and to compute the outer message's size.  Caching
  // the size avoids computing it multiple times.
  // Note that the submessage size is unnecessary when using
  // group encoding / delimited since we have SGROUP/EGROUP bounds.
  //
  // ByteSize() does not automatically use the cached size when available
  // because this would require invalidating it every time the message was
  // modified, which would be too hard and expensive.  (E.g. if a deeply-nested
  // sub-message is changed, all of its parents' cached sizes would need to be
  // invalidated, which is too much work for an otherwise inlined setter
  // method.)
#if defined(PROTOBUF_CUSTOM_VTABLE)
  [[nodiscard]] int GetCachedSize() const { return AccessCachedSize().Get(); }
#else
  [[nodiscard]] int GetCachedSize() const;
#endif

  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD const char* _InternalParse(
      const char* ptr, internal::ParseContext* ctx);

 protected:
#if defined(PROTOBUF_PROTECTED_MESSAGE_BASE_DESTRUCTOR)
  ~MessageLite() = default;
#endif  // PROTOBUF_PROTECTED_MESSAGE_BASE_DESTRUCTOR

  // Message implementations require access to internally visible API.
  static constexpr internal::InternalVisibility internal_visibility() {
    return internal::InternalVisibility{};
  }

  template <typename T>
  PROTOBUF_ALWAYS_INLINE static T* DefaultConstruct(Arena* arena) {
    return static_cast<T*>(Arena::DefaultConstruct<T>(arena));
  }

  template <typename T>
  static void* NewImpl(const void*, void* mem, Arena* arena) {
    return ::new (mem) T(arena);
  }
  template <typename T>
  static constexpr internal::MessageCreator GetNewImpl() {
    if constexpr (internal::EnableCustomNewFor<T>()) {
      return T::InternalNewImpl_();
    } else {
      return internal::MessageCreator(&T::PlacementNew_, sizeof(T), alignof(T));
    }
  }

  template <typename T>
  PROTOBUF_ALWAYS_INLINE static T* CopyConstruct(Arena* arena, const T& from) {
    return static_cast<T*>(Arena::CopyConstruct<T>(arena, &from));
  }

  // As above, but for fields that use base class type. Eg foreign weak fields.
  static MessageLite* CopyConstruct(Arena* arena, const MessageLite& from);

  PROTOBUF_ALWAYS_INLINE static Message* CopyConstruct(Arena* arena,
                                                       const Message& from) {
    return reinterpret_cast<Message*>(
        CopyConstruct(arena, reinterpret_cast<const MessageLite&>(from)));
  }

  const internal::TcParseTableBase* GetTcParseTable() const {
    auto* data = GetClassData();
    ABSL_DCHECK(data != nullptr);
    return data->GetTcParseTable();
  }

#if defined(PROTOBUF_CUSTOM_VTABLE)
  explicit constexpr MessageLite(const internal::ClassData* data)
      : _class_data_(data) {}
  explicit MessageLite(Arena* arena, const internal::ClassData* data)
      : _internal_metadata_(arena), _class_data_(data) {}
#else   // PROTOBUF_CUSTOM_VTABLE
  constexpr MessageLite() {}
  explicit MessageLite(Arena* arena) : _internal_metadata_(arena) {}
  explicit constexpr MessageLite(const internal::ClassData*) {}
  explicit MessageLite(Arena* arena, const internal::ClassData*)
      : _internal_metadata_(arena) {}
#endif  // PROTOBUF_CUSTOM_VTABLE

  // GetClassData() returns a pointer to a ClassData struct which
  // exists in global memory and is unique to each subclass.  This uniqueness
  // property is used in order to quickly determine whether two messages are
  // of the same type.
  //
  // This is a work in progress. There are still some types (eg MapEntry) that
  // return a default table instead of a unique one.
#if defined(PROTOBUF_CUSTOM_VTABLE)
  const internal::ClassData* class_data() const { return _class_data_; }
  const internal::ClassData* GetClassData() const {
    ::absl::PrefetchToLocalCache(_class_data_);
    return class_data();
  }
#else   // PROTOBUF_CUSTOM_VTABLE
  virtual const internal::ClassData* GetClassData() const = 0;
#endif  // PROTOBUF_CUSTOM_VTABLE

  // NOLINTNEXTLINE(google3-readability-class-member-naming)
  internal::InternalMetadata _internal_metadata_;
#if defined(PROTOBUF_CUSTOM_VTABLE)
  const internal::ClassData* _class_data_;
#endif  // PROTOBUF_CUSTOM_VTABLE

  // Return the cached size object as described by
  // ClassData::cached_size_offset.
  const internal::CachedSize& AccessCachedSize() const {
    return *reinterpret_cast<const internal::CachedSize*>(
        reinterpret_cast<const char*>(this) +
        GetClassData()->cached_size_offset);
  }

  // The following methods should be used to access has bits. They enable
  // measuring the cost of checking/setting has bits with inline frame data.
  static PROTOBUF_ALWAYS_INLINE constexpr void SetHasBit(
      uint32_t& cached_has_bits, uint32_t has_bit_mask) {
    cached_has_bits |= has_bit_mask;
  }

  static PROTOBUF_ALWAYS_INLINE constexpr void ClearHasBit(
      uint32_t& cached_has_bits, uint32_t has_bit_mask) {
    cached_has_bits &= ~has_bit_mask;
  }

  static PROTOBUF_ALWAYS_INLINE constexpr bool CheckHasBit(
      uint32_t cached_has_bits, uint32_t has_bit_mask) {
    return (cached_has_bits & has_bit_mask) != 0;
  }

  static PROTOBUF_ALWAYS_INLINE constexpr bool BatchCheckHasBit(
      uint32_t cached_has_bits, uint32_t batch_has_bits_mask) {
    return (cached_has_bits & batch_has_bits_mask) != 0;
  }

  void CheckHasBitConsistency() const;

 public:
  enum ParseFlags {
    // Merge vs. Parse:
    // Merge: overwrites scalar fields but appends to repeated fields in the
    //        destination; other fields in the destination remain untouched.
    // Parse: clears all fields in the destination before calling Merge.
    kMerge = 0,
    kParse = 1,
    // Default behaviour vs. Partial:
    // Default: a missing required field is deemed as parsing failure.
    // Partial: parse or merge will not give an error if input is missing
    //          required fields.
    kMergePartial = 2,
    kParsePartial = 3,
    // Default behaviour vs. Aliasing:
    // Default:  when merging, pointer is followed and expanded (deep-copy).
    // Aliasing: when merging, the destination message is allowed to retain
    //           pointers to the original structure (shallow-copy). This mostly
    //           is intended for use with STRING_PIECE.
    // NOTE: STRING_PIECE is not recommended for new usage. Prefer Cords.
    kMergeWithAliasing = 4,
    kParseWithAliasing = 5,
    kMergePartialWithAliasing = 6,
    kParsePartialWithAliasing = 7
  };

  template <ParseFlags flags, typename T>
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool ParseFrom(const T& input);

  // Fast path when conditions match (ie. non-deterministic)
  //  uint8_t* _InternalSerialize(uint8_t* ptr) const;
#if defined(PROTOBUF_CUSTOM_VTABLE)
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD uint8_t* _InternalSerialize(
      uint8_t* ptr, io::EpsCopyOutputStream* stream) const {
    return class_data()->serialize(*this, ptr, stream);
  }
#else   // PROTOBUF_CUSTOM_VTABLE
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD virtual uint8_t* _InternalSerialize(
      uint8_t* ptr, io::EpsCopyOutputStream* stream) const = 0;
#endif  // PROTOBUF_CUSTOM_VTABLE

  // Identical to IsInitialized() except that it logs an error message.
  PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool IsInitializedWithErrors() const {
    if (IsInitialized()) return true;
    LogInitializationErrorMessage();
    return false;
  }

#if defined(PROTOBUF_CUSTOM_VTABLE)
  void operator delete(MessageLite* msg, std::destroying_delete_t) {
    msg->DeleteInstance();
  }
#endif

 private:
  friend internal::ClassData;
  friend class internal::MessageCreator;
  friend class FastReflectionMessageMutator;
  friend class AssignDescriptorsHelper;
  friend class FastReflectionStringSetter;
  friend class Message;
  friend class Reflection;
  friend class TypeId;
  friend class compiler::cpp::MessageTableTester;
  friend class internal::DescriptorPoolExtensionFinder;
  friend class internal::ExtensionSet;
  friend class internal::HasBitsTestPeer;
  friend class internal::InternalMetadataOffset;
  template <typename T, size_t kFieldOffset>
  friend struct internal::InternalMetadataOffsetHelper;
  friend class internal::LazyField;
  friend internal::RepeatedPtrFieldBase;
  friend class internal::SwapFieldHelper;
  friend class internal::TcParser;
  friend struct internal::PrivateAccess;
  friend struct internal::TcParseTableBase;
  friend class internal::UntypedMapBase;
  friend class internal::WeakFieldMap;
  friend class internal::WireFormatLite;
  friend class internal::RustMapHelper;
  template <typename Type>
  friend class Arena::InternalHelper;

  template <typename MessageT>
  friend const internal::ClassData* internal::GetClassData(const MessageT& msg);

  static bool CheckFieldPresence(const internal::ParseContext& ctx,
                                 const MessageLite& msg,
                                 MessageLite::ParseFlags parse_flags);

  void LogInitializationErrorMessage() const;

 private:
  bool MergeFromImpl(io::CodedInputStream* input, ParseFlags parse_flags);

  // Runs the destructor for this instance.
  void DestroyInstance();
  // Runs the destructor for this instance and deletes the memory via
  // `operator delete`
  void DeleteInstance();

  // For tests that need to inspect private _oneof_case_. It is the callers
  // responsibility to ensure T has the right member.
  template <typename T>
  static uint32_t GetOneofCaseOffsetForTesting() {
    return offsetof(T, _impl_._oneof_case_);
  }
};

namespace internal {

template <bool alias>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool MergeFromImpl(
    absl::string_view input, MessageLite* msg,
    const internal::TcParseTableBase* tc_table,
    MessageLite::ParseFlags parse_flags);
extern template PROTOBUF_EXPORT_TEMPLATE_DECLARE bool MergeFromImpl<false>(
    absl::string_view input, MessageLite* msg,
    const internal::TcParseTableBase* tc_table,
    MessageLite::ParseFlags parse_flags);
extern template PROTOBUF_EXPORT_TEMPLATE_DECLARE bool MergeFromImpl<true>(
    absl::string_view input, MessageLite* msg,
    const internal::TcParseTableBase* tc_table,
    MessageLite::ParseFlags parse_flags);

template <bool alias>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool MergeFromImpl(
    io::ZeroCopyInputStream* input, MessageLite* msg,
    const internal::TcParseTableBase* tc_table,
    MessageLite::ParseFlags parse_flags);
extern template PROTOBUF_EXPORT_TEMPLATE_DECLARE bool MergeFromImpl<false>(
    io::ZeroCopyInputStream* input, MessageLite* msg,
    const internal::TcParseTableBase* tc_table,
    MessageLite::ParseFlags parse_flags);
extern template PROTOBUF_EXPORT_TEMPLATE_DECLARE bool MergeFromImpl<true>(
    io::ZeroCopyInputStream* input, MessageLite* msg,
    const internal::TcParseTableBase* tc_table,
    MessageLite::ParseFlags parse_flags);

struct BoundedZCIS {
  io::ZeroCopyInputStream* zcis;
  int limit;
};

template <bool alias>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool MergeFromImpl(
    BoundedZCIS input, MessageLite* msg,
    const internal::TcParseTableBase* tc_table,
    MessageLite::ParseFlags parse_flags);
extern template PROTOBUF_EXPORT_TEMPLATE_DECLARE bool MergeFromImpl<false>(
    BoundedZCIS input, MessageLite* msg,
    const internal::TcParseTableBase* tc_table,
    MessageLite::ParseFlags parse_flags);
extern template PROTOBUF_EXPORT_TEMPLATE_DECLARE bool MergeFromImpl<true>(
    BoundedZCIS input, MessageLite* msg,
    const internal::TcParseTableBase* tc_table,
    MessageLite::ParseFlags parse_flags);

template <typename T>
struct SourceWrapper;

template <bool alias, typename T>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool MergeFromImpl(
    const SourceWrapper<T>& input, MessageLite* msg,
    const internal::TcParseTableBase* tc_table,
    MessageLite::ParseFlags parse_flags) {
  return input.template MergeInto<alias>(msg, tc_table, parse_flags);
}

}  // namespace internal

template <MessageLite::ParseFlags flags, typename T>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD bool MessageLite::ParseFrom(
    const T& input) {
  if (flags & kParse) Clear();
  constexpr bool alias = (flags & kMergeWithAliasing) != 0;
  const internal::TcParseTableBase* tc_table;
  PROTOBUF_ALWAYS_INLINE_CALL tc_table = GetTcParseTable();
  return internal::MergeFromImpl<alias>(input, this, tc_table, flags);
}

// ===================================================================
// Shutdown support.


// Shut down the entire protocol buffers library, deleting all static-duration
// objects allocated by the library or by generated .pb.cc files.
//
// There are two reasons you might want to call this:
// * You use a draconian definition of "memory leak" in which you expect
//   every single malloc() to have a corresponding free(), even for objects
//   which live until program exit.
// * You are writing a dynamically-loaded library which needs to clean up
//   after itself when the library is unloaded.
//
// It is safe to call this multiple times.  However, it is not safe to use
// any other part of the protocol buffers library after
// ShutdownProtobufLibrary() has been called. Furthermore this call is not
// thread safe, user needs to synchronize multiple calls.
PROTOBUF_EXPORT void ShutdownProtobufLibrary();

namespace internal {

// Register a function to be called when ShutdownProtocolBuffers() is called.
PROTOBUF_EXPORT void OnShutdown(void (*func)());
// Run an arbitrary function on an arg
PROTOBUF_EXPORT void OnShutdownRun(void (*f)(const void*), const void* arg);

template <typename T>
T* OnShutdownDelete(T* p) {
  OnShutdownRun([](const void* pp) { delete static_cast<const T*>(pp); }, p);
  return p;
}

PROTOBUF_ALWAYS_INLINE MessageLite* ClassData::New(Arena* arena) const {
  // Allocate the memory first, to reduce the number of spills.
  // This way we only spill `this` and `arena`.
  void* mem = message_creator.AllocateMessage(arena);
  const MessageLite* def = default_instance();
  return message_creator.PlacementNew(def, def, mem, arena);
}

PROTOBUF_ALWAYS_INLINE MessageLite* ClassData::PlacementNew(
    void* mem, Arena* arena) const {
  const MessageLite* def = default_instance();
  return message_creator.PlacementNew(def, def, mem, arena);
}

template <typename MessageLite>
PROTOBUF_ALWAYS_INLINE MessageLite* MessageCreator::PlacementNew(
    const MessageLite* prototype_for_func,
    const MessageLite* prototype_for_copy, void* mem, Arena* arena) const {
  ABSL_DCHECK_EQ(reinterpret_cast<uintptr_t>(mem) % alignment_, 0u);
  const Tag as_tag = tag();
  static_assert(kFunc < 0 && !(kZeroInit < 0) && !(kMemcpy < 0),
                "Only kFunc must be the only negative value");
  if (ABSL_PREDICT_FALSE(static_cast<int8_t>(as_tag) < 0)) {
    PROTOBUF_DEBUG_COUNTER("MessageCreator.Func").Inc();
    return static_cast<MessageLite*>(func_(prototype_for_func, mem, arena));
  }

  char* dst = static_cast<char*>(mem);
  const size_t size = allocation_size_;
  const char* src = reinterpret_cast<const char*>(prototype_for_copy);

  // These are a bit more efficient than calling normal memset/memcpy because:
  //  - We know the minimum size is 16. We have a fallback for when it is not.
  //  - We can "underflow" the buffer because those are the MessageLite bytes
  //    we will set later.
  if (as_tag == kZeroInit) {
    PROTOBUF_DEBUG_COUNTER("MessageCreator.ZeroInit").IncLog(size);
    // Make sure the input is really all zeros.
    ABSL_DCHECK(std::all_of(src + sizeof(MessageLite), src + size,
                            [](auto c) { return c == 0; }));

    if (sizeof(MessageLite) != 16) {
      memset(dst, 0, size);
    } else if (size <= 32) {
      memset(dst + size - 16, 0, 16);
    } else if (size <= 64) {
      memset(dst + 16, 0, 16);
      memset(dst + size - 32, 0, 32);
    } else {
      for (size_t offset = 16; offset + 64 < size; offset += 64) {
        absl::PrefetchToLocalCacheForWrite(dst + offset + 64);
        memset(dst + offset, 0, 64);
      }
      memset(dst + size - 64, 0, 64);
    }
  } else {
    PROTOBUF_DEBUG_COUNTER("MessageCreator.Memcpy").IncLog(size);
    ABSL_DCHECK_EQ(+as_tag, +kMemcpy);

    if (sizeof(MessageLite) != 16) {
      memcpy(dst, src, size);
    } else if (size <= 32) {
      memcpy(dst + size - 16, src + size - 16, 16);
    } else if (size <= 64) {
      memcpy(dst + 16, src + 16, 16);
      memcpy(dst + size - 32, src + size - 32, 32);
    } else {
      for (size_t offset = 16; offset + 64 < size; offset += 64) {
        absl::PrefetchToLocalCache(src + offset + 64);
        absl::PrefetchToLocalCacheForWrite(dst + offset + 64);
        memcpy(dst + offset, src + offset, 64);
      }
      memcpy(dst + size - 64, src + size - 64, 64);
    }
  }

  // The second memcpy overwrites part of the first, but the compiler should
  // avoid the double-write. It's easier than trying to avoid the overlap.
  memcpy(dst, static_cast<const void*>(prototype_for_copy),
         sizeof(MessageLite));
  memcpy(dst + PROTOBUF_FIELD_OFFSET(MessageLite, _internal_metadata_), &arena,
         sizeof(arena));
  return Launder(reinterpret_cast<MessageLite*>(mem));
}

// Returns either a string literal "Message" / "MessageLite", or a pointer to a
// default message instance which we can call `GetTypeName()` on.
template <typename T>
auto GetTypeNameResolver() {
  if constexpr (std::is_same_v<T, MessageLite>) {
    return "MessageLite";
  } else if constexpr (std::is_same_v<T, Message>) {
    return "Message";
  } else {
    return &T::default_instance();
  }
}

}  // namespace internal

PROTOBUF_FUTURE_ADD_EARLY_NODISCARD
std::string ShortFormat(const MessageLite& message_lite);
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD
std::string Utf8Format(const MessageLite& message_lite);

// Cast functions for message pointer/references.
// This is the supported API to cast from a Message/MessageLite to derived
// types. These work even when RTTI is disabled on message types.
//
// The template parameter is simplified and the return type is inferred from the
// input. Eg just `DynamicCastMessage<Foo>(x)` instead of
// `DynamicCastMessage<const Foo*>(x)`.
//
// `DynamicCastMessage` is similar to `dynamic_cast`, returns `nullptr` when the
// input is not an instance of `T`. The overloads that take a reference will
// throw std::bad_cast on mismatch, or terminate if compiled without exceptions.
//
// `DownCastMessage` is a lightweight function for downcasting base
// `MessageLite` pointer to derived type, where it only does type checking if
// !NDEBUG. It should only be used when the caller is certain that the input
// message is of instance `T`.
template <typename T>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD const T* DynamicCastMessage(
    const MessageLite* from) {
  static_assert(std::is_base_of_v<MessageLite, T>, "");

  if constexpr (std::is_same_v<T, MessageLite>) {
    return from;
  } else if constexpr (std::is_same_v<T, Message>) {
    if (from == nullptr || internal::GetClassData(*from)->is_lite) {
      return nullptr;
    }
    // We have to reinterpret_cast here in case `Message` is incomplete.
    return reinterpret_cast<const Message*>(from);
  } else {
    if (from == nullptr || TypeId::Get<T>() != TypeId::Get(*from)) {
      return nullptr;
    }
    return static_cast<const T*>(from);
  }
}

template <typename T>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD T* DynamicCastMessage(MessageLite* from) {
  return const_cast<T*>(
      DynamicCastMessage<T>(static_cast<const MessageLite*>(from)));
}

namespace internal {
// Takes either a `const char*` string literal as the `To` type name, or a
// pointer to a message prototype that we can call `GetTypeName()` on. This is
// done to minimize code bloat in the caller, since dynamic casts are inlined.
[[noreturn]] PROTOBUF_EXPORT void FailDynamicCast(
    const MessageLite& from,
    std::variant<const char*, const MessageLite*> to_type_name);
}  // namespace internal

template <typename T>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD const T& DynamicCastMessage(
    const MessageLite& from) {
  const T* destination_message = DynamicCastMessage<T>(&from);
  if (ABSL_PREDICT_FALSE(destination_message == nullptr)) {
    // If exceptions are enabled, throw.
    // Otherwise, log a fatal error.
#if defined(ABSL_HAVE_EXCEPTIONS)
    throw std::bad_cast();
#endif
    // Move the logging into an out-of-line function to reduce bloat in the
    // caller.
    internal::FailDynamicCast(from, internal::GetTypeNameResolver<T>());
  }
  return *destination_message;
}

template <typename T>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD T& DynamicCastMessage(MessageLite& from) {
  return const_cast<T&>(
      DynamicCastMessage<T>(static_cast<const MessageLite&>(from)));
}

template <typename T>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD const T* DownCastMessage(
    const MessageLite* from) {
  if constexpr (!std::is_same_v<T, MessageLite> &&
                !std::is_same_v<T, Message>) {
    internal::StrongReferenceToType<T>();
  }
  if constexpr (internal::PerformDebugChecks()) {
    if (DynamicCastMessage<T>(from) != from) {
      internal::FailDynamicCast(*from, internal::GetTypeNameResolver<T>());
    }
  }
  return static_cast<const T*>(from);
}

template <typename T>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD T* DownCastMessage(MessageLite* from) {
  return const_cast<T*>(
      DownCastMessage<T>(static_cast<const MessageLite*>(from)));
}

template <typename T>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD const T& DownCastMessage(
    const MessageLite& from) {
  return *DownCastMessage<T>(&from);
}

template <typename T>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD T& DownCastMessage(MessageLite& from) {
  return *DownCastMessage<T>(&from);
}

// Deprecated names for the cast functions.
// Prefer the ones above.
template <typename T>
PROTOBUF_DEPRECATE_AND_INLINE()
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD const T* DynamicCastToGenerated(
    const MessageLite* from) {
  return DynamicCastMessage<T>(from);
}

template <typename T>
PROTOBUF_DEPRECATE_AND_INLINE()
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD T* DynamicCastToGenerated(
    MessageLite* from) {
  return DynamicCastMessage<T>(from);
}

template <typename T>
PROTOBUF_DEPRECATE_AND_INLINE()
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD const T& DynamicCastToGenerated(
    const MessageLite& from) {
  return DynamicCastMessage<T>(from);
}

template <typename T>
PROTOBUF_DEPRECATE_AND_INLINE()
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD T& DynamicCastToGenerated(
    MessageLite& from) {
  return DynamicCastMessage<T>(from);
}

template <typename T>
PROTOBUF_DEPRECATE_AND_INLINE()
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD const T* DownCastToGenerated(
    const MessageLite* from) {
  return DownCastMessage<T>(from);
}

template <typename T>
PROTOBUF_DEPRECATE_AND_INLINE()

PROTOBUF_FUTURE_ADD_EARLY_NODISCARD T* DownCastToGenerated(MessageLite* from) {
  return DownCastMessage<T>(from);
}

template <typename T>

PROTOBUF_DEPRECATE_AND_INLINE()
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD const T& DownCastToGenerated(
    const MessageLite& from) {
  return DownCastMessage<T>(from);
}

template <typename T>
PROTOBUF_DEPRECATE_AND_INLINE()
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD T& DownCastToGenerated(MessageLite& from) {
  return DownCastMessage<T>(from);
}

// Overloads for `std::shared_ptr` to substitute `std::dynamic_pointer_cast`
template <typename T>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD std::shared_ptr<T> DynamicCastMessage(
    std::shared_ptr<MessageLite> ptr) {
  if (auto* res = DynamicCastMessage<T>(ptr.get())) {
    // Use aliasing constructor to keep the same control block.
    return std::shared_ptr<T>(std::move(ptr), res);
  } else {
    return nullptr;
  }
}

template <typename T>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD std::shared_ptr<const T> DynamicCastMessage(
    std::shared_ptr<const MessageLite> ptr) {
  if (auto* res = DynamicCastMessage<T>(ptr.get())) {
    // Use aliasing constructor to keep the same control block.
    return std::shared_ptr<const T>(std::move(ptr), res);
  } else {
    return nullptr;
  }
}

// Overloads for `std::shared_ptr` to substitute `down_pointer_cast`
template <typename T>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD std::shared_ptr<T> DownCastMessage(
    std::shared_ptr<MessageLite> ptr) {
  auto* res = DownCastMessage<T>(ptr.get());
  // Use aliasing constructor to keep the same control block.
  return std::shared_ptr<T>(std::move(ptr), res);
}

template <typename T>
PROTOBUF_FUTURE_ADD_EARLY_NODISCARD std::shared_ptr<const T> DownCastMessage(
    std::shared_ptr<const MessageLite> ptr) {
  auto* res = DownCastMessage<T>(ptr.get());
  // Use aliasing constructor to keep the same control block.
  return std::shared_ptr<const T>(std::move(ptr), res);
}

}  // namespace protobuf
}  // namespace google

#include "google/protobuf/port_undef.inc"

#endif  // GOOGLE_PROTOBUF_MESSAGE_LITE_H__