FlattenedGeneratedMessageV3.java

// 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

package com.google.protobuf;

import com.google.protobuf.Descriptors.Descriptor;
import com.google.protobuf.Descriptors.EnumDescriptor;
import com.google.protobuf.Descriptors.EnumValueDescriptor;
import com.google.protobuf.Descriptors.FieldDescriptor;
import com.google.protobuf.Descriptors.FileDescriptor;
import com.google.protobuf.Descriptors.OneofDescriptor;
import com.google.protobuf.Internal.BooleanList;
import com.google.protobuf.Internal.DoubleList;
import com.google.protobuf.Internal.FloatList;
import com.google.protobuf.Internal.IntList;
import com.google.protobuf.Internal.LongList;
import com.google.protobuf.Internal.ProtobufList;

import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.ObjectStreamException;
import java.io.OutputStream;
import java.io.Serializable;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;

import static com.google.protobuf.Internal.checkNotNull;

/**
 * All generated protocol message classes extend this class. This class implements most of the
 * Message and Builder interfaces using Java reflection. Users can ignore this class and pretend
 * that generated messages implement the Message interface directly.
 *
 * @author kenton@google.com Kenton Varda
 */
abstract class FlattenedGeneratedMessageV3 extends AbstractMessage implements Serializable {
  private static final long serialVersionUID = 1L;

  /**
   * For testing. Allows a test to disable the optimization that avoids using field builders for
   * nested messages until they are requested. By disabling this optimization, existing tests can be
   * reused to test the field builders.
   */
  protected static boolean alwaysUseFieldBuilders = false;

  /**
   * For use by generated code only.
   *
   * <p>TODO: mark this private and final (breaking change)
   */
  protected UnknownFieldSet unknownFields;

  protected FlattenedGeneratedMessageV3() {
    unknownFields = UnknownFieldSet.getDefaultInstance();
  }

  protected FlattenedGeneratedMessageV3(Builder<?> builder) {
    unknownFields = builder.getUnknownFields();
  }

  protected int memoizedHashCode = 0;

  public ByteString toByteString() {
    try {
      final ByteString.CodedBuilder out = ByteString.newCodedBuilder(getSerializedSize());
      writeTo(out.getCodedOutput());
      return out.build();
    } catch (IOException e) {
      throw new RuntimeException(getSerializingExceptionMessage("ByteString"), e);
    }
  }

  public byte[] toByteArray() {
    try {
      final byte[] result = new byte[getSerializedSize()];
      final CodedOutputStream output = CodedOutputStream.newInstance(result);
      writeTo(output);
      output.checkNoSpaceLeft();
      return result;
    } catch (IOException e) {
      throw new RuntimeException(getSerializingExceptionMessage("byte array"), e);
    }
  }

  public void writeTo(final OutputStream output) throws IOException {
    final int bufferSize = CodedOutputStream.computePreferredBufferSize(getSerializedSize());
    final CodedOutputStream codedOutput = CodedOutputStream.newInstance(output, bufferSize);
    writeTo(codedOutput);
    codedOutput.flush();
  }

  public void writeDelimitedTo(final OutputStream output) throws IOException {
    final int serialized = getSerializedSize();
    final int bufferSize =
            CodedOutputStream.computePreferredBufferSize(
                    CodedOutputStream.computeUInt32SizeNoTag(serialized) + serialized);
    final CodedOutputStream codedOutput = CodedOutputStream.newInstance(output, bufferSize);
    codedOutput.writeUInt32NoTag(serialized);
    writeTo(codedOutput);
    codedOutput.flush();
  }

  int getSerializedSize(
          Schema schema) {
    int memoizedSerializedSize = getMemoizedSerializedSize();
    if (memoizedSerializedSize == -1) {
      memoizedSerializedSize = schema.getSerializedSize(this);
      setMemoizedSerializedSize(memoizedSerializedSize);
    }
    return memoizedSerializedSize;
  }

  private String getSerializingExceptionMessage(String target) {
    return "Serializing "
            + getClass().getName()
            + " to a "
            + target
            + " threw an IOException (should never happen).";
  }

  protected static void checkByteStringIsUtf8(ByteString byteString)
          throws IllegalArgumentException {
    if (!byteString.isValidUtf8()) {
      throw new IllegalArgumentException("Byte string is not UTF-8.");
    }
  }

  /** Interface for an enum which signifies which field in a {@code oneof} was specified. */
  protected interface InternalOneOfEnum {
    /**
     * Retrieves the field number of the field which was set in this {@code oneof}, or {@code 0} if
     * none were.
     */
    int getNumber();
  }

  /**
   * Interface for the parent of a Builder that allows the builder to communicate invalidations back
   * to the parent for use when using nested builders.
   */
  protected interface BuilderParent extends Message.BuilderParent{

    /**
     * A builder becomes dirty whenever a field is modified -- including fields in nested builders
     * -- and becomes clean when build() is called. Thus, when a builder becomes dirty, all its
     * parents become dirty as well, and when it becomes clean, all its children become clean. The
     * dirtiness state is used to invalidate certain cached values.
     *
     * <p>To this end, a builder calls markDirty() on its parent whenever it transitions from clean
     * to dirty. The parent must propagate this call to its own parent, unless it was already dirty,
     * in which case the grandparent must necessarily already be dirty as well. The parent can only
     * transition back to "clean" after calling build() on all children.
     */
    void markDirty();
  }

  public List<String> findInitializationErrors() {
    return MessageReflection.findMissingFields(this);
  }

  public String getInitializationErrorString() {
    return MessageReflection.delimitWithCommas(findInitializationErrors());
  }

  protected int memoizedSize = -1;

  int getMemoizedSerializedSize() {
    return memoizedSize;
  }

  void setMemoizedSerializedSize(int size) {
    memoizedSize = size;
  }

  @Override
  public boolean equals(final Object other) {
    if (other == this) {
      return true;
    }
    if (!(other instanceof Message)) {
      return false;
    }
    final Message otherMessage = (Message) other;
    if (getDescriptorForType() != otherMessage.getDescriptorForType()) {
      return false;
    }
    return compareFields(getAllFields(), otherMessage.getAllFields())
            && getUnknownFields().equals(otherMessage.getUnknownFields());
  }

  @Override
  public int hashCode() {
    int hash = memoizedHashCode;
    if (hash == 0) {
      hash = 41;
      hash = (19 * hash) + getDescriptorForType().hashCode();
      hash = hashFields(hash, getAllFields());
      hash = (29 * hash) + getUnknownFields().hashCode();
      memoizedHashCode = hash;
    }
    return hash;
  }

  private static ByteString toByteString(Object value) {
    if (value instanceof byte[]) {
      return ByteString.copyFrom((byte[]) value);
    } else {
      return (ByteString) value;
    }
  }

  /**
   * Compares two bytes fields. The parameters must be either a byte array or a ByteString object.
   * They can be of different type though.
   */
  private static boolean compareBytes(Object a, Object b) {
    if (a instanceof byte[] && b instanceof byte[]) {
      return Arrays.equals((byte[]) a, (byte[]) b);
    }
    return toByteString(a).equals(toByteString(b));
  }

  /** Converts a list of MapEntry messages into a Map used for equals() and hashCode(). */
  @SuppressWarnings({"rawtypes", "unchecked"})
  private static Map convertMapEntryListToMap(List list) {
    if (list.isEmpty()) {
      return Collections.emptyMap();
    }
    Map result = new HashMap<>();
    Iterator iterator = list.iterator();
    Message entry = (Message) iterator.next();
    Descriptor descriptor = entry.getDescriptorForType();
    FieldDescriptor key = descriptor.findFieldByName("key");
    FieldDescriptor value = descriptor.findFieldByName("value");
    Object fieldValue = entry.getField(value);
    if (fieldValue instanceof EnumValueDescriptor) {
      fieldValue = ((EnumValueDescriptor) fieldValue).getNumber();
    }
    result.put(entry.getField(key), fieldValue);
    while (iterator.hasNext()) {
      entry = (Message) iterator.next();
      fieldValue = entry.getField(value);
      if (fieldValue instanceof EnumValueDescriptor) {
        fieldValue = ((EnumValueDescriptor) fieldValue).getNumber();
      }
      result.put(entry.getField(key), fieldValue);
    }
    return result;
  }

  /** Compares two map fields. The parameters must be a list of MapEntry messages. */
  @SuppressWarnings({"rawtypes", "unchecked"})
  private static boolean compareMapField(Object a, Object b) {
    Map ma = convertMapEntryListToMap((List) a);
    Map mb = convertMapEntryListToMap((List) b);
    return MapFieldLite.equals(ma, mb);
  }

  /**
   * Compares two sets of fields. This method is used to implement {@link
   * AbstractMessage#equals(Object)} and {@link AbstractMutableMessage#equals(Object)}. It takes
   * special care of bytes fields because immutable messages and mutable messages use different Java
   * type to represent a bytes field and this method should be able to compare immutable messages,
   * mutable messages and also an immutable message to a mutable message.
   */
  static boolean compareFields(Map<FieldDescriptor, Object> a, Map<FieldDescriptor, Object> b) {
    if (a.size() != b.size()) {
      return false;
    }
    for (FieldDescriptor descriptor : a.keySet()) {
      if (!b.containsKey(descriptor)) {
        return false;
      }
      Object value1 = a.get(descriptor);
      Object value2 = b.get(descriptor);
      if (descriptor.getType() == FieldDescriptor.Type.BYTES) {
        if (descriptor.isRepeated()) {
          List<?> list1 = (List) value1;
          List<?> list2 = (List) value2;
          if (list1.size() != list2.size()) {
            return false;
          }
          for (int i = 0; i < list1.size(); i++) {
            if (!compareBytes(list1.get(i), list2.get(i))) {
              return false;
            }
          }
        } else {
          // Compares a singular bytes field.
          if (!compareBytes(value1, value2)) {
            return false;
          }
        }
      } else if (descriptor.isMapField()) {
        if (!compareMapField(value1, value2)) {
          return false;
        }
      } else {
        // Compare non-bytes fields.
        if (!value1.equals(value2)) {
          return false;
        }
      }
    }
    return true;
  }

  /** Calculates the hash code of a map field. {@code value} must be a list of MapEntry messages. */
  @SuppressWarnings("unchecked")
  private static int hashMapField(Object value) {
    return MapFieldLite.calculateHashCodeForMap(convertMapEntryListToMap((List) value));
  }

  /** Get a hash code for given fields and values, using the given seed. */
  @SuppressWarnings("unchecked")
  protected static int hashFields(int hash, Map<FieldDescriptor, Object> map) {
    for (Map.Entry<FieldDescriptor, Object> entry : map.entrySet()) {
      FieldDescriptor field = entry.getKey();
      Object value = entry.getValue();
      hash = (37 * hash) + field.getNumber();
      if (field.isMapField()) {
        hash = (53 * hash) + hashMapField(value);
      } else if (field.getType() != FieldDescriptor.Type.ENUM) {
        hash = (53 * hash) + value.hashCode();
      } else if (field.isRepeated()) {
        List<? extends Internal.EnumLite> list = (List<? extends Internal.EnumLite>) value;
        hash = (53 * hash) + Internal.hashEnumList(list);
      } else {
        hash = (53 * hash) + Internal.hashEnum((Internal.EnumLite) value);
      }
    }
    return hash;
  }

//  /**
//   * Package private helper method for AbstractParser to create UninitializedMessageException with
//   * missing field information.
//   */
//  UninitializedMessageException newUninitializedMessageException() {
//    return AbstractMessage.Builder.newUninitializedMessageException(this);
//  }

  /** TODO: Remove this unnecessary intermediate implementation of this method. */
  @Override
  public Parser<? extends FlattenedGeneratedMessageV3> getParserForType() {
    throw new UnsupportedOperationException("This is supposed to be overridden by subclasses.");
  }

  /**
   * TODO: Stop using SingleFieldBuilder and remove this setting
   *
   * @see #setAlwaysUseFieldBuildersForTesting(boolean)
   */
  static void enableAlwaysUseFieldBuildersForTesting() {
    setAlwaysUseFieldBuildersForTesting(true);
  }

  /**
   * For testing. Allows a test to disable/re-enable the optimization that avoids using field
   * builders for nested messages until they are requested. By disabling this optimization, existing
   * tests can be reused to test the field builders. See {@link RepeatedFieldBuilder} and {@link
   * SingleFieldBuilder}.
   *
   * <p>TODO: Stop using SingleFieldBuilder and remove this setting
   */
  static void setAlwaysUseFieldBuildersForTesting(boolean useBuilders) {
    alwaysUseFieldBuilders = useBuilders;
  }

  /**
   * Get the FieldAccessorTable for this type. We can't have the message class pass this in to the
   * constructor because of bootstrapping trouble with DescriptorProtos.
   */
  protected abstract FieldAccessorTable internalGetFieldAccessorTable();

  public Descriptor getDescriptorForType() {
    return internalGetFieldAccessorTable().descriptor;
  }

  /**
   * TODO: This method should be removed. It enables parsing directly into an
   * "immutable" message. Have to leave it for now to support old gencode.
   *
   * @deprecated use newBuilder().mergeFrom() instead
   */
  @Deprecated
  protected void mergeFromAndMakeImmutableInternal(
      CodedInputStream input, ExtensionRegistryLite extensionRegistry)
      throws InvalidProtocolBufferException {
    Schema<FlattenedGeneratedMessageV3> schema = Protobuf.getInstance().schemaFor(this);
    try {
      schema.mergeFrom(this, CodedInputStreamReader.forCodedInput(input), extensionRegistry);
    } catch (InvalidProtocolBufferException e) {
      throw e.setUnfinishedMessage(this);
    } catch (IOException e) {
      throw new InvalidProtocolBufferException(e).setUnfinishedMessage(this);
    }
    schema.makeImmutable(this);
  }

  /**
   * Internal helper to return a modifiable map containing all the fields. The returned Map is
   * modifiable so that the caller can add additional extension fields to implement {@link
   * #getAllFields()}.
   *
   * @param getBytesForString whether to generate ByteString for string fields
   */
  private Map<FieldDescriptor, Object> getAllFieldsMutable(boolean getBytesForString) {
    final TreeMap<FieldDescriptor, Object> result = new TreeMap<>();
    final Descriptor descriptor = internalGetFieldAccessorTable().descriptor;
    final List<FieldDescriptor> fields = descriptor.getFields();

    for (int i = 0; i < fields.size(); i++) {
      FieldDescriptor field = fields.get(i);
      final OneofDescriptor oneofDescriptor = field.getContainingOneof();

      /*
       * If the field is part of a Oneof, then at maximum one field in the Oneof is set
       * and it is not repeated. There is no need to iterate through the others.
       */
      if (oneofDescriptor != null) {
        // Skip other fields in the Oneof we know are not set
        i += oneofDescriptor.getFieldCount() - 1;
        if (!hasOneof(oneofDescriptor)) {
          // If no field is set in the Oneof, skip all the fields in the Oneof
          continue;
        }
        // Get the pointer to the only field which is set in the Oneof
        field = getOneofFieldDescriptor(oneofDescriptor);
      } else {
        // If we are not in a Oneof, we need to check if the field is set and if it is repeated
        if (field.isRepeated()) {
          final List<?> value = (List<?>) getField(field);
          if (!value.isEmpty()) {
            result.put(field, value);
          }
          continue;
        }
        if (!hasField(field)) {
          continue;
        }
      }
      // Add the field to the map
      if (getBytesForString && field.getJavaType() == FieldDescriptor.JavaType.STRING) {
        result.put(field, getFieldRaw(field));
      } else {
        result.put(field, getField(field));
      }
    }
    return result;
  }

  // TODO: compute this at {@code build()} time in the Builder class.
  public boolean isInitialized() {
    for (final FieldDescriptor field : getDescriptorForType().getFields()) {
      // Check that all required fields are present.
      if (field.isRequired()) {
        if (!hasField(field)) {
          return false;
        }
      }
      // Check that embedded messages are initialized.
      if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
        if (field.isRepeated()) {
          @SuppressWarnings("unchecked")
          final List<Message> messageList = (List<Message>) getField(field);
          for (final Message element : messageList) {
            if (!element.isInitialized()) {
              return false;
            }
          }
        } else {
          if (hasField(field) && !((Message) getField(field)).isInitialized()) {
            return false;
          }
        }
      }
    }

    return true;
  }

  public Map<FieldDescriptor, Object> getAllFields() {
    return Collections.unmodifiableMap(getAllFieldsMutable(/* getBytesForString= */ false));
  }

  /**
   * Returns a collection of all the fields in this message which are set and their corresponding
   * values. A singular ("required" or "optional") field is set iff hasField() returns true for that
   * field. A "repeated" field is set iff getRepeatedFieldCount() is greater than zero. The values
   * are exactly what would be returned by calling {@link #getFieldRaw(FieldDescriptor)}
   * for each field. The map is guaranteed to be a sorted map, so iterating over it will return
   * fields in order by field number.
   */
  Map<FieldDescriptor, Object> getAllFieldsRaw() {
    return Collections.unmodifiableMap(getAllFieldsMutable(/* getBytesForString= */ true));
  }

  public boolean hasOneof(final OneofDescriptor oneof) {
    return internalGetFieldAccessorTable().getOneof(oneof).has(this);
  }

  public FieldDescriptor getOneofFieldDescriptor(final OneofDescriptor oneof) {
    return internalGetFieldAccessorTable().getOneof(oneof).get(this);
  }

  public boolean hasField(final FieldDescriptor field) {
    return internalGetFieldAccessorTable().getField(field).has(this);
  }

  public Object getField(final FieldDescriptor field) {
    return internalGetFieldAccessorTable().getField(field).get(this);
  }

  /**
   * Obtains the value of the given field, or the default value if it is not set. For primitive
   * fields, the boxed primitive value is returned. For enum fields, the EnumValueDescriptor for the
   * value is returned. For embedded message fields, the sub-message is returned. For repeated
   * fields, a java.util.List is returned. For present string fields, a ByteString is returned
   * representing the bytes that the field contains.
   */
  Object getFieldRaw(final FieldDescriptor field) {
    return internalGetFieldAccessorTable().getField(field).getRaw(this);
  }

  public int getRepeatedFieldCount(final FieldDescriptor field) {
    return internalGetFieldAccessorTable().getField(field).getRepeatedCount(this);
  }

  public Object getRepeatedField(final FieldDescriptor field, final int index) {
    return internalGetFieldAccessorTable().getField(field).getRepeated(this, index);
  }

  // TODO: This method should be final.
  public UnknownFieldSet getUnknownFields() {
    return unknownFields;
  }

  // TODO: This should go away when Schema classes cannot modify immutable
  // GeneratedMessageV3 objects anymore.
  void setUnknownFields(UnknownFieldSet unknownFields) {
    this.unknownFields = unknownFields;
  }

  /**
   * Called by subclasses to parse an unknown field.
   *
   * <p>TODO remove this method
   *
   * @return {@code true} unless the tag is an end-group tag.
   */
  protected boolean parseUnknownField(
      CodedInputStream input,
      UnknownFieldSet.Builder unknownFields,
      ExtensionRegistryLite extensionRegistry,
      int tag)
      throws IOException {
    if (input.shouldDiscardUnknownFields()) {
      return input.skipField(tag);
    }
    return unknownFields.mergeFieldFrom(tag, input);
  }

  /**
   * Delegates to parseUnknownField. This method is obsolete, but we must retain it for
   * compatibility with older generated code.
   *
   * <p>TODO remove this method
   */
  protected boolean parseUnknownFieldProto3(
      CodedInputStream input,
      UnknownFieldSet.Builder unknownFields,
      ExtensionRegistryLite extensionRegistry,
      int tag)
      throws IOException {
    return parseUnknownField(input, unknownFields, extensionRegistry, tag);
  }

  /** Used by generated code. */
  @SuppressWarnings("ProtoParseWithRegistry")
  protected static <M extends Message> M parseWithIOException(Parser<M> parser, InputStream input)
      throws IOException {
    try {
      return parser.parseFrom(input);
    } catch (InvalidProtocolBufferException e) {
      throw e.unwrapIOException();
    }
  }

  /** Used by generated code. */
  protected static <M extends Message> M parseWithIOException(
      Parser<M> parser, InputStream input, ExtensionRegistryLite extensions) throws IOException {
    try {
      return parser.parseFrom(input, extensions);
    } catch (InvalidProtocolBufferException e) {
      throw e.unwrapIOException();
    }
  }

  /** Used by generated code. */
  @SuppressWarnings("ProtoParseWithRegistry")
  protected static <M extends Message> M parseWithIOException(
      Parser<M> parser, CodedInputStream input) throws IOException {
    try {
      return parser.parseFrom(input);
    } catch (InvalidProtocolBufferException e) {
      throw e.unwrapIOException();
    }
  }

  /** Used by generated code. */
  protected static <M extends Message> M parseWithIOException(
      Parser<M> parser, CodedInputStream input, ExtensionRegistryLite extensions)
      throws IOException {
    try {
      return parser.parseFrom(input, extensions);
    } catch (InvalidProtocolBufferException e) {
      throw e.unwrapIOException();
    }
  }

  /** Used by generated code. */
  @SuppressWarnings("ProtoParseWithRegistry")
  protected static <M extends Message> M parseDelimitedWithIOException(
      Parser<M> parser, InputStream input) throws IOException {
    try {
      return parser.parseDelimitedFrom(input);
    } catch (InvalidProtocolBufferException e) {
      throw e.unwrapIOException();
    }
  }

  /** Used by generated code. */
  protected static <M extends Message> M parseDelimitedWithIOException(
      Parser<M> parser, InputStream input, ExtensionRegistryLite extensions) throws IOException {
    try {
      return parser.parseDelimitedFrom(input, extensions);
    } catch (InvalidProtocolBufferException e) {
      throw e.unwrapIOException();
    }
  }

  protected static boolean canUseUnsafe() {
    return UnsafeUtil.hasUnsafeArrayOperations() && UnsafeUtil.hasUnsafeByteBufferOperations();
  }

  protected static IntList emptyIntList() {
    return IntArrayList.emptyList();
  }

  // TODO: Unused. Remove.
  protected static IntList newIntList() {
    return new IntArrayList();
  }

  // TODO: Redundant with makeMutableCopy(). Remove.
  protected static IntList mutableCopy(IntList list) {
    return makeMutableCopy(list);
  }

  // TODO: Redundant with makeMutableCopy(). Remove.
  protected static LongList mutableCopy(LongList list) {
    return makeMutableCopy(list);
  }

  // TODO: Redundant with makeMutableCopy(). Remove.
  protected static FloatList mutableCopy(FloatList list) {
    return makeMutableCopy(list);
  }

  // TODO: Redundant with makeMutableCopy(). Remove.
  protected static DoubleList mutableCopy(DoubleList list) {
    return makeMutableCopy(list);
  }

  // TODO: Redundant with makeMutableCopy(). Remove.
  protected static BooleanList mutableCopy(BooleanList list) {
    return makeMutableCopy(list);
  }

  protected static LongList emptyLongList() {
    return LongArrayList.emptyList();
  }

  // TODO: Unused. Remove.
  protected static LongList newLongList() {
    return new LongArrayList();
  }

  protected static FloatList emptyFloatList() {
    return FloatArrayList.emptyList();
  }

  // TODO: Unused. Remove.
  protected static FloatList newFloatList() {
    return new FloatArrayList();
  }

  protected static DoubleList emptyDoubleList() {
    return DoubleArrayList.emptyList();
  }

  // TODO: Unused. Remove.
  protected static DoubleList newDoubleList() {
    return new DoubleArrayList();
  }

  protected static BooleanList emptyBooleanList() {
    return BooleanArrayList.emptyList();
  }

  // TODO: Unused. Remove.
  protected static BooleanList newBooleanList() {
    return new BooleanArrayList();
  }

  protected static <ListT extends ProtobufList<?>> ListT makeMutableCopy(ListT list) {
    return makeMutableCopy(list, 0);
  }

  @SuppressWarnings("unchecked") // Guaranteed by proto runtime.
  protected static <ListT extends ProtobufList<?>> ListT makeMutableCopy(
      ListT list, int minCapacity) {
    int size = list.size();
    if (minCapacity <= size) {
      minCapacity = size * 2;
    }
    if (minCapacity <= 0) {
      minCapacity = AbstractProtobufList.DEFAULT_CAPACITY;
    }

    return (ListT) list.mutableCopyWithCapacity(minCapacity);
  }

  @SuppressWarnings("unchecked") // The empty list can be safely cast
  protected static <T> ProtobufList<T> emptyList(Class<T> elementType) {
    return (ProtobufList<T>) ProtobufArrayList.emptyList();
  }

  public void writeTo(final CodedOutputStream output) throws IOException {
    MessageReflection.writeMessageTo(this, getAllFieldsRaw(), output, false);
  }

  public int getSerializedSize() {
    int size = memoizedSize;
    if (size != -1) {
      return size;
    }

    memoizedSize = MessageReflection.getSerializedSize(
        this, getAllFieldsRaw());
    return memoizedSize;
  }

  /**
   * This class is used to make a generated protected method inaccessible from user's code (e.g.,
   * the {@link #newInstance} method below). When this class is used as a parameter's type in a
   * generated protected method, the method is visible to user's code in the same package, but since
   * the constructor of this class is private to protobuf runtime, user's code can't obtain an
   * instance of this class and as such can't actually make a method call on the protected method.
   */
  protected static final class UnusedPrivateParameter {
    static final UnusedPrivateParameter INSTANCE = new UnusedPrivateParameter();

    private UnusedPrivateParameter() {}
  }

  /** Creates a new instance of this message type. Overridden in the generated code. */
  @SuppressWarnings({"unused"})
  protected Object newInstance(UnusedPrivateParameter unused) {
    throw new UnsupportedOperationException("This method must be overridden by the subclass.");
  }

  /**
   * Used by parsing constructors in generated classes.
   *
   * <p>TODO: remove unused method (extensions should be immutable after build)
   */
  protected void makeExtensionsImmutable() {
    // Noop for messages without extensions.
  }

  /** TODO: remove this together with GeneratedMessageV3.BuilderParent. */
  protected abstract Message.Builder newBuilderForType(BuilderParent parent);

  /** TODO: generated class should implement this directly */
  protected Message.Builder newBuilderForType(final Message.BuilderParent parent) {
    return newBuilderForType(
        new BuilderParent() {
          @Override
          public void markDirty() {
            parent.markDirty();
          }
        });
  }

  /** Builder class for {@link FlattenedGeneratedMessageV3}. */
  @SuppressWarnings("unchecked")
  public abstract static class Builder<BuilderT extends Builder<BuilderT>>
      implements Message.Builder {

    private BuilderParent builderParent;

    private BuilderParentImpl meAsParent;

    // Indicates that we've built a message and so we are now obligated
    // to dispatch dirty invalidations. See GeneratedMessageV3.BuilderListener.
    private boolean isClean;

    /**
     * This field holds either an {@link UnknownFieldSet} or {@link UnknownFieldSet.Builder}.
     *
     * <p>We use an object because it should only be one or the other of those things at a time and
     * Object is the only common base. This also saves space.
     *
     * <p>Conversions are lazy: if {@link #setUnknownFields} is called, this will contain {@link
     * UnknownFieldSet}. If unknown fields are merged into this builder, the current {@link
     * UnknownFieldSet} will be converted to a {@link UnknownFieldSet.Builder} and left that way
     * until either {@link #setUnknownFields} or {@link #buildPartial} or {@link #build} is called.
     */
    private Object unknownFieldsOrBuilder = UnknownFieldSet.getDefaultInstance();

    protected Builder() {
      this(null);
    }

    protected Builder(BuilderParent builderParent) {
      this.builderParent = builderParent;
    }

    static final class LimitedInputStream extends FilterInputStream {
      private int limit;

      LimitedInputStream(InputStream in, int limit) {
        super(in);
        this.limit = limit;
      }

      @Override
      public int available() throws IOException {
        return Math.min(super.available(), limit);
      }

      @Override
      public int read() throws IOException {
        if (limit <= 0) {
          return -1;
        }
        final int result = super.read();
        if (result >= 0) {
          --limit;
        }
        return result;
      }

      @Override
      public int read(final byte[] b, final int off, int len) throws IOException {
        if (limit <= 0) {
          return -1;
        }
        len = Math.min(len, limit);
        final int result = super.read(b, off, len);
        if (result >= 0) {
          limit -= result;
        }
        return result;
      }

      @Override
      public long skip(final long n) throws IOException {
        // because we take the minimum of an int and a long, result is guaranteed to be
        // less than or equal to Integer.MAX_INT so this cast is safe
        int result = (int) super.skip(Math.min(n, limit));
        if (result >= 0) {
          // if the superclass adheres to the contract for skip, this condition is always true
          limit -= result;
        }
        return result;
      }
    }

    @Override
    public boolean mergeDelimitedFrom(
            final InputStream input, final ExtensionRegistryLite extensionRegistry) throws IOException {
      final int firstByte = input.read();
      if (firstByte == -1) {
        return false;
      }
      final int size = CodedInputStream.readRawVarint32(firstByte, input);
      final InputStream limitedInput = new AbstractMessageLite.Builder.LimitedInputStream(input, size);
      mergeFrom(limitedInput, extensionRegistry);
      return true;
    }

    @Override
    public boolean mergeDelimitedFrom(final InputStream input) throws IOException {
      return mergeDelimitedFrom(input, ExtensionRegistryLite.getEmptyRegistry());
    }

    @Override
    @SuppressWarnings("unchecked") // isInstance takes care of this
    public BuilderT mergeFrom(final MessageLite other) {
      if (!getDefaultInstanceForType().getClass().isInstance(other)) {
        throw new IllegalArgumentException(
                "mergeFrom(MessageLite) can only merge messages of the same type.");
      }

      return internalMergeFrom(other);
    }

    private String getReadingExceptionMessage(String target) {
      return "Reading "
              + getClass().getName()
              + " from a "
              + target
              + " threw an IOException (should never happen).";
    }

    // We check nulls as we iterate to avoid iterating over values twice.
    private static <T> void addAllCheckingNulls(Iterable<T> values, List<? super T> list) {
      if (list instanceof ArrayList && values instanceof Collection) {
        ((ArrayList<T>) list).ensureCapacity(list.size() + ((Collection<T>) values).size());
      }
      int begin = list.size();
      for (T value : values) {
        if (value == null) {
          // encountered a null value so we must undo our modifications prior to throwing
          String message = "Element at index " + (list.size() - begin) + " is null.";
          for (int i = list.size() - 1; i >= begin; i--) {
            list.remove(i);
          }
          throw new NullPointerException(message);
        }
        list.add(value);
      }
    }

    /** Construct an UninitializedMessageException reporting missing fields in the given message. */
    protected static UninitializedMessageException newUninitializedMessageException(
            MessageLite message) {
      return new UninitializedMessageException(message);
    }

    // For binary compatibility.
    @Deprecated
    protected static <T> void addAll(final Iterable<T> values, final Collection<? super T> list) {
      addAll(values, (List<T>) list);
    }

    /**
     * Adds the {@code values} to the {@code list}. This is a helper method used by generated code.
     * Users should ignore it.
     *
     * @throws NullPointerException if {@code values} or any of the elements of {@code values} is
     *     null.
     */
    protected static <T> void addAll(final Iterable<T> values, final List<? super T> list) {
      checkNotNull(values);
      if (values instanceof LazyStringList) {
        // For StringOrByteStringLists, check the underlying elements to avoid
        // forcing conversions of ByteStrings to Strings.
        // TODO: Could we just prohibit nulls in all protobuf lists and get rid of this? Is
        // if even possible to hit this condition as all protobuf methods check for null first,
        // right?
        List<?> lazyValues = ((LazyStringList) values).getUnderlyingElements();
        LazyStringList lazyList = (LazyStringList) list;
        int begin = list.size();
        for (Object value : lazyValues) {
          if (value == null) {
            // encountered a null value so we must undo our modifications prior to throwing
            String message = "Element at index " + (lazyList.size() - begin) + " is null.";
            for (int i = lazyList.size() - 1; i >= begin; i--) {
              lazyList.remove(i);
            }
            throw new NullPointerException(message);
          }
          if (value instanceof ByteString) {
            lazyList.add((ByteString) value);
          } else {
            lazyList.add((String) value);
          }
        }
      } else {
        if (values instanceof PrimitiveNonBoxingCollection) {
          list.addAll((Collection<T>) values);
        } else {
          addAllCheckingNulls(values, list);
        }
      }
    }

    @Override
    public List<String> findInitializationErrors() {
      return MessageReflection.findMissingFields(this);
    }

    @Override
    public String getInitializationErrorString() {
      return MessageReflection.delimitWithCommas(findInitializationErrors());
    }

    protected BuilderT internalMergeFrom(MessageLite other) {
      return mergeFrom((Message) other);
    }

    @Override
    public BuilderT mergeFrom(final Message other) {
      return mergeFrom(other, other.getAllFields());
    }

    BuilderT mergeFrom(final Message other, Map<FieldDescriptor, Object> allFields) {
      if (other.getDescriptorForType() != getDescriptorForType()) {
        throw new IllegalArgumentException(
                "mergeFrom(Message) can only merge messages of the same type.");
      }

      // Note:  We don't attempt to verify that other's fields have valid
      //   types.  Doing so would be a losing battle.  We'd have to verify
      //   all sub-messages as well, and we'd have to make copies of all of
      //   them to insure that they don't change after verification (since
      //   the Message interface itself cannot enforce immutability of
      //   implementations).

      for (final Map.Entry<FieldDescriptor, Object> entry : allFields.entrySet()) {
        final FieldDescriptor field = entry.getKey();
        if (field.isRepeated()) {
          for (final Object element : (List) entry.getValue()) {
            addRepeatedField(field, element);
          }
        } else if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
          final Message existingValue = (Message) getField(field);
          if (existingValue == existingValue.getDefaultInstanceForType()) {
            setField(field, entry.getValue());
          } else {
            setField(
                    field,
                    existingValue
                            .newBuilderForType()
                            .mergeFrom(existingValue)
                            .mergeFrom((Message) entry.getValue())
                            .build());
          }
        } else {
          setField(field, entry.getValue());
        }
      }

      mergeUnknownFields(other.getUnknownFields());

      return (BuilderT) this;
    }

    @Override
    public BuilderT mergeFrom(final CodedInputStream input) throws IOException {
      return mergeFrom(input, ExtensionRegistry.getEmptyRegistry());
    }

    @Override
    public BuilderT mergeFrom(
            final CodedInputStream input, final ExtensionRegistryLite extensionRegistry)
            throws IOException {
      boolean discardUnknown = input.shouldDiscardUnknownFields();
      final UnknownFieldSet.Builder unknownFields =
              discardUnknown ? null : getUnknownFieldSetBuilder();
      MessageReflection.mergeMessageFrom(this, unknownFields, input, extensionRegistry);
      if (unknownFields != null) {
        setUnknownFieldSetBuilder(unknownFields);
      }
      return (BuilderT) this;
    }

    @Override
    public String toString() {
      return TextFormat.printer().printToString(this);
    }

    /** Construct an UninitializedMessageException reporting missing fields in the given message. */
    protected static UninitializedMessageException newUninitializedMessageException(
            Message message) {
      return new UninitializedMessageException(MessageReflection.findMissingFields(message));
    }

    // ===============================================================
    // The following definitions seem to be required in order to make javac
    // not produce weird errors like:
    //
    // java/com/google/protobuf/DynamicMessage.java:203: types
    //   com.google.protobuf.AbstractMessage.Builder<
    //     com.google.protobuf.DynamicMessage.Builder> and
    //   com.google.protobuf.AbstractMessage.Builder<
    //     com.google.protobuf.DynamicMessage.Builder> are incompatible; both
    //   define mergeFrom(com.google.protobuf.ByteString), but with unrelated
    //   return types.
    //
    // Strangely, these lines are only needed if javac is invoked separately
    // on AbstractMessage.java and AbstractMessageLite.java.  If javac is
    // invoked on both simultaneously, it works.  (Or maybe the important
    // point is whether or not DynamicMessage.java is compiled together with
    // AbstractMessageLite.java -- not sure.)  I suspect this is a compiler
    // bug.

    public BuilderT mergeFrom(final ByteString data) throws InvalidProtocolBufferException {
      try {
        final CodedInputStream input = data.newCodedInput();
        mergeFrom(input);
        input.checkLastTagWas(0);
        return (BuilderT) this;
      } catch (InvalidProtocolBufferException e) {
        throw e;
      } catch (IOException e) {
        throw new RuntimeException(getReadingExceptionMessage("ByteString"), e);
      }
    }

    public BuilderT mergeFrom(
            final ByteString data, final ExtensionRegistryLite extensionRegistry)
            throws InvalidProtocolBufferException {
      try {
        final CodedInputStream input = data.newCodedInput();
        mergeFrom(input, extensionRegistry);
        input.checkLastTagWas(0);
        return (BuilderT) this;
      } catch (InvalidProtocolBufferException e) {
        throw e;
      } catch (IOException e) {
        throw new RuntimeException(getReadingExceptionMessage("ByteString"), e);
      }
    }

    public BuilderT mergeFrom(final byte[] data) throws InvalidProtocolBufferException {
      return mergeFrom(data, 0, data.length);
    }

    public BuilderT mergeFrom(final byte[] data, final int off, final int len)
            throws InvalidProtocolBufferException {
      try {
        final CodedInputStream input = CodedInputStream.newInstance(data, off, len);
        mergeFrom(input);
        input.checkLastTagWas(0);
        return (BuilderT) this;
      } catch (InvalidProtocolBufferException e) {
        throw e;
      } catch (IOException e) {
        throw new RuntimeException(getReadingExceptionMessage("byte array"), e);
      }
    }

    public BuilderT mergeFrom(final byte[] data, final ExtensionRegistryLite extensionRegistry)
            throws InvalidProtocolBufferException {
      return mergeFrom(data, 0, data.length, extensionRegistry);
    }

    public BuilderT mergeFrom(
            final byte[] data,
            final int off,
            final int len,
            final ExtensionRegistryLite extensionRegistry)
            throws InvalidProtocolBufferException {
      try {
        final CodedInputStream input = CodedInputStream.newInstance(data, off, len);
        mergeFrom(input, extensionRegistry);
        input.checkLastTagWas(0);
        return (BuilderT) this;
      } catch (InvalidProtocolBufferException e) {
        throw e;
      } catch (IOException e) {
        throw new RuntimeException(getReadingExceptionMessage("byte array"), e);
      }
    }

    public BuilderT mergeFrom(final InputStream input) throws IOException {
      final CodedInputStream codedInput = CodedInputStream.newInstance(input);
      mergeFrom(codedInput);
      codedInput.checkLastTagWas(0);
      return (BuilderT) this;
    }

    public BuilderT mergeFrom(
            final InputStream input, final ExtensionRegistryLite extensionRegistry) throws IOException {
      final CodedInputStream codedInput = CodedInputStream.newInstance(input);
      mergeFrom(codedInput, extensionRegistry);
      codedInput.checkLastTagWas(0);
      return (BuilderT) this;
    }

    /**
     * @deprecated from v3.0.0-beta-3+, for compatibility with v2.5.0 and v2.6.1
     * generated code.
     */
    @Deprecated
    protected static int hashLong(long n) {
      return (int) (n ^ (n >>> 32));
    }

    /**
     * @deprecated from v3.0.0-beta-3+, for compatibility with v2.5.0 and v2.6.1
     * generated code.
     */
    @Deprecated
    protected static int hashBoolean(boolean b) {
      return b ? 1231 : 1237;
    }

    /**
     * @deprecated from v3.0.0-beta-3+, for compatibility with v2.5.0 and v2.6.1
     * generated code.
     */
    @Deprecated
    protected static int hashEnum(Internal.EnumLite e) {
      return e.getNumber();
    }

    /**
     * @deprecated from v3.0.0-beta-3+, for compatibility with v2.5.0 and v2.6.1
     * generated code.
     */
    @Deprecated
    protected static int hashEnumList(List<? extends Internal.EnumLite> list) {
      int hash = 1;
      for (Internal.EnumLite e : list) {
        hash = 31 * hash + hashEnum(e);
      }
      return hash;
    }

    void dispose() {
      builderParent = null;
    }

    /** Called by the subclass when a message is built. */
    protected void onBuilt() {
      if (builderParent != null) {
        markClean();
      }
    }

    /**
     * Called by the subclass or a builder to notify us that a message was built and may be cached
     * and therefore invalidations are needed.
     */
    protected void markClean() {
      this.isClean = true;
    }

    /**
     * Gets whether invalidations are needed
     *
     * @return whether invalidations are needed
     */
    protected boolean isClean() {
      return isClean;
    }

    @Override
    public BuilderT clone() {
      BuilderT builder = (BuilderT) getDefaultInstanceForType().newBuilderForType();
      builder.mergeFrom(buildPartial());
      return builder;
    }

    /**
     * Called by the initialization and clear code paths to allow subclasses to reset any of their
     * builtin fields back to the initial values.
     */
    @Override
    public BuilderT clear() {
      unknownFieldsOrBuilder = UnknownFieldSet.getDefaultInstance();
      onChanged();
      return (BuilderT) this;
    }

    /**
     * Get the FieldAccessorTable for this type. We can't have the message class pass this in to the
     * constructor because of bootstrapping trouble with DescriptorProtos.
     */
    protected abstract FieldAccessorTable internalGetFieldAccessorTable();

    @Override
    public Descriptor getDescriptorForType() {
      return internalGetFieldAccessorTable().descriptor;
    }

    @Override
    public Map<FieldDescriptor, Object> getAllFields() {
      return Collections.unmodifiableMap(getAllFieldsMutable());
    }

    /** Internal helper which returns a mutable map. */
    private Map<FieldDescriptor, Object> getAllFieldsMutable() {
      final TreeMap<FieldDescriptor, Object> result = new TreeMap<>();
      final Descriptor descriptor = internalGetFieldAccessorTable().descriptor;
      final List<FieldDescriptor> fields = descriptor.getFields();

      for (int i = 0; i < fields.size(); i++) {
        FieldDescriptor field = fields.get(i);
        final OneofDescriptor oneofDescriptor = field.getContainingOneof();

        /*
         * If the field is part of a Oneof, then at maximum one field in the Oneof is set
         * and it is not repeated. There is no need to iterate through the others.
         */
        if (oneofDescriptor != null) {
          // Skip other fields in the Oneof we know are not set
          i += oneofDescriptor.getFieldCount() - 1;
          if (!hasOneof(oneofDescriptor)) {
            // If no field is set in the Oneof, skip all the fields in the Oneof
            continue;
          }
          // Get the pointer to the only field which is set in the Oneof
          field = getOneofFieldDescriptor(oneofDescriptor);
        } else {
          // If we are not in a Oneof, we need to check if the field is set and if it is repeated
          if (field.isRepeated()) {
            final List<?> value = (List<?>) getField(field);
            if (!value.isEmpty()) {
              result.put(field, value);
            }
            continue;
          }
          if (!hasField(field)) {
            continue;
          }
        }
        // Add the field to the map
        result.put(field, getField(field));
      }
      return result;
    }

    @Override
    public Message.Builder newBuilderForField(final FieldDescriptor field) {
      return internalGetFieldAccessorTable().getField(field).newBuilder();
    }

    @Override
    public Message.Builder getFieldBuilder(final FieldDescriptor field) {
      return internalGetFieldAccessorTable().getField(field).getBuilder(this);
    }

    @Override
    public Message.Builder getRepeatedFieldBuilder(final FieldDescriptor field, int index) {
      return internalGetFieldAccessorTable().getField(field).getRepeatedBuilder(this, index);
    }

    @Override
    public boolean hasOneof(final OneofDescriptor oneof) {
      return internalGetFieldAccessorTable().getOneof(oneof).has(this);
    }

    @Override
    public FieldDescriptor getOneofFieldDescriptor(final OneofDescriptor oneof) {
      return internalGetFieldAccessorTable().getOneof(oneof).get(this);
    }

    @Override
    public boolean hasField(final FieldDescriptor field) {
      return internalGetFieldAccessorTable().getField(field).has(this);
    }

    @Override
    public Object getField(final FieldDescriptor field) {
      Object object = internalGetFieldAccessorTable().getField(field).get(this);
      if (field.isRepeated()) {
        // The underlying list object is still modifiable at this point.
        // Make sure not to expose the modifiable list to the caller.
        return Collections.unmodifiableList((List<?>) object);
      } else {
        return object;
      }
    }

    @Override
    public BuilderT setField(final FieldDescriptor field, final Object value) {
      internalGetFieldAccessorTable().getField(field).set(this, value);
      return (BuilderT) this;
    }

    @Override
    public BuilderT clearField(final FieldDescriptor field) {
      internalGetFieldAccessorTable().getField(field).clear(this);
      return (BuilderT) this;
    }

    @Override
    public BuilderT clearOneof(final OneofDescriptor oneof) {
      internalGetFieldAccessorTable().getOneof(oneof).clear(this);
      return (BuilderT) this;
    }

    @Override
    public int getRepeatedFieldCount(final FieldDescriptor field) {
      return internalGetFieldAccessorTable().getField(field).getRepeatedCount(this);
    }

    @Override
    public Object getRepeatedField(final FieldDescriptor field, final int index) {
      return internalGetFieldAccessorTable().getField(field).getRepeated(this, index);
    }

    @Override
    public BuilderT setRepeatedField(
        final FieldDescriptor field, final int index, final Object value) {
      internalGetFieldAccessorTable().getField(field).setRepeated(this, index, value);
      return (BuilderT) this;
    }

    @Override
    public BuilderT addRepeatedField(final FieldDescriptor field, final Object value) {
      internalGetFieldAccessorTable().getField(field).addRepeated(this, value);
      return (BuilderT) this;
    }

    private BuilderT setUnknownFieldsInternal(final UnknownFieldSet unknownFields) {
      unknownFieldsOrBuilder = unknownFields;
      onChanged();
      return (BuilderT) this;
    }

    @Override
    public BuilderT setUnknownFields(final UnknownFieldSet unknownFields) {
      return setUnknownFieldsInternal(unknownFields);
    }

    /**
     * This method is obsolete, but we must retain it for compatibility with older generated code.
     */
    protected BuilderT setUnknownFieldsProto3(final UnknownFieldSet unknownFields) {
      return setUnknownFieldsInternal(unknownFields);
    }

    @Override
    public BuilderT mergeUnknownFields(final UnknownFieldSet unknownFields) {
      if (UnknownFieldSet.getDefaultInstance().equals(unknownFields)) {
        return (BuilderT) this;
      }

      if (UnknownFieldSet.getDefaultInstance().equals(unknownFieldsOrBuilder)) {
        unknownFieldsOrBuilder = unknownFields;
        onChanged();
        return (BuilderT) this;
      }

      getUnknownFieldSetBuilder().mergeFrom(unknownFields);
      onChanged();
      return (BuilderT) this;
    }

    @Override
    public boolean isInitialized() {
      for (final FieldDescriptor field : getDescriptorForType().getFields()) {
        // Check that all required fields are present.
        if (field.isRequired()) {
          if (!hasField(field)) {
            return false;
          }
        }
        // Check that embedded messages are initialized.
        if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
          if (field.isRepeated()) {
            @SuppressWarnings("unchecked")
            final List<Message> messageList = (List<Message>) getField(field);
            for (final Message element : messageList) {
              if (!element.isInitialized()) {
                return false;
              }
            }
          } else {
            if (hasField(field) && !((Message) getField(field)).isInitialized()) {
              return false;
            }
          }
        }
      }
      return true;
    }

    @Override
    public final UnknownFieldSet getUnknownFields() {
      if (unknownFieldsOrBuilder instanceof UnknownFieldSet) {
        return (UnknownFieldSet) unknownFieldsOrBuilder;
      } else {
        return ((UnknownFieldSet.Builder) unknownFieldsOrBuilder).buildPartial();
      }
    }

    /**
     * Called by generated subclasses to parse an unknown field.
     *
     * @return {@code true} unless the tag is an end-group tag.
     */
    protected boolean parseUnknownField(
        CodedInputStream input, ExtensionRegistryLite extensionRegistry, int tag)
        throws IOException {
      if (input.shouldDiscardUnknownFields()) {
        return input.skipField(tag);
      }
      return getUnknownFieldSetBuilder().mergeFieldFrom(tag, input);
    }

    /** Called by generated subclasses to add to the unknown field set. */
    protected final void mergeUnknownLengthDelimitedField(int number, ByteString bytes) {
      getUnknownFieldSetBuilder().mergeLengthDelimitedField(number, bytes);
    }

    /** Called by generated subclasses to add to the unknown field set. */
    protected final void mergeUnknownVarintField(int number, int value) {
      getUnknownFieldSetBuilder().mergeVarintField(number, value);
    }

    protected UnknownFieldSet.Builder getUnknownFieldSetBuilder() {
      if (unknownFieldsOrBuilder instanceof UnknownFieldSet) {
        unknownFieldsOrBuilder = ((UnknownFieldSet) unknownFieldsOrBuilder).toBuilder();
      }
      onChanged();
      return (UnknownFieldSet.Builder) unknownFieldsOrBuilder;
    }

    protected void setUnknownFieldSetBuilder(UnknownFieldSet.Builder builder) {
      unknownFieldsOrBuilder = builder;
      onChanged();
    }

    /**
     * Implementation of {@link BuilderParent} for giving to our children. This small inner class
     * makes it so we don't publicly expose the BuilderParent methods.
     */
    private class BuilderParentImpl implements BuilderParent {

      @Override
      public void markDirty() {
        onChanged();
      }
    }

    /**
     * Gets the {@link BuilderParent} for giving to our children.
     *
     * @return The builder parent for our children.
     */
    protected BuilderParent getParentForChildren() {
      if (meAsParent == null) {
        meAsParent = new BuilderParentImpl();
      }
      return meAsParent;
    }

    /**
     * Called when a builder or one of its nested children has changed and any parent should be
     * notified of its invalidation.
     */
    protected final void onChanged() {
      if (isClean && builderParent != null) {
        builderParent.markDirty();

        // Don't keep dispatching invalidations until build is called again.
        isClean = false;
      }
    }

    /**
     * Gets the map field with the given field number. This method should be overridden in the
     * generated message class if the message contains map fields.
     *
     * <p>Unlike other field types, reflection support for map fields can't be implemented based on
     * generated public API because we need to access a map field as a list in reflection API but
     * the generated API only allows us to access it as a map. This method returns the underlying
     * map field directly and thus enables us to access the map field as a list.
     */
    @SuppressWarnings({"unused", "rawtypes"})
    protected MapFieldReflectionAccessor internalGetMapFieldReflection(int fieldNumber) {
      return internalGetMapField(fieldNumber);
    }

    /** TODO: Remove, exists for compatibility with generated code. */
    @Deprecated
    @SuppressWarnings({"unused", "rawtypes"})
    protected MapField internalGetMapField(int fieldNumber) {
      // Note that we can't use descriptor names here because this method will
      // be called when descriptor is being initialized.
      throw new IllegalArgumentException("No map fields found in " + getClass().getName());
    }

    /** Like {@link #internalGetMapFieldReflection} but return a mutable version. */
    @SuppressWarnings({"unused", "rawtypes"})
    protected MapFieldReflectionAccessor internalGetMutableMapFieldReflection(int fieldNumber) {
      return internalGetMutableMapField(fieldNumber);
    }

    /** TODO: Remove, exists for compatibility with generated code. */
    @Deprecated
    @SuppressWarnings({"unused", "rawtypes"})
    protected MapField internalGetMutableMapField(int fieldNumber) {
      // Note that we can't use descriptor names here because this method will
      // be called when descriptor is being initialized.
      throw new IllegalArgumentException("No map fields found in " + getClass().getName());
    }
  }

  // =================================================================
  // Extensions-related stuff

  /** Extends {@link MessageOrBuilder} with extension-related functions. */
  public interface ExtendableMessageOrBuilder<MessageT extends ExtendableMessage<MessageT>>
      extends MessageOrBuilder {
    // Re-define for return type covariance.
    @Override
    Message getDefaultInstanceForType();

    /** Check if a singular extension is present. */
    <T> boolean hasExtension(ExtensionLite<MessageT, T> extension);

    /** Get the number of elements in a repeated extension. */
    <T> int getExtensionCount(ExtensionLite<MessageT, List<T>> extension);

    /** Get the value of an extension. */
    <T> T getExtension(ExtensionLite<MessageT, T> extension);

    /** Get one element of a repeated extension. */
    <T> T getExtension(ExtensionLite<MessageT, List<T>> extension, int index);

    /**
     * Check if a singular extension is present.
     * <p>TODO: handled by ExtensionLite version
     */
    <T> boolean hasExtension(
        Extension<MessageT, T> extension);
    /**
     * Check if a singular extension is present.
     * <p>TODO: handled by ExtensionLite version
     */
    <T> boolean hasExtension(
        GeneratedExtension<MessageT, T> extension);
    /**
     * Get the number of elements in a repeated extension.
     * <p>TODO: handled by ExtensionLite version
     */
    <T> int getExtensionCount(
        Extension<MessageT, List<T>> extension);
    /**
     * Get the number of elements in a repeated extension.
     * <p>TODO: handled by ExtensionLite version
     */
    <T> int getExtensionCount(
        GeneratedExtension<MessageT, List<T>> extension);
    /**
     * Get the value of an extension.
     * <p>TODO: handled by ExtensionLite version
     */
    <T> T getExtension(
        Extension<MessageT, T> extension);
    /**
     * Get the value of an extension.
     * <p>TODO: handled by ExtensionLite version
     */
    <T> T getExtension(
        GeneratedExtension<MessageT, T> extension);
    /**
     * Get one element of a repeated extension.
     * <p>TODO: handled by ExtensionLite version
     */
    <T> T getExtension(
        Extension<MessageT, List<T>> extension,
        int index);
    /**
     * Get one element of a repeated extension.
     * <p>TODO: handled by ExtensionLite version
     */
    <T> T getExtension(
        GeneratedExtension<MessageT, List<T>> extension,
        int index);
  }

  /**
   * Generated message classes for message types that contain extension ranges subclass this.
   *
   * <p>This class implements type-safe accessors for extensions. They implement all the same
   * operations that you can do with normal fields -- e.g. "has", "get", and "getCount" -- but for
   * extensions. The extensions are identified using instances of the class {@link
   * GeneratedExtension}; the protocol compiler generates a static instance of this class for every
   * extension in its input. Through the magic of generics, all is made type-safe.
   *
   * <p>For example, imagine you have the {@code .proto} file:
   *
   * <pre>
   * option java_class = "MyProto";
   *
   * message Foo {
   *   extensions 1000 to max;
   * }
   *
   * extend Foo {
   *   optional int32 bar;
   * }
   * </pre>
   *
   * <p>Then you might write code like:
   *
   * <pre>
   * MyProto.Foo foo = getFoo();
   * int i = foo.getExtension(MyProto.bar);
   * </pre>
   *
   * <p>See also {@link ExtendableBuilder}.
   */
  public abstract static class ExtendableMessage<MessageT extends ExtendableMessage<MessageT>>
      extends FlattenedGeneratedMessageV3 implements ExtendableMessageOrBuilder<MessageT> {

    private static final long serialVersionUID = 1L;

    private final FieldSet<FieldDescriptor> extensions;

    protected ExtendableMessage() {
      this.extensions = FieldSet.newFieldSet();
    }

    protected ExtendableMessage(ExtendableBuilder<MessageT, ?> builder) {
      super(builder);
      this.extensions = builder.buildExtensions();
    }

    private void verifyExtensionContainingType(final Extension<MessageT, ?> extension) {
      if (extension.getDescriptor().getContainingType() != getDescriptorForType()) {
        // This can only happen if someone uses unchecked operations.
        throw new IllegalArgumentException(
            "Extension is for type \""
                + extension.getDescriptor().getContainingType().getFullName()
                + "\" which does not match message type \""
                + getDescriptorForType().getFullName()
                + "\".");
      }
    }

    /** Check if a singular extension is present. */
    @Override
    public final <T> boolean hasExtension(final ExtensionLite<MessageT, T> extensionLite) {
      Extension<MessageT, T> extension = checkNotLite(extensionLite);

      verifyExtensionContainingType(extension);
      return extensions.hasField(extension.getDescriptor());
    }

    /** Get the number of elements in a repeated extension. */
    @Override
    public final <T> int getExtensionCount(final ExtensionLite<MessageT, List<T>> extensionLite) {
      Extension<MessageT, List<T>> extension = checkNotLite(extensionLite);

      verifyExtensionContainingType(extension);
      final FieldDescriptor descriptor = extension.getDescriptor();
      return extensions.getRepeatedFieldCount(descriptor);
    }

    /** Get the value of an extension. */
    @Override
    @SuppressWarnings("unchecked")
    public final <T> T getExtension(final ExtensionLite<MessageT, T> extensionLite) {
      Extension<MessageT, T> extension = checkNotLite(extensionLite);

      verifyExtensionContainingType(extension);
      FieldDescriptor descriptor = extension.getDescriptor();
      final Object value = extensions.getField(descriptor);
      if (value == null) {
        if (descriptor.isRepeated()) {
          return (T) Collections.emptyList();
        } else if (descriptor.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
          return (T) extension.getMessageDefaultInstance();
        } else {
          return (T) extension.fromReflectionType(descriptor.getDefaultValue());
        }
      } else {
        return (T) extension.fromReflectionType(value);
      }
    }

    /** Get one element of a repeated extension. */
    @Override
    @SuppressWarnings("unchecked")
    public final <T> T getExtension(
        final ExtensionLite<MessageT, List<T>> extensionLite, final int index) {
      Extension<MessageT, List<T>> extension = checkNotLite(extensionLite);

      verifyExtensionContainingType(extension);
      FieldDescriptor descriptor = extension.getDescriptor();
      return (T)
          extension.singularFromReflectionType(extensions.getRepeatedField(descriptor, index));
    }

    /**
     * Check if a singular extension is present.
     * <p>TODO: handled by ExtensionLite version
     */
    @Override
    public final <T> boolean hasExtension(final Extension<MessageT, T> extension) {
      return hasExtension((ExtensionLite<MessageT, T>) extension);
    }
    /**
     * Check if a singular extension is present.
     * <p>TODO: handled by ExtensionLite version
     */
    @Override
    public final <T> boolean hasExtension(
        final GeneratedExtension<MessageT, T> extension) {
      return hasExtension((ExtensionLite<MessageT, T>) extension);
    }
    /**
     * Get the number of elements in a repeated extension.
     * <p>TODO: handled by ExtensionLite version
     */
    @Override
    public final <T> int getExtensionCount(
        final Extension<MessageT, List<T>> extension) {
      return getExtensionCount((ExtensionLite<MessageT, List<T>>) extension);
    }
    /**
     * Get the number of elements in a repeated extension.
     * <p>TODO: handled by ExtensionLite version
     */
    @Override
    public final <T> int getExtensionCount(
        final GeneratedExtension<MessageT, List<T>> extension) {
      return getExtensionCount((ExtensionLite<MessageT, List<T>>) extension);
    }
    /**
     * Get the value of an extension.
     * <p>TODO: handled by ExtensionLite version
     */
    @Override
    public final <T> T getExtension(final Extension<MessageT, T> extension) {
      return getExtension((ExtensionLite<MessageT, T>) extension);
    }
    /**
     * Get the value of an extension.
     * <p>TODO: handled by ExtensionLite version
     */
    @Override
    public final <T> T getExtension(
        final GeneratedExtension<MessageT, T> extension) {
      return getExtension((ExtensionLite<MessageT, T>) extension);
    }
    /**
     * Get one element of a repeated extension.
     * <p>TODO: handled by ExtensionLite version
     */
    @Override
    public final <T> T getExtension(
        final Extension<MessageT, List<T>> extension, final int index) {
      return getExtension((ExtensionLite<MessageT, List<T>>) extension, index);
    }
    /**
     * Get one element of a repeated extension.
     * <p>TODO: handled by ExtensionLite version
     */
    @Override
    public final <T> T getExtension(
        final GeneratedExtension<MessageT, List<T>> extension, final int index) {
      return getExtension((ExtensionLite<MessageT, List<T>>) extension, index);
    }

    /** Called by subclasses to check if all extensions are initialized. */
    protected boolean extensionsAreInitialized() {
      return extensions.isInitialized();
    }

    // TODO: compute this in the builder at {@code build()} time.
    @Override
    public boolean isInitialized() {
      return super.isInitialized() && extensionsAreInitialized();
    }

    // TODO: remove mutating method from immutable type
    @Override
    protected boolean parseUnknownField(
        CodedInputStream input,
        UnknownFieldSet.Builder unknownFields,
        ExtensionRegistryLite extensionRegistry,
        int tag)
        throws IOException {
      return MessageReflection.mergeFieldFrom(
          input,
          input.shouldDiscardUnknownFields() ? null : unknownFields,
          extensionRegistry,
          getDescriptorForType(),
          new MessageReflection.ExtensionAdapter(extensions),
          tag);
    }

    /**
     * Delegates to parseUnknownField. This method is obsolete, but we must retain it for
     * compatibility with older generated code.
     *
     * <p>TODO: remove mutating method from immutable type
     */
    @Override
    protected boolean parseUnknownFieldProto3(
        CodedInputStream input,
        UnknownFieldSet.Builder unknownFields,
        ExtensionRegistryLite extensionRegistry,
        int tag)
        throws IOException {
      return parseUnknownField(input, unknownFields, extensionRegistry, tag);
    }

    /**
     * Used by parsing constructors in generated classes.
     *
     * <p>TODO: remove unused method (extensions should be immutable after build)
     */
    @Override
    protected void makeExtensionsImmutable() {
      extensions.makeImmutable();
    }

    /**
     * Used by subclasses to serialize extensions. Extension ranges may be interleaved with field
     * numbers, but we must write them in canonical (sorted by field number) order. ExtensionWriter
     * helps us write individual ranges of extensions at once.
     */
    protected class ExtensionWriter {
      // Imagine how much simpler this code would be if Java iterators had
      // a way to get the next element without advancing the iterator.

      private final Iterator<Map.Entry<FieldDescriptor, Object>> iter = extensions.iterator();
      private Map.Entry<FieldDescriptor, Object> next;
      private final boolean messageSetWireFormat;

      private ExtensionWriter(final boolean messageSetWireFormat) {
        if (iter.hasNext()) {
          next = iter.next();
        }
        this.messageSetWireFormat = messageSetWireFormat;
      }

      public void writeUntil(final int end, final CodedOutputStream output) throws IOException {
        while (next != null && next.getKey().getNumber() < end) {
          FieldDescriptor descriptor = next.getKey();
          if (messageSetWireFormat
              && descriptor.getLiteJavaType() == WireFormat.JavaType.MESSAGE
              && !descriptor.isRepeated()) {
            if (next instanceof LazyField.LazyEntry<?>) {
              output.writeRawMessageSetExtension(
                  descriptor.getNumber(),
                  ((LazyField.LazyEntry<?>) next).getField().toByteString());
            } else {
              output.writeMessageSetExtension(descriptor.getNumber(), (Message) next.getValue());
            }
          } else {
            // TODO: Taken care of following code, it may cause
            // problem when we use LazyField for normal fields/extensions.
            // Due to the optional field can be duplicated at the end of
            // serialized bytes, which will make the serialized size change
            // after lazy field parsed. So when we use LazyField globally,
            // we need to change the following write method to write cached
            // bytes directly rather than write the parsed message.
            FieldSet.writeField(descriptor, next.getValue(), output);
          }
          if (iter.hasNext()) {
            next = iter.next();
          } else {
            next = null;
          }
        }
      }
    }

    protected ExtensionWriter newExtensionWriter() {
      return new ExtensionWriter(false);
    }

    protected ExtensionWriter newMessageSetExtensionWriter() {
      return new ExtensionWriter(true);
    }

    /** Called by subclasses to compute the size of extensions. */
    protected int extensionsSerializedSize() {
      return extensions.getSerializedSize();
    }

    protected int extensionsSerializedSizeAsMessageSet() {
      return extensions.getMessageSetSerializedSize();
    }

    // ---------------------------------------------------------------
    // Reflection

    protected Map<FieldDescriptor, Object> getExtensionFields() {
      return extensions.getAllFields();
    }

    @Override
    public Map<FieldDescriptor, Object> getAllFields() {
      final Map<FieldDescriptor, Object> result =
          super.getAllFieldsMutable(/* getBytesForString= */ false);
      result.putAll(getExtensionFields());
      return Collections.unmodifiableMap(result);
    }

    @Override
    public Map<FieldDescriptor, Object> getAllFieldsRaw() {
      final Map<FieldDescriptor, Object> result =
          super.getAllFieldsMutable(/* getBytesForString= */ false);
      result.putAll(getExtensionFields());
      return Collections.unmodifiableMap(result);
    }

    @Override
    public boolean hasField(final FieldDescriptor field) {
      if (field.isExtension()) {
        verifyContainingType(field);
        return extensions.hasField(field);
      } else {
        return super.hasField(field);
      }
    }

    @Override
    public Object getField(final FieldDescriptor field) {
      if (field.isExtension()) {
        verifyContainingType(field);
        final Object value = extensions.getField(field);
        if (value == null) {
          if (field.isRepeated()) {
            return Collections.emptyList();
          } else if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
            // Lacking an ExtensionRegistry, we have no way to determine the
            // extension's real type, so we return a DynamicMessage.
            return DynamicMessage.getDefaultInstance(field.getMessageType());
          } else {
            return field.getDefaultValue();
          }
        } else {
          return value;
        }
      } else {
        return super.getField(field);
      }
    }

    @Override
    public int getRepeatedFieldCount(final FieldDescriptor field) {
      if (field.isExtension()) {
        verifyContainingType(field);
        return extensions.getRepeatedFieldCount(field);
      } else {
        return super.getRepeatedFieldCount(field);
      }
    }

    @Override
    public Object getRepeatedField(final FieldDescriptor field, final int index) {
      if (field.isExtension()) {
        verifyContainingType(field);
        return extensions.getRepeatedField(field, index);
      } else {
        return super.getRepeatedField(field, index);
      }
    }

    private void verifyContainingType(final FieldDescriptor field) {
      if (field.getContainingType() != getDescriptorForType()) {
        throw new IllegalArgumentException("FieldDescriptor does not match message type.");
      }
    }
  }

  /**
   * Type used to represent generated extensions. The protocol compiler generates a static singleton
   * instance of this class for each extension.
   *
   * <p>For example, imagine you have the {@code .proto} file:
   *
   * <pre>
   * option java_class = "MyProto";
   *
   * message Foo {
   *   extensions 1000 to max;
   * }
   *
   * extend Foo {
   *   optional int32 bar;
   * }
   * </pre>
   *
   * <p>Then, {@code MyProto.Foo.bar} has type {@code GeneratedExtension<MyProto.Foo, Integer>}.
   *
   * <p>In general, users should ignore the details of this type, and simply use these static
   * singletons as parameters to the extension accessors defined in {@link GeneratedMessage.ExtendableMessage} and
   * {@link GeneratedMessage.ExtendableBuilder}.
   */
  public static class GeneratedExtension<ContainingType extends Message, Type>
          extends Extension<ContainingType, Type> {
    // TODO:  Find ways to avoid using Java reflection within this
    //   class.  Also try to avoid suppressing unchecked warnings.

    // We can't always initialize the descriptor of a GeneratedExtension when
    // we first construct it due to initialization order difficulties (namely,
    // the descriptor may not have been constructed yet, since it is often
    // constructed by the initializer of a separate module).
    //
    // In the case of nested extensions, we initialize the
    // ExtensionDescriptorRetriever with an instance that uses the scoping
    // Message's default instance to retrieve the extension's descriptor.
    //
    // In the case of non-nested extensions, we initialize the
    // ExtensionDescriptorRetriever to null and rely on the outer class's static
    // initializer to call internalInit() after the descriptor has been parsed.
    GeneratedExtension(
            ExtensionDescriptorRetriever descriptorRetriever,
            Class singularType,
            Message messageDefaultInstance,
            ExtensionType extensionType) {
      if (Message.class.isAssignableFrom(singularType)
              && !singularType.isInstance(messageDefaultInstance)) {
        throw new IllegalArgumentException(
                "Bad messageDefaultInstance for " + singularType.getName());
      }
      this.descriptorRetriever = descriptorRetriever;
      this.singularType = singularType;
      this.messageDefaultInstance = messageDefaultInstance;

      if (ProtocolMessageEnum.class.isAssignableFrom(singularType)) {
        this.enumValueOf = getMethodOrDie(singularType, "valueOf", EnumValueDescriptor.class);
        this.enumGetValueDescriptor = getMethodOrDie(singularType, "getValueDescriptor");
      } else {
        this.enumValueOf = null;
        this.enumGetValueDescriptor = null;
      }
      this.extensionType = extensionType;
    }

    /** For use by generated code only. */
    public void internalInit(final FieldDescriptor descriptor) {
      if (descriptorRetriever != null) {
        throw new IllegalStateException("Already initialized.");
      }
      descriptorRetriever =
              new ExtensionDescriptorRetriever() {
                @Override
                public FieldDescriptor getDescriptor() {
                  return descriptor;
                }
              };
    }

    /**
     * Gets the descriptor for an extension. The implementation depends on whether the extension is
     * scoped in the top level of a file or scoped in a Message.
     */
    static interface ExtensionDescriptorRetriever {
      FieldDescriptor getDescriptor();
    }

    private ExtensionDescriptorRetriever descriptorRetriever;
    private final Class singularType;
    private final Message messageDefaultInstance;
    private final Method enumValueOf;
    private final Method enumGetValueDescriptor;
    private final ExtensionType extensionType;

    @Override
    public FieldDescriptor getDescriptor() {
      if (descriptorRetriever == null) {
        throw new IllegalStateException("getDescriptor() called before internalInit()");
      }
      return descriptorRetriever.getDescriptor();
    }

    /**
     * If the extension is an embedded message or group, returns the default instance of the
     * message.
     */
    @Override
    public Message getMessageDefaultInstance() {
      return messageDefaultInstance;
    }

    @Override
    protected ExtensionType getExtensionType() {
      return extensionType;
    }

    /**
     * Convert from the type used by the reflection accessors to the type used by native accessors.
     * E.g., for enums, the reflection accessors use EnumValueDescriptors but the native accessors
     * use the generated enum type.
     */
    @Override
    @SuppressWarnings("unchecked")
    protected Object fromReflectionType(final Object value) {
      FieldDescriptor descriptor = getDescriptor();
      if (descriptor.isRepeated()) {
        if (descriptor.getJavaType() == FieldDescriptor.JavaType.MESSAGE
                || descriptor.getJavaType() == FieldDescriptor.JavaType.ENUM) {
          // Must convert the whole list.
          final List result = new ArrayList();
          for (final Object element : (List) value) {
            result.add(singularFromReflectionType(element));
          }
          return result;
        } else {
          return value;
        }
      } else {
        return singularFromReflectionType(value);
      }
    }

    /**
     * Like {@link #fromReflectionType(Object)}, but if the type is a repeated type, this converts a
     * single element.
     */
    @Override
    protected Object singularFromReflectionType(final Object value) {
      FieldDescriptor descriptor = getDescriptor();
      switch (descriptor.getJavaType()) {
        case MESSAGE:
          if (singularType.isInstance(value)) {
            return value;
          } else {
            return messageDefaultInstance.newBuilderForType().mergeFrom((Message) value).build();
          }
        case ENUM:
          return invokeOrDie(enumValueOf, null, (EnumValueDescriptor) value);
        default:
          return value;
      }
    }

    /**
     * Convert from the type used by the native accessors to the type used by reflection accessors.
     * E.g., for enums, the reflection accessors use EnumValueDescriptors but the native accessors
     * use the generated enum type.
     */
    @Override
    @SuppressWarnings("unchecked")
    protected Object toReflectionType(final Object value) {
      FieldDescriptor descriptor = getDescriptor();
      if (descriptor.isRepeated()) {
        if (descriptor.getJavaType() == FieldDescriptor.JavaType.ENUM) {
          // Must convert the whole list.
          final List result = new ArrayList();
          for (final Object element : (List) value) {
            result.add(singularToReflectionType(element));
          }
          return result;
        } else {
          return value;
        }
      } else {
        return singularToReflectionType(value);
      }
    }

    /**
     * Like {@link #toReflectionType(Object)}, but if the type is a repeated type, this converts a
     * single element.
     */
    @Override
    protected Object singularToReflectionType(final Object value) {
      FieldDescriptor descriptor = getDescriptor();
      switch (descriptor.getJavaType()) {
        case ENUM:
          return invokeOrDie(enumGetValueDescriptor, value);
        default:
          return value;
      }
    }

    @Override
    public int getNumber() {
      return getDescriptor().getNumber();
    }

    @Override
    public WireFormat.FieldType getLiteType() {
      return getDescriptor().getLiteType();
    }

    @Override
    public boolean isRepeated() {
      return getDescriptor().isRepeated();
    }

    @Override
    @SuppressWarnings("unchecked")
    public Type getDefaultValue() {
      if (isRepeated()) {
        return (Type) Collections.emptyList();
      }
      if (getDescriptor().getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
        return (Type) messageDefaultInstance;
      }
      return (Type) singularFromReflectionType(getDescriptor().getDefaultValue());
    }
  }


  /**
   * Generated message builders for message types that contain extension ranges subclass this.
   *
   * <p>This class implements type-safe accessors for extensions. They implement all the same
   * operations that you can do with normal fields -- e.g. "get", "set", and "add" -- but for
   * extensions. The extensions are identified using instances of the class {@link
   * GeneratedExtension}; the protocol compiler generates a static instance of this class for every
   * extension in its input. Through the magic of generics, all is made type-safe.
   *
   * <p>For example, imagine you have the {@code .proto} file:
   *
   * <pre>
   * option java_class = "MyProto";
   *
   * message Foo {
   *   extensions 1000 to max;
   * }
   *
   * extend Foo {
   *   optional int32 bar;
   * }
   * </pre>
   *
   * <p>Then you might write code like:
   *
   * <pre>
   * MyProto.Foo foo =
   *   MyProto.Foo.newBuilder()
   *     .setExtension(MyProto.bar, 123)
   *     .build();
   * </pre>
   *
   * <p>See also {@link ExtendableMessage}.
   */
  @SuppressWarnings("unchecked")
  public abstract static class ExtendableBuilder<
          MessageT extends ExtendableMessage<MessageT>,
          BuilderT extends ExtendableBuilder<MessageT, BuilderT>>
      extends Builder<BuilderT> implements ExtendableMessageOrBuilder<MessageT> {

    private FieldSet.Builder<FieldDescriptor> extensions;

    protected ExtendableBuilder() {}

    protected ExtendableBuilder(BuilderParent parent) {
      super(parent);
    }

    // For immutable message conversion.
    void internalSetExtensionSet(FieldSet<FieldDescriptor> extensions) {
      this.extensions = FieldSet.Builder.fromFieldSet(extensions);
    }

    @Override
    public BuilderT clear() {
      extensions = null;
      return super.clear();
    }

    private void ensureExtensionsIsMutable() {
      if (extensions == null) {
        extensions = FieldSet.newBuilder();
      }
    }

    private void verifyExtensionContainingType(final Extension<MessageT, ?> extension) {
      if (extension.getDescriptor().getContainingType() != getDescriptorForType()) {
        // This can only happen if someone uses unchecked operations.
        throw new IllegalArgumentException(
            "Extension is for type \""
                + extension.getDescriptor().getContainingType().getFullName()
                + "\" which does not match message type \""
                + getDescriptorForType().getFullName()
                + "\".");
      }
    }

    /** Check if a singular extension is present. */
    @Override
    public final <T> boolean hasExtension(final ExtensionLite<MessageT, T> extensionLite) {
      Extension<MessageT, T> extension = checkNotLite(extensionLite);

      verifyExtensionContainingType(extension);
      return extensions != null && extensions.hasField(extension.getDescriptor());
    }

    /** Get the number of elements in a repeated extension. */
    @Override
    public final <T> int getExtensionCount(final ExtensionLite<MessageT, List<T>> extensionLite) {
      Extension<MessageT, List<T>> extension = checkNotLite(extensionLite);

      verifyExtensionContainingType(extension);
      final FieldDescriptor descriptor = extension.getDescriptor();
      return extensions == null ? 0 : extensions.getRepeatedFieldCount(descriptor);
    }

    /** Get the value of an extension. */
    @Override
    public final <T> T getExtension(final ExtensionLite<MessageT, T> extensionLite) {
      Extension<MessageT, T> extension = checkNotLite(extensionLite);

      verifyExtensionContainingType(extension);
      FieldDescriptor descriptor = extension.getDescriptor();
      final Object value = extensions == null ? null : extensions.getField(descriptor);
      if (value == null) {
        if (descriptor.isRepeated()) {
          return (T) Collections.emptyList();
        } else if (descriptor.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
          return (T) extension.getMessageDefaultInstance();
        } else {
          return (T) extension.fromReflectionType(descriptor.getDefaultValue());
        }
      } else {
        return (T) extension.fromReflectionType(value);
      }
    }

    /** Get one element of a repeated extension. */
    @Override
    public final <T> T getExtension(
        final ExtensionLite<MessageT, List<T>> extensionLite, final int index) {
      Extension<MessageT, List<T>> extension = checkNotLite(extensionLite);

      verifyExtensionContainingType(extension);
      FieldDescriptor descriptor = extension.getDescriptor();
      if (extensions == null) {
        throw new IndexOutOfBoundsException();
      }
      return (T)
          extension.singularFromReflectionType(extensions.getRepeatedField(descriptor, index));
    }

    /** Set the value of an extension. */
    public final <T> BuilderT setExtension(
        final ExtensionLite<MessageT, T> extensionLite, final T value) {
      Extension<MessageT, T> extension = checkNotLite(extensionLite);

      verifyExtensionContainingType(extension);
      ensureExtensionsIsMutable();
      final FieldDescriptor descriptor = extension.getDescriptor();
      extensions.setField(descriptor, extension.toReflectionType(value));
      onChanged();
      return (BuilderT) this;
    }

    /** Set the value of one element of a repeated extension. */
    public final <T> BuilderT setExtension(
        final ExtensionLite<MessageT, List<T>> extensionLite, final int index, final T value) {
      Extension<MessageT, List<T>> extension = checkNotLite(extensionLite);

      verifyExtensionContainingType(extension);
      ensureExtensionsIsMutable();
      final FieldDescriptor descriptor = extension.getDescriptor();
      extensions.setRepeatedField(descriptor, index, extension.singularToReflectionType(value));
      onChanged();
      return (BuilderT) this;
    }

    /** Append a value to a repeated extension. */
    public final <T> BuilderT addExtension(
        final ExtensionLite<MessageT, List<T>> extensionLite, final T value) {
      Extension<MessageT, List<T>> extension = checkNotLite(extensionLite);

      verifyExtensionContainingType(extension);
      ensureExtensionsIsMutable();
      final FieldDescriptor descriptor = extension.getDescriptor();
      extensions.addRepeatedField(descriptor, extension.singularToReflectionType(value));
      onChanged();
      return (BuilderT) this;
    }

    /** Clear an extension. */
    public final <T> BuilderT clearExtension(final ExtensionLite<MessageT, T> extensionLite) {
      Extension<MessageT, T> extension = checkNotLite(extensionLite);

      verifyExtensionContainingType(extension);
      ensureExtensionsIsMutable();
      extensions.clearField(extension.getDescriptor());
      onChanged();
      return (BuilderT) this;
    }

    /**
     * Check if a singular extension is present.
     * <p>TODO: handled by ExtensionLite version
     */
    @Override
    public final <T> boolean hasExtension(final Extension<MessageT, T> extension) {
      return hasExtension((ExtensionLite<MessageT, T>) extension);
    }
    /**
     * Check if a singular extension is present.
     * <p>TODO: handled by ExtensionLite version
     */
    @Override
    public final <T> boolean hasExtension(
        final FlattenedGeneratedMessageV3.GeneratedExtension<MessageT, T> extension) {
      return hasExtension((ExtensionLite<MessageT, T>) extension);
    }
    /**
     * Get the number of elements in a repeated extension.
     * <p>TODO: handled by ExtensionLite version
     */
    @Override
    public final <T> int getExtensionCount(
        final Extension<MessageT, List<T>> extension) {
      return getExtensionCount((ExtensionLite<MessageT, List<T>>) extension);
    }
    /**
     * Get the number of elements in a repeated extension.
     * <p>TODO: handled by ExtensionLite version
     */
    @Override
    public final <T> int getExtensionCount(
        final FlattenedGeneratedMessageV3.GeneratedExtension<MessageT, List<T>> extension) {
      return getExtensionCount((ExtensionLite<MessageT, List<T>>) extension);
    }
    /**
     * Get the value of an extension.
     * <p>TODO: handled by ExtensionLite version
     */
    @Override
    public final <T> T getExtension(final Extension<MessageT, T> extension) {
      return getExtension((ExtensionLite<MessageT, T>) extension);
    }
    /** Get the value of an extension.
     * <p>TODO: handled by ExtensionLite version
     */
    @Override
    public final <T> T getExtension(
        final GeneratedExtension<MessageT, T> extension) {
      return getExtension((ExtensionLite<MessageT, T>) extension);
    }
    /**
     * Get the value of an extension.
     * <p>TODO: handled by ExtensionLite version
     */
    @Override
    public final <T> T getExtension(
        final Extension<MessageT, List<T>> extension, final int index) {
      return getExtension((ExtensionLite<MessageT, List<T>>) extension, index);
    }
    /**
     * Get the value of an extension.
     * <p>TODO: handled by ExtensionLite version
     */
    @Override
    public final <T> T getExtension(
        final GeneratedExtension<MessageT, List<T>> extension, final int index) {
      return getExtension((ExtensionLite<MessageT, List<T>>) extension, index);
    }
    /**
     * Set the value of an extension.
     * <p>TODO: handled by ExtensionLite version
     */
    public final <T> BuilderT setExtension(
        final Extension<MessageT, T> extension, final T value) {
      return setExtension((ExtensionLite<MessageT, T>) extension, value);
    }
    /**
     * Set the value of an extension.
     * <p>TODO: handled by ExtensionLite version
     */
    public <T> BuilderT setExtension(
        final GeneratedExtension<MessageT, T> extension, final T value) {
      return setExtension((ExtensionLite<MessageT, T>) extension, value);
    }
    /**
     * Set the value of one element of a repeated extension.
     * <p>TODO: handled by ExtensionLite version
     */
    public final <T> BuilderT setExtension(
        final Extension<MessageT, List<T>> extension,
        final int index, final T value) {
      return setExtension((ExtensionLite<MessageT, List<T>>) extension, index, value);
    }
    /**
     * Set the value of one element of a repeated extension.
     * <p>TODO: handled by ExtensionLite version
     */
    public <T> BuilderT setExtension(
        final GeneratedExtension<MessageT, List<T>> extension,
        final int index, final T value) {
      return setExtension((ExtensionLite<MessageT, List<T>>) extension, index, value);
    }
    /**
     * Append a value to a repeated extension.
     * <p>TODO: handled by ExtensionLite version
     */
    public final <T> BuilderT addExtension(
        final Extension<MessageT, List<T>> extension, final T value) {
      return addExtension((ExtensionLite<MessageT, List<T>>) extension, value);
    }
    /**
     * Append a value to a repeated extension.
     * <p>TODO: handled by ExtensionLite version
     */
    public <T> BuilderT addExtension(
        final GeneratedExtension<MessageT, List<T>> extension, final T value) {
      return addExtension((ExtensionLite<MessageT, List<T>>) extension, value);
    }
    /**
     * Clear an extension.
     * <p>TODO: handled by ExtensionLite version
     */
    public final <T> BuilderT clearExtension(
        final Extension<MessageT, T> extension) {
      return clearExtension((ExtensionLite<MessageT, T>) extension);
    }
    /**
     * Clears an extension.
     * <p>TODO: handled by ExtensionLite version
     */
    public <T> BuilderT clearExtension(
        final GeneratedExtension<MessageT, T> extension) {
      return clearExtension((ExtensionLite<MessageT, T>) extension);
    }

    /** Called by subclasses to check if all extensions are initialized. */
    protected boolean extensionsAreInitialized() {
      return extensions == null || extensions.isInitialized();
    }

    /**
     * Called by the build code path to create a copy of the extensions for building the message.
     */
    private FieldSet<FieldDescriptor> buildExtensions() {
      return extensions == null
          ? (FieldSet<FieldDescriptor>) FieldSet.emptySet()
          : extensions.buildPartial();
    }

    @Override
    public boolean isInitialized() {
      return super.isInitialized() && extensionsAreInitialized();
    }

    // ---------------------------------------------------------------
    // Reflection

    @Override
    public Map<FieldDescriptor, Object> getAllFields() {
      final Map<FieldDescriptor, Object> result = super.getAllFieldsMutable();
      if (extensions != null) {
        result.putAll(extensions.getAllFields());
      }
      return Collections.unmodifiableMap(result);
    }

    @Override
    public Object getField(final FieldDescriptor field) {
      if (field.isExtension()) {
        verifyContainingType(field);
        final Object value = extensions == null ? null : extensions.getField(field);
        if (value == null) {
          if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
            // Lacking an ExtensionRegistry, we have no way to determine the
            // extension's real type, so we return a DynamicMessage.
            return DynamicMessage.getDefaultInstance(field.getMessageType());
          } else {
            return field.getDefaultValue();
          }
        } else {
          return value;
        }
      } else {
        return super.getField(field);
      }
    }

    @Override
    public Message.Builder getFieldBuilder(final FieldDescriptor field) {
      if (field.isExtension()) {
        verifyContainingType(field);
        if (field.getJavaType() != FieldDescriptor.JavaType.MESSAGE) {
          throw new UnsupportedOperationException(
              "getFieldBuilder() called on a non-Message type.");
        }
        ensureExtensionsIsMutable();
        final Object value = extensions.getFieldAllowBuilders(field);
        if (value == null) {
          Message.Builder builder = DynamicMessage.newBuilder(field.getMessageType());
          extensions.setField(field, builder);
          onChanged();
          return builder;
        } else {
          if (value instanceof Message.Builder) {
            return (Message.Builder) value;
          } else if (value instanceof Message) {
            Message.Builder builder = ((Message) value).toBuilder();
            extensions.setField(field, builder);
            onChanged();
            return builder;
          } else {
            throw new UnsupportedOperationException(
                "getRepeatedFieldBuilder() called on a non-Message type.");
          }
        }
      } else {
        return super.getFieldBuilder(field);
      }
    }

    @Override
    public int getRepeatedFieldCount(final FieldDescriptor field) {
      if (field.isExtension()) {
        verifyContainingType(field);
        return extensions == null ? 0 : extensions.getRepeatedFieldCount(field);
      } else {
        return super.getRepeatedFieldCount(field);
      }
    }

    @Override
    public Object getRepeatedField(final FieldDescriptor field, final int index) {
      if (field.isExtension()) {
        verifyContainingType(field);
        if (extensions == null) {
          throw new IndexOutOfBoundsException();
        }
        return extensions.getRepeatedField(field, index);
      } else {
        return super.getRepeatedField(field, index);
      }
    }

    @Override
    public Message.Builder getRepeatedFieldBuilder(final FieldDescriptor field, final int index) {
      if (field.isExtension()) {
        verifyContainingType(field);
        ensureExtensionsIsMutable();
        if (field.getJavaType() != FieldDescriptor.JavaType.MESSAGE) {
          throw new UnsupportedOperationException(
              "getRepeatedFieldBuilder() called on a non-Message type.");
        }
        final Object value = extensions.getRepeatedFieldAllowBuilders(field, index);
        if (value instanceof Message.Builder) {
          return (Message.Builder) value;
        } else if (value instanceof Message) {
          Message.Builder builder = ((Message) value).toBuilder();
          extensions.setRepeatedField(field, index, builder);
          onChanged();
          return builder;
        } else {
          throw new UnsupportedOperationException(
              "getRepeatedFieldBuilder() called on a non-Message type.");
        }
      } else {
        return super.getRepeatedFieldBuilder(field, index);
      }
    }

    @Override
    public boolean hasField(final FieldDescriptor field) {
      if (field.isExtension()) {
        verifyContainingType(field);
        return extensions != null && extensions.hasField(field);
      } else {
        return super.hasField(field);
      }
    }

    @Override
    public BuilderT setField(final FieldDescriptor field, final Object value) {
      if (field.isExtension()) {
        verifyContainingType(field);
        ensureExtensionsIsMutable();
        extensions.setField(field, value);
        onChanged();
        return (BuilderT) this;
      } else {
        return super.setField(field, value);
      }
    }

    @Override
    public BuilderT clearField(final FieldDescriptor field) {
      if (field.isExtension()) {
        verifyContainingType(field);
        ensureExtensionsIsMutable();
        extensions.clearField(field);
        onChanged();
        return (BuilderT) this;
      } else {
        return super.clearField(field);
      }
    }

    @Override
    public BuilderT setRepeatedField(
        final FieldDescriptor field, final int index, final Object value) {
      if (field.isExtension()) {
        verifyContainingType(field);
        ensureExtensionsIsMutable();
        extensions.setRepeatedField(field, index, value);
        onChanged();
        return (BuilderT) this;
      } else {
        return super.setRepeatedField(field, index, value);
      }
    }

    @Override
    public BuilderT addRepeatedField(final FieldDescriptor field, final Object value) {
      if (field.isExtension()) {
        verifyContainingType(field);
        ensureExtensionsIsMutable();
        extensions.addRepeatedField(field, value);
        onChanged();
        return (BuilderT) this;
      } else {
        return super.addRepeatedField(field, value);
      }
    }

    @Override
    public Message.Builder newBuilderForField(final FieldDescriptor field) {
      if (field.isExtension()) {
        return DynamicMessage.newBuilder(field.getMessageType());
      } else {
        return super.newBuilderForField(field);
      }
    }

    protected final void mergeExtensionFields(final ExtendableMessage<?> other) {
      if (other.extensions != null) {
        ensureExtensionsIsMutable();
        extensions.mergeFrom(other.extensions);
        onChanged();
      }
    }

    @Override
    protected boolean parseUnknownField(
        CodedInputStream input, ExtensionRegistryLite extensionRegistry, int tag)
        throws IOException {
      ensureExtensionsIsMutable();
      return MessageReflection.mergeFieldFrom(
          input,
          input.shouldDiscardUnknownFields() ? null : getUnknownFieldSetBuilder(),
          extensionRegistry,
          getDescriptorForType(),
          new MessageReflection.ExtensionBuilderAdapter(extensions),
          tag);
    }

    private void verifyContainingType(final FieldDescriptor field) {
      if (field.getContainingType() != getDescriptorForType()) {
        throw new IllegalArgumentException("FieldDescriptor does not match message type.");
      }
    }
  }

  // -----------------------------------------------------------------

  /**
   * Gets the descriptor for an extension. The implementation depends on whether the extension is
   * scoped in the top level of a file or scoped in a Message.
   */
  interface ExtensionDescriptorRetriever {
    FieldDescriptor getDescriptor();
  }

  // =================================================================

  /** Calls Class.getMethod and throws a RuntimeException if it fails. */
  private static Method getMethodOrDie(
      final Class<?> clazz, final String name, final Class<?>... params) {
    try {
      return clazz.getMethod(name, params);
    } catch (NoSuchMethodException e) {
      throw new IllegalStateException(
          "Generated message class \"" + clazz.getName() + "\" missing method \"" + name + "\".",
          e);
    }
  }

  /** Calls invoke and throws a RuntimeException if it fails. */
  @CanIgnoreReturnValue
  private static Object invokeOrDie(
      final Method method, final Object object, final Object... params) {
    try {
      return method.invoke(object, params);
    } catch (IllegalAccessException e) {
      throw new IllegalStateException(
          "Couldn't use Java reflection to implement protocol message reflection.", e);
    } catch (InvocationTargetException e) {
      final Throwable cause = e.getCause();
      if (cause instanceof RuntimeException) {
        throw (RuntimeException) cause;
      } else if (cause instanceof Error) {
        throw (Error) cause;
      } else {
        throw new IllegalStateException(
            "Unexpected exception thrown by generated accessor method.", cause);
      }
    }
  }

  /**
   * Gets the map field with the given field number. This method should be overridden in the
   * generated message class if the message contains map fields.
   *
   * <p>Unlike other field types, reflection support for map fields can't be implemented based on
   * generated public API because we need to access a map field as a list in reflection API but the
   * generated API only allows us to access it as a map. This method returns the underlying map
   * field directly and thus enables us to access the map field as a list.
   */
  @SuppressWarnings("unused")
  protected MapFieldReflectionAccessor internalGetMapFieldReflection(int fieldNumber) {
    return internalGetMapField(fieldNumber);
  }

  /** TODO: Remove, exists for compatibility with generated code. */
  @Deprecated
  @SuppressWarnings({"rawtypes", "unused"})
  protected MapField internalGetMapField(int fieldNumber) {
    // Note that we can't use descriptor names here because this method will
    // be called when descriptor is being initialized.
    throw new IllegalArgumentException("No map fields found in " + getClass().getName());
  }

  /**
   * Users should ignore this class. This class provides the implementation with access to the
   * fields of a message object using Java reflection.
   */
  public static final class FieldAccessorTable {

    /**
     * Construct a FieldAccessorTable for a particular message class. Only one FieldAccessorTable
     * should ever be constructed per class.
     *
     * @param descriptor The type's descriptor.
     * @param camelCaseNames The camelcase names of all fields in the message. These are used to
     *     derive the accessor method names.
     * @param messageClass The message type.
     * @param builderClass The builder type.
     */
    public FieldAccessorTable(
        final Descriptor descriptor,
        final String[] camelCaseNames,
        final Class<? extends FlattenedGeneratedMessageV3> messageClass,
        final Class<? extends Builder<?>> builderClass) {
      this(descriptor, camelCaseNames);
      ensureFieldAccessorsInitialized(messageClass, builderClass);
    }

    /**
     * Construct a FieldAccessorTable for a particular message class without initializing
     * FieldAccessors.
     */
    public FieldAccessorTable(final Descriptor descriptor, final String[] camelCaseNames) {
      this.descriptor = descriptor;
      this.camelCaseNames = camelCaseNames;
      fields = new FieldAccessor[descriptor.getFields().size()];
      oneofs = new OneofAccessor[descriptor.getOneofs().size()];
      initialized = false;
    }

    /**
     * Ensures the field accessors are initialized. This method is thread-safe.
     *
     * @param messageClass The message type.
     * @param builderClass The builder type.
     * @return this
     */
    public FieldAccessorTable ensureFieldAccessorsInitialized(
            Class<? extends FlattenedGeneratedMessageV3> messageClass, Class<? extends Builder<?>> builderClass) {
      if (initialized) {
        return this;
      }
      synchronized (this) {
        if (initialized) {
          return this;
        }
        int fieldsSize = fields.length;
        for (int i = 0; i < fieldsSize; i++) {
          FieldDescriptor field = descriptor.getFields().get(i);
          String containingOneofCamelCaseName = null;
          if (field.getContainingOneof() != null) {
            int index = fieldsSize + field.getContainingOneof().getIndex();
            if (index < camelCaseNames.length) {
              containingOneofCamelCaseName = camelCaseNames[index];
            }
          }
          if (field.isRepeated()) {
            if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
              if (field.isMapField()) {
                fields[i] = new MapFieldAccessor(field, messageClass);
              } else {
                fields[i] =
                    new RepeatedMessageFieldAccessor(
                        field, camelCaseNames[i], messageClass, builderClass);
              }
            } else if (field.getJavaType() == FieldDescriptor.JavaType.ENUM) {
              fields[i] =
                  new RepeatedEnumFieldAccessor(
                      field, camelCaseNames[i], messageClass, builderClass);
            } else {
              fields[i] =
                  new RepeatedFieldAccessor(field, camelCaseNames[i], messageClass, builderClass);
            }
          } else {
            if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
              fields[i] =
                  new SingularMessageFieldAccessor(
                      field,
                      camelCaseNames[i],
                      messageClass,
                      builderClass,
                      containingOneofCamelCaseName);
            } else if (field.getJavaType() == FieldDescriptor.JavaType.ENUM) {
              fields[i] =
                  new SingularEnumFieldAccessor(
                      field,
                      camelCaseNames[i],
                      messageClass,
                      builderClass,
                      containingOneofCamelCaseName);
            } else if (field.getJavaType() == FieldDescriptor.JavaType.STRING) {
              fields[i] =
                  new SingularStringFieldAccessor(
                      field,
                      camelCaseNames[i],
                      messageClass,
                      builderClass,
                      containingOneofCamelCaseName);
            } else {
              fields[i] =
                  new SingularFieldAccessor(
                      field,
                      camelCaseNames[i],
                      messageClass,
                      builderClass,
                      containingOneofCamelCaseName);
            }
          }
        }

        for (int i = 0; i < descriptor.getOneofs().size(); i++) {
          if (i < descriptor.getRealOneofs().size()) {
            oneofs[i] =
                new RealOneofAccessor(
                    descriptor, i, camelCaseNames[i + fieldsSize], messageClass, builderClass);
          } else {
            oneofs[i] = new SyntheticOneofAccessor(descriptor, i);
          }
        }

        initialized = true;
        camelCaseNames = null;
        return this;
      }
    }

    private final Descriptor descriptor;
    private final FieldAccessor[] fields;
    private String[] camelCaseNames;
    private final OneofAccessor[] oneofs;
    private volatile boolean initialized;

    /** Get the FieldAccessor for a particular field. */
    private FieldAccessor getField(final FieldDescriptor field) {
      if (field.getContainingType() != descriptor) {
        throw new IllegalArgumentException("FieldDescriptor does not match message type.");
      } else if (field.isExtension()) {
        // If this type had extensions, it would subclass ExtendableMessage,
        // which overrides the reflection interface to handle extensions.
        throw new IllegalArgumentException("This type does not have extensions.");
      }
      return fields[field.getIndex()];
    }

    /** Get the OneofAccessor for a particular oneof. */
    private OneofAccessor getOneof(final OneofDescriptor oneof) {
      if (oneof.getContainingType() != descriptor) {
        throw new IllegalArgumentException("OneofDescriptor does not match message type.");
      }
      return oneofs[oneof.getIndex()];
    }

    /**
     * Abstract interface that provides access to a single field. This is implemented differently
     * depending on the field type and cardinality.
     */
    private interface FieldAccessor {
      Object get(FlattenedGeneratedMessageV3 message);

      Object get(FlattenedGeneratedMessageV3.Builder<?> builder);

      Object getRaw(FlattenedGeneratedMessageV3 message);

      void set(Builder<?> builder, Object value);

      Object getRepeated(FlattenedGeneratedMessageV3 message, int index);

      Object getRepeated(FlattenedGeneratedMessageV3.Builder<?> builder, int index);

      void setRepeated(Builder<?> builder, int index, Object value);

      void addRepeated(Builder<?> builder, Object value);

      boolean has(FlattenedGeneratedMessageV3 message);

      boolean has(FlattenedGeneratedMessageV3.Builder<?> builder);

      int getRepeatedCount(FlattenedGeneratedMessageV3 message);

      int getRepeatedCount(FlattenedGeneratedMessageV3.Builder<?> builder);

      void clear(Builder<?> builder);

      Message.Builder newBuilder();

      Message.Builder getBuilder(FlattenedGeneratedMessageV3.Builder<?> builder);

      Message.Builder getRepeatedBuilder(FlattenedGeneratedMessageV3.Builder<?> builder, int index);
    }

    /** OneofAccessor provides access to a single oneof. */
    private static interface OneofAccessor {
      public boolean has(final FlattenedGeneratedMessageV3 message);

      public boolean has(FlattenedGeneratedMessageV3.Builder<?> builder);

      public FieldDescriptor get(final FlattenedGeneratedMessageV3 message);

      public FieldDescriptor get(FlattenedGeneratedMessageV3.Builder<?> builder);

      public void clear(final Builder<?> builder);
    }

    /** RealOneofAccessor provides access to a single real oneof. */
    private static class RealOneofAccessor implements OneofAccessor {
      RealOneofAccessor(
          final Descriptor descriptor,
          final int oneofIndex,
          final String camelCaseName,
          final Class<? extends FlattenedGeneratedMessageV3> messageClass,
          final Class<? extends Builder<?>> builderClass) {
        this.descriptor = descriptor;
        caseMethod = getMethodOrDie(messageClass, "get" + camelCaseName + "Case");
        caseMethodBuilder = getMethodOrDie(builderClass, "get" + camelCaseName + "Case");
        clearMethod = getMethodOrDie(builderClass, "clear" + camelCaseName);
      }

      private final Descriptor descriptor;
      private final Method caseMethod;
      private final Method caseMethodBuilder;
      private final Method clearMethod;

      @Override
      public boolean has(final FlattenedGeneratedMessageV3 message) {
        return ((Internal.EnumLite) invokeOrDie(caseMethod, message)).getNumber() != 0;
      }

      @Override
      public boolean has(FlattenedGeneratedMessageV3.Builder<?> builder) {
        return ((Internal.EnumLite) invokeOrDie(caseMethodBuilder, builder)).getNumber() != 0;
      }

      @Override
      public FieldDescriptor get(final FlattenedGeneratedMessageV3 message) {
        int fieldNumber = ((Internal.EnumLite) invokeOrDie(caseMethod, message)).getNumber();
        if (fieldNumber > 0) {
          return descriptor.findFieldByNumber(fieldNumber);
        }
        return null;
      }

      @Override
      public FieldDescriptor get(FlattenedGeneratedMessageV3.Builder<?> builder) {
        int fieldNumber = ((Internal.EnumLite) invokeOrDie(caseMethodBuilder, builder)).getNumber();
        if (fieldNumber > 0) {
          return descriptor.findFieldByNumber(fieldNumber);
        }
        return null;
      }

      @Override
      public void clear(final Builder<?> builder) {
        // TODO: remove the unused variable
        Object unused = invokeOrDie(clearMethod, builder);
      }
    }

    /** SyntheticOneofAccessor provides access to a single synthetic oneof. */
    private static class SyntheticOneofAccessor implements OneofAccessor {
      SyntheticOneofAccessor(final Descriptor descriptor, final int oneofIndex) {
        OneofDescriptor oneofDescriptor = descriptor.getOneofs().get(oneofIndex);
        fieldDescriptor = oneofDescriptor.getFields().get(0);
      }

      private final FieldDescriptor fieldDescriptor;

      @Override
      public boolean has(final FlattenedGeneratedMessageV3 message) {
        return message.hasField(fieldDescriptor);
      }

      @Override
      public boolean has(FlattenedGeneratedMessageV3.Builder<?> builder) {
        return builder.hasField(fieldDescriptor);
      }

      @Override
      public FieldDescriptor get(final FlattenedGeneratedMessageV3 message) {
        return message.hasField(fieldDescriptor) ? fieldDescriptor : null;
      }

      public FieldDescriptor get(FlattenedGeneratedMessageV3.Builder<?> builder) {
        return builder.hasField(fieldDescriptor) ? fieldDescriptor : null;
      }

      @Override
      public void clear(final Builder<?> builder) {
        builder.clearField(fieldDescriptor);
      }
    }

    // ---------------------------------------------------------------

    @SuppressWarnings("SameNameButDifferent")
    private static class SingularFieldAccessor implements FieldAccessor {
      private interface MethodInvoker {
        Object get(final FlattenedGeneratedMessageV3 message);

        Object get(FlattenedGeneratedMessageV3.Builder<?> builder);

        int getOneofFieldNumber(final FlattenedGeneratedMessageV3 message);

        int getOneofFieldNumber(final FlattenedGeneratedMessageV3.Builder<?> builder);

        void set(final FlattenedGeneratedMessageV3.Builder<?> builder, final Object value);

        boolean has(final FlattenedGeneratedMessageV3 message);

        boolean has(FlattenedGeneratedMessageV3.Builder<?> builder);

        void clear(final FlattenedGeneratedMessageV3.Builder<?> builder);
      }

      private static final class ReflectionInvoker implements MethodInvoker {
        private final Method getMethod;
        private final Method getMethodBuilder;
        private final Method setMethod;
        private final Method hasMethod;
        private final Method hasMethodBuilder;
        private final Method clearMethod;
        private final Method caseMethod;
        private final Method caseMethodBuilder;

        ReflectionInvoker(
            final FieldDescriptor descriptor,
            final String camelCaseName,
            final Class<? extends FlattenedGeneratedMessageV3> messageClass,
            final Class<? extends Builder<?>> builderClass,
            final String containingOneofCamelCaseName,
            boolean isOneofField,
            boolean hasHasMethod) {
          getMethod = getMethodOrDie(messageClass, "get" + camelCaseName);
          getMethodBuilder = getMethodOrDie(builderClass, "get" + camelCaseName);
          Class<?> type = getMethod.getReturnType();
          setMethod = getMethodOrDie(builderClass, "set" + camelCaseName, type);
          hasMethod = hasHasMethod ? getMethodOrDie(messageClass, "has" + camelCaseName) : null;
          hasMethodBuilder =
              hasHasMethod ? getMethodOrDie(builderClass, "has" + camelCaseName) : null;
          clearMethod = getMethodOrDie(builderClass, "clear" + camelCaseName);
          caseMethod =
              isOneofField
                  ? getMethodOrDie(messageClass, "get" + containingOneofCamelCaseName + "Case")
                  : null;
          caseMethodBuilder =
              isOneofField
                  ? getMethodOrDie(builderClass, "get" + containingOneofCamelCaseName + "Case")
                  : null;
        }

        @Override
        public Object get(final FlattenedGeneratedMessageV3 message) {
          return invokeOrDie(getMethod, message);
        }

        @Override
        public Object get(FlattenedGeneratedMessageV3.Builder<?> builder) {
          return invokeOrDie(getMethodBuilder, builder);
        }

        @Override
        public int getOneofFieldNumber(final FlattenedGeneratedMessageV3 message) {
          return ((Internal.EnumLite) invokeOrDie(caseMethod, message)).getNumber();
        }

        @Override
        public int getOneofFieldNumber(final FlattenedGeneratedMessageV3.Builder<?> builder) {
          return ((Internal.EnumLite) invokeOrDie(caseMethodBuilder, builder)).getNumber();
        }

        @Override
        public void set(final FlattenedGeneratedMessageV3.Builder<?> builder, final Object value) {
          // TODO: remove the unused variable
          Object unused = invokeOrDie(setMethod, builder, value);
        }

        @Override
        public boolean has(final FlattenedGeneratedMessageV3 message) {
          return (Boolean) invokeOrDie(hasMethod, message);
        }

        @Override
        public boolean has(FlattenedGeneratedMessageV3.Builder<?> builder) {
          return (Boolean) invokeOrDie(hasMethodBuilder, builder);
        }

        @Override
        public void clear(final FlattenedGeneratedMessageV3.Builder<?> builder) {
          // TODO: remove the unused variable
          Object unused = invokeOrDie(clearMethod, builder);
        }
      }

      SingularFieldAccessor(
          final FieldDescriptor descriptor,
          final String camelCaseName,
          final Class<? extends FlattenedGeneratedMessageV3> messageClass,
          final Class<? extends Builder<?>> builderClass,
          final String containingOneofCamelCaseName) {
        isOneofField =
            descriptor.getRealContainingOneof() != null;
        hasHasMethod =
            descriptor.getFile().getSyntax() == FileDescriptor.Syntax.EDITIONS && descriptor.hasPresence()
                || descriptor.getFile().getSyntax() == FileDescriptor.Syntax.PROTO2
                || descriptor.hasOptionalKeyword()
                || (!isOneofField && descriptor.getJavaType() == FieldDescriptor.JavaType.MESSAGE);
        ReflectionInvoker reflectionInvoker =
            new ReflectionInvoker(
                descriptor,
                camelCaseName,
                messageClass,
                builderClass,
                containingOneofCamelCaseName,
                isOneofField,
                hasHasMethod);
        field = descriptor;
        type = reflectionInvoker.getMethod.getReturnType();
        invoker = getMethodInvoker(reflectionInvoker);
      }

      static MethodInvoker getMethodInvoker(ReflectionInvoker accessor) {
        return accessor;
      }

      // Note:  We use Java reflection to call public methods rather than
      //   access private fields directly as this avoids runtime security
      //   checks.
      protected final Class<?> type;
      protected final FieldDescriptor field;
      protected final boolean isOneofField;
      protected final boolean hasHasMethod;
      protected final MethodInvoker invoker;

      @Override
      public Object get(final FlattenedGeneratedMessageV3 message) {
        return invoker.get(message);
      }

      @Override
      public Object get(FlattenedGeneratedMessageV3.Builder<?> builder) {
        return invoker.get(builder);
      }

      @Override
      public Object getRaw(final FlattenedGeneratedMessageV3 message) {
        return get(message);
      }

      @Override
      public void set(final Builder<?> builder, final Object value) {
        invoker.set(builder, value);
      }

      @Override
      public Object getRepeated(final FlattenedGeneratedMessageV3 message, final int index) {
        throw new UnsupportedOperationException("getRepeatedField() called on a singular field.");
      }

      @Override
      public Object getRepeated(FlattenedGeneratedMessageV3.Builder<?> builder, int index) {
        throw new UnsupportedOperationException("getRepeatedField() called on a singular field.");
      }

      @Override
      public void setRepeated(final Builder<?> builder, final int index, final Object value) {
        throw new UnsupportedOperationException("setRepeatedField() called on a singular field.");
      }

      @Override
      public void addRepeated(final Builder<?> builder, final Object value) {
        throw new UnsupportedOperationException("addRepeatedField() called on a singular field.");
      }

      @Override
      public boolean has(final FlattenedGeneratedMessageV3 message) {
        if (!hasHasMethod) {
          if (isOneofField) {
            return invoker.getOneofFieldNumber(message) == field.getNumber();
          }
          return !get(message).equals(field.getDefaultValue());
        }
        return invoker.has(message);
      }

      @Override
      public boolean has(FlattenedGeneratedMessageV3.Builder<?> builder) {
        if (!hasHasMethod) {
          if (isOneofField) {
            return invoker.getOneofFieldNumber(builder) == field.getNumber();
          }
          return !get(builder).equals(field.getDefaultValue());
        }
        return invoker.has(builder);
      }

      @Override
      public int getRepeatedCount(final FlattenedGeneratedMessageV3 message) {
        throw new UnsupportedOperationException(
            "getRepeatedFieldSize() called on a singular field.");
      }

      @Override
      public int getRepeatedCount(FlattenedGeneratedMessageV3.Builder<?> builder) {
        throw new UnsupportedOperationException(
            "getRepeatedFieldSize() called on a singular field.");
      }

      @Override
      public void clear(final Builder<?> builder) {
        invoker.clear(builder);
      }

      @Override
      public Message.Builder newBuilder() {
        throw new UnsupportedOperationException(
            "newBuilderForField() called on a non-Message type.");
      }

      @Override
      public Message.Builder getBuilder(FlattenedGeneratedMessageV3.Builder<?> builder) {
        throw new UnsupportedOperationException("getFieldBuilder() called on a non-Message type.");
      }

      @Override
      public Message.Builder getRepeatedBuilder(FlattenedGeneratedMessageV3.Builder<?> builder, int index) {
        throw new UnsupportedOperationException(
            "getRepeatedFieldBuilder() called on a non-Message type.");
      }
    }

    @SuppressWarnings("SameNameButDifferent")
    private static class RepeatedFieldAccessor implements FieldAccessor {
      interface MethodInvoker {
        Object get(final FlattenedGeneratedMessageV3 message);

        Object get(FlattenedGeneratedMessageV3.Builder<?> builder);

        Object getRepeated(final FlattenedGeneratedMessageV3 message, final int index);

        Object getRepeated(FlattenedGeneratedMessageV3.Builder<?> builder, int index);

        void setRepeated(
                final FlattenedGeneratedMessageV3.Builder<?> builder, final int index, final Object value);

        void addRepeated(final FlattenedGeneratedMessageV3.Builder<?> builder, final Object value);

        int getRepeatedCount(final FlattenedGeneratedMessageV3 message);

        int getRepeatedCount(FlattenedGeneratedMessageV3.Builder<?> builder);

        void clear(final FlattenedGeneratedMessageV3.Builder<?> builder);
      }

      private static final class ReflectionInvoker implements MethodInvoker {
        private final Method getMethod;
        private final Method getMethodBuilder;
        private final Method getRepeatedMethod;
        private final Method getRepeatedMethodBuilder;
        private final Method setRepeatedMethod;
        private final Method addRepeatedMethod;
        private final Method getCountMethod;
        private final Method getCountMethodBuilder;
        private final Method clearMethod;

        ReflectionInvoker(
            final FieldDescriptor descriptor,
            final String camelCaseName,
            final Class<? extends FlattenedGeneratedMessageV3> messageClass,
            final Class<? extends Builder<?>> builderClass) {
          getMethod = getMethodOrDie(messageClass, "get" + camelCaseName + "List");
          getMethodBuilder = getMethodOrDie(builderClass, "get" + camelCaseName + "List");
          getRepeatedMethod = getMethodOrDie(messageClass, "get" + camelCaseName, Integer.TYPE);
          getRepeatedMethodBuilder =
              getMethodOrDie(builderClass, "get" + camelCaseName, Integer.TYPE);
          Class<?> type = getRepeatedMethod.getReturnType();
          setRepeatedMethod =
              getMethodOrDie(builderClass, "set" + camelCaseName, Integer.TYPE, type);
          addRepeatedMethod = getMethodOrDie(builderClass, "add" + camelCaseName, type);
          getCountMethod = getMethodOrDie(messageClass, "get" + camelCaseName + "Count");
          getCountMethodBuilder = getMethodOrDie(builderClass, "get" + camelCaseName + "Count");
          clearMethod = getMethodOrDie(builderClass, "clear" + camelCaseName);
        }

        @Override
        public Object get(final FlattenedGeneratedMessageV3 message) {
          return invokeOrDie(getMethod, message);
        }

        @Override
        public Object get(FlattenedGeneratedMessageV3.Builder<?> builder) {
          return invokeOrDie(getMethodBuilder, builder);
        }

        @Override
        public Object getRepeated(final FlattenedGeneratedMessageV3 message, final int index) {
          return invokeOrDie(getRepeatedMethod, message, index);
        }

        @Override
        public Object getRepeated(FlattenedGeneratedMessageV3.Builder<?> builder, int index) {
          return invokeOrDie(getRepeatedMethodBuilder, builder, index);
        }

        @Override
        public void setRepeated(
                final FlattenedGeneratedMessageV3.Builder<?> builder, final int index, final Object value) {
          // TODO: remove the unused variable
          Object unused = invokeOrDie(setRepeatedMethod, builder, index, value);
        }

        @Override
        public void addRepeated(final FlattenedGeneratedMessageV3.Builder<?> builder, final Object value) {
          // TODO: remove the unused variable
          Object unused = invokeOrDie(addRepeatedMethod, builder, value);
        }

        @Override
        public int getRepeatedCount(final FlattenedGeneratedMessageV3 message) {
          return (Integer) invokeOrDie(getCountMethod, message);
        }

        @Override
        public int getRepeatedCount(FlattenedGeneratedMessageV3.Builder<?> builder) {
          return (Integer) invokeOrDie(getCountMethodBuilder, builder);
        }

        @Override
        public void clear(final FlattenedGeneratedMessageV3.Builder<?> builder) {
          // TODO: remove the unused variable
          Object unused = invokeOrDie(clearMethod, builder);
        }
      }

      protected final Class<?> type;
      protected final MethodInvoker invoker;

      RepeatedFieldAccessor(
          final FieldDescriptor descriptor,
          final String camelCaseName,
          final Class<? extends FlattenedGeneratedMessageV3> messageClass,
          final Class<? extends Builder<?>> builderClass) {
        ReflectionInvoker reflectionInvoker =
            new ReflectionInvoker(descriptor, camelCaseName, messageClass, builderClass);
        type = reflectionInvoker.getRepeatedMethod.getReturnType();
        invoker = getMethodInvoker(reflectionInvoker);
      }

      static MethodInvoker getMethodInvoker(ReflectionInvoker accessor) {
        return accessor;
      }

      @Override
      public Object get(final FlattenedGeneratedMessageV3 message) {
        return invoker.get(message);
      }

      @Override
      public Object get(FlattenedGeneratedMessageV3.Builder<?> builder) {
        return invoker.get(builder);
      }

      @Override
      public Object getRaw(final FlattenedGeneratedMessageV3 message) {
        return get(message);
      }

      @Override
      public void set(final Builder<?> builder, final Object value) {
        // Add all the elements individually.  This serves two purposes:
        // 1) Verifies that each element has the correct type.
        // 2) Insures that the caller cannot modify the list later on and
        //    have the modifications be reflected in the message.
        clear(builder);
        for (final Object element : (List<?>) value) {
          addRepeated(builder, element);
        }
      }

      @Override
      public Object getRepeated(final FlattenedGeneratedMessageV3 message, final int index) {
        return invoker.getRepeated(message, index);
      }

      @Override
      public Object getRepeated(FlattenedGeneratedMessageV3.Builder<?> builder, int index) {
        return invoker.getRepeated(builder, index);
      }

      @Override
      public void setRepeated(final Builder<?> builder, final int index, final Object value) {
        invoker.setRepeated(builder, index, value);
      }

      @Override
      public void addRepeated(final Builder<?> builder, final Object value) {
        invoker.addRepeated(builder, value);
      }

      @Override
      public boolean has(final FlattenedGeneratedMessageV3 message) {
        throw new UnsupportedOperationException("hasField() called on a repeated field.");
      }

      @Override
      public boolean has(FlattenedGeneratedMessageV3.Builder<?> builder) {
        throw new UnsupportedOperationException("hasField() called on a repeated field.");
      }

      @Override
      public int getRepeatedCount(final FlattenedGeneratedMessageV3 message) {
        return invoker.getRepeatedCount(message);
      }

      @Override
      public int getRepeatedCount(FlattenedGeneratedMessageV3.Builder<?> builder) {
        return invoker.getRepeatedCount(builder);
      }

      @Override
      public void clear(final Builder<?> builder) {
        invoker.clear(builder);
      }

      @Override
      public Message.Builder newBuilder() {
        throw new UnsupportedOperationException(
            "newBuilderForField() called on a non-Message type.");
      }

      @Override
      public Message.Builder getBuilder(FlattenedGeneratedMessageV3.Builder<?> builder) {
        throw new UnsupportedOperationException("getFieldBuilder() called on a non-Message type.");
      }

      @Override
      public Message.Builder getRepeatedBuilder(FlattenedGeneratedMessageV3.Builder<?> builder, int index) {
        throw new UnsupportedOperationException(
            "getRepeatedFieldBuilder() called on a non-Message type.");
      }
    }

    private static class MapFieldAccessor implements FieldAccessor {
      MapFieldAccessor(
          final FieldDescriptor descriptor, final Class<? extends FlattenedGeneratedMessageV3> messageClass) {
        field = descriptor;
        Method getDefaultInstanceMethod = getMethodOrDie(messageClass, "getDefaultInstance");
        MapFieldReflectionAccessor defaultMapField =
            getMapField((FlattenedGeneratedMessageV3) invokeOrDie(getDefaultInstanceMethod, null));
        mapEntryMessageDefaultInstance = defaultMapField.getMapEntryMessageDefaultInstance();
      }

      private final FieldDescriptor field;
      private final Message mapEntryMessageDefaultInstance;

      private MapFieldReflectionAccessor getMapField(FlattenedGeneratedMessageV3 message) {
        return message.internalGetMapFieldReflection(field.getNumber());
      }

      private MapFieldReflectionAccessor getMapField(FlattenedGeneratedMessageV3.Builder<?> builder) {
        return builder.internalGetMapFieldReflection(field.getNumber());
      }

      private MapFieldReflectionAccessor getMutableMapField(FlattenedGeneratedMessageV3.Builder<?> builder) {
        return builder.internalGetMutableMapFieldReflection(field.getNumber());
      }

      private Message coerceType(Message value) {
        if (value == null) {
          return null;
        }
        if (mapEntryMessageDefaultInstance.getClass().isInstance(value)) {
          return value;
        }
        // The value is not the exact right message type.  However, if it
        // is an alternative implementation of the same type -- e.g. a
        // DynamicMessage -- we should accept it.  In this case we can make
        // a copy of the message.
        return mapEntryMessageDefaultInstance.toBuilder().mergeFrom(value).build();
      }

      @Override
      public Object get(FlattenedGeneratedMessageV3 message) {
        List<Object> result = new ArrayList<>();
        for (int i = 0; i < getRepeatedCount(message); i++) {
          result.add(getRepeated(message, i));
        }
        return Collections.unmodifiableList(result);
      }

      @Override
      public Object get(Builder<?> builder) {
        List<Object> result = new ArrayList<>();
        for (int i = 0; i < getRepeatedCount(builder); i++) {
          result.add(getRepeated(builder, i));
        }
        return Collections.unmodifiableList(result);
      }

      @Override
      public Object getRaw(FlattenedGeneratedMessageV3 message) {
        return get(message);
      }

      @Override
      public void set(Builder<?> builder, Object value) {
        clear(builder);
        for (Object entry : (List<?>) value) {
          addRepeated(builder, entry);
        }
      }

      @Override
      public Object getRepeated(FlattenedGeneratedMessageV3 message, int index) {
        return getMapField(message).getList().get(index);
      }

      @Override
      public Object getRepeated(Builder<?> builder, int index) {
        return getMapField(builder).getList().get(index);
      }

      @Override
      public void setRepeated(Builder<?> builder, int index, Object value) {
        getMutableMapField(builder).getMutableList().set(index, coerceType((Message) value));
      }

      @Override
      public void addRepeated(Builder<?> builder, Object value) {
        getMutableMapField(builder).getMutableList().add(coerceType((Message) value));
      }

      @Override
      public boolean has(FlattenedGeneratedMessageV3 message) {
        throw new UnsupportedOperationException("hasField() is not supported for repeated fields.");
      }

      @Override
      public boolean has(Builder<?> builder) {
        throw new UnsupportedOperationException("hasField() is not supported for repeated fields.");
      }

      @Override
      public int getRepeatedCount(FlattenedGeneratedMessageV3 message) {
        return getMapField(message).getList().size();
      }

      @Override
      public int getRepeatedCount(Builder<?> builder) {
        return getMapField(builder).getList().size();
      }

      @Override
      public void clear(Builder<?> builder) {
        getMutableMapField(builder).getMutableList().clear();
      }

      @Override
      public Message.Builder newBuilder() {
        return mapEntryMessageDefaultInstance.newBuilderForType();
      }

      @Override
      public Message.Builder getBuilder(Builder<?> builder) {
        throw new UnsupportedOperationException("Nested builder not supported for map fields.");
      }

      @Override
      public Message.Builder getRepeatedBuilder(Builder<?> builder, int index) {
        throw new UnsupportedOperationException("Map fields cannot be repeated");
      }
    }

    // ---------------------------------------------------------------

    private static final class SingularEnumFieldAccessor extends SingularFieldAccessor {
      SingularEnumFieldAccessor(
          final FieldDescriptor descriptor,
          final String camelCaseName,
          final Class<? extends FlattenedGeneratedMessageV3> messageClass,
          final Class<? extends Builder<?>> builderClass,
          final String containingOneofCamelCaseName) {
        super(descriptor, camelCaseName, messageClass, builderClass, containingOneofCamelCaseName);

        enumDescriptor = descriptor.getEnumType();

        valueOfMethod = getMethodOrDie(type, "valueOf", EnumValueDescriptor.class);
        getValueDescriptorMethod = getMethodOrDie(type, "getValueDescriptor");

        supportUnknownEnumValue = !descriptor.legacyEnumFieldTreatedAsClosed();
        if (supportUnknownEnumValue) {
          getValueMethod = getMethodOrDie(messageClass, "get" + camelCaseName + "Value");
          getValueMethodBuilder = getMethodOrDie(builderClass, "get" + camelCaseName + "Value");
          setValueMethod = getMethodOrDie(builderClass, "set" + camelCaseName + "Value", int.class);
        }
      }

      private final EnumDescriptor enumDescriptor;

      private final Method valueOfMethod;
      private final Method getValueDescriptorMethod;

      private final boolean supportUnknownEnumValue;
      private Method getValueMethod;
      private Method getValueMethodBuilder;
      private Method setValueMethod;

      @Override
      public Object get(final FlattenedGeneratedMessageV3 message) {
        if (supportUnknownEnumValue) {
          int value = (Integer) invokeOrDie(getValueMethod, message);
          return enumDescriptor.findValueByNumberCreatingIfUnknown(value);
        }
        return invokeOrDie(getValueDescriptorMethod, super.get(message));
      }

      @Override
      public Object get(final FlattenedGeneratedMessageV3.Builder<?> builder) {
        if (supportUnknownEnumValue) {
          int value = (Integer) invokeOrDie(getValueMethodBuilder, builder);
          return enumDescriptor.findValueByNumberCreatingIfUnknown(value);
        }
        return invokeOrDie(getValueDescriptorMethod, super.get(builder));
      }

      @Override
      public void set(final Builder<?> builder, final Object value) {
        if (supportUnknownEnumValue) {
          // TODO: remove the unused variable
          Object unused =
              invokeOrDie(setValueMethod, builder, ((EnumValueDescriptor) value).getNumber());
          return;
        }
        super.set(builder, invokeOrDie(valueOfMethod, null, value));
      }
    }

    private static final class RepeatedEnumFieldAccessor extends RepeatedFieldAccessor {
      RepeatedEnumFieldAccessor(
          final FieldDescriptor descriptor,
          final String camelCaseName,
          final Class<? extends FlattenedGeneratedMessageV3> messageClass,
          final Class<? extends Builder<?>> builderClass) {
        super(descriptor, camelCaseName, messageClass, builderClass);

        enumDescriptor = descriptor.getEnumType();

        valueOfMethod = getMethodOrDie(type, "valueOf", EnumValueDescriptor.class);
        getValueDescriptorMethod = getMethodOrDie(type, "getValueDescriptor");

        supportUnknownEnumValue = !descriptor.legacyEnumFieldTreatedAsClosed();
        if (supportUnknownEnumValue) {
          getRepeatedValueMethod =
              getMethodOrDie(messageClass, "get" + camelCaseName + "Value", int.class);
          getRepeatedValueMethodBuilder =
              getMethodOrDie(builderClass, "get" + camelCaseName + "Value", int.class);
          setRepeatedValueMethod =
              getMethodOrDie(builderClass, "set" + camelCaseName + "Value", int.class, int.class);
          addRepeatedValueMethod =
              getMethodOrDie(builderClass, "add" + camelCaseName + "Value", int.class);
        }
      }

      private final EnumDescriptor enumDescriptor;

      private final Method valueOfMethod;
      private final Method getValueDescriptorMethod;

      private final boolean supportUnknownEnumValue;

      private Method getRepeatedValueMethod;
      private Method getRepeatedValueMethodBuilder;
      private Method setRepeatedValueMethod;
      private Method addRepeatedValueMethod;

      @Override
      public Object get(final FlattenedGeneratedMessageV3 message) {
        final List<Object> newList = new ArrayList<>();
        final int size = getRepeatedCount(message);
        for (int i = 0; i < size; i++) {
          newList.add(getRepeated(message, i));
        }
        return Collections.unmodifiableList(newList);
      }

      @Override
      public Object get(final FlattenedGeneratedMessageV3.Builder<?> builder) {
        final List<Object> newList = new ArrayList<>();
        final int size = getRepeatedCount(builder);
        for (int i = 0; i < size; i++) {
          newList.add(getRepeated(builder, i));
        }
        return Collections.unmodifiableList(newList);
      }

      @Override
      public Object getRepeated(final FlattenedGeneratedMessageV3 message, final int index) {
        if (supportUnknownEnumValue) {
          int value = (Integer) invokeOrDie(getRepeatedValueMethod, message, index);
          return enumDescriptor.findValueByNumberCreatingIfUnknown(value);
        }
        return invokeOrDie(getValueDescriptorMethod, super.getRepeated(message, index));
      }

      @Override
      public Object getRepeated(final FlattenedGeneratedMessageV3.Builder<?> builder, final int index) {
        if (supportUnknownEnumValue) {
          int value = (Integer) invokeOrDie(getRepeatedValueMethodBuilder, builder, index);
          return enumDescriptor.findValueByNumberCreatingIfUnknown(value);
        }
        return invokeOrDie(getValueDescriptorMethod, super.getRepeated(builder, index));
      }

      @Override
      public void setRepeated(final Builder<?> builder, final int index, final Object value) {
        if (supportUnknownEnumValue) {
          // TODO: remove the unused variable
          Object unused =
              invokeOrDie(
                  setRepeatedValueMethod,
                  builder,
                  index,
                  ((EnumValueDescriptor) value).getNumber());
          return;
        }
        super.setRepeated(builder, index, invokeOrDie(valueOfMethod, null, value));
      }

      @Override
      public void addRepeated(final Builder<?> builder, final Object value) {
        if (supportUnknownEnumValue) {
          // TODO: remove the unused variable
          Object unused =
              invokeOrDie(
                  addRepeatedValueMethod, builder, ((EnumValueDescriptor) value).getNumber());
          return;
        }
        super.addRepeated(builder, invokeOrDie(valueOfMethod, null, value));
      }
    }

    // ---------------------------------------------------------------

    /**
     * Field accessor for string fields.
     *
     * <p>This class makes getFooBytes() and setFooBytes() available for reflection API so that
     * reflection based serialize/parse functions can access the raw bytes of the field to preserve
     * non-UTF8 bytes in the string.
     *
     * <p>This ensures the serialize/parse round-trip safety, which is important for servers which
     * forward messages.
     */
    private static final class SingularStringFieldAccessor extends SingularFieldAccessor {
      SingularStringFieldAccessor(
          final FieldDescriptor descriptor,
          final String camelCaseName,
          final Class<? extends FlattenedGeneratedMessageV3> messageClass,
          final Class<? extends Builder<?>> builderClass,
          final String containingOneofCamelCaseName) {
        super(descriptor, camelCaseName, messageClass, builderClass, containingOneofCamelCaseName);
        getBytesMethod = getMethodOrDie(messageClass, "get" + camelCaseName + "Bytes");
        setBytesMethodBuilder =
            getMethodOrDie(builderClass, "set" + camelCaseName + "Bytes", ByteString.class);
      }

      private final Method getBytesMethod;
      private final Method setBytesMethodBuilder;

      @Override
      public Object getRaw(final FlattenedGeneratedMessageV3 message) {
        return invokeOrDie(getBytesMethod, message);
      }

      @Override
      public void set(FlattenedGeneratedMessageV3.Builder<?> builder, Object value) {
        if (value instanceof ByteString) {
          // TODO: remove the unused variable
          Object unused = invokeOrDie(setBytesMethodBuilder, builder, value);
        } else {
          super.set(builder, value);
        }
      }
    }

    // ---------------------------------------------------------------

    private static final class SingularMessageFieldAccessor extends SingularFieldAccessor {
      SingularMessageFieldAccessor(
          final FieldDescriptor descriptor,
          final String camelCaseName,
          final Class<? extends FlattenedGeneratedMessageV3> messageClass,
          final Class<? extends Builder<?>> builderClass,
          final String containingOneofCamelCaseName) {
        super(descriptor, camelCaseName, messageClass, builderClass, containingOneofCamelCaseName);

        newBuilderMethod = getMethodOrDie(type, "newBuilder");
        getBuilderMethodBuilder = getMethodOrDie(builderClass, "get" + camelCaseName + "Builder");
      }

      private final Method newBuilderMethod;
      private final Method getBuilderMethodBuilder;

      private Object coerceType(final Object value) {
        if (type.isInstance(value)) {
          return value;
        } else {
          // The value is not the exact right message type.  However, if it
          // is an alternative implementation of the same type -- e.g. a
          // DynamicMessage -- we should accept it.  In this case we can make
          // a copy of the message.
          return ((Message.Builder) invokeOrDie(newBuilderMethod, null))
              .mergeFrom((Message) value)
              .buildPartial();
        }
      }

      @Override
      public void set(final Builder<?> builder, final Object value) {
        super.set(builder, coerceType(value));
      }

      @Override
      public Message.Builder newBuilder() {
        return (Message.Builder) invokeOrDie(newBuilderMethod, null);
      }

      @Override
      public Message.Builder getBuilder(FlattenedGeneratedMessageV3.Builder<?> builder) {
        return (Message.Builder) invokeOrDie(getBuilderMethodBuilder, builder);
      }
    }

    private static final class RepeatedMessageFieldAccessor extends RepeatedFieldAccessor {
      RepeatedMessageFieldAccessor(
          final FieldDescriptor descriptor,
          final String camelCaseName,
          final Class<? extends FlattenedGeneratedMessageV3> messageClass,
          final Class<? extends Builder<?>> builderClass) {
        super(descriptor, camelCaseName, messageClass, builderClass);

        newBuilderMethod = getMethodOrDie(type, "newBuilder");
        getBuilderMethodBuilder =
            getMethodOrDie(builderClass, "get" + camelCaseName + "Builder", Integer.TYPE);
      }

      private final Method newBuilderMethod;
      private final Method getBuilderMethodBuilder;

      private Object coerceType(final Object value) {
        if (type.isInstance(value)) {
          return value;
        } else {
          // The value is not the exact right message type.  However, if it
          // is an alternative implementation of the same type -- e.g. a
          // DynamicMessage -- we should accept it.  In this case we can make
          // a copy of the message.
          return ((Message.Builder) invokeOrDie(newBuilderMethod, null))
              .mergeFrom((Message) value)
              .build();
        }
      }

      @Override
      public void setRepeated(final Builder<?> builder, final int index, final Object value) {
        super.setRepeated(builder, index, coerceType(value));
      }

      @Override
      public void addRepeated(final Builder<?> builder, final Object value) {
        super.addRepeated(builder, coerceType(value));
      }

      @Override
      public Message.Builder newBuilder() {
        return (Message.Builder) invokeOrDie(newBuilderMethod, null);
      }

      @Override
      public Message.Builder getRepeatedBuilder(
              final FlattenedGeneratedMessageV3.Builder<?> builder, final int index) {
        return (Message.Builder) invokeOrDie(getBuilderMethodBuilder, builder, index);
      }
    }
  }

  /**
   * Replaces this object in the output stream with a serialized form. Part of Java's serialization
   * magic. Generated sub-classes must override this method by calling {@code return
   * super.writeReplace();}
   *
   * @return a SerializedForm of this message
   */
  protected Object writeReplace() throws ObjectStreamException {
    return new GeneratedMessageLite.SerializedForm(this);
  }

  /**
   * Checks that the {@link Extension} is non-Lite and returns it as a {@link GeneratedExtension}.
   */
  private static <MessageT extends ExtendableMessage<MessageT>, T>
      Extension<MessageT, T> checkNotLite(ExtensionLite<MessageT, T> extension) {
    if (extension.isLite()) {
      throw new IllegalArgumentException("Expected non-lite extension.");
    }

    return (Extension<MessageT, T>) extension;
  }

  protected static boolean isStringEmpty(final Object value) {
    if (value instanceof String) {
      return ((String) value).isEmpty();
    } else {
      return ((ByteString) value).isEmpty();
    }
  }

  protected static int computeStringSize(final int fieldNumber, final Object value) {
    if (value instanceof String) {
      return CodedOutputStream.computeStringSize(fieldNumber, (String) value);
    } else {
      return CodedOutputStream.computeBytesSize(fieldNumber, (ByteString) value);
    }
  }

  protected static int computeStringSizeNoTag(final Object value) {
    if (value instanceof String) {
      return CodedOutputStream.computeStringSizeNoTag((String) value);
    } else {
      return CodedOutputStream.computeBytesSizeNoTag((ByteString) value);
    }
  }

  protected static void writeString(
      CodedOutputStream output, final int fieldNumber, final Object value) throws IOException {
    if (value instanceof String) {
      output.writeString(fieldNumber, (String) value);
    } else {
      output.writeBytes(fieldNumber, (ByteString) value);
    }
  }

  protected static void writeStringNoTag(CodedOutputStream output, final Object value)
      throws IOException {
    if (value instanceof String) {
      output.writeStringNoTag((String) value);
    } else {
      output.writeBytesNoTag((ByteString) value);
    }
  }

  protected static <V> void serializeIntegerMapTo(
      CodedOutputStream out,
      MapField<Integer, V> field,
      MapEntry<Integer, V> defaultEntry,
      int fieldNumber)
      throws IOException {
    Map<Integer, V> m = field.getMap();
    if (!out.isSerializationDeterministic()) {
      serializeMapTo(out, m, defaultEntry, fieldNumber);
      return;
    }
    // Sorting the unboxed keys and then look up the values during serialization is 2x faster
    // than sorting map entries with a custom comparator directly.
    int[] keys = new int[m.size()];
    int index = 0;
    for (int k : m.keySet()) {
      keys[index++] = k;
    }
    Arrays.sort(keys);
    for (int key : keys) {
      out.writeMessage(
          fieldNumber, defaultEntry.newBuilderForType().setKey(key).setValue(m.get(key)).build());
    }
  }

  protected static <V> void serializeLongMapTo(
      CodedOutputStream out,
      MapField<Long, V> field,
      MapEntry<Long, V> defaultEntry,
      int fieldNumber)
      throws IOException {
    Map<Long, V> m = field.getMap();
    if (!out.isSerializationDeterministic()) {
      serializeMapTo(out, m, defaultEntry, fieldNumber);
      return;
    }

    long[] keys = new long[m.size()];
    int index = 0;
    for (long k : m.keySet()) {
      keys[index++] = k;
    }
    Arrays.sort(keys);
    for (long key : keys) {
      out.writeMessage(
          fieldNumber, defaultEntry.newBuilderForType().setKey(key).setValue(m.get(key)).build());
    }
  }

  protected static <V> void serializeStringMapTo(
      CodedOutputStream out,
      MapField<String, V> field,
      MapEntry<String, V> defaultEntry,
      int fieldNumber)
      throws IOException {
    Map<String, V> m = field.getMap();
    if (!out.isSerializationDeterministic()) {
      serializeMapTo(out, m, defaultEntry, fieldNumber);
      return;
    }

    // Sorting the String keys and then look up the values during serialization is 25% faster than
    // sorting map entries with a custom comparator directly.
    String[] keys = new String[m.size()];
    keys = m.keySet().toArray(keys);
    Arrays.sort(keys);
    for (String key : keys) {
      out.writeMessage(
          fieldNumber, defaultEntry.newBuilderForType().setKey(key).setValue(m.get(key)).build());
    }
  }

  protected static <V> void serializeBooleanMapTo(
      CodedOutputStream out,
      MapField<Boolean, V> field,
      MapEntry<Boolean, V> defaultEntry,
      int fieldNumber)
      throws IOException {
    Map<Boolean, V> m = field.getMap();
    if (!out.isSerializationDeterministic()) {
      serializeMapTo(out, m, defaultEntry, fieldNumber);
      return;
    }
    maybeSerializeBooleanEntryTo(out, m, defaultEntry, fieldNumber, false);
    maybeSerializeBooleanEntryTo(out, m, defaultEntry, fieldNumber, true);
  }

  private static <V> void maybeSerializeBooleanEntryTo(
      CodedOutputStream out,
      Map<Boolean, V> m,
      MapEntry<Boolean, V> defaultEntry,
      int fieldNumber,
      boolean key)
      throws IOException {
    if (m.containsKey(key)) {
      out.writeMessage(
          fieldNumber, defaultEntry.newBuilderForType().setKey(key).setValue(m.get(key)).build());
    }
  }

  /** Serialize the map using the iteration order. */
  private static <K, V> void serializeMapTo(
      CodedOutputStream out, Map<K, V> m, MapEntry<K, V> defaultEntry, int fieldNumber)
      throws IOException {
    for (Map.Entry<K, V> entry : m.entrySet()) {
      out.writeMessage(
          fieldNumber,
          defaultEntry
              .newBuilderForType()
              .setKey(entry.getKey())
              .setValue(entry.getValue())
              .build());
    }
  }
}