diff --git a/BUILD b/BUILD
index 07ee629..1788cfc 100644
--- a/BUILD
+++ b/BUILD
@@ -369,6 +369,7 @@
         "src/google/protobuf/compiler/cpp/cpp_message.cc",
         "src/google/protobuf/compiler/cpp/cpp_message_field.cc",
         "src/google/protobuf/compiler/cpp/cpp_padding_optimizer.cc",
+        "src/google/protobuf/compiler/cpp/cpp_parse_function_generator.cc",
         "src/google/protobuf/compiler/cpp/cpp_primitive_field.cc",
         "src/google/protobuf/compiler/cpp/cpp_service.cc",
         "src/google/protobuf/compiler/cpp/cpp_string_field.cc",
diff --git a/CHANGES.txt b/CHANGES.txt
index 93ee2b8..9e6eb44 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,6 +1,17 @@
+
 Unreleased Changes (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
 
   C++
+  * Fix bug where `Descriptor::DebugString()` printed proto3 synthetic oneofs.
+  * Provide stable versions of `SortAndUnique()`.
+  * Make sure to cache proto3 optional message fields when they are cleared.
+
+  Kotlin
+  * Restrict extension setter and getter operators to non-nullable T.
+
+3.16.0 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
+
+  C++
   * The ::pb namespace is no longer exposed due to conflicts.
   * Allow MessageDifferencer::TreatAsSet() (and friends) to override previous
     calls instead of crashing.
diff --git a/build_files_updated_unittest.sh b/build_files_updated_unittest.sh
index c863071..87541c3 100755
--- a/build_files_updated_unittest.sh
+++ b/build_files_updated_unittest.sh
@@ -58,5 +58,5 @@
 
 # Test whether there are any differences
 for file in ${generated_files[@]}; do
-  diff "${golden_dir}/${file}" "${test_dir}/${file}"
+  diff -du "${golden_dir}/${file}" "${test_dir}/${file}"
 done
diff --git a/cmake/libprotoc.cmake b/cmake/libprotoc.cmake
index ecb5a85..899304d 100644
--- a/cmake/libprotoc.cmake
+++ b/cmake/libprotoc.cmake
@@ -12,6 +12,7 @@
   ${protobuf_source_dir}/src/google/protobuf/compiler/cpp/cpp_message.cc
   ${protobuf_source_dir}/src/google/protobuf/compiler/cpp/cpp_message_field.cc
   ${protobuf_source_dir}/src/google/protobuf/compiler/cpp/cpp_padding_optimizer.cc
+  ${protobuf_source_dir}/src/google/protobuf/compiler/cpp/cpp_parse_function_generator.cc
   ${protobuf_source_dir}/src/google/protobuf/compiler/cpp/cpp_primitive_field.cc
   ${protobuf_source_dir}/src/google/protobuf/compiler/cpp/cpp_service.cc
   ${protobuf_source_dir}/src/google/protobuf/compiler/cpp/cpp_string_field.cc
@@ -96,6 +97,7 @@
   ${protobuf_source_dir}/src/google/protobuf/compiler/cpp/cpp_names.h
   ${protobuf_source_dir}/src/google/protobuf/compiler/cpp/cpp_options.h
   ${protobuf_source_dir}/src/google/protobuf/compiler/cpp/cpp_padding_optimizer.h
+  ${protobuf_source_dir}/src/google/protobuf/compiler/cpp/cpp_parse_function_generator.h
   ${protobuf_source_dir}/src/google/protobuf/compiler/cpp/cpp_primitive_field.h
   ${protobuf_source_dir}/src/google/protobuf/compiler/cpp/cpp_service.h
   ${protobuf_source_dir}/src/google/protobuf/compiler/cpp/cpp_string_field.h
diff --git a/conformance/ConformanceJava.java b/conformance/ConformanceJava.java
index 5319982..100bec4 100644
--- a/conformance/ConformanceJava.java
+++ b/conformance/ConformanceJava.java
@@ -54,7 +54,7 @@
     while (len > 0) {
       int read = System.in.read(buf, ofs, len);
       if (read == -1) {
-        return false;  // EOF
+        return false; // EOF
       }
       ofs += read;
       len -= read;
@@ -81,10 +81,10 @@
 
   private void writeLittleEndianIntToStdout(int val) throws Exception {
     byte[] buf = new byte[4];
-    buf[0] = (byte)val;
-    buf[1] = (byte)(val >> 8);
-    buf[2] = (byte)(val >> 16);
-    buf[3] = (byte)(val >> 24);
+    buf[0] = (byte) val;
+    buf[1] = (byte) (val >> 8);
+    buf[2] = (byte) (val >> 16);
+    buf[3] = (byte) (val >> 24);
     writeToStdout(buf);
   }
 
@@ -98,85 +98,71 @@
     INPUT_STREAM_DECODER;
   }
 
-  private static class BinaryDecoder <MessageType extends AbstractMessage> {
-    public MessageType decode (ByteString bytes, BinaryDecoderType type,
-        Parser <MessageType> parser, ExtensionRegistry extensions)
-      throws InvalidProtocolBufferException {
+  private static class BinaryDecoder<T extends AbstractMessage> {
+    public T decode(
+        ByteString bytes, BinaryDecoderType type, Parser<T> parser, ExtensionRegistry extensions)
+        throws InvalidProtocolBufferException {
       switch (type) {
         case BTYE_STRING_DECODER:
-          return parser.parseFrom(bytes, extensions);
         case BYTE_ARRAY_DECODER:
-          return parser.parseFrom(bytes.toByteArray(), extensions);
-        case ARRAY_BYTE_BUFFER_DECODER: {
-          ByteBuffer buffer = ByteBuffer.allocate(bytes.size());
-          bytes.copyTo(buffer);
-          buffer.flip();
-          try {
+          return parser.parseFrom(bytes, extensions);
+        case ARRAY_BYTE_BUFFER_DECODER:
+          {
+            ByteBuffer buffer = ByteBuffer.allocate(bytes.size());
+            bytes.copyTo(buffer);
+            buffer.flip();
             return parser.parseFrom(CodedInputStream.newInstance(buffer), extensions);
-          } catch (InvalidProtocolBufferException e) {
-            throw e;
           }
-        }
-        case READONLY_ARRAY_BYTE_BUFFER_DECODER: {
-          try {
+        case READONLY_ARRAY_BYTE_BUFFER_DECODER:
+          {
             return parser.parseFrom(
                 CodedInputStream.newInstance(bytes.asReadOnlyByteBuffer()), extensions);
-          } catch (InvalidProtocolBufferException e) {
-            throw e;
           }
-        }
-        case DIRECT_BYTE_BUFFER_DECODER: {
-          ByteBuffer buffer = ByteBuffer.allocateDirect(bytes.size());
-          bytes.copyTo(buffer);
-          buffer.flip();
-          try {
+        case DIRECT_BYTE_BUFFER_DECODER:
+          {
+            ByteBuffer buffer = ByteBuffer.allocateDirect(bytes.size());
+            bytes.copyTo(buffer);
+            buffer.flip();
             return parser.parseFrom(CodedInputStream.newInstance(buffer), extensions);
-          } catch (InvalidProtocolBufferException e) {
-            throw e;
           }
-        }
-        case READONLY_DIRECT_BYTE_BUFFER_DECODER: {
-          ByteBuffer buffer = ByteBuffer.allocateDirect(bytes.size());
-          bytes.copyTo(buffer);
-          buffer.flip();
-          try {
+        case READONLY_DIRECT_BYTE_BUFFER_DECODER:
+          {
+            ByteBuffer buffer = ByteBuffer.allocateDirect(bytes.size());
+            bytes.copyTo(buffer);
+            buffer.flip();
             return parser.parseFrom(
                 CodedInputStream.newInstance(buffer.asReadOnlyBuffer()), extensions);
-          } catch (InvalidProtocolBufferException e) {
-            throw e;
           }
-        }
-        case INPUT_STREAM_DECODER: {
-          try {
+        case INPUT_STREAM_DECODER:
+          {
             return parser.parseFrom(bytes.newInput(), extensions);
-          } catch (InvalidProtocolBufferException e) {
-            throw e;
           }
-        }
-        default :
-          return null;
       }
+      return null;
     }
   }
 
-  private <MessageType extends AbstractMessage> MessageType parseBinary(
-      ByteString bytes, Parser <MessageType> parser, ExtensionRegistry extensions)
+  private <T extends AbstractMessage> T parseBinary(
+      ByteString bytes, Parser<T> parser, ExtensionRegistry extensions)
       throws InvalidProtocolBufferException {
-    ArrayList <MessageType> messages = new ArrayList <MessageType> ();
-    ArrayList <InvalidProtocolBufferException> exceptions =
-        new ArrayList <InvalidProtocolBufferException>();
+    ArrayList<T> messages = new ArrayList<>();
+    ArrayList<InvalidProtocolBufferException> exceptions = new ArrayList<>();
 
     for (int i = 0; i < BinaryDecoderType.values().length; i++) {
       messages.add(null);
       exceptions.add(null);
     }
-    BinaryDecoder <MessageType> decoder = new BinaryDecoder <MessageType> ();
+    if (messages.isEmpty()) {
+      throw new RuntimeException("binary decoder types missing");
+    }
+
+    BinaryDecoder<T> decoder = new BinaryDecoder<>();
 
     boolean hasMessage = false;
     boolean hasException = false;
     for (int i = 0; i < BinaryDecoderType.values().length; ++i) {
       try {
-        //= BinaryDecoderType.values()[i].parseProto3(bytes);
+        // = BinaryDecoderType.values()[i].parseProto3(bytes);
         messages.set(i, decoder.decode(bytes, BinaryDecoderType.values()[i], parser, extensions));
         hasMessage = true;
       } catch (InvalidProtocolBufferException e) {
@@ -202,7 +188,15 @@
     if (hasException) {
       // We do not check if exceptions are equal. Different implementations may return different
       // exception messages. Throw an arbitrary one out instead.
-      throw exceptions.get(0);
+      InvalidProtocolBufferException exception = null;
+      for (InvalidProtocolBufferException e : exceptions) {
+        if (exception != null) {
+          exception.addSuppressed(e);
+        } else {
+          exception = e;
+        }
+      }
+      throw exception;
     }
 
     // Fast path comparing all the messages with the first message, assuming equality being
@@ -242,115 +236,138 @@
         request.getMessageType().equals("protobuf_test_messages.proto2.TestAllTypesProto2");
 
     switch (request.getPayloadCase()) {
-      case PROTOBUF_PAYLOAD: {
-        if (isProto3) {
-          try {
-            ExtensionRegistry extensions = ExtensionRegistry.newInstance();
-            TestMessagesProto3.registerAllExtensions(extensions);
-            testMessage = parseBinary(request.getProtobufPayload(), TestAllTypesProto3.parser(), extensions);
-          } catch (InvalidProtocolBufferException e) {
-            return Conformance.ConformanceResponse.newBuilder().setParseError(e.getMessage()).build();
-          }
-        } else if (isProto2) {
-          try {
-            ExtensionRegistry extensions = ExtensionRegistry.newInstance();
-            TestMessagesProto2.registerAllExtensions(extensions);
-            testMessage = parseBinary(request.getProtobufPayload(), TestAllTypesProto2.parser(), extensions);
-          } catch (InvalidProtocolBufferException e) {
-            return Conformance.ConformanceResponse.newBuilder().setParseError(e.getMessage()).build();
-          }
-        } else {
-          throw new RuntimeException("Protobuf request doesn't have specific payload type.");
-        }
-        break;
-      }
-      case JSON_PAYLOAD: {
-        try {
-          JsonFormat.Parser parser = JsonFormat.parser().usingTypeRegistry(typeRegistry);
-          if (request.getTestCategory()
-              == Conformance.TestCategory.JSON_IGNORE_UNKNOWN_PARSING_TEST) {
-            parser = parser.ignoringUnknownFields();
-          }
+      case PROTOBUF_PAYLOAD:
+        {
           if (isProto3) {
-            TestMessagesProto3.TestAllTypesProto3.Builder builder =
-                TestMessagesProto3.TestAllTypesProto3.newBuilder();
-            parser.merge(request.getJsonPayload(), builder);
-            testMessage = builder.build();
+            try {
+              ExtensionRegistry extensions = ExtensionRegistry.newInstance();
+              TestMessagesProto3.registerAllExtensions(extensions);
+              testMessage =
+                  parseBinary(
+                      request.getProtobufPayload(), TestAllTypesProto3.parser(), extensions);
+            } catch (InvalidProtocolBufferException e) {
+              return Conformance.ConformanceResponse.newBuilder()
+                  .setParseError(e.getMessage())
+                  .build();
+            }
           } else if (isProto2) {
-            TestMessagesProto2.TestAllTypesProto2.Builder builder =
-                TestMessagesProto2.TestAllTypesProto2.newBuilder();
-            parser.merge(request.getJsonPayload(), builder);
-            testMessage = builder.build();
+            try {
+              ExtensionRegistry extensions = ExtensionRegistry.newInstance();
+              TestMessagesProto2.registerAllExtensions(extensions);
+              testMessage =
+                  parseBinary(
+                      request.getProtobufPayload(), TestAllTypesProto2.parser(), extensions);
+            } catch (InvalidProtocolBufferException e) {
+              return Conformance.ConformanceResponse.newBuilder()
+                  .setParseError(e.getMessage())
+                  .build();
+            }
           } else {
             throw new RuntimeException("Protobuf request doesn't have specific payload type.");
           }
-        } catch (InvalidProtocolBufferException e) {
-          return Conformance.ConformanceResponse.newBuilder().setParseError(e.getMessage()).build();
+          break;
         }
-        break;
-      }
-      case TEXT_PAYLOAD: {
-        if (isProto3) {
+      case JSON_PAYLOAD:
+        {
           try {
-            TestMessagesProto3.TestAllTypesProto3.Builder builder =
-                TestMessagesProto3.TestAllTypesProto3.newBuilder();
-            TextFormat.merge(request.getTextPayload(), builder);
-            testMessage = builder.build();
-          } catch (TextFormat.ParseException e) {
+            JsonFormat.Parser parser = JsonFormat.parser().usingTypeRegistry(typeRegistry);
+            if (request.getTestCategory()
+                == Conformance.TestCategory.JSON_IGNORE_UNKNOWN_PARSING_TEST) {
+              parser = parser.ignoringUnknownFields();
+            }
+            if (isProto3) {
+              TestMessagesProto3.TestAllTypesProto3.Builder builder =
+                  TestMessagesProto3.TestAllTypesProto3.newBuilder();
+              parser.merge(request.getJsonPayload(), builder);
+              testMessage = builder.build();
+            } else if (isProto2) {
+              TestMessagesProto2.TestAllTypesProto2.Builder builder =
+                  TestMessagesProto2.TestAllTypesProto2.newBuilder();
+              parser.merge(request.getJsonPayload(), builder);
+              testMessage = builder.build();
+            } else {
+              throw new RuntimeException("Protobuf request doesn't have specific payload type.");
+            }
+          } catch (InvalidProtocolBufferException e) {
+            return Conformance.ConformanceResponse.newBuilder()
+                .setParseError(e.getMessage())
+                .build();
+          }
+          break;
+        }
+      case TEXT_PAYLOAD:
+        {
+          if (isProto3) {
+            try {
+              TestMessagesProto3.TestAllTypesProto3.Builder builder =
+                  TestMessagesProto3.TestAllTypesProto3.newBuilder();
+              TextFormat.merge(request.getTextPayload(), builder);
+              testMessage = builder.build();
+            } catch (TextFormat.ParseException e) {
               return Conformance.ConformanceResponse.newBuilder()
                   .setParseError(e.getMessage())
                   .build();
-          }
-        } else if (isProto2) {
-          try {
-            TestMessagesProto2.TestAllTypesProto2.Builder builder =
-                TestMessagesProto2.TestAllTypesProto2.newBuilder();
-            TextFormat.merge(request.getTextPayload(), builder);
-            testMessage = builder.build();
-          } catch (TextFormat.ParseException e) {
+            }
+          } else if (isProto2) {
+            try {
+              TestMessagesProto2.TestAllTypesProto2.Builder builder =
+                  TestMessagesProto2.TestAllTypesProto2.newBuilder();
+              TextFormat.merge(request.getTextPayload(), builder);
+              testMessage = builder.build();
+            } catch (TextFormat.ParseException e) {
               return Conformance.ConformanceResponse.newBuilder()
                   .setParseError(e.getMessage())
                   .build();
+            }
+          } else {
+            throw new RuntimeException("Protobuf request doesn't have specific payload type.");
           }
-        } else {
-          throw new RuntimeException("Protobuf request doesn't have specific payload type.");
+          break;
         }
-        break;
-      }
-      case PAYLOAD_NOT_SET: {
-        throw new RuntimeException("Request didn't have payload.");
-      }
+      case PAYLOAD_NOT_SET:
+        {
+          throw new RuntimeException("Request didn't have payload.");
+        }
 
-      default: {
-        throw new RuntimeException("Unexpected payload case.");
-      }
+      default:
+        {
+          throw new RuntimeException("Unexpected payload case.");
+        }
     }
 
     switch (request.getRequestedOutputFormat()) {
       case UNSPECIFIED:
         throw new RuntimeException("Unspecified output format.");
 
-      case PROTOBUF: {
-        ByteString MessageString = testMessage.toByteString();
-        return Conformance.ConformanceResponse.newBuilder().setProtobufPayload(MessageString).build();
-      }
+      case PROTOBUF:
+        {
+          ByteString messageString = testMessage.toByteString();
+          return Conformance.ConformanceResponse.newBuilder()
+              .setProtobufPayload(messageString)
+              .build();
+        }
 
       case JSON:
         try {
-          return Conformance.ConformanceResponse.newBuilder().setJsonPayload(
-              JsonFormat.printer().usingTypeRegistry(typeRegistry).print(testMessage)).build();
+          return Conformance.ConformanceResponse.newBuilder()
+              .setJsonPayload(
+                  JsonFormat.printer().usingTypeRegistry(typeRegistry).print(testMessage))
+              .build();
         } catch (InvalidProtocolBufferException | IllegalArgumentException e) {
-          return Conformance.ConformanceResponse.newBuilder().setSerializeError(
-              e.getMessage()).build();
+          return Conformance.ConformanceResponse.newBuilder()
+              .setSerializeError(e.getMessage())
+              .build();
         }
 
       case TEXT_FORMAT:
-        return Conformance.ConformanceResponse.newBuilder().setTextPayload(
-            TextFormat.printToString(testMessage)).build();
+        return Conformance.ConformanceResponse.newBuilder()
+            .setTextPayload(TextFormat.printToString(testMessage))
+            .build();
 
-      default: {
-        throw new RuntimeException("Unexpected request output.");
-      }
+      default:
+        {
+          throw new RuntimeException("Unexpected request output.");
+        }
     }
   }
 
@@ -358,7 +375,7 @@
     int bytes = readLittleEndianIntFromStdin();
 
     if (bytes == -1) {
-      return false;  // EOF
+      return false; // EOF
     }
 
     byte[] serializedInput = new byte[bytes];
@@ -379,14 +396,16 @@
   }
 
   public void run() throws Exception {
-    typeRegistry = TypeRegistry.newBuilder().add(
-        TestMessagesProto3.TestAllTypesProto3.getDescriptor()).build();
+    typeRegistry =
+        TypeRegistry.newBuilder()
+            .add(TestMessagesProto3.TestAllTypesProto3.getDescriptor())
+            .build();
     while (doTestIo()) {
       this.testCount++;
     }
 
-    System.err.println("ConformanceJava: received EOF from test runner after " +
-        this.testCount + " tests");
+    System.err.println(
+        "ConformanceJava: received EOF from test runner after " + this.testCount + " tests");
   }
 
   public static void main(String[] args) throws Exception {
diff --git a/conformance/ConformanceJavaLite.java b/conformance/ConformanceJavaLite.java
index 147738d..eb3d06a 100644
--- a/conformance/ConformanceJavaLite.java
+++ b/conformance/ConformanceJavaLite.java
@@ -28,8 +28,19 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-import com.google.protobuf.conformance.Conformance;
+import com.google.protobuf.ByteString;
+import com.google.protobuf.CodedInputStream;
+import com.google.protobuf.ExtensionRegistryLite;
 import com.google.protobuf.InvalidProtocolBufferException;
+import com.google.protobuf.MessageLite;
+import com.google.protobuf.Parser;
+import com.google.protobuf.conformance.Conformance;
+import com.google.protobuf_test_messages.proto2.TestMessagesProto2;
+import com.google.protobuf_test_messages.proto2.TestMessagesProto2.TestAllTypesProto2;
+import com.google.protobuf_test_messages.proto3.TestMessagesProto3;
+import com.google.protobuf_test_messages.proto3.TestMessagesProto3.TestAllTypesProto3;
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
 
 class ConformanceJavaLite {
   private int testCount = 0;
@@ -39,7 +50,7 @@
     while (len > 0) {
       int read = System.in.read(buf, ofs, len);
       if (read == -1) {
-        return false;  // EOF
+        return false; // EOF
       }
       ofs += read;
       len -= read;
@@ -66,36 +77,214 @@
 
   private void writeLittleEndianIntToStdout(int val) throws Exception {
     byte[] buf = new byte[4];
-    buf[0] = (byte)val;
-    buf[1] = (byte)(val >> 8);
-    buf[2] = (byte)(val >> 16);
-    buf[3] = (byte)(val >> 24);
+    buf[0] = (byte) val;
+    buf[1] = (byte) (val >> 8);
+    buf[2] = (byte) (val >> 16);
+    buf[3] = (byte) (val >> 24);
     writeToStdout(buf);
   }
 
-  private Conformance.ConformanceResponse doTest(Conformance.ConformanceRequest request) {
-    Conformance.TestAllTypes testMessage;
+  private enum BinaryDecoderType {
+    BTYE_STRING_DECODER,
+    BYTE_ARRAY_DECODER,
+    ARRAY_BYTE_BUFFER_DECODER,
+    READONLY_ARRAY_BYTE_BUFFER_DECODER,
+    DIRECT_BYTE_BUFFER_DECODER,
+    READONLY_DIRECT_BYTE_BUFFER_DECODER,
+    INPUT_STREAM_DECODER;
+  }
 
-    switch (request.getPayloadCase()) {
-      case PROTOBUF_PAYLOAD: {
-        try {
-          testMessage = Conformance.TestAllTypes.parseFrom(request.getProtobufPayload());
-        } catch (InvalidProtocolBufferException e) {
-          return Conformance.ConformanceResponse.newBuilder().setParseError(e.getMessage()).build();
+  private static class BinaryDecoder<T extends MessageLite> {
+    public T decode(
+        ByteString bytes,
+        BinaryDecoderType type,
+        Parser<T> parser,
+        ExtensionRegistryLite extensions)
+        throws InvalidProtocolBufferException {
+      switch (type) {
+        case BTYE_STRING_DECODER:
+        case BYTE_ARRAY_DECODER:
+          return parser.parseFrom(bytes, extensions);
+        case ARRAY_BYTE_BUFFER_DECODER:
+          {
+            ByteBuffer buffer = ByteBuffer.allocate(bytes.size());
+            bytes.copyTo(buffer);
+            buffer.flip();
+            return parser.parseFrom(CodedInputStream.newInstance(buffer), extensions);
+          }
+        case READONLY_ARRAY_BYTE_BUFFER_DECODER:
+          {
+            return parser.parseFrom(
+                CodedInputStream.newInstance(bytes.asReadOnlyByteBuffer()), extensions);
+          }
+        case DIRECT_BYTE_BUFFER_DECODER:
+          {
+            ByteBuffer buffer = ByteBuffer.allocateDirect(bytes.size());
+            bytes.copyTo(buffer);
+            buffer.flip();
+            return parser.parseFrom(CodedInputStream.newInstance(buffer), extensions);
+          }
+        case READONLY_DIRECT_BYTE_BUFFER_DECODER:
+          {
+            ByteBuffer buffer = ByteBuffer.allocateDirect(bytes.size());
+            bytes.copyTo(buffer);
+            buffer.flip();
+            return parser.parseFrom(
+                CodedInputStream.newInstance(buffer.asReadOnlyBuffer()), extensions);
+          }
+        case INPUT_STREAM_DECODER:
+          {
+            return parser.parseFrom(bytes.newInput(), extensions);
+          }
+      }
+      return null;
+    }
+  }
+
+  private <T extends MessageLite> T parseBinary(
+      ByteString bytes, Parser<T> parser, ExtensionRegistryLite extensions)
+      throws InvalidProtocolBufferException {
+    ArrayList<T> messages = new ArrayList<>();
+    ArrayList<InvalidProtocolBufferException> exceptions = new ArrayList<>();
+
+    for (int i = 0; i < BinaryDecoderType.values().length; i++) {
+      messages.add(null);
+      exceptions.add(null);
+    }
+    if (messages.isEmpty()) {
+      throw new RuntimeException("binary decoder types missing");
+    }
+
+    BinaryDecoder<T> decoder = new BinaryDecoder<>();
+
+    boolean hasMessage = false;
+    boolean hasException = false;
+    for (int i = 0; i < BinaryDecoderType.values().length; ++i) {
+      try {
+        messages.set(i, decoder.decode(bytes, BinaryDecoderType.values()[i], parser, extensions));
+        hasMessage = true;
+      } catch (InvalidProtocolBufferException e) {
+        exceptions.set(i, e);
+        hasException = true;
+      }
+    }
+
+    if (hasMessage && hasException) {
+      StringBuilder sb =
+          new StringBuilder("Binary decoders disagreed on whether the payload was valid.\n");
+      for (int i = 0; i < BinaryDecoderType.values().length; ++i) {
+        sb.append(BinaryDecoderType.values()[i].name());
+        if (messages.get(i) != null) {
+          sb.append(" accepted the payload.\n");
+        } else {
+          sb.append(" rejected the payload.\n");
         }
+      }
+      throw new RuntimeException(sb.toString());
+    }
+
+    if (hasException) {
+      // We do not check if exceptions are equal. Different implementations may return different
+      // exception messages. Throw an arbitrary one out instead.
+      InvalidProtocolBufferException exception = null;
+      for (InvalidProtocolBufferException e : exceptions) {
+        if (exception != null) {
+          exception.addSuppressed(e);
+        } else {
+          exception = e;
+        }
+      }
+      throw exception;
+    }
+
+    // Fast path comparing all the messages with the first message, assuming equality being
+    // symmetric and transitive.
+    boolean allEqual = true;
+    for (int i = 1; i < messages.size(); ++i) {
+      if (!messages.get(0).equals(messages.get(i))) {
+        allEqual = false;
         break;
       }
-      case JSON_PAYLOAD: {
-        return Conformance.ConformanceResponse.newBuilder().setSkipped(
-            "Lite runtime does not support JSON format.").build();
-      }
-      case PAYLOAD_NOT_SET: {
-        throw new RuntimeException("Request didn't have payload.");
-      }
+    }
 
-      default: {
-        throw new RuntimeException("Unexpected payload case.");
+    // Slow path: compare and find out all unequal pairs.
+    if (!allEqual) {
+      StringBuilder sb = new StringBuilder();
+      for (int i = 0; i < messages.size() - 1; ++i) {
+        for (int j = i + 1; j < messages.size(); ++j) {
+          if (!messages.get(i).equals(messages.get(j))) {
+            sb.append(BinaryDecoderType.values()[i].name())
+                .append(" and ")
+                .append(BinaryDecoderType.values()[j].name())
+                .append(" parsed the payload differently.\n");
+          }
+        }
       }
+      throw new RuntimeException(sb.toString());
+    }
+
+    return messages.get(0);
+  }
+
+  private Conformance.ConformanceResponse doTest(Conformance.ConformanceRequest request) {
+    com.google.protobuf.MessageLite testMessage;
+    boolean isProto3 =
+        request.getMessageType().equals("protobuf_test_messages.proto3.TestAllTypesProto3");
+    boolean isProto2 =
+        request.getMessageType().equals("protobuf_test_messages.proto2.TestAllTypesProto2");
+
+    switch (request.getPayloadCase()) {
+      case PROTOBUF_PAYLOAD:
+        {
+          if (isProto3) {
+            try {
+              ExtensionRegistryLite extensions = ExtensionRegistryLite.newInstance();
+              TestMessagesProto3.registerAllExtensions(extensions);
+              testMessage =
+                  parseBinary(
+                      request.getProtobufPayload(), TestAllTypesProto3.parser(), extensions);
+            } catch (InvalidProtocolBufferException e) {
+              return Conformance.ConformanceResponse.newBuilder()
+                  .setParseError(e.getMessage())
+                  .build();
+            }
+          } else if (isProto2) {
+            try {
+              ExtensionRegistryLite extensions = ExtensionRegistryLite.newInstance();
+              TestMessagesProto2.registerAllExtensions(extensions);
+              testMessage =
+                  parseBinary(
+                      request.getProtobufPayload(), TestAllTypesProto2.parser(), extensions);
+            } catch (InvalidProtocolBufferException e) {
+              return Conformance.ConformanceResponse.newBuilder()
+                  .setParseError(e.getMessage())
+                  .build();
+            }
+          } else {
+            throw new RuntimeException("Protobuf request doesn't have specific payload type.");
+          }
+          break;
+        }
+      case JSON_PAYLOAD:
+        {
+          return Conformance.ConformanceResponse.newBuilder()
+              .setSkipped("Lite runtime does not support JSON format.")
+              .build();
+        }
+      case TEXT_PAYLOAD:
+        {
+          return Conformance.ConformanceResponse.newBuilder()
+              .setSkipped("Lite runtime does not support Text format.")
+              .build();
+        }
+      case PAYLOAD_NOT_SET:
+        {
+          throw new RuntimeException("Request didn't have payload.");
+        }
+      default:
+        {
+          throw new RuntimeException("Unexpected payload case.");
+        }
     }
 
     switch (request.getRequestedOutputFormat()) {
@@ -103,15 +292,23 @@
         throw new RuntimeException("Unspecified output format.");
 
       case PROTOBUF:
-        return Conformance.ConformanceResponse.newBuilder().setProtobufPayload(testMessage.toByteString()).build();
+        return Conformance.ConformanceResponse.newBuilder()
+            .setProtobufPayload(testMessage.toByteString())
+            .build();
 
       case JSON:
-        return Conformance.ConformanceResponse.newBuilder().setSkipped(
-            "Lite runtime does not support JSON format.").build();
+        return Conformance.ConformanceResponse.newBuilder()
+            .setSkipped("Lite runtime does not support JSON format.")
+            .build();
 
-      default: {
-        throw new RuntimeException("Unexpected request output.");
-      }
+      case TEXT_FORMAT:
+        return Conformance.ConformanceResponse.newBuilder()
+            .setSkipped("Lite runtime does not support Text format.")
+            .build();
+      default:
+        {
+          throw new RuntimeException("Unexpected request output.");
+        }
     }
   }
 
@@ -119,7 +316,7 @@
     int bytes = readLittleEndianIntFromStdin();
 
     if (bytes == -1) {
-      return false;  // EOF
+      return false; // EOF
     }
 
     byte[] serializedInput = new byte[bytes];
@@ -144,8 +341,8 @@
       this.testCount++;
     }
 
-    System.err.println("ConformanceJavaLite: received EOF from test runner after " +
-        this.testCount + " tests");
+    System.err.println(
+        "ConformanceJavaLite: received EOF from test runner after " + this.testCount + " tests");
   }
 
   public static void main(String[] args) throws Exception {
diff --git a/csharp/src/AddressBook/Addressbook.cs b/csharp/src/AddressBook/Addressbook.cs
index 042f69e..8b21683 100644
--- a/csharp/src/AddressBook/Addressbook.cs
+++ b/csharp/src/AddressBook/Addressbook.cs
@@ -32,9 +32,9 @@
             "Eg4KBm51bWJlchgBIAEoCRIoCgR0eXBlGAIgASgOMhoudHV0b3JpYWwuUGVy",
             "c29uLlBob25lVHlwZSIrCglQaG9uZVR5cGUSCgoGTU9CSUxFEAASCAoESE9N",
             "RRABEggKBFdPUksQAiIvCgtBZGRyZXNzQm9vaxIgCgZwZW9wbGUYASADKAsy",
-            "EC50dXRvcmlhbC5QZXJzb25CUAoUY29tLmV4YW1wbGUudHV0b3JpYWxCEUFk",
-            "ZHJlc3NCb29rUHJvdG9zqgIkR29vZ2xlLlByb3RvYnVmLkV4YW1wbGVzLkFk",
-            "ZHJlc3NCb29rYgZwcm90bzM="));
+            "EC50dXRvcmlhbC5QZXJzb25CWQobY29tLmV4YW1wbGUudHV0b3JpYWwucHJv",
+            "dG9zQhFBZGRyZXNzQm9va1Byb3Rvc1ABqgIkR29vZ2xlLlByb3RvYnVmLkV4",
+            "YW1wbGVzLkFkZHJlc3NCb29rYgZwcm90bzM="));
       descriptor = pbr::FileDescriptor.FromGeneratedCode(descriptorData,
           new pbr::FileDescriptor[] { global::Google.Protobuf.WellKnownTypes.TimestampReflection.Descriptor, },
           new pbr::GeneratedClrTypeInfo(null, null, new pbr::GeneratedClrTypeInfo[] {
diff --git a/python/google/protobuf/internal/api_implementation.py b/python/google/protobuf/internal/api_implementation.py
index 7592be4..be1af7d 100644
--- a/python/google/protobuf/internal/api_implementation.py
+++ b/python/google/protobuf/internal/api_implementation.py
@@ -32,8 +32,8 @@
 """
 
 import os
-import warnings
 import sys
+import warnings
 
 try:
   # pylint: disable=g-import-not-at-top
@@ -60,10 +60,11 @@
       raise ImportError('_use_fast_cpp_protos import succeeded but was None')
     del _use_fast_cpp_protos
     _api_version = 2
-    # Can not import both use_fast_cpp_protos and use_pure_python.
     from google.protobuf import use_pure_python
     raise RuntimeError(
-        'Conflict depend on both use_fast_cpp_protos and use_pure_python')
+        'Conflicting deps on both :use_fast_cpp_protos and :use_pure_python.\n'
+        ' go/build_deps_on_BOTH_use_fast_cpp_protos_AND_use_pure_python\n'
+        'This should be impossible via a link error at build time...')
   except ImportError:
     try:
       # pylint: disable=g-import-not-at-top
diff --git a/src/Makefile.am b/src/Makefile.am
index 49fe6ed..18b1a43 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -345,6 +345,8 @@
   google/protobuf/compiler/cpp/cpp_options.h                   \
   google/protobuf/compiler/cpp/cpp_padding_optimizer.cc        \
   google/protobuf/compiler/cpp/cpp_padding_optimizer.h         \
+  google/protobuf/compiler/cpp/cpp_parse_function_generator.cc \
+  google/protobuf/compiler/cpp/cpp_parse_function_generator.h  \
   google/protobuf/compiler/cpp/cpp_primitive_field.cc          \
   google/protobuf/compiler/cpp/cpp_primitive_field.h           \
   google/protobuf/compiler/cpp/cpp_service.cc                  \
diff --git a/src/google/protobuf/any.pb.cc b/src/google/protobuf/any.pb.cc
index 5ecf63f..f061f5a 100644
--- a/src/google/protobuf/any.pb.cc
+++ b/src/google/protobuf/any.pb.cc
@@ -315,7 +315,7 @@
 
 void Any::InternalSwap(Any* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   type_url_.Swap(&other->type_url_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
   value_.Swap(&other->value_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
 }
diff --git a/src/google/protobuf/api.pb.cc b/src/google/protobuf/api.pb.cc
index 0f4facd..e818046 100644
--- a/src/google/protobuf/api.pb.cc
+++ b/src/google/protobuf/api.pb.cc
@@ -558,7 +558,7 @@
 
 void Api::InternalSwap(Api* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   methods_.InternalSwap(&other->methods_);
   options_.InternalSwap(&other->options_);
   mixins_.InternalSwap(&other->mixins_);
@@ -953,7 +953,7 @@
 
 void Method::InternalSwap(Method* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   options_.InternalSwap(&other->options_);
   name_.Swap(&other->name_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
   request_type_url_.Swap(&other->request_type_url_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
@@ -1200,7 +1200,7 @@
 
 void Mixin::InternalSwap(Mixin* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   name_.Swap(&other->name_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
   root_.Swap(&other->root_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
 }
diff --git a/src/google/protobuf/api.pb.h b/src/google/protobuf/api.pb.h
index 75b0428..15ee4c1 100644
--- a/src/google/protobuf/api.pb.h
+++ b/src/google/protobuf/api.pb.h
@@ -279,7 +279,7 @@
   public:
   void clear_source_context();
   const PROTOBUF_NAMESPACE_ID::SourceContext& source_context() const;
-  PROTOBUF_NAMESPACE_ID::SourceContext* release_source_context();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::SourceContext* release_source_context();
   PROTOBUF_NAMESPACE_ID::SourceContext* mutable_source_context();
   void set_allocated_source_context(PROTOBUF_NAMESPACE_ID::SourceContext* source_context);
   private:
diff --git a/src/google/protobuf/arena.h b/src/google/protobuf/arena.h
index 8b5c7f1..59c9317 100644
--- a/src/google/protobuf/arena.h
+++ b/src/google/protobuf/arena.h
@@ -618,7 +618,6 @@
           new (arena->AllocateInternal(sizeof(T), alignof(T), destructor,
                                        RTTI_TYPE_ID(T)))
           T(std::forward<Args>(args)...);
-      result->SetOwningArena(arena);
       return result;
     }
   }
@@ -646,7 +645,6 @@
   PROTOBUF_ALWAYS_INLINE void OwnInternal(T* object, std::true_type) {
     if (object != NULL) {
       impl_.AddCleanup(object, &internal::arena_delete_object<MessageLite>);
-      object->SetOwningArena(this);
     }
   }
   template <typename T>
diff --git a/src/google/protobuf/arena_test_util.h b/src/google/protobuf/arena_test_util.h
index 8ceab91..33f5cf4 100644
--- a/src/google/protobuf/arena_test_util.h
+++ b/src/google/protobuf/arena_test_util.h
@@ -92,6 +92,33 @@
   } capture_alloc;
 };
 
+// Owns the internal T only if it's not owned by an arena.
+// T needs to be arena constructible and destructor skippable.
+template <typename T>
+class ArenaHolder {
+ public:
+  explicit ArenaHolder(Arena* arena)
+      : field_(Arena::CreateMessage<T>(arena)),
+        owned_by_arena_(arena != nullptr) {
+    GOOGLE_DCHECK(google::protobuf::Arena::is_arena_constructable<T>::value);
+    GOOGLE_DCHECK(google::protobuf::Arena::is_destructor_skippable<T>::value);
+  }
+
+  ~ArenaHolder() {
+    if (!owned_by_arena_) {
+      delete field_;
+    }
+  }
+
+  T* get() { return field_; }
+  T* operator->() { return field_; }
+  T& operator*() { return *field_; }
+
+ private:
+  T* field_;
+  bool owned_by_arena_;
+};
+
 }  // namespace internal
 }  // namespace protobuf
 }  // namespace google
diff --git a/src/google/protobuf/compiler/cpp/cpp_helpers.cc b/src/google/protobuf/compiler/cpp/cpp_helpers.cc
index dcbb14f..fbca72c 100644
--- a/src/google/protobuf/compiler/cpp/cpp_helpers.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_helpers.cc
@@ -206,10 +206,6 @@
   (*variables)[type] = IntTypeName(options, type);
 }
 
-bool HasInternalAccessors(const FieldOptions::CType ctype) {
-  return ctype == FieldOptions::STRING || ctype == FieldOptions::CORD;
-}
-
 }  // namespace
 
 void SetCommonVars(const Options& options,
@@ -1349,523 +1345,6 @@
   }
 }
 
-class ParseLoopGenerator {
- public:
-  ParseLoopGenerator(int num_hasbits, const Options& options,
-                     MessageSCCAnalyzer* scc_analyzer, io::Printer* printer)
-      : scc_analyzer_(scc_analyzer),
-        options_(options),
-        format_(printer),
-        num_hasbits_(num_hasbits) {}
-
-  void GenerateParserLoop(const Descriptor* descriptor) {
-    format_.Set("classname", ClassName(descriptor));
-    format_.Set("p_ns", "::" + ProtobufNamespace(options_));
-    format_.Set("pi_ns",
-                StrCat("::", ProtobufNamespace(options_), "::internal"));
-    format_.Set("GOOGLE_PROTOBUF", MacroPrefix(options_));
-    std::map<std::string, std::string> vars;
-    SetCommonVars(options_, &vars);
-    SetUnknkownFieldsVariable(descriptor, options_, &vars);
-    format_.AddMap(vars);
-
-    std::vector<const FieldDescriptor*> ordered_fields;
-    for (auto field : FieldRange(descriptor)) {
-      if (!IsFieldStripped(field, options_)) {
-        ordered_fields.push_back(field);
-      }
-    }
-    std::sort(ordered_fields.begin(), ordered_fields.end(),
-              [](const FieldDescriptor* a, const FieldDescriptor* b) {
-                return a->number() < b->number();
-              });
-
-    format_(
-        "const char* $classname$::_InternalParse(const char* ptr, "
-        "$pi_ns$::ParseContext* ctx) {\n"
-        "#define CHK_(x) if (PROTOBUF_PREDICT_FALSE(!(x))) goto failure\n");
-    format_.Indent();
-    int hasbits_size = 0;
-    if (num_hasbits_ > 0) {
-      hasbits_size = (num_hasbits_ + 31) / 32;
-    }
-    // For now only optimize small hasbits.
-    if (hasbits_size != 1) hasbits_size = 0;
-    if (hasbits_size) {
-      format_("_Internal::HasBits has_bits{};\n");
-      format_.Set("has_bits", "has_bits");
-    } else {
-      format_.Set("has_bits", "_has_bits_");
-    }
-
-    GenerateParseLoop(descriptor, ordered_fields);
-    format_.Outdent();
-    format_("success:\n");
-    if (hasbits_size) format_("  _has_bits_.Or(has_bits);\n");
-
-    format_(
-        "  return ptr;\n"
-        "failure:\n"
-        "  ptr = nullptr;\n"
-        "  goto success;\n"
-        "#undef CHK_\n"
-        "}\n");
-  }
-
- private:
-  MessageSCCAnalyzer* scc_analyzer_;
-  const Options& options_;
-  Formatter format_;
-  int num_hasbits_;
-
-  using WireFormat = internal::WireFormat;
-  using WireFormatLite = internal::WireFormatLite;
-
-  void GenerateArenaString(const FieldDescriptor* field) {
-    if (HasHasbit(field)) {
-      format_("_Internal::set_has_$1$(&$has_bits$);\n", FieldName(field));
-    }
-    std::string default_string =
-        field->default_value_string().empty()
-            ? "::" + ProtobufNamespace(options_) +
-                  "::internal::GetEmptyStringAlreadyInited()"
-            : QualifiedClassName(field->containing_type(), options_) +
-                  "::" + MakeDefaultName(field) + ".get()";
-    format_(
-        "if (arena != nullptr) {\n"
-        "  ptr = ctx->ReadArenaString(ptr, &$1$_, arena);\n"
-        "} else {\n"
-        "  ptr = "
-        "$pi_ns$::InlineGreedyStringParser($1$_.MutableNoArenaNoDefault(&$2$"
-        "), ptr, ctx);"
-        "\n}\n"
-        "const std::string* str = &$1$_.Get(); (void)str;\n",
-        FieldName(field), default_string);
-  }
-
-  void GenerateStrings(const FieldDescriptor* field, bool check_utf8) {
-    FieldOptions::CType ctype = FieldOptions::STRING;
-    if (!options_.opensource_runtime) {
-      // Open source doesn't support other ctypes;
-      ctype = field->options().ctype();
-    }
-    if (!field->is_repeated() && !options_.opensource_runtime &&
-        GetOptimizeFor(field->file(), options_) != FileOptions::LITE_RUNTIME &&
-        // For now only use arena string for strings with empty defaults.
-        field->default_value_string().empty() &&
-        !field->real_containing_oneof() && ctype == FieldOptions::STRING) {
-      GenerateArenaString(field);
-    } else {
-      std::string name;
-      switch (ctype) {
-        case FieldOptions::STRING:
-          name = "GreedyStringParser";
-          break;
-        case FieldOptions::CORD:
-          name = "CordParser";
-          break;
-        case FieldOptions::STRING_PIECE:
-          name = "StringPieceParser";
-          break;
-      }
-      format_(
-          "auto str = $1$$2$_$3$();\n"
-          "ptr = $pi_ns$::Inline$4$(str, ptr, ctx);\n",
-          HasInternalAccessors(ctype) ? "_internal_" : "",
-          field->is_repeated() && !field->is_packable() ? "add" : "mutable",
-          FieldName(field), name);
-    }
-    if (!check_utf8) return;  // return if this is a bytes field
-    auto level = GetUtf8CheckMode(field, options_);
-    switch (level) {
-      case Utf8CheckMode::kNone:
-        return;
-      case Utf8CheckMode::kVerify:
-        format_("#ifndef NDEBUG\n");
-        break;
-      case Utf8CheckMode::kStrict:
-        format_("CHK_(");
-        break;
-    }
-    std::string field_name;
-    field_name = "nullptr";
-    if (HasDescriptorMethods(field->file(), options_)) {
-      field_name = StrCat("\"", field->full_name(), "\"");
-    }
-    format_("$pi_ns$::VerifyUTF8(str, $1$)", field_name);
-    switch (level) {
-      case Utf8CheckMode::kNone:
-        return;
-      case Utf8CheckMode::kVerify:
-        format_(
-            ";\n"
-            "#endif  // !NDEBUG\n");
-        break;
-      case Utf8CheckMode::kStrict:
-        format_(");\n");
-        break;
-    }
-  }
-
-  void GenerateLengthDelim(const FieldDescriptor* field) {
-    if (field->is_packable()) {
-      std::string enum_validator;
-      if (field->type() == FieldDescriptor::TYPE_ENUM &&
-          !HasPreservingUnknownEnumSemantics(field)) {
-        enum_validator =
-            StrCat(", ", QualifiedClassName(field->enum_type(), options_),
-                         "_IsValid, &_internal_metadata_, ", field->number());
-        format_(
-            "ptr = "
-            "$pi_ns$::Packed$1$Parser<$unknown_fields_type$>(_internal_mutable_"
-            "$2$(), ptr, "
-            "ctx$3$);\n",
-            DeclaredTypeMethodName(field->type()), FieldName(field),
-            enum_validator);
-      } else {
-        format_(
-            "ptr = $pi_ns$::Packed$1$Parser(_internal_mutable_$2$(), ptr, "
-            "ctx$3$);\n",
-            DeclaredTypeMethodName(field->type()), FieldName(field),
-            enum_validator);
-      }
-    } else {
-      auto field_type = field->type();
-      switch (field_type) {
-        case FieldDescriptor::TYPE_STRING:
-          GenerateStrings(field, true /* utf8 */);
-          break;
-        case FieldDescriptor::TYPE_BYTES:
-          GenerateStrings(field, false /* utf8 */);
-          break;
-        case FieldDescriptor::TYPE_MESSAGE: {
-          if (field->is_map()) {
-            const FieldDescriptor* val =
-                field->message_type()->FindFieldByName("value");
-            GOOGLE_CHECK(val);
-            if (val->type() == FieldDescriptor::TYPE_ENUM &&
-                !HasPreservingUnknownEnumSemantics(field)) {
-              format_(
-                  "auto object = "
-                  "::$proto_ns$::internal::InitEnumParseWrapper<$unknown_"
-                  "fields_type$>("
-                  "&$1$_, $2$_IsValid, $3$, &_internal_metadata_);\n"
-                  "ptr = ctx->ParseMessage(&object, ptr);\n",
-                  FieldName(field), QualifiedClassName(val->enum_type()),
-                  field->number());
-            } else {
-              format_("ptr = ctx->ParseMessage(&$1$_, ptr);\n",
-                      FieldName(field));
-            }
-          } else if (IsLazy(field, options_)) {
-            if (field->real_containing_oneof()) {
-              format_(
-                  "if (!_internal_has_$1$()) {\n"
-                  "  clear_$2$();\n"
-                  "  $2$_.$1$_ = ::$proto_ns$::Arena::CreateMessage<\n"
-                  "      $pi_ns$::LazyField>(GetArena());\n"
-                  "  set_has_$1$();\n"
-                  "}\n"
-                  "ptr = ctx->ParseMessage($2$_.$1$_, ptr);\n",
-                  FieldName(field), field->containing_oneof()->name());
-            } else if (HasHasbit(field)) {
-              format_(
-                  "_Internal::set_has_$1$(&$has_bits$);\n"
-                  "ptr = ctx->ParseMessage(&$1$_, ptr);\n",
-                  FieldName(field));
-            } else {
-              format_("ptr = ctx->ParseMessage(&$1$_, ptr);\n",
-                      FieldName(field));
-            }
-          } else if (IsImplicitWeakField(field, options_, scc_analyzer_)) {
-            if (!field->is_repeated()) {
-              format_(
-                  "ptr = ctx->ParseMessage(_Internal::mutable_$1$(this), "
-                  "ptr);\n",
-                  FieldName(field));
-            } else {
-              format_(
-                  "ptr = ctx->ParseMessage($1$_.AddWeak(reinterpret_cast<const "
-                  "::$proto_ns$::MessageLite*>($2$::_$3$_default_instance_ptr_)"
-                  "), ptr);\n",
-                  FieldName(field), Namespace(field->message_type(), options_),
-                  ClassName(field->message_type()));
-            }
-          } else if (IsWeak(field, options_)) {
-            format_(
-                "{\n"
-                "  auto* default_ = &reinterpret_cast<const Message&>($1$);\n"
-                "  ptr = ctx->ParseMessage(_weak_field_map_.MutableMessage($2$,"
-                " default_), ptr);\n"
-                "}\n",
-                QualifiedDefaultInstanceName(field->message_type(), options_),
-                field->number());
-          } else {
-            format_("ptr = ctx->ParseMessage(_internal_$1$_$2$(), ptr);\n",
-                    field->is_repeated() ? "add" : "mutable", FieldName(field));
-          }
-          break;
-        }
-        default:
-          GOOGLE_LOG(FATAL) << "Illegal combination for length delimited wiretype "
-                     << " filed type is " << field->type();
-      }
-    }
-  }
-
-  // Convert a 1 or 2 byte varint into the equivalent value upon a direct load.
-  static uint32_t SmallVarintValue(uint32_t x) {
-    GOOGLE_DCHECK(x < 128 * 128);
-    if (x >= 128) x += (x & 0xFF80) + 128;
-    return x;
-  }
-
-  static bool ShouldRepeat(const FieldDescriptor* descriptor,
-                           internal::WireFormatLite::WireType wiretype) {
-    constexpr int kMaxTwoByteFieldNumber = 16 * 128;
-    return descriptor->number() < kMaxTwoByteFieldNumber &&
-           descriptor->is_repeated() &&
-           (!descriptor->is_packable() ||
-            wiretype != internal::WireFormatLite::WIRETYPE_LENGTH_DELIMITED);
-  }
-
-  void GenerateFieldBody(internal::WireFormatLite::WireType wiretype,
-                         const FieldDescriptor* field) {
-    uint32_t tag = WireFormatLite::MakeTag(field->number(), wiretype);
-    switch (wiretype) {
-      case WireFormatLite::WIRETYPE_VARINT: {
-        std::string type = PrimitiveTypeName(options_, field->cpp_type());
-        std::string prefix = field->is_repeated() ? "add" : "set";
-        if (field->type() == FieldDescriptor::TYPE_ENUM) {
-          format_(
-              "$uint64$ val = $pi_ns$::ReadVarint64(&ptr);\n"
-              "CHK_(ptr);\n");
-          if (!HasPreservingUnknownEnumSemantics(field)) {
-            format_("if (PROTOBUF_PREDICT_TRUE($1$_IsValid(val))) {\n",
-                    QualifiedClassName(field->enum_type(), options_));
-            format_.Indent();
-          }
-          format_("_internal_$1$_$2$(static_cast<$3$>(val));\n", prefix,
-                  FieldName(field),
-                  QualifiedClassName(field->enum_type(), options_));
-          if (!HasPreservingUnknownEnumSemantics(field)) {
-            format_.Outdent();
-            format_(
-                "} else {\n"
-                "  $pi_ns$::WriteVarint($1$, val, mutable_unknown_fields());\n"
-                "}\n",
-                field->number());
-          }
-        } else {
-          std::string size = (field->type() == FieldDescriptor::TYPE_SINT32 ||
-                              field->type() == FieldDescriptor::TYPE_UINT32)
-                                 ? "32"
-                                 : "64";
-          std::string zigzag;
-          if ((field->type() == FieldDescriptor::TYPE_SINT32 ||
-               field->type() == FieldDescriptor::TYPE_SINT64)) {
-            zigzag = "ZigZag";
-          }
-          if (field->is_repeated() || field->real_containing_oneof()) {
-            std::string prefix = field->is_repeated() ? "add" : "set";
-            format_(
-                "_internal_$1$_$2$($pi_ns$::ReadVarint$3$$4$(&ptr));\n"
-                "CHK_(ptr);\n",
-                prefix, FieldName(field), zigzag, size);
-          } else {
-            if (HasHasbit(field)) {
-              format_("_Internal::set_has_$1$(&$has_bits$);\n",
-                      FieldName(field));
-            }
-            format_(
-                "$1$_ = $pi_ns$::ReadVarint$2$$3$(&ptr);\n"
-                "CHK_(ptr);\n",
-                FieldName(field), zigzag, size);
-          }
-        }
-        break;
-      }
-      case WireFormatLite::WIRETYPE_FIXED32:
-      case WireFormatLite::WIRETYPE_FIXED64: {
-        std::string type = PrimitiveTypeName(options_, field->cpp_type());
-        if (field->is_repeated() || field->real_containing_oneof()) {
-          std::string prefix = field->is_repeated() ? "add" : "set";
-          format_(
-              "_internal_$1$_$2$($pi_ns$::UnalignedLoad<$3$>(ptr));\n"
-              "ptr += sizeof($3$);\n",
-              prefix, FieldName(field), type);
-        } else {
-          if (HasHasbit(field)) {
-            format_("_Internal::set_has_$1$(&$has_bits$);\n", FieldName(field));
-          }
-          format_(
-              "$1$_ = $pi_ns$::UnalignedLoad<$2$>(ptr);\n"
-              "ptr += sizeof($2$);\n",
-              FieldName(field), type);
-        }
-        break;
-      }
-      case WireFormatLite::WIRETYPE_LENGTH_DELIMITED: {
-        GenerateLengthDelim(field);
-        format_("CHK_(ptr);\n");
-        break;
-      }
-      case WireFormatLite::WIRETYPE_START_GROUP: {
-        format_(
-            "ptr = ctx->ParseGroup(_internal_$1$_$2$(), ptr, $3$);\n"
-            "CHK_(ptr);\n",
-            field->is_repeated() ? "add" : "mutable", FieldName(field), tag);
-        break;
-      }
-      case WireFormatLite::WIRETYPE_END_GROUP: {
-        GOOGLE_LOG(FATAL) << "Can't have end group field\n";
-        break;
-      }
-    }  // switch (wire_type)
-  }
-
-  // Returns the tag for this field and in case of repeated packable fields,
-  // sets a fallback tag in fallback_tag_ptr.
-  static uint32_t ExpectedTag(const FieldDescriptor* field,
-                              uint32_t* fallback_tag_ptr) {
-    uint32_t expected_tag;
-    if (field->is_packable()) {
-      auto expected_wiretype = WireFormat::WireTypeForFieldType(field->type());
-      expected_tag =
-          WireFormatLite::MakeTag(field->number(), expected_wiretype);
-      GOOGLE_CHECK(expected_wiretype != WireFormatLite::WIRETYPE_LENGTH_DELIMITED);
-      auto fallback_wiretype = WireFormatLite::WIRETYPE_LENGTH_DELIMITED;
-      uint32_t fallback_tag =
-          WireFormatLite::MakeTag(field->number(), fallback_wiretype);
-
-      if (field->is_packed()) std::swap(expected_tag, fallback_tag);
-      *fallback_tag_ptr = fallback_tag;
-    } else {
-      auto expected_wiretype = WireFormat::WireTypeForField(field);
-      expected_tag =
-          WireFormatLite::MakeTag(field->number(), expected_wiretype);
-    }
-    return expected_tag;
-  }
-
-  void GenerateParseLoop(
-      const Descriptor* descriptor,
-      const std::vector<const FieldDescriptor*>& ordered_fields) {
-    format_(
-        "while (!ctx->Done(&ptr)) {\n"
-        "  $uint32$ tag;\n"
-        "  ptr = $pi_ns$::ReadTag(ptr, &tag);\n");
-    if (!ordered_fields.empty()) format_("  switch (tag >> 3) {\n");
-
-    format_.Indent();
-    format_.Indent();
-
-    for (const auto* field : ordered_fields) {
-      PrintFieldComment(format_, field);
-      format_("case $1$:\n", field->number());
-      format_.Indent();
-      uint32_t fallback_tag = 0;
-      uint32_t expected_tag = ExpectedTag(field, &fallback_tag);
-      format_(
-          "if (PROTOBUF_PREDICT_TRUE(static_cast<$uint8$>(tag) == $1$)) {\n",
-          expected_tag & 0xFF);
-      format_.Indent();
-      auto wiretype = WireFormatLite::GetTagWireType(expected_tag);
-      uint32_t tag = WireFormatLite::MakeTag(field->number(), wiretype);
-      int tag_size = io::CodedOutputStream::VarintSize32(tag);
-      bool is_repeat = ShouldRepeat(field, wiretype);
-      if (is_repeat) {
-        format_(
-            "ptr -= $1$;\n"
-            "do {\n"
-            "  ptr += $1$;\n",
-            tag_size);
-        format_.Indent();
-      }
-      GenerateFieldBody(wiretype, field);
-      if (is_repeat) {
-        format_.Outdent();
-        format_(
-            "  if (!ctx->DataAvailable(ptr)) break;\n"
-            "} while ($pi_ns$::ExpectTag<$1$>(ptr));\n",
-            tag);
-      }
-      format_.Outdent();
-      if (fallback_tag) {
-        format_("} else if (static_cast<$uint8$>(tag) == $1$) {\n",
-                fallback_tag & 0xFF);
-        format_.Indent();
-        GenerateFieldBody(WireFormatLite::GetTagWireType(fallback_tag), field);
-        format_.Outdent();
-      }
-      format_.Outdent();
-      format_(
-          "  } else goto handle_unusual;\n"
-          "  continue;\n");
-    }  // for loop over ordered fields
-
-    // Default case
-    if (!ordered_fields.empty()) format_("default: {\n");
-    if (!ordered_fields.empty()) format_("handle_unusual:\n");
-    format_(
-        "  if ((tag == 0) || ((tag & 7) == 4)) {\n"
-        "    CHK_(ptr);\n"
-        "    ctx->SetLastTag(tag);\n"
-        "    goto success;\n"
-        "  }\n");
-    if (IsMapEntryMessage(descriptor)) {
-      format_("  continue;\n");
-    } else {
-      if (descriptor->extension_range_count() > 0) {
-        format_("if (");
-        for (int i = 0; i < descriptor->extension_range_count(); i++) {
-          const Descriptor::ExtensionRange* range =
-              descriptor->extension_range(i);
-          if (i > 0) format_(" ||\n    ");
-
-          uint32_t start_tag = WireFormatLite::MakeTag(
-              range->start, static_cast<WireFormatLite::WireType>(0));
-          uint32_t end_tag = WireFormatLite::MakeTag(
-              range->end, static_cast<WireFormatLite::WireType>(0));
-
-          if (range->end > FieldDescriptor::kMaxNumber) {
-            format_("($1$u <= tag)", start_tag);
-          } else {
-            format_("($1$u <= tag && tag < $2$u)", start_tag, end_tag);
-          }
-        }
-        format_(") {\n");
-        format_(
-            "  ptr = _extensions_.ParseField(tag, ptr,\n"
-            "      internal_default_instance(), &_internal_metadata_, ctx);\n"
-            "  CHK_(ptr != nullptr);\n"
-            "  continue;\n"
-            "}\n");
-      }
-      format_(
-          "  ptr = UnknownFieldParse(tag,\n"
-          "      _internal_metadata_.mutable_unknown_fields<$unknown_"
-          "fields_type$>(),\n"
-          "      ptr, ctx);\n"
-          "  CHK_(ptr != nullptr);\n"
-          "  continue;\n");
-    }
-    if (!ordered_fields.empty()) format_("}\n");  // default case
-    format_.Outdent();
-    format_.Outdent();
-    if (!ordered_fields.empty()) format_("  }  // switch\n");
-    format_("}  // while\n");
-  }
-};
-
-void GenerateParserLoop(const Descriptor* descriptor, int num_hasbits,
-                        const Options& options,
-                        MessageSCCAnalyzer* scc_analyzer,
-                        io::Printer* printer) {
-  ParseLoopGenerator generator(num_hasbits, options, scc_analyzer, printer);
-  generator.GenerateParserLoop(descriptor);
-}
-
 static bool HasExtensionFromFile(const Message& msg, const FileDescriptor* file,
                                  const Options& options,
                                  bool* has_opt_codesize_extension) {
diff --git a/src/google/protobuf/compiler/cpp/cpp_helpers.h b/src/google/protobuf/compiler/cpp/cpp_helpers.h
index 8e509c1..5fa019d 100644
--- a/src/google/protobuf/compiler/cpp/cpp_helpers.h
+++ b/src/google/protobuf/compiler/cpp/cpp_helpers.h
@@ -418,8 +418,8 @@
 std::string UnderscoresToCamelCase(const std::string& input,
                                    bool cap_next_letter);
 
-inline bool HasFieldPresence(const FileDescriptor* file) {
-  return file->syntax() != FileDescriptor::SYNTAX_PROTO3;
+inline bool IsProto3(const FileDescriptor* file) {
+  return file->syntax() == FileDescriptor::SYNTAX_PROTO3;
 }
 
 inline bool HasHasbit(const FieldDescriptor* field) {
@@ -865,10 +865,6 @@
 
 inline OneOfRangeImpl OneOfRange(const Descriptor* desc) { return {desc}; }
 
-void GenerateParserLoop(const Descriptor* descriptor, int num_hasbits,
-                        const Options& options,
-                        MessageSCCAnalyzer* scc_analyzer, io::Printer* printer);
-
 PROTOC_EXPORT std::string StripProto(const std::string& filename);
 
 }  // namespace cpp
diff --git a/src/google/protobuf/compiler/cpp/cpp_map_field.cc b/src/google/protobuf/compiler/cpp/cpp_map_field.cc
index c9c30e0..44c9138 100644
--- a/src/google/protobuf/compiler/cpp/cpp_map_field.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_map_field.cc
@@ -157,7 +157,7 @@
 
 void MapFieldGenerator::GenerateSwappingCode(io::Printer* printer) const {
   Formatter format(printer, variables_);
-  format("$name$_.Swap(&other->$name$_);\n");
+  format("$name$_.InternalSwap(&other->$name$_);\n");
 }
 
 void MapFieldGenerator::GenerateCopyConstructorCode(
diff --git a/src/google/protobuf/compiler/cpp/cpp_message.cc b/src/google/protobuf/compiler/cpp/cpp_message.cc
index 0a41acf..f2d1aab 100644
--- a/src/google/protobuf/compiler/cpp/cpp_message.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_message.cc
@@ -48,6 +48,7 @@
 #include <google/protobuf/compiler/cpp/cpp_field.h>
 #include <google/protobuf/compiler/cpp/cpp_helpers.h>
 #include <google/protobuf/compiler/cpp/cpp_padding_optimizer.h>
+#include <google/protobuf/compiler/cpp/cpp_parse_function_generator.h>
 #include <google/protobuf/descriptor.pb.h>
 #include <google/protobuf/io/coded_stream.h>
 #include <google/protobuf/io/printer.h>
@@ -237,7 +238,7 @@
 
 // Does the given field have a has_$name$() method?
 bool HasHasMethod(const FieldDescriptor* field) {
-  if (HasFieldPresence(field->file())) {
+  if (!IsProto3(field->file())) {
     // In proto1/proto2, every field has a has_$name$() method.
     return true;
   }
@@ -276,7 +277,7 @@
 bool HasPrivateHasMethod(const FieldDescriptor* field) {
   // Only for oneofs in message types with no field presence. has_$name$(),
   // based on the oneof case, is still useful internally for generated code.
-  return (!HasFieldPresence(field->file()) && field->real_containing_oneof());
+  return IsProto3(field->file()) && field->real_containing_oneof();
 }
 
 // TODO(ckennelly):  Cull these exclusions if/when these protos do not have
@@ -2896,15 +2897,13 @@
 
   if (HasGeneratedMethods(descriptor_->file(), options_)) {
     if (descriptor_->extension_range_count() > 0) {
-      format("_extensions_.Swap(&other->_extensions_);\n");
+      format("_extensions_.InternalSwap(&other->_extensions_);\n");
     }
 
     std::map<std::string, std::string> vars;
     SetUnknkownFieldsVariable(descriptor_, options_, &vars);
     format.AddMap(vars);
-    format(
-        "_internal_metadata_.Swap<$unknown_fields_type$>(&other->_internal_"
-        "metadata_);\n");
+    format("_internal_metadata_.InternalSwap(&other->_internal_metadata_);\n");
 
     if (!has_bit_indices_.empty()) {
       for (int i = 0; i < HasBitsSize(); ++i) {
@@ -3255,8 +3254,8 @@
         "}\n");
     return;
   }
-  GenerateParserLoop(descriptor_, max_has_bit_index_, options_, scc_analyzer_,
-                     printer);
+  GenerateParseFunction(descriptor_, max_has_bit_index_, options_,
+                        scc_analyzer_, printer);
 }
 
 void MessageGenerator::GenerateSerializeOneofFields(
@@ -3410,7 +3409,7 @@
     LazySerializerEmitter(MessageGenerator* mg, io::Printer* printer)
         : mg_(mg),
           format_(printer),
-          eager_(!HasFieldPresence(mg->descriptor_->file())),
+          eager_(IsProto3(mg->descriptor_->file())),
           cached_has_bit_index_(kNoHasbit) {}
 
     ~LazySerializerEmitter() { Flush(); }
diff --git a/src/google/protobuf/compiler/cpp/cpp_message_field.cc b/src/google/protobuf/compiler/cpp/cpp_message_field.cc
index 7bad24c..18c6f09 100644
--- a/src/google/protobuf/compiler/cpp/cpp_message_field.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_message_field.cc
@@ -125,7 +125,8 @@
   }
   format(
       "$deprecated_attr$const $type$& ${1$$name$$}$() const;\n"
-      "$deprecated_attr$$type$* ${1$$release_name$$}$();\n"
+      "PROTOBUF_FUTURE_MUST_USE_RESULT $deprecated_attr$$type$* "
+      "${1$$release_name$$}$();\n"
       "$deprecated_attr$$type$* ${1$mutable_$name$$}$();\n"
       "$deprecated_attr$void ${1$set_allocated_$name$$}$"
       "($type$* $name$);\n",
@@ -320,7 +321,7 @@
     format(
         "::$proto_ns$::MessageLite*\n"
         "$classname$::_Internal::mutable_$name$($classname$* msg) {\n");
-    if (HasFieldPresence(descriptor_->file())) {
+    if (HasHasbit(descriptor_)) {
       format("  msg->$set_hasbit$\n");
     }
     format(
@@ -353,7 +354,7 @@
   GOOGLE_CHECK(!IsFieldStripped(descriptor_, options_));
 
   Formatter format(printer, variables_);
-  if (!HasFieldPresence(descriptor_->file())) {
+  if (!HasHasbit(descriptor_)) {
     // If we don't have has-bits, message presence is indicated only by ptr !=
     // NULL. Thus on clear, we need to delete the object.
     format(
@@ -371,7 +372,7 @@
   GOOGLE_CHECK(!IsFieldStripped(descriptor_, options_));
 
   Formatter format(printer, variables_);
-  if (!HasFieldPresence(descriptor_->file())) {
+  if (!HasHasbit(descriptor_)) {
     // If we don't have has-bits, message presence is indicated only by ptr !=
     // NULL. Thus on clear, we need to delete the object.
     format(
diff --git a/src/google/protobuf/compiler/cpp/cpp_parse_function_generator.cc b/src/google/protobuf/compiler/cpp/cpp_parse_function_generator.cc
new file mode 100644
index 0000000..41be0b5
--- /dev/null
+++ b/src/google/protobuf/compiler/cpp/cpp_parse_function_generator.cc
@@ -0,0 +1,580 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include <google/protobuf/compiler/cpp/cpp_parse_function_generator.h>
+
+#include <google/protobuf/wire_format.h>
+#include <google/protobuf/wire_format_lite.h>
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace cpp {
+
+namespace {
+using google::protobuf::internal::WireFormat;
+using google::protobuf::internal::WireFormatLite;
+
+std::vector<const FieldDescriptor*> GetOrderedFields(
+    const Descriptor* descriptor, const Options& options) {
+  std::vector<const FieldDescriptor*> ordered_fields;
+  for (auto field : FieldRange(descriptor)) {
+    if (!IsFieldStripped(field, options)) {
+      ordered_fields.push_back(field);
+    }
+  }
+  std::sort(ordered_fields.begin(), ordered_fields.end(),
+            [](const FieldDescriptor* a, const FieldDescriptor* b) {
+              return a->number() < b->number();
+            });
+  return ordered_fields;
+}
+
+bool HasInternalAccessors(const FieldOptions::CType ctype) {
+  return ctype == FieldOptions::STRING || ctype == FieldOptions::CORD;
+}
+
+class ParseFunctionGenerator {
+ public:
+  ParseFunctionGenerator(const Descriptor* descriptor, int num_hasbits,
+                         const Options& options,
+                         MessageSCCAnalyzer* scc_analyzer, io::Printer* printer)
+      : descriptor_(descriptor),
+        scc_analyzer_(scc_analyzer),
+        options_(options),
+        format_(printer),
+        num_hasbits_(num_hasbits) {
+    format_.Set("classname", ClassName(descriptor));
+    format_.Set("p_ns", "::" + ProtobufNamespace(options_));
+    format_.Set("pi_ns",
+                StrCat("::", ProtobufNamespace(options_), "::internal"));
+    format_.Set("GOOGLE_PROTOBUF", MacroPrefix(options_));
+    std::map<std::string, std::string> vars;
+    SetCommonVars(options_, &vars);
+    SetUnknkownFieldsVariable(descriptor, options_, &vars);
+    format_.AddMap(vars);
+  }
+
+  void GenerateLoopingParseFunction() {
+    format_(
+        "const char* $classname$::_InternalParse(const char* ptr, "
+        "$pi_ns$::ParseContext* ctx) {\n"
+        "#define CHK_(x) if (PROTOBUF_PREDICT_FALSE(!(x))) goto failure\n");
+    format_.Indent();
+    int hasbits_size = 0;
+    if (num_hasbits_ > 0) {
+      hasbits_size = (num_hasbits_ + 31) / 32;
+    }
+    // For now only optimize small hasbits.
+    if (hasbits_size != 1) hasbits_size = 0;
+    if (hasbits_size) {
+      format_("_Internal::HasBits has_bits{};\n");
+      format_.Set("has_bits", "has_bits");
+    } else {
+      format_.Set("has_bits", "_has_bits_");
+    }
+    format_.Set("continue", "continue");
+    format_("while (!ctx->Done(&ptr)) {\n");
+    format_.Indent();
+
+    GenerateParseIterationBody(descriptor_,
+                               GetOrderedFields(descriptor_, options_));
+
+    format_.Outdent();
+    format_("}  // while\n");
+
+    format_.Outdent();
+    format_("success:\n");
+    if (hasbits_size) format_("  _has_bits_.Or(has_bits);\n");
+
+    format_(
+        "  return ptr;\n"
+        "failure:\n"
+        "  ptr = nullptr;\n"
+        "  goto success;\n"
+        "#undef CHK_\n"
+        "}\n");
+  }
+
+ private:
+  const Descriptor* descriptor_;
+  MessageSCCAnalyzer* scc_analyzer_;
+  const Options& options_;
+  Formatter format_;
+  int num_hasbits_;
+
+  void GenerateArenaString(const FieldDescriptor* field) {
+    if (HasHasbit(field)) {
+      format_("_Internal::set_has_$1$(&$has_bits$);\n", FieldName(field));
+    }
+    std::string default_string =
+        field->default_value_string().empty()
+            ? "::" + ProtobufNamespace(options_) +
+                  "::internal::GetEmptyStringAlreadyInited()"
+            : QualifiedClassName(field->containing_type(), options_) +
+                  "::" + MakeDefaultName(field) + ".get()";
+    format_(
+        "if (arena != nullptr) {\n"
+        "  ptr = ctx->ReadArenaString(ptr, &$1$_, arena);\n"
+        "} else {\n"
+        "  ptr = "
+        "$pi_ns$::InlineGreedyStringParser($1$_.MutableNoArenaNoDefault(&$2$"
+        "), ptr, ctx);"
+        "\n}\n"
+        "const std::string* str = &$1$_.Get(); (void)str;\n",
+        FieldName(field), default_string);
+  }
+
+  void GenerateStrings(const FieldDescriptor* field, bool check_utf8) {
+    FieldOptions::CType ctype = FieldOptions::STRING;
+    if (!options_.opensource_runtime) {
+      // Open source doesn't support other ctypes;
+      ctype = field->options().ctype();
+    }
+    if (!field->is_repeated() && !options_.opensource_runtime &&
+        GetOptimizeFor(field->file(), options_) != FileOptions::LITE_RUNTIME &&
+        // For now only use arena string for strings with empty defaults.
+        field->default_value_string().empty() &&
+        !field->real_containing_oneof() && ctype == FieldOptions::STRING) {
+      GenerateArenaString(field);
+    } else {
+      std::string name;
+      switch (ctype) {
+        case FieldOptions::STRING:
+          name = "GreedyStringParser";
+          break;
+        case FieldOptions::CORD:
+          name = "CordParser";
+          break;
+        case FieldOptions::STRING_PIECE:
+          name = "StringPieceParser";
+          break;
+      }
+      format_(
+          "auto str = $1$$2$_$3$();\n"
+          "ptr = $pi_ns$::Inline$4$(str, ptr, ctx);\n",
+          HasInternalAccessors(ctype) ? "_internal_" : "",
+          field->is_repeated() && !field->is_packable() ? "add" : "mutable",
+          FieldName(field), name);
+    }
+    if (!check_utf8) return;  // return if this is a bytes field
+    auto level = GetUtf8CheckMode(field, options_);
+    switch (level) {
+      case Utf8CheckMode::kNone:
+        return;
+      case Utf8CheckMode::kVerify:
+        format_("#ifndef NDEBUG\n");
+        break;
+      case Utf8CheckMode::kStrict:
+        format_("CHK_(");
+        break;
+    }
+    std::string field_name;
+    field_name = "nullptr";
+    if (HasDescriptorMethods(field->file(), options_)) {
+      field_name = StrCat("\"", field->full_name(), "\"");
+    }
+    format_("$pi_ns$::VerifyUTF8(str, $1$)", field_name);
+    switch (level) {
+      case Utf8CheckMode::kNone:
+        return;
+      case Utf8CheckMode::kVerify:
+        format_(
+            ";\n"
+            "#endif  // !NDEBUG\n");
+        break;
+      case Utf8CheckMode::kStrict:
+        format_(");\n");
+        break;
+    }
+  }
+
+  void GenerateLengthDelim(const FieldDescriptor* field) {
+    if (field->is_packable()) {
+      std::string enum_validator;
+      if (field->type() == FieldDescriptor::TYPE_ENUM &&
+          !HasPreservingUnknownEnumSemantics(field)) {
+        enum_validator =
+            StrCat(", ", QualifiedClassName(field->enum_type(), options_),
+                         "_IsValid, &_internal_metadata_, ", field->number());
+        format_(
+            "ptr = "
+            "$pi_ns$::Packed$1$Parser<$unknown_fields_type$>(_internal_mutable_"
+            "$2$(), ptr, "
+            "ctx$3$);\n",
+            DeclaredTypeMethodName(field->type()), FieldName(field),
+            enum_validator);
+      } else {
+        format_(
+            "ptr = $pi_ns$::Packed$1$Parser(_internal_mutable_$2$(), ptr, "
+            "ctx$3$);\n",
+            DeclaredTypeMethodName(field->type()), FieldName(field),
+            enum_validator);
+      }
+    } else {
+      auto field_type = field->type();
+      switch (field_type) {
+        case FieldDescriptor::TYPE_STRING:
+          GenerateStrings(field, true /* utf8 */);
+          break;
+        case FieldDescriptor::TYPE_BYTES:
+          GenerateStrings(field, false /* utf8 */);
+          break;
+        case FieldDescriptor::TYPE_MESSAGE: {
+          if (field->is_map()) {
+            const FieldDescriptor* val =
+                field->message_type()->FindFieldByName("value");
+            GOOGLE_CHECK(val);
+            if (val->type() == FieldDescriptor::TYPE_ENUM &&
+                !HasPreservingUnknownEnumSemantics(field)) {
+              format_(
+                  "auto object = "
+                  "::$proto_ns$::internal::InitEnumParseWrapper<$unknown_"
+                  "fields_type$>("
+                  "&$1$_, $2$_IsValid, $3$, &_internal_metadata_);\n"
+                  "ptr = ctx->ParseMessage(&object, ptr);\n",
+                  FieldName(field), QualifiedClassName(val->enum_type()),
+                  field->number());
+            } else {
+              format_("ptr = ctx->ParseMessage(&$1$_, ptr);\n",
+                      FieldName(field));
+            }
+          } else if (IsLazy(field, options_)) {
+            if (field->real_containing_oneof()) {
+              format_(
+                  "if (!_internal_has_$1$()) {\n"
+                  "  clear_$2$();\n"
+                  "  $2$_.$1$_ = ::$proto_ns$::Arena::CreateMessage<\n"
+                  "      $pi_ns$::LazyField>(GetArena());\n"
+                  "  set_has_$1$();\n"
+                  "}\n"
+                  "ptr = ctx->ParseMessage($2$_.$1$_, ptr);\n",
+                  FieldName(field), field->containing_oneof()->name());
+            } else if (HasHasbit(field)) {
+              format_(
+                  "_Internal::set_has_$1$(&$has_bits$);\n"
+                  "ptr = ctx->ParseMessage(&$1$_, ptr);\n",
+                  FieldName(field));
+            } else {
+              format_("ptr = ctx->ParseMessage(&$1$_, ptr);\n",
+                      FieldName(field));
+            }
+          } else if (IsImplicitWeakField(field, options_, scc_analyzer_)) {
+            if (!field->is_repeated()) {
+              format_(
+                  "ptr = ctx->ParseMessage(_Internal::mutable_$1$(this), "
+                  "ptr);\n",
+                  FieldName(field));
+            } else {
+              format_(
+                  "ptr = ctx->ParseMessage($1$_.AddWeak(reinterpret_cast<const "
+                  "::$proto_ns$::MessageLite*>($2$::_$3$_default_instance_ptr_)"
+                  "), ptr);\n",
+                  FieldName(field), Namespace(field->message_type(), options_),
+                  ClassName(field->message_type()));
+            }
+          } else if (IsWeak(field, options_)) {
+            format_(
+                "{\n"
+                "  auto* default_ = &reinterpret_cast<const Message&>($1$);\n"
+                "  ptr = ctx->ParseMessage(_weak_field_map_.MutableMessage($2$,"
+                " default_), ptr);\n"
+                "}\n",
+                QualifiedDefaultInstanceName(field->message_type(), options_),
+                field->number());
+          } else {
+            format_("ptr = ctx->ParseMessage(_internal_$1$_$2$(), ptr);\n",
+                    field->is_repeated() ? "add" : "mutable", FieldName(field));
+          }
+          break;
+        }
+        default:
+          GOOGLE_LOG(FATAL) << "Illegal combination for length delimited wiretype "
+                     << " filed type is " << field->type();
+      }
+    }
+  }
+
+  // Convert a 1 or 2 byte varint into the equivalent value upon a direct load.
+  static uint32_t SmallVarintValue(uint32_t x) {
+    GOOGLE_DCHECK(x < 128 * 128);
+    if (x >= 128) x += (x & 0xFF80) + 128;
+    return x;
+  }
+
+  static bool ShouldRepeat(const FieldDescriptor* descriptor,
+                           internal::WireFormatLite::WireType wiretype) {
+    constexpr int kMaxTwoByteFieldNumber = 16 * 128;
+    return descriptor->number() < kMaxTwoByteFieldNumber &&
+           descriptor->is_repeated() &&
+           (!descriptor->is_packable() ||
+            wiretype != internal::WireFormatLite::WIRETYPE_LENGTH_DELIMITED);
+  }
+
+  void GenerateFieldBody(internal::WireFormatLite::WireType wiretype,
+                         const FieldDescriptor* field) {
+    uint32_t tag = WireFormatLite::MakeTag(field->number(), wiretype);
+    switch (wiretype) {
+      case WireFormatLite::WIRETYPE_VARINT: {
+        std::string type = PrimitiveTypeName(options_, field->cpp_type());
+        std::string prefix = field->is_repeated() ? "add" : "set";
+        if (field->type() == FieldDescriptor::TYPE_ENUM) {
+          format_(
+              "$uint64$ val = $pi_ns$::ReadVarint64(&ptr);\n"
+              "CHK_(ptr);\n");
+          if (!HasPreservingUnknownEnumSemantics(field)) {
+            format_("if (PROTOBUF_PREDICT_TRUE($1$_IsValid(val))) {\n",
+                    QualifiedClassName(field->enum_type(), options_));
+            format_.Indent();
+          }
+          format_("_internal_$1$_$2$(static_cast<$3$>(val));\n", prefix,
+                  FieldName(field),
+                  QualifiedClassName(field->enum_type(), options_));
+          if (!HasPreservingUnknownEnumSemantics(field)) {
+            format_.Outdent();
+            format_(
+                "} else {\n"
+                "  $pi_ns$::WriteVarint($1$, val, mutable_unknown_fields());\n"
+                "}\n",
+                field->number());
+          }
+        } else {
+          std::string size = (field->type() == FieldDescriptor::TYPE_SINT32 ||
+                              field->type() == FieldDescriptor::TYPE_UINT32)
+                                 ? "32"
+                                 : "64";
+          std::string zigzag;
+          if ((field->type() == FieldDescriptor::TYPE_SINT32 ||
+               field->type() == FieldDescriptor::TYPE_SINT64)) {
+            zigzag = "ZigZag";
+          }
+          if (field->is_repeated() || field->real_containing_oneof()) {
+            std::string prefix = field->is_repeated() ? "add" : "set";
+            format_(
+                "_internal_$1$_$2$($pi_ns$::ReadVarint$3$$4$(&ptr));\n"
+                "CHK_(ptr);\n",
+                prefix, FieldName(field), zigzag, size);
+          } else {
+            if (HasHasbit(field)) {
+              format_("_Internal::set_has_$1$(&$has_bits$);\n",
+                      FieldName(field));
+            }
+            format_(
+                "$1$_ = $pi_ns$::ReadVarint$2$$3$(&ptr);\n"
+                "CHK_(ptr);\n",
+                FieldName(field), zigzag, size);
+          }
+        }
+        break;
+      }
+      case WireFormatLite::WIRETYPE_FIXED32:
+      case WireFormatLite::WIRETYPE_FIXED64: {
+        std::string type = PrimitiveTypeName(options_, field->cpp_type());
+        if (field->is_repeated() || field->real_containing_oneof()) {
+          std::string prefix = field->is_repeated() ? "add" : "set";
+          format_(
+              "_internal_$1$_$2$($pi_ns$::UnalignedLoad<$3$>(ptr));\n"
+              "ptr += sizeof($3$);\n",
+              prefix, FieldName(field), type);
+        } else {
+          if (HasHasbit(field)) {
+            format_("_Internal::set_has_$1$(&$has_bits$);\n", FieldName(field));
+          }
+          format_(
+              "$1$_ = $pi_ns$::UnalignedLoad<$2$>(ptr);\n"
+              "ptr += sizeof($2$);\n",
+              FieldName(field), type);
+        }
+        break;
+      }
+      case WireFormatLite::WIRETYPE_LENGTH_DELIMITED: {
+        GenerateLengthDelim(field);
+        format_("CHK_(ptr);\n");
+        break;
+      }
+      case WireFormatLite::WIRETYPE_START_GROUP: {
+        format_(
+            "ptr = ctx->ParseGroup(_internal_$1$_$2$(), ptr, $3$);\n"
+            "CHK_(ptr);\n",
+            field->is_repeated() ? "add" : "mutable", FieldName(field), tag);
+        break;
+      }
+      case WireFormatLite::WIRETYPE_END_GROUP: {
+        GOOGLE_LOG(FATAL) << "Can't have end group field\n";
+        break;
+      }
+    }  // switch (wire_type)
+  }
+
+  // Returns the tag for this field and in case of repeated packable fields,
+  // sets a fallback tag in fallback_tag_ptr.
+  static uint32_t ExpectedTag(const FieldDescriptor* field,
+                              uint32_t* fallback_tag_ptr) {
+    uint32_t expected_tag;
+    if (field->is_packable()) {
+      auto expected_wiretype = WireFormat::WireTypeForFieldType(field->type());
+      expected_tag =
+          WireFormatLite::MakeTag(field->number(), expected_wiretype);
+      GOOGLE_CHECK(expected_wiretype != WireFormatLite::WIRETYPE_LENGTH_DELIMITED);
+      auto fallback_wiretype = WireFormatLite::WIRETYPE_LENGTH_DELIMITED;
+      uint32_t fallback_tag =
+          WireFormatLite::MakeTag(field->number(), fallback_wiretype);
+
+      if (field->is_packed()) std::swap(expected_tag, fallback_tag);
+      *fallback_tag_ptr = fallback_tag;
+    } else {
+      auto expected_wiretype = WireFormat::WireTypeForField(field);
+      expected_tag =
+          WireFormatLite::MakeTag(field->number(), expected_wiretype);
+    }
+    return expected_tag;
+  }
+
+  void GenerateParseIterationBody(
+      const Descriptor* descriptor,
+      const std::vector<const FieldDescriptor*>& ordered_fields) {
+    format_(
+        "$uint32$ tag;\n"
+        "ptr = $pi_ns$::ReadTag(ptr, &tag);\n");
+    if (!ordered_fields.empty()) format_("switch (tag >> 3) {\n");
+
+    format_.Indent();
+
+    for (const auto* field : ordered_fields) {
+      PrintFieldComment(format_, field);
+      format_("case $1$:\n", field->number());
+      format_.Indent();
+      uint32_t fallback_tag = 0;
+      uint32_t expected_tag = ExpectedTag(field, &fallback_tag);
+      format_(
+          "if (PROTOBUF_PREDICT_TRUE(static_cast<$uint8$>(tag) == $1$)) {\n",
+          expected_tag & 0xFF);
+      format_.Indent();
+      auto wiretype = WireFormatLite::GetTagWireType(expected_tag);
+      uint32_t tag = WireFormatLite::MakeTag(field->number(), wiretype);
+      int tag_size = io::CodedOutputStream::VarintSize32(tag);
+      bool is_repeat = ShouldRepeat(field, wiretype);
+      if (is_repeat) {
+        format_(
+            "ptr -= $1$;\n"
+            "do {\n"
+            "  ptr += $1$;\n",
+            tag_size);
+        format_.Indent();
+      }
+      GenerateFieldBody(wiretype, field);
+      if (is_repeat) {
+        format_.Outdent();
+        format_(
+            "  if (!ctx->DataAvailable(ptr)) break;\n"
+            "} while ($pi_ns$::ExpectTag<$1$>(ptr));\n",
+            tag);
+      }
+      format_.Outdent();
+      if (fallback_tag) {
+        format_("} else if (static_cast<$uint8$>(tag) == $1$) {\n",
+                fallback_tag & 0xFF);
+        format_.Indent();
+        GenerateFieldBody(WireFormatLite::GetTagWireType(fallback_tag), field);
+        format_.Outdent();
+      }
+      format_.Outdent();
+      format_(
+          "  } else goto handle_unusual;\n"
+          "  $continue$;\n");
+    }  // for loop over ordered fields
+
+    // Default case
+    if (!ordered_fields.empty()) format_("default: {\n");
+    if (!ordered_fields.empty()) format_("handle_unusual:\n");
+    format_(
+        "  if ((tag == 0) || ((tag & 7) == 4)) {\n"
+        "    CHK_(ptr);\n"
+        "    ctx->SetLastTag(tag);\n"
+        "    goto success;\n"
+        "  }\n");
+    if (IsMapEntryMessage(descriptor)) {
+      format_("  $continue$;\n");
+    } else {
+      if (descriptor->extension_range_count() > 0) {
+        format_("if (");
+        for (int i = 0; i < descriptor->extension_range_count(); i++) {
+          const Descriptor::ExtensionRange* range =
+              descriptor->extension_range(i);
+          if (i > 0) format_(" ||\n    ");
+
+          uint32_t start_tag = WireFormatLite::MakeTag(
+              range->start, static_cast<WireFormatLite::WireType>(0));
+          uint32_t end_tag = WireFormatLite::MakeTag(
+              range->end, static_cast<WireFormatLite::WireType>(0));
+
+          if (range->end > FieldDescriptor::kMaxNumber) {
+            format_("($1$u <= tag)", start_tag);
+          } else {
+            format_("($1$u <= tag && tag < $2$u)", start_tag, end_tag);
+          }
+        }
+        format_(") {\n");
+        format_(
+            "  ptr = _extensions_.ParseField(tag, ptr,\n"
+            "      internal_default_instance(), &_internal_metadata_, ctx);\n"
+            "  CHK_(ptr != nullptr);\n"
+            "  $continue$;\n"
+            "}\n");
+      }
+      format_(
+          "  ptr = UnknownFieldParse(tag,\n"
+          "      _internal_metadata_.mutable_unknown_fields<$unknown_"
+          "fields_type$>(),\n"
+          "      ptr, ctx);\n"
+          "  CHK_(ptr != nullptr);\n"
+          "  $continue$;\n");
+    }
+    if (!ordered_fields.empty()) format_("}\n");  // default case
+    format_.Outdent();
+    if (!ordered_fields.empty()) format_("}  // switch\n");
+  }
+};
+
+}  // namespace
+
+void GenerateParseFunction(const Descriptor* descriptor, int num_hasbits,
+                           const Options& options,
+                           MessageSCCAnalyzer* scc_analyzer,
+                           io::Printer* printer) {
+  ParseFunctionGenerator generator(descriptor, num_hasbits, options,
+                                   scc_analyzer, printer);
+  generator.GenerateLoopingParseFunction();
+}
+
+}  // namespace cpp
+}  // namespace compiler
+}  // namespace protobuf
+}  // namespace google
diff --git a/src/google/protobuf/compiler/cpp/cpp_parse_function_generator.h b/src/google/protobuf/compiler/cpp/cpp_parse_function_generator.h
new file mode 100644
index 0000000..5166903
--- /dev/null
+++ b/src/google/protobuf/compiler/cpp/cpp_parse_function_generator.h
@@ -0,0 +1,54 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef GOOGLE_PROTOBUF_COMPILER_CPP_PARSE_FUNCTION_GENERATOR_H__
+#define GOOGLE_PROTOBUF_COMPILER_CPP_PARSE_FUNCTION_GENERATOR_H__
+
+#include <google/protobuf/compiler/cpp/cpp_helpers.h>
+#include <google/protobuf/compiler/cpp/cpp_options.h>
+#include <google/protobuf/io/printer.h>
+#include <google/protobuf/descriptor.h>
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace cpp {
+
+void GenerateParseFunction(const Descriptor* descriptor, int num_hasbits,
+                           const Options& options,
+                           MessageSCCAnalyzer* scc_analyzer,
+                           io::Printer* printer);
+
+}  // namespace cpp
+}  // namespace compiler
+}  // namespace protobuf
+}  // namespace google
+
+#endif  // GOOGLE_PROTOBUF_COMPILER_CPP_PARSE_FUNCTION_GENERATOR_H__
diff --git a/src/google/protobuf/compiler/parser.cc b/src/google/protobuf/compiler/parser.cc
index b1bf288..bbcc8e5 100644
--- a/src/google/protobuf/compiler/parser.cc
+++ b/src/google/protobuf/compiler/parser.cc
@@ -2215,7 +2215,6 @@
   return true;
 }
 
-
 bool Parser::ParseMethodOptions(const LocationRecorder& parent_location,
                                 const FileDescriptorProto* containing_file,
                                 const int optionsFieldNumber,
diff --git a/src/google/protobuf/compiler/parser.h b/src/google/protobuf/compiler/parser.h
index e0ba90f..b5a5df8 100644
--- a/src/google/protobuf/compiler/parser.h
+++ b/src/google/protobuf/compiler/parser.h
@@ -523,7 +523,6 @@
     return syntax_identifier_ == "proto3";
   }
 
-
   bool ValidateEnum(const EnumDescriptorProto* proto);
 
   // =================================================================
diff --git a/src/google/protobuf/compiler/plugin.pb.cc b/src/google/protobuf/compiler/plugin.pb.cc
index 374a444..1fd80a1 100644
--- a/src/google/protobuf/compiler/plugin.pb.cc
+++ b/src/google/protobuf/compiler/plugin.pb.cc
@@ -516,7 +516,7 @@
 
 void Version::InternalSwap(Version* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   suffix_.Swap(&other->suffix_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
   ::PROTOBUF_NAMESPACE_ID::internal::memswap<
@@ -863,7 +863,7 @@
 
 void CodeGeneratorRequest::InternalSwap(CodeGeneratorRequest* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   file_to_generate_.InternalSwap(&other->file_to_generate_);
   proto_file_.InternalSwap(&other->proto_file_);
@@ -1226,7 +1226,7 @@
 
 void CodeGeneratorResponse_File::InternalSwap(CodeGeneratorResponse_File* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   name_.Swap(&other->name_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
   insertion_point_.Swap(&other->insertion_point_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
@@ -1513,7 +1513,7 @@
 
 void CodeGeneratorResponse::InternalSwap(CodeGeneratorResponse* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   file_.InternalSwap(&other->file_);
   error_.Swap(&other->error_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
diff --git a/src/google/protobuf/compiler/plugin.pb.h b/src/google/protobuf/compiler/plugin.pb.h
index 9ac275a..67eeabb 100644
--- a/src/google/protobuf/compiler/plugin.pb.h
+++ b/src/google/protobuf/compiler/plugin.pb.h
@@ -490,7 +490,7 @@
   public:
   void clear_compiler_version();
   const PROTOBUF_NAMESPACE_ID::compiler::Version& compiler_version() const;
-  PROTOBUF_NAMESPACE_ID::compiler::Version* release_compiler_version();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::compiler::Version* release_compiler_version();
   PROTOBUF_NAMESPACE_ID::compiler::Version* mutable_compiler_version();
   void set_allocated_compiler_version(PROTOBUF_NAMESPACE_ID::compiler::Version* compiler_version);
   private:
@@ -698,7 +698,7 @@
   public:
   void clear_generated_code_info();
   const PROTOBUF_NAMESPACE_ID::GeneratedCodeInfo& generated_code_info() const;
-  PROTOBUF_NAMESPACE_ID::GeneratedCodeInfo* release_generated_code_info();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::GeneratedCodeInfo* release_generated_code_info();
   PROTOBUF_NAMESPACE_ID::GeneratedCodeInfo* mutable_generated_code_info();
   void set_allocated_generated_code_info(PROTOBUF_NAMESPACE_ID::GeneratedCodeInfo* generated_code_info);
   private:
diff --git a/src/google/protobuf/descriptor.cc b/src/google/protobuf/descriptor.cc
index 03c4e2b..40ded3a 100644
--- a/src/google/protobuf/descriptor.cc
+++ b/src/google/protobuf/descriptor.cc
@@ -2591,7 +2591,7 @@
     enum_type(i)->DebugString(depth, contents, debug_string_options);
   }
   for (int i = 0; i < field_count(); i++) {
-    if (field(i)->containing_oneof() == nullptr) {
+    if (field(i)->real_containing_oneof() == nullptr) {
       field(i)->DebugString(depth, contents, debug_string_options);
     } else if (field(i)->containing_oneof()->field(0) == field(i)) {
       // This is the first field in this oneof, so print the whole oneof.
@@ -2701,7 +2701,7 @@
   std::string label = StrCat(kLabelToName[this->label()], " ");
 
   // Label is omitted for maps, oneof, and plain proto3 fields.
-  if (is_map() || containing_oneof() ||
+  if (is_map() || real_containing_oneof() ||
       (is_optional() && !has_optional_keyword())) {
     label.clear();
   }
diff --git a/src/google/protobuf/descriptor.pb.cc b/src/google/protobuf/descriptor.pb.cc
index c22ae43..047a401 100644
--- a/src/google/protobuf/descriptor.pb.cc
+++ b/src/google/protobuf/descriptor.pb.cc
@@ -1418,7 +1418,7 @@
 
 void FileDescriptorSet::InternalSwap(FileDescriptorSet* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   file_.InternalSwap(&other->file_);
 }
 
@@ -2056,7 +2056,7 @@
 
 void FileDescriptorProto::InternalSwap(FileDescriptorProto* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   dependency_.InternalSwap(&other->dependency_);
   message_type_.InternalSwap(&other->message_type_);
@@ -2362,7 +2362,7 @@
 
 void DescriptorProto_ExtensionRange::InternalSwap(DescriptorProto_ExtensionRange* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   ::PROTOBUF_NAMESPACE_ID::internal::memswap<
       PROTOBUF_FIELD_OFFSET(DescriptorProto_ExtensionRange, end_)
@@ -2612,7 +2612,7 @@
 
 void DescriptorProto_ReservedRange::InternalSwap(DescriptorProto_ReservedRange* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   ::PROTOBUF_NAMESPACE_ID::internal::memswap<
       PROTOBUF_FIELD_OFFSET(DescriptorProto_ReservedRange, end_)
@@ -3149,7 +3149,7 @@
 
 void DescriptorProto::InternalSwap(DescriptorProto* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   field_.InternalSwap(&other->field_);
   nested_type_.InternalSwap(&other->nested_type_);
@@ -3375,8 +3375,8 @@
 
 void ExtensionRangeOptions::InternalSwap(ExtensionRangeOptions* other) {
   using std::swap;
-  _extensions_.Swap(&other->_extensions_);
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _extensions_.InternalSwap(&other->_extensions_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   uninterpreted_option_.InternalSwap(&other->uninterpreted_option_);
 }
 
@@ -3987,7 +3987,7 @@
 
 void FieldDescriptorProto::InternalSwap(FieldDescriptorProto* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   name_.Swap(&other->name_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
   extendee_.Swap(&other->extendee_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
@@ -4270,7 +4270,7 @@
 
 void OneofDescriptorProto::InternalSwap(OneofDescriptorProto* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   name_.Swap(&other->name_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
   swap(options_, other->options_);
@@ -4516,7 +4516,7 @@
 
 void EnumDescriptorProto_EnumReservedRange::InternalSwap(EnumDescriptorProto_EnumReservedRange* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   ::PROTOBUF_NAMESPACE_ID::internal::memswap<
       PROTOBUF_FIELD_OFFSET(EnumDescriptorProto_EnumReservedRange, end_)
@@ -4893,7 +4893,7 @@
 
 void EnumDescriptorProto::InternalSwap(EnumDescriptorProto* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   value_.InternalSwap(&other->value_);
   reserved_range_.InternalSwap(&other->reserved_range_);
@@ -5201,7 +5201,7 @@
 
 void EnumValueDescriptorProto::InternalSwap(EnumValueDescriptorProto* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   name_.Swap(&other->name_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
   ::PROTOBUF_NAMESPACE_ID::internal::memswap<
@@ -5510,7 +5510,7 @@
 
 void ServiceDescriptorProto::InternalSwap(ServiceDescriptorProto* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   method_.InternalSwap(&other->method_);
   name_.Swap(&other->name_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
@@ -5931,7 +5931,7 @@
 
 void MethodDescriptorProto::InternalSwap(MethodDescriptorProto* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   name_.Swap(&other->name_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
   input_type_.Swap(&other->input_type_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
@@ -6900,8 +6900,8 @@
 
 void FileOptions::InternalSwap(FileOptions* other) {
   using std::swap;
-  _extensions_.Swap(&other->_extensions_);
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _extensions_.InternalSwap(&other->_extensions_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   uninterpreted_option_.InternalSwap(&other->uninterpreted_option_);
   java_package_.Swap(&other->java_package_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
@@ -7259,8 +7259,8 @@
 
 void MessageOptions::InternalSwap(MessageOptions* other) {
   using std::swap;
-  _extensions_.Swap(&other->_extensions_);
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _extensions_.InternalSwap(&other->_extensions_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   uninterpreted_option_.InternalSwap(&other->uninterpreted_option_);
   ::PROTOBUF_NAMESPACE_ID::internal::memswap<
@@ -7671,8 +7671,8 @@
 
 void FieldOptions::InternalSwap(FieldOptions* other) {
   using std::swap;
-  _extensions_.Swap(&other->_extensions_);
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _extensions_.InternalSwap(&other->_extensions_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   uninterpreted_option_.InternalSwap(&other->uninterpreted_option_);
   ::PROTOBUF_NAMESPACE_ID::internal::memswap<
@@ -7895,8 +7895,8 @@
 
 void OneofOptions::InternalSwap(OneofOptions* other) {
   using std::swap;
-  _extensions_.Swap(&other->_extensions_);
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _extensions_.InternalSwap(&other->_extensions_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   uninterpreted_option_.InternalSwap(&other->uninterpreted_option_);
 }
 
@@ -8185,8 +8185,8 @@
 
 void EnumOptions::InternalSwap(EnumOptions* other) {
   using std::swap;
-  _extensions_.Swap(&other->_extensions_);
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _extensions_.InternalSwap(&other->_extensions_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   uninterpreted_option_.InternalSwap(&other->uninterpreted_option_);
   ::PROTOBUF_NAMESPACE_ID::internal::memswap<
@@ -8444,8 +8444,8 @@
 
 void EnumValueOptions::InternalSwap(EnumValueOptions* other) {
   using std::swap;
-  _extensions_.Swap(&other->_extensions_);
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _extensions_.InternalSwap(&other->_extensions_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   uninterpreted_option_.InternalSwap(&other->uninterpreted_option_);
   swap(deprecated_, other->deprecated_);
@@ -8698,8 +8698,8 @@
 
 void ServiceOptions::InternalSwap(ServiceOptions* other) {
   using std::swap;
-  _extensions_.Swap(&other->_extensions_);
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _extensions_.InternalSwap(&other->_extensions_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   uninterpreted_option_.InternalSwap(&other->uninterpreted_option_);
   swap(deprecated_, other->deprecated_);
@@ -8999,8 +8999,8 @@
 
 void MethodOptions::InternalSwap(MethodOptions* other) {
   using std::swap;
-  _extensions_.Swap(&other->_extensions_);
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _extensions_.InternalSwap(&other->_extensions_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   uninterpreted_option_.InternalSwap(&other->uninterpreted_option_);
   ::PROTOBUF_NAMESPACE_ID::internal::memswap<
@@ -9276,7 +9276,7 @@
 
 void UninterpretedOption_NamePart::InternalSwap(UninterpretedOption_NamePart* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   name_part_.Swap(&other->name_part_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
   swap(is_extension_, other->is_extension_);
@@ -9706,7 +9706,7 @@
 
 void UninterpretedOption::InternalSwap(UninterpretedOption* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   name_.InternalSwap(&other->name_);
   identifier_value_.Swap(&other->identifier_value_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
@@ -10097,7 +10097,7 @@
 
 void SourceCodeInfo_Location::InternalSwap(SourceCodeInfo_Location* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   path_.InternalSwap(&other->path_);
   span_.InternalSwap(&other->span_);
@@ -10297,7 +10297,7 @@
 
 void SourceCodeInfo::InternalSwap(SourceCodeInfo* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   location_.InternalSwap(&other->location_);
 }
 
@@ -10623,7 +10623,7 @@
 
 void GeneratedCodeInfo_Annotation::InternalSwap(GeneratedCodeInfo_Annotation* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(_has_bits_[0], other->_has_bits_[0]);
   path_.InternalSwap(&other->path_);
   source_file_.Swap(&other->source_file_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
@@ -10826,7 +10826,7 @@
 
 void GeneratedCodeInfo::InternalSwap(GeneratedCodeInfo* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   annotation_.InternalSwap(&other->annotation_);
 }
 
diff --git a/src/google/protobuf/descriptor.pb.h b/src/google/protobuf/descriptor.pb.h
index 8f109ab..c3b7ed2 100644
--- a/src/google/protobuf/descriptor.pb.h
+++ b/src/google/protobuf/descriptor.pb.h
@@ -804,7 +804,7 @@
   public:
   void clear_options();
   const PROTOBUF_NAMESPACE_ID::FileOptions& options() const;
-  PROTOBUF_NAMESPACE_ID::FileOptions* release_options();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::FileOptions* release_options();
   PROTOBUF_NAMESPACE_ID::FileOptions* mutable_options();
   void set_allocated_options(PROTOBUF_NAMESPACE_ID::FileOptions* options);
   private:
@@ -822,7 +822,7 @@
   public:
   void clear_source_code_info();
   const PROTOBUF_NAMESPACE_ID::SourceCodeInfo& source_code_info() const;
-  PROTOBUF_NAMESPACE_ID::SourceCodeInfo* release_source_code_info();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::SourceCodeInfo* release_source_code_info();
   PROTOBUF_NAMESPACE_ID::SourceCodeInfo* mutable_source_code_info();
   void set_allocated_source_code_info(PROTOBUF_NAMESPACE_ID::SourceCodeInfo* source_code_info);
   private:
@@ -983,7 +983,7 @@
   public:
   void clear_options();
   const PROTOBUF_NAMESPACE_ID::ExtensionRangeOptions& options() const;
-  PROTOBUF_NAMESPACE_ID::ExtensionRangeOptions* release_options();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::ExtensionRangeOptions* release_options();
   PROTOBUF_NAMESPACE_ID::ExtensionRangeOptions* mutable_options();
   void set_allocated_options(PROTOBUF_NAMESPACE_ID::ExtensionRangeOptions* options);
   private:
@@ -1497,7 +1497,7 @@
   public:
   void clear_options();
   const PROTOBUF_NAMESPACE_ID::MessageOptions& options() const;
-  PROTOBUF_NAMESPACE_ID::MessageOptions* release_options();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::MessageOptions* release_options();
   PROTOBUF_NAMESPACE_ID::MessageOptions* mutable_options();
   void set_allocated_options(PROTOBUF_NAMESPACE_ID::MessageOptions* options);
   private:
@@ -1998,7 +1998,7 @@
   public:
   void clear_options();
   const PROTOBUF_NAMESPACE_ID::FieldOptions& options() const;
-  PROTOBUF_NAMESPACE_ID::FieldOptions* release_options();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::FieldOptions* release_options();
   PROTOBUF_NAMESPACE_ID::FieldOptions* mutable_options();
   void set_allocated_options(PROTOBUF_NAMESPACE_ID::FieldOptions* options);
   private:
@@ -2240,7 +2240,7 @@
   public:
   void clear_options();
   const PROTOBUF_NAMESPACE_ID::OneofOptions& options() const;
-  PROTOBUF_NAMESPACE_ID::OneofOptions* release_options();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::OneofOptions* release_options();
   PROTOBUF_NAMESPACE_ID::OneofOptions* mutable_options();
   void set_allocated_options(PROTOBUF_NAMESPACE_ID::OneofOptions* options);
   private:
@@ -2631,7 +2631,7 @@
   public:
   void clear_options();
   const PROTOBUF_NAMESPACE_ID::EnumOptions& options() const;
-  PROTOBUF_NAMESPACE_ID::EnumOptions* release_options();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::EnumOptions* release_options();
   PROTOBUF_NAMESPACE_ID::EnumOptions* mutable_options();
   void set_allocated_options(PROTOBUF_NAMESPACE_ID::EnumOptions* options);
   private:
@@ -2803,7 +2803,7 @@
   public:
   void clear_options();
   const PROTOBUF_NAMESPACE_ID::EnumValueOptions& options() const;
-  PROTOBUF_NAMESPACE_ID::EnumValueOptions* release_options();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::EnumValueOptions* release_options();
   PROTOBUF_NAMESPACE_ID::EnumValueOptions* mutable_options();
   void set_allocated_options(PROTOBUF_NAMESPACE_ID::EnumValueOptions* options);
   private:
@@ -3004,7 +3004,7 @@
   public:
   void clear_options();
   const PROTOBUF_NAMESPACE_ID::ServiceOptions& options() const;
-  PROTOBUF_NAMESPACE_ID::ServiceOptions* release_options();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::ServiceOptions* release_options();
   PROTOBUF_NAMESPACE_ID::ServiceOptions* mutable_options();
   void set_allocated_options(PROTOBUF_NAMESPACE_ID::ServiceOptions* options);
   private:
@@ -3213,7 +3213,7 @@
   public:
   void clear_options();
   const PROTOBUF_NAMESPACE_ID::MethodOptions& options() const;
-  PROTOBUF_NAMESPACE_ID::MethodOptions* release_options();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::MethodOptions* release_options();
   PROTOBUF_NAMESPACE_ID::MethodOptions* mutable_options();
   void set_allocated_options(PROTOBUF_NAMESPACE_ID::MethodOptions* options);
   private:
diff --git a/src/google/protobuf/duration.pb.cc b/src/google/protobuf/duration.pb.cc
index 01cd8d7..5330763 100644
--- a/src/google/protobuf/duration.pb.cc
+++ b/src/google/protobuf/duration.pb.cc
@@ -285,7 +285,7 @@
 
 void Duration::InternalSwap(Duration* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   ::PROTOBUF_NAMESPACE_ID::internal::memswap<
       PROTOBUF_FIELD_OFFSET(Duration, nanos_)
       + sizeof(Duration::nanos_)
diff --git a/src/google/protobuf/empty.pb.cc b/src/google/protobuf/empty.pb.cc
index b2149ab..2adc793 100644
--- a/src/google/protobuf/empty.pb.cc
+++ b/src/google/protobuf/empty.pb.cc
@@ -219,7 +219,7 @@
 
 void Empty::InternalSwap(Empty* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
 }
 
 ::PROTOBUF_NAMESPACE_ID::Metadata Empty::GetMetadata() const {
diff --git a/src/google/protobuf/extension_set.cc b/src/google/protobuf/extension_set.cc
index bc53480..aa57e67 100644
--- a/src/google/protobuf/extension_set.cc
+++ b/src/google/protobuf/extension_set.cc
@@ -1055,10 +1055,7 @@
 
 void ExtensionSet::Swap(ExtensionSet* x) {
   if (GetArena() == x->GetArena()) {
-    using std::swap;
-    swap(flat_capacity_, x->flat_capacity_);
-    swap(flat_size_, x->flat_size_);
-    swap(map_, x->map_);
+    InternalSwap(x);
   } else {
     // TODO(cfallin, rohananil): We maybe able to optimize a case where we are
     // swapping from heap to arena-allocated extension set, by just Own()'ing
@@ -1072,6 +1069,13 @@
   }
 }
 
+void ExtensionSet::InternalSwap(ExtensionSet* other) {
+  using std::swap;
+  swap(flat_capacity_, other->flat_capacity_);
+  swap(flat_size_, other->flat_size_);
+  swap(map_, other->map_);
+}
+
 void ExtensionSet::SwapExtension(ExtensionSet* other, int number) {
   if (this == other) return;
   Extension* this_ext = FindOrNull(number);
diff --git a/src/google/protobuf/extension_set.h b/src/google/protobuf/extension_set.h
index c4b845a..55492a6 100644
--- a/src/google/protobuf/extension_set.h
+++ b/src/google/protobuf/extension_set.h
@@ -369,6 +369,7 @@
   void Clear();
   void MergeFrom(const ExtensionSet& other);
   void Swap(ExtensionSet* other);
+  void InternalSwap(ExtensionSet* other);
   void SwapExtension(ExtensionSet* other, int number);
   bool IsInitialized() const;
 
diff --git a/src/google/protobuf/extension_set_unittest.cc b/src/google/protobuf/extension_set_unittest.cc
index 6a6fc25..7971fe5 100644
--- a/src/google/protobuf/extension_set_unittest.cc
+++ b/src/google/protobuf/extension_set_unittest.cc
@@ -198,7 +198,8 @@
   // ReleaseExtension will return the underlying object even after
   // ClearExtension is called.
   message.SetAllocatedExtension(
-      unittest::TestMessageSetExtension1::message_set_extension, extension);
+      unittest::TestMessageSetExtension1::message_set_extension,
+      released_extension);
   message.ClearExtension(
       unittest::TestMessageSetExtension1::message_set_extension);
   released_extension = message.ReleaseExtension(
@@ -1335,5 +1336,3 @@
 }  // namespace internal
 }  // namespace protobuf
 }  // namespace google
-
-#include <google/protobuf/port_undef.inc>
diff --git a/src/google/protobuf/field_mask.pb.cc b/src/google/protobuf/field_mask.pb.cc
index 5890bb2..f83f62d 100644
--- a/src/google/protobuf/field_mask.pb.cc
+++ b/src/google/protobuf/field_mask.pb.cc
@@ -263,7 +263,7 @@
 
 void FieldMask::InternalSwap(FieldMask* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   paths_.InternalSwap(&other->paths_);
 }
 
diff --git a/src/google/protobuf/generated_message_reflection_unittest.cc b/src/google/protobuf/generated_message_reflection_unittest.cc
index 7234f5f..8b14662 100644
--- a/src/google/protobuf/generated_message_reflection_unittest.cc
+++ b/src/google/protobuf/generated_message_reflection_unittest.cc
@@ -55,6 +55,9 @@
 #include <google/protobuf/testing/googletest.h>
 #include <gtest/gtest.h>
 
+// Must be included last.
+#include <google/protobuf/port_def.inc>
+
 namespace google {
 namespace protobuf {
 
@@ -358,6 +361,7 @@
   ASSERT_EQ(2, message.repeated_foreign_message_size());
   const protobuf_unittest::ForeignMessage* expected =
       message.mutable_repeated_foreign_message(1);
+  (void)expected;  // unused in somce configurations
   std::unique_ptr<Message> released(message.GetReflection()->ReleaseLast(
       &message, descriptor->FindFieldByName("repeated_foreign_message")));
   EXPECT_EQ(expected, released.get());
@@ -781,6 +785,7 @@
                                                               &to_message);
   const Message& sub_message = reflection->GetMessage(
       to_message, descriptor->FindFieldByName("foo_lazy_message"));
+  (void)sub_message;  // unused in somce configurations
   released = reflection->ReleaseMessage(
       &to_message, descriptor->FindFieldByName("foo_lazy_message"));
   EXPECT_TRUE(released != NULL);
@@ -798,6 +803,7 @@
 
   const Message& sub_message2 = reflection->GetMessage(
       to_message, descriptor->FindFieldByName("foo_message"));
+  (void)sub_message2;  // unused in somce configurations
   released = reflection->ReleaseMessage(
       &to_message, descriptor->FindFieldByName("foo_message"));
   EXPECT_TRUE(released != NULL);
@@ -917,6 +923,7 @@
   const Reflection* reflection = message.GetReflection();
   const Message& sub_message = reflection->GetMessage(
       message, descriptor->FindFieldByName("foo_lazy_message"));
+  (void)sub_message;  // unused in somce configurations
   Message* released = reflection->ReleaseMessage(
       &message, descriptor->FindFieldByName("foo_lazy_message"));
 
diff --git a/src/google/protobuf/map.h b/src/google/protobuf/map.h
index 7efee12..df84e1e 100644
--- a/src/google/protobuf/map.h
+++ b/src/google/protobuf/map.h
@@ -1321,7 +1321,7 @@
 
   void swap(Map& other) {
     if (arena() == other.arena()) {
-      elements_.Swap(&other.elements_);
+      InternalSwap(other);
     } else {
       // TODO(zuguang): optimize this. The temporary copy can be allocated
       // in the same arena as the other message, and the "other = copy" can
@@ -1332,6 +1332,8 @@
     }
   }
 
+  void InternalSwap(Map& other) { elements_.Swap(&other.elements_); }
+
   // Access to hasher.  Currently this returns a copy, but it may
   // be modified to return a const reference in the future.
   hasher hash_function() const { return elements_.hash_function(); }
diff --git a/src/google/protobuf/map_field.cc b/src/google/protobuf/map_field.cc
index 542a1f8..23f36d0 100644
--- a/src/google/protobuf/map_field.cc
+++ b/src/google/protobuf/map_field.cc
@@ -56,6 +56,20 @@
   return reinterpret_cast<RepeatedPtrFieldBase*>(repeated_field_);
 }
 
+void MapFieldBase::Swap(MapFieldBase* other) {
+  // TODO(teboring): This is incorrect when on different arenas.
+  InternalSwap(other);
+}
+
+void MapFieldBase::InternalSwap(MapFieldBase* other) {
+  std::swap(repeated_field_, other->repeated_field_);
+  // a relaxed swap of the atomic
+  auto other_state = other->state_.load(std::memory_order_relaxed);
+  auto this_state = state_.load(std::memory_order_relaxed);
+  other->state_.store(this_state, std::memory_order_relaxed);
+  state_.store(other_state, std::memory_order_relaxed);
+}
+
 size_t MapFieldBase::SpaceUsedExcludingSelfLong() const {
   ConstAccess();
   mutex_.Lock();
diff --git a/src/google/protobuf/map_field.h b/src/google/protobuf/map_field.h
index e05d3ee..452c463 100644
--- a/src/google/protobuf/map_field.h
+++ b/src/google/protobuf/map_field.h
@@ -371,7 +371,7 @@
   virtual void MapBegin(MapIterator* map_iter) const = 0;
   virtual void MapEnd(MapIterator* map_iter) const = 0;
   virtual void MergeFrom(const MapFieldBase& other) = 0;
-  virtual void Swap(MapFieldBase* other) = 0;
+  virtual void Swap(MapFieldBase* other);
   // Sync Map with repeated field and returns the size of map.
   virtual int size() const = 0;
   virtual void Clear() = 0;
@@ -407,6 +407,8 @@
   // Provides derived class the access to repeated field.
   void* MutableRepeatedPtrField() const;
 
+  void InternalSwap(MapFieldBase* other);
+
   // Support thread sanitizer (tsan) by making const / mutable races
   // more apparent.  If one thread calls MutableAccess() while another
   // thread calls either ConstAccess() or MutableAccess(), on the same
@@ -571,6 +573,7 @@
   void Clear() override;
   void MergeFrom(const MapFieldBase& other) override;
   void Swap(MapFieldBase* other) override;
+  void InternalSwap(MapField* other);
 
   // Used in the implementation of parsing. Caller should take the ownership iff
   // arena_ is NULL.
diff --git a/src/google/protobuf/map_field_inl.h b/src/google/protobuf/map_field_inl.h
index 8e92170..5564895 100644
--- a/src/google/protobuf/map_field_inl.h
+++ b/src/google/protobuf/map_field_inl.h
@@ -277,14 +277,18 @@
           WireFormatLite::FieldType kValueFieldType>
 void MapField<Derived, Key, T, kKeyFieldType, kValueFieldType>::Swap(
     MapFieldBase* other) {
+  MapFieldBase::Swap(other);
   MapField* other_field = down_cast<MapField*>(other);
-  std::swap(this->MapFieldBase::repeated_field_, other_field->repeated_field_);
   impl_.Swap(&other_field->impl_);
-  // a relaxed swap of the atomic
-  auto other_state = other_field->state_.load(std::memory_order_relaxed);
-  auto this_state = this->MapFieldBase::state_.load(std::memory_order_relaxed);
-  other_field->state_.store(this_state, std::memory_order_relaxed);
-  this->MapFieldBase::state_.store(other_state, std::memory_order_relaxed);
+}
+
+template <typename Derived, typename Key, typename T,
+          WireFormatLite::FieldType kKeyFieldType,
+          WireFormatLite::FieldType kValueFieldType>
+void MapField<Derived, Key, T, kKeyFieldType, kValueFieldType>::InternalSwap(
+    MapField* other) {
+  MapFieldBase::InternalSwap(other);
+  impl_.InternalSwap(&other->impl_);
 }
 
 template <typename Derived, typename Key, typename T,
diff --git a/src/google/protobuf/map_field_lite.h b/src/google/protobuf/map_field_lite.h
index 665cb0e..46658d4 100644
--- a/src/google/protobuf/map_field_lite.h
+++ b/src/google/protobuf/map_field_lite.h
@@ -81,6 +81,7 @@
     }
   }
   void Swap(MapFieldLite* other) { map_.swap(other->map_); }
+  void InternalSwap(MapFieldLite* other) { map_.InternalSwap(other->map_); }
 
   // Used in the implementation of parsing. Caller should take the ownership iff
   // arena_ is NULL.
diff --git a/src/google/protobuf/map_field_test.cc b/src/google/protobuf/map_field_test.cc
index dd70e98..e581f20 100644
--- a/src/google/protobuf/map_field_test.cc
+++ b/src/google/protobuf/map_field_test.cc
@@ -102,14 +102,17 @@
   void IncreaseIterator(MapIterator* map_iter) const override {}
 };
 
-class MapFieldBasePrimitiveTest : public ::testing::Test {
+class MapFieldBasePrimitiveTest : public testing::TestWithParam<bool> {
  protected:
   typedef unittest::TestMap_MapInt32Int32Entry_DoNotUse EntryType;
   typedef MapField<EntryType, int32, int32, WireFormatLite::TYPE_INT32,
                    WireFormatLite::TYPE_INT32>
       MapFieldType;
 
-  MapFieldBasePrimitiveTest() {
+  MapFieldBasePrimitiveTest()
+      : arena_(GetParam() ? new Arena() : nullptr),
+        map_field_(arena_.get()),
+        map_field_base_(map_field_.get()) {
     // Get descriptors
     map_descriptor_ = unittest::TestMap::descriptor()
                           ->FindFieldByName("map_int32_int32")
@@ -118,7 +121,6 @@
     value_descriptor_ = map_descriptor_->map_value();
 
     // Build map field
-    map_field_.reset(new MapFieldType);
     map_field_base_ = map_field_.get();
     map_ = map_field_->MutableMap();
     initial_value_map_[0] = 100;
@@ -127,7 +129,8 @@
     EXPECT_EQ(2, map_->size());
   }
 
-  std::unique_ptr<MapFieldType> map_field_;
+  std::unique_ptr<Arena> arena_;
+  ArenaHolder<MapFieldType> map_field_;
   MapFieldBase* map_field_base_;
   Map<int32, int32>* map_;
   const Descriptor* map_descriptor_;
@@ -136,11 +139,15 @@
   std::map<int32, int32> initial_value_map_;  // copy of initial values inserted
 };
 
-TEST_F(MapFieldBasePrimitiveTest, SpaceUsedExcludingSelf) {
+INSTANTIATE_TEST_SUITE_P(MapFieldBasePrimitiveTestInstance,
+                         MapFieldBasePrimitiveTest,
+                         testing::Values(true, false));
+
+TEST_P(MapFieldBasePrimitiveTest, SpaceUsedExcludingSelf) {
   EXPECT_LT(0, map_field_base_->SpaceUsedExcludingSelf());
 }
 
-TEST_F(MapFieldBasePrimitiveTest, GetRepeatedField) {
+TEST_P(MapFieldBasePrimitiveTest, GetRepeatedField) {
   const RepeatedPtrField<Message>& repeated =
       reinterpret_cast<const RepeatedPtrField<Message>&>(
           map_field_base_->GetRepeatedField());
@@ -153,7 +160,7 @@
   }
 }
 
-TEST_F(MapFieldBasePrimitiveTest, MutableRepeatedField) {
+TEST_P(MapFieldBasePrimitiveTest, MutableRepeatedField) {
   RepeatedPtrField<Message>* repeated =
       reinterpret_cast<RepeatedPtrField<Message>*>(
           map_field_base_->MutableRepeatedField());
@@ -166,7 +173,7 @@
   }
 }
 
-TEST_F(MapFieldBasePrimitiveTest, Arena) {
+TEST_P(MapFieldBasePrimitiveTest, Arena) {
   // Allocate a large initial block to avoid mallocs during hooked test.
   std::vector<char> arena_block(128 * 1024);
   ArenaOptions options;
@@ -205,18 +212,19 @@
 enum State { CLEAN, MAP_DIRTY, REPEATED_DIRTY };
 }  // anonymous namespace
 
-class MapFieldStateTest : public testing::TestWithParam<State> {
- public:
+class MapFieldStateTest
+    : public testing::TestWithParam<std::tuple<State, bool>> {
  protected:
   typedef unittest::TestMap_MapInt32Int32Entry_DoNotUse EntryType;
   typedef MapField<EntryType, int32, int32, WireFormatLite::TYPE_INT32,
                    WireFormatLite::TYPE_INT32>
       MapFieldType;
-  MapFieldStateTest() : state_(GetParam()) {
+  MapFieldStateTest()
+      : arena_(std::get<1>(GetParam()) ? new Arena() : nullptr),
+        map_field_(arena_.get()),
+        map_field_base_(map_field_.get()),
+        state_(std::get<0>(GetParam())) {
     // Build map field
-    map_field_.reset(new MapFieldType());
-    map_field_base_ = map_field_.get();
-
     Expect(map_field_.get(), MAP_DIRTY, 0, 0, true);
     switch (state_) {
       case CLEAN:
@@ -297,13 +305,16 @@
     }
   }
 
-  std::unique_ptr<MapFieldType> map_field_;
+  std::unique_ptr<Arena> arena_;
+  ArenaHolder<MapFieldType> map_field_;
   MapFieldBase* map_field_base_;
   State state_;
 };
 
 INSTANTIATE_TEST_SUITE_P(MapFieldStateTestInstance, MapFieldStateTest,
-                         ::testing::Values(CLEAN, MAP_DIRTY, REPEATED_DIRTY));
+                         testing::Combine(testing::Values(CLEAN, MAP_DIRTY,
+                                                          REPEATED_DIRTY),
+                                          testing::Values(true, false)));
 
 TEST_P(MapFieldStateTest, GetMap) {
   map_field_->GetMap();
@@ -324,10 +335,10 @@
 }
 
 TEST_P(MapFieldStateTest, MergeFromClean) {
-  MapFieldType other;
-  AddOneStillClean(&other);
+  ArenaHolder<MapFieldType> other(arena_.get());
+  AddOneStillClean(other.get());
 
-  map_field_->MergeFrom(other);
+  map_field_->MergeFrom(*other);
 
   if (state_ != MAP_DIRTY) {
     Expect(map_field_.get(), MAP_DIRTY, 1, 1, false);
@@ -335,14 +346,14 @@
     Expect(map_field_.get(), MAP_DIRTY, 1, 0, true);
   }
 
-  Expect(&other, CLEAN, 1, 1, false);
+  Expect(other.get(), CLEAN, 1, 1, false);
 }
 
 TEST_P(MapFieldStateTest, MergeFromMapDirty) {
-  MapFieldType other;
-  MakeMapDirty(&other);
+  ArenaHolder<MapFieldType> other(arena_.get());
+  MakeMapDirty(other.get());
 
-  map_field_->MergeFrom(other);
+  map_field_->MergeFrom(*other);
 
   if (state_ != MAP_DIRTY) {
     Expect(map_field_.get(), MAP_DIRTY, 1, 1, false);
@@ -350,14 +361,14 @@
     Expect(map_field_.get(), MAP_DIRTY, 1, 0, true);
   }
 
-  Expect(&other, MAP_DIRTY, 1, 0, true);
+  Expect(other.get(), MAP_DIRTY, 1, 0, true);
 }
 
 TEST_P(MapFieldStateTest, MergeFromRepeatedDirty) {
-  MapFieldType other;
-  MakeRepeatedDirty(&other);
+  ArenaHolder<MapFieldType> other(arena_.get());
+  MakeRepeatedDirty(other.get());
 
-  map_field_->MergeFrom(other);
+  map_field_->MergeFrom(*other);
 
   if (state_ != MAP_DIRTY) {
     Expect(map_field_.get(), MAP_DIRTY, 1, 1, false);
@@ -365,26 +376,26 @@
     Expect(map_field_.get(), MAP_DIRTY, 1, 0, true);
   }
 
-  Expect(&other, CLEAN, 1, 1, false);
+  Expect(other.get(), CLEAN, 1, 1, false);
 }
 
 TEST_P(MapFieldStateTest, SwapClean) {
-  MapFieldType other;
-  AddOneStillClean(&other);
+  ArenaHolder<MapFieldType> other(arena_.get());
+  AddOneStillClean(other.get());
 
-  map_field_->Swap(&other);
+  map_field_->Swap(other.get());
 
   Expect(map_field_.get(), CLEAN, 1, 1, false);
 
   switch (state_) {
     case CLEAN:
-      Expect(&other, CLEAN, 1, 1, false);
+      Expect(other.get(), CLEAN, 1, 1, false);
       break;
     case MAP_DIRTY:
-      Expect(&other, MAP_DIRTY, 1, 0, true);
+      Expect(other.get(), MAP_DIRTY, 1, 0, true);
       break;
     case REPEATED_DIRTY:
-      Expect(&other, REPEATED_DIRTY, 0, 1, false);
+      Expect(other.get(), REPEATED_DIRTY, 0, 1, false);
       break;
     default:
       break;
@@ -392,22 +403,22 @@
 }
 
 TEST_P(MapFieldStateTest, SwapMapDirty) {
-  MapFieldType other;
-  MakeMapDirty(&other);
+  ArenaHolder<MapFieldType> other(arena_.get());
+  MakeMapDirty(other.get());
 
-  map_field_->Swap(&other);
+  map_field_->Swap(other.get());
 
   Expect(map_field_.get(), MAP_DIRTY, 1, 0, true);
 
   switch (state_) {
     case CLEAN:
-      Expect(&other, CLEAN, 1, 1, false);
+      Expect(other.get(), CLEAN, 1, 1, false);
       break;
     case MAP_DIRTY:
-      Expect(&other, MAP_DIRTY, 1, 0, true);
+      Expect(other.get(), MAP_DIRTY, 1, 0, true);
       break;
     case REPEATED_DIRTY:
-      Expect(&other, REPEATED_DIRTY, 0, 1, false);
+      Expect(other.get(), REPEATED_DIRTY, 0, 1, false);
       break;
     default:
       break;
@@ -415,22 +426,22 @@
 }
 
 TEST_P(MapFieldStateTest, SwapRepeatedDirty) {
-  MapFieldType other;
-  MakeRepeatedDirty(&other);
+  ArenaHolder<MapFieldType> other(arena_.get());
+  MakeRepeatedDirty(other.get());
 
-  map_field_->Swap(&other);
+  map_field_->Swap(other.get());
 
   Expect(map_field_.get(), REPEATED_DIRTY, 0, 1, false);
 
   switch (state_) {
     case CLEAN:
-      Expect(&other, CLEAN, 1, 1, false);
+      Expect(other.get(), CLEAN, 1, 1, false);
       break;
     case MAP_DIRTY:
-      Expect(&other, MAP_DIRTY, 1, 0, true);
+      Expect(other.get(), MAP_DIRTY, 1, 0, true);
       break;
     case REPEATED_DIRTY:
-      Expect(&other, REPEATED_DIRTY, 0, 1, false);
+      Expect(other.get(), REPEATED_DIRTY, 0, 1, false);
       break;
     default:
       break;
@@ -501,5 +512,3 @@
 }  // namespace internal
 }  // namespace protobuf
 }  // namespace google
-
-#include <google/protobuf/port_undef.inc>
diff --git a/src/google/protobuf/map_test.cc b/src/google/protobuf/map_test.cc
index 768858f..335756e 100644
--- a/src/google/protobuf/map_test.cc
+++ b/src/google/protobuf/map_test.cc
@@ -1471,19 +1471,19 @@
   std::unique_ptr<Message> entry_int32_int32(
       MessageFactory::generated_factory()
           ->GetPrototype(fd_map_int32_int32->message_type())
-          ->New());
+          ->New(message.GetArena()));
   std::unique_ptr<Message> entry_int32_double(
       MessageFactory::generated_factory()
           ->GetPrototype(fd_map_int32_double->message_type())
-          ->New());
+          ->New(message.GetArena()));
   std::unique_ptr<Message> entry_string_string(
       MessageFactory::generated_factory()
           ->GetPrototype(fd_map_string_string->message_type())
-          ->New());
+          ->New(message.GetArena()));
   std::unique_ptr<Message> entry_int32_foreign_message(
       MessageFactory::generated_factory()
           ->GetPrototype(fd_map_int32_foreign_message->message_type())
-          ->New());
+          ->New(message.GetArena()));
 
   EXPECT_EQ(10, mf_int32_int32.size());
   EXPECT_EQ(10, mmf_int32_int32.size());
@@ -1890,6 +1890,15 @@
     EXPECT_EQ(int32_value9a, int32_value0b);
     EXPECT_EQ(int32_value0a, int32_value9b);
   }
+
+  // TODO(b/181148674): After supporting arena agnostic delete or let map entry
+  // handle heap allocation, this could be removed.
+  if (message.GetArena() != nullptr) {
+    entry_int32_int32.release();
+    entry_int32_double.release();
+    entry_string_string.release();
+    entry_int32_foreign_message.release();
+  }
 }
 
 TEST_F(MapFieldReflectionTest, RepeatedFieldRefMergeFromAndSwap) {
@@ -3771,5 +3780,3 @@
 }  // namespace internal
 }  // namespace protobuf
 }  // namespace google
-
-#include <google/protobuf/port_undef.inc>
diff --git a/src/google/protobuf/message.h b/src/google/protobuf/message.h
index 52e6a1d..c9db4e8 100644
--- a/src/google/protobuf/message.h
+++ b/src/google/protobuf/message.h
@@ -476,7 +476,8 @@
   void RemoveLast(Message* message, const FieldDescriptor* field) const;
   // Removes the last element of a repeated message field, and returns the
   // pointer to the caller.  Caller takes ownership of the returned pointer.
-  Message* ReleaseLast(Message* message, const FieldDescriptor* field) const;
+  PROTOBUF_FUTURE_MUST_USE_RESULT Message* ReleaseLast(
+      Message* message, const FieldDescriptor* field) const;
 
   // Swap the complete contents of two messages.
   void Swap(Message* message1, Message* message2) const;
@@ -604,8 +605,9 @@
   // If the field existed (HasField() is true), then the returned pointer will
   // be the same as the pointer returned by MutableMessage().
   // This function has the same effect as ClearField().
-  Message* ReleaseMessage(Message* message, const FieldDescriptor* field,
-                          MessageFactory* factory = nullptr) const;
+  PROTOBUF_FUTURE_MUST_USE_RESULT Message* ReleaseMessage(
+      Message* message, const FieldDescriptor* field,
+      MessageFactory* factory = nullptr) const;
 
 
   // Repeated field getters ------------------------------------------
diff --git a/src/google/protobuf/message_lite.h b/src/google/protobuf/message_lite.h
index 8a9b79d..68cfa03 100644
--- a/src/google/protobuf/message_lite.h
+++ b/src/google/protobuf/message_lite.h
@@ -83,7 +83,6 @@
 // See parse_context.h for explanation
 class ParseContext;
 
-class Proto3ArenaTestHelper;
 class RepeatedPtrFieldBase;
 class WireFormatLite;
 class WeakFieldMap;
@@ -210,11 +209,11 @@
   // if arena is a NULL. Default implementation for backwards compatibility.
   virtual MessageLite* New(Arena* arena) const;
 
-  // Get the arena for allocating submessages, if any, associated with this
-  // message. Virtual method required for generic operations but most
-  // arena-related operations should use the GetArena() generated-code method.
-  // Default implementation to reduce code size by avoiding the need for
-  // per-type implementations when types do not implement arena support.
+  // Get the arena, if any, associated with this message. Virtual method
+  // required for generic operations but most arena-related operations should
+  // use the GetArena() generated-code method. Default implementation
+  // to reduce code size by avoiding the need for per-type implementations
+  // when types do not implement arena support.
   Arena* GetArena() const { return _internal_metadata_.arena(); }
 
   // Get a pointer that may be equal to this message's arena, or may not be.
@@ -503,18 +502,8 @@
   // TODO(gerbens) make this a pure abstract function
   virtual const void* InternalGetTable() const { return NULL; }
 
-  // Get the arena that owns this message.
-  Arena* GetOwningArena() const { return _internal_metadata_.GetOwningArena(); }
-
-  // Set the owning arena to the given one.
-  void SetOwningArena(Arena* arena) {
-    _internal_metadata_.SetOwningArena(arena);
-  }
-
-  friend class Arena;
   friend class internal::WireFormatLite;
   friend class Message;
-  friend class internal::Proto3ArenaTestHelper;
   friend class internal::WeakFieldMap;
 
   void LogInitializationErrorMessage() const;
diff --git a/src/google/protobuf/message_unittest.inc b/src/google/protobuf/message_unittest.inc
index 0d97d40..78a1297 100644
--- a/src/google/protobuf/message_unittest.inc
+++ b/src/google/protobuf/message_unittest.inc
@@ -374,6 +374,17 @@
   EXPECT_EQ("c", errors[2]);
 }
 
+TEST(MESSAGE_TEST_NAME, ReleaseMustUseResult) {
+  UNITTEST::TestAllTypes message;
+  auto* f = new UNITTEST::ForeignMessage();
+  f->set_c(1000);
+  message.set_allocated_optional_foreign_message(f);
+  auto* mf = message.mutable_optional_foreign_message();
+  EXPECT_EQ(mf, f);
+  EXPECT_NE(message.release_optional_foreign_message(), nullptr);
+  delete f;
+}
+
 TEST(MESSAGE_TEST_NAME, ParseFailsOnInvalidMessageEnd) {
   UNITTEST::TestAllTypes message;
 
diff --git a/src/google/protobuf/metadata_lite.h b/src/google/protobuf/metadata_lite.h
index 1f8d8fc..ad5710c 100644
--- a/src/google/protobuf/metadata_lite.h
+++ b/src/google/protobuf/metadata_lite.h
@@ -73,17 +73,15 @@
   }
 
   PROTOBUF_NDEBUG_INLINE Arena* arena() const {
-    if (PROTOBUF_PREDICT_TRUE(!has_tag())) {
-      return PtrValue<Arena>();
-    } else if (is_heap_allocating()) {
-      return nullptr;
-    } else {
+    if (PROTOBUF_PREDICT_FALSE(have_unknown_fields())) {
       return PtrValue<ContainerBase>()->arena;
+    } else {
+      return PtrValue<Arena>();
     }
   }
 
   PROTOBUF_NDEBUG_INLINE bool have_unknown_fields() const {
-    return UnknownTag() == kUnknownTagMask;
+    return PtrTag() == kTagContainer;
   }
 
   PROTOBUF_NDEBUG_INLINE void* raw_arena_ptr() const { return ptr_; }
@@ -120,6 +118,10 @@
     }
   }
 
+  PROTOBUF_NDEBUG_INLINE void InternalSwap(InternalMetadata* other) {
+    std::swap(ptr_, other->ptr_);
+  }
+
   template <typename T>
   PROTOBUF_NDEBUG_INLINE void MergeFrom(const InternalMetadata& other) {
     if (other.have_unknown_fields()) {
@@ -134,56 +136,23 @@
     }
   }
 
-  PROTOBUF_ALWAYS_INLINE Arena* GetOwningArena() const {
-    if (PROTOBUF_PREDICT_FALSE(have_unknown_fields())) {
-      return PtrValue<ContainerBase>()->arena;
-    } else {
-      return PtrValue<Arena>();
-    }
-  }
-
-  PROTOBUF_ALWAYS_INLINE void SetOwningArena(Arena* arena) {
-    Arena* owning_arena = GetOwningArena();
-    GOOGLE_DCHECK(arena != nullptr);         // Heap can't own.
-    GOOGLE_DCHECK(owning_arena == nullptr);  // Only heap can be owned.
-
-    if (have_unknown_fields()) {
-      ContainerBase* container = PtrValue<ContainerBase>();
-      container->arena = arena;
-      ptr_ = reinterpret_cast<void*>(reinterpret_cast<intptr_t>(ptr_) |
-                                     kHeapAllocatingTagMask);
-    } else {
-      ptr_ = reinterpret_cast<void*>(reinterpret_cast<intptr_t>(arena) |
-                                     kHeapAllocatingTagMask);
-    }
-  }
-
  private:
   void* ptr_;
 
   // Tagged pointer implementation.
-  static constexpr intptr_t kUnknownTagMask = 1;
-  static constexpr intptr_t kHeapAllocatingTagMask = 2;
-  static constexpr intptr_t kPtrTagMask =
-      kUnknownTagMask | kHeapAllocatingTagMask;
+  enum {
+    // ptr_ is an Arena*.
+    kTagArena = 0,
+    // ptr_ is a Container*.
+    kTagContainer = 1,
+  };
+  static constexpr intptr_t kPtrTagMask = 1;
   static constexpr intptr_t kPtrValueMask = ~kPtrTagMask;
 
   // Accessors for pointer tag and pointer value.
   PROTOBUF_NDEBUG_INLINE int PtrTag() const {
     return reinterpret_cast<intptr_t>(ptr_) & kPtrTagMask;
   }
-  PROTOBUF_ALWAYS_INLINE int UnknownTag() const {
-    return reinterpret_cast<intptr_t>(ptr_) & kUnknownTagMask;
-  }
-  PROTOBUF_ALWAYS_INLINE int HeapAllocatingTag() const {
-    return reinterpret_cast<intptr_t>(ptr_) & kHeapAllocatingTagMask;
-  }
-  PROTOBUF_ALWAYS_INLINE bool has_tag() const {
-    return (reinterpret_cast<intptr_t>(ptr_) & kPtrTagMask) != 0;
-  }
-  PROTOBUF_ALWAYS_INLINE bool is_heap_allocating() const {
-    return HeapAllocatingTag() == kHeapAllocatingTagMask;
-  }
 
   template <typename U>
   U* PtrValue() const {
@@ -191,8 +160,7 @@
                                 kPtrValueMask);
   }
 
-  // If ptr_'s tag is kUnknownTagMask, it points to an instance of this
-  // struct.
+  // If ptr_'s tag is kTagContainer, it points to an instance of this struct.
   struct ContainerBase {
     Arena* arena;
   };
@@ -212,16 +180,13 @@
   template <typename T>
   PROTOBUF_NOINLINE T* mutable_unknown_fields_slow() {
     Arena* my_arena = arena();
-    Arena* owning_arena = GetOwningArena();
     Container<T>* container = Arena::Create<Container<T>>(my_arena);
     // Two-step assignment works around a bug in clang's static analyzer:
     // https://bugs.llvm.org/show_bug.cgi?id=34198.
-    intptr_t allocating_tag =
-        reinterpret_cast<intptr_t>(ptr_) & kHeapAllocatingTagMask;
     ptr_ = container;
     ptr_ = reinterpret_cast<void*>(reinterpret_cast<intptr_t>(ptr_) |
-                                   kUnknownTagMask | allocating_tag);
-    container->arena = owning_arena;
+                                   kTagContainer);
+    container->arena = my_arena;
     return &(container->unknown_fields);
   }
 
diff --git a/src/google/protobuf/port_def.inc b/src/google/protobuf/port_def.inc
index 4c29134..8a64749 100644
--- a/src/google/protobuf/port_def.inc
+++ b/src/google/protobuf/port_def.inc
@@ -48,10 +48,10 @@
 // detect/prohibit anytime it is #included twice without a corresponding
 // #undef.
 
-// These macros are private and should always be
-// ::util::RetrieveErrorSpace(*this) headers. If any of these errors fire, you
-// should either properly #include port_undef.h at the end of your header that
-// #includes port.h, or don't #include port.h twice in a .cc file.
+// These macros are private and should always be #undef'd from headers.
+// If any of these errors fire, you should either properly #include
+// port_undef.h at the end of your header that #includes port.h, or
+// don't #include port.h twice in a .cc file.
 #ifdef PROTOBUF_NAMESPACE
 #error PROTOBUF_NAMESPACE was previously defined
 #endif
@@ -160,6 +160,15 @@
 #ifdef PROTOBUF_ATTRIBUTE_WEAK
 #error PROTOBUF_ATTRIBUTE_WEAK was previously defined
 #endif
+#ifdef PROTOBUF_ASAN
+#error PROTOBUF_ASAN was previously defined
+#endif
+#ifdef PROTOBUF_MSAN
+#error PROTOBUF_MSAN was previously defined
+#endif
+#ifdef PROTOBUF_TSAN
+#error PROTOBUF_TSAN was previously defined
+#endif
 
 
 #define PROTOBUF_NAMESPACE "google::protobuf"
@@ -191,6 +200,7 @@
 
 #define PROTOBUF_SECTION_VARIABLE(x)
 #define PROTOBUF_MUST_USE_RESULT
+#define PROTOBUF_FUTURE_MUST_USE_RESULT
 
 // ----------------------------------------------------------------------------
 // Annotations:  Some parts of the code have been annotated in ways that might
@@ -335,8 +345,6 @@
 #endif
 
 
-// Shared google3/opensource definitions. //////////////////////////////////////
-
 #define PROTOBUF_VERSION 3015008
 #define PROTOBUF_MIN_HEADER_VERSION_FOR_PROTOC 3015000
 #define PROTOBUF_MIN_PROTOC_VERSION 3015000
@@ -372,7 +380,7 @@
 #if defined(__clang__)
 // For Clang we use __builtin_offsetof() and suppress the warning,
 // to avoid Control Flow Integrity and UBSan vptr sanitizers from
-// crashing while trying to validate the invalid reinterpet_casts.
+// crashing while trying to validate the invalid reinterpret_casts.
 #define PROTOBUF_FIELD_OFFSET(TYPE, FIELD)                   \
   _Pragma("clang diagnostic push")                           \
   _Pragma("clang diagnostic ignored \"-Winvalid-offsetof\"") \
@@ -444,6 +452,8 @@
 #undef ERROR
 #pragma push_macro("ERROR_BUSY")
 #undef ERROR_BUSY
+#pragma push_macro("ERROR_INSTALL_FAILED")
+#undef ERROR_INSTALL_FAILED
 #pragma push_macro("ERROR_NOT_FOUND")
 #undef ERROR_NOT_FOUND
 #pragma push_macro("GetMessage")
@@ -619,6 +629,22 @@
 #define PROTOBUF_ATTRIBUTE_WEAK
 #endif
 
+// Macros to detect sanitizers.
+#if defined(__clang__)
+#  if __has_feature(address_sanitizer)
+#    define PROTOBUF_ASAN 1
+#  endif
+#  if __has_feature(thread_sanitizer)
+#    define PROTOBUF_TSAN 1
+#  endif
+#  if __has_feature(memory_sanitizer)
+#    define PROTOBUF_MSAN 1
+#  endif
+#elif defined(__GNUC__)
+#  define PROTOBUF_ASAN __SANITIZE_ADDRESS__
+#  define PROTOBUF_TSAN __SANITIZE_THREAD__
+#endif
+
 // Silence some MSVC warnings in all our code.
 #if _MSC_VER
 #pragma warning(push)
diff --git a/src/google/protobuf/port_undef.inc b/src/google/protobuf/port_undef.inc
index 80bfd30..e40ac0d 100644
--- a/src/google/protobuf/port_undef.inc
+++ b/src/google/protobuf/port_undef.inc
@@ -78,6 +78,9 @@
 #undef PROTOBUF_ATTRIBUTE_NO_DESTROY
 #undef PROTOBUF_ATTRIBUTE_INIT_PRIORITY
 #undef PROTOBUF_PRAGMA_INIT_SEG
+#undef PROTOBUF_ASAN
+#undef PROTOBUF_MSAN
+#undef PROTOBUF_TSAN
 
 #ifdef PROTOBUF_FUTURE_BREAKING_CHANGES
 #undef PROTOBUF_FUTURE_BREAKING_CHANGES
@@ -90,6 +93,7 @@
 #pragma pop_macro("DOUBLE_CLICK")
 #pragma pop_macro("ERROR")
 #pragma pop_macro("ERROR_BUSY")
+#pragma pop_macro("ERROR_INSTALL_FAILED")
 #pragma pop_macro("ERROR_NOT_FOUND")
 #pragma pop_macro("GetMessage")
 #pragma pop_macro("IGNORE")
diff --git a/src/google/protobuf/proto3_arena_unittest.cc b/src/google/protobuf/proto3_arena_unittest.cc
index 83be3d8..5588f91 100644
--- a/src/google/protobuf/proto3_arena_unittest.cc
+++ b/src/google/protobuf/proto3_arena_unittest.cc
@@ -42,6 +42,9 @@
 #include <gtest/gtest.h>
 #include <google/protobuf/stubs/strutil.h>
 
+// Must be included last.
+#include <google/protobuf/port_def.inc>
+
 using proto3_arena_unittest::ForeignMessage;
 using proto3_arena_unittest::TestAllTypes;
 
@@ -166,8 +169,6 @@
   auto* arena_repeated_submessage1 =
       arena_message1->add_repeated_foreign_message();
   EXPECT_EQ(&arena, arena_message1->GetArena());
-  EXPECT_EQ(&arena,
-            internal::Proto3ArenaTestHelper::GetOwningArena(*arena_message1));
   EXPECT_EQ(&arena, arena_submessage1->GetArena());
   EXPECT_EQ(&arena, arena_repeated_submessage1->GetArena());
 
@@ -180,17 +181,11 @@
   const auto& repeated_submessage2 =
       arena_message2->repeated_foreign_message(0);
   EXPECT_EQ(nullptr, submessage2.GetArena());
-  EXPECT_EQ(&arena,
-            internal::Proto3ArenaTestHelper::GetOwningArena(submessage2));
   EXPECT_EQ(nullptr, repeated_submessage2.GetArena());
-  EXPECT_EQ(&arena, internal::Proto3ArenaTestHelper::GetOwningArena(
-                        repeated_submessage2));
 
   // Tests message created by Arena::Create.
   auto* arena_message3 = Arena::Create<TestAllTypes>(&arena);
   EXPECT_EQ(nullptr, arena_message3->GetArena());
-  EXPECT_EQ(&arena,
-            internal::Proto3ArenaTestHelper::GetOwningArena(*arena_message3));
 }
 
 TEST(Proto3ArenaTest, GetArenaWithUnknown) {
@@ -206,8 +201,6 @@
   arena_repeated_submessage1->GetReflection()->MutableUnknownFields(
       arena_repeated_submessage1);
   EXPECT_EQ(&arena, arena_message1->GetArena());
-  EXPECT_EQ(&arena,
-            internal::Proto3ArenaTestHelper::GetOwningArena(*arena_message1));
   EXPECT_EQ(&arena, arena_submessage1->GetArena());
   EXPECT_EQ(&arena, arena_repeated_submessage1->GetArena());
 
@@ -223,11 +216,7 @@
   repeated_submessage2->GetReflection()->MutableUnknownFields(
       repeated_submessage2);
   EXPECT_EQ(nullptr, submessage2->GetArena());
-  EXPECT_EQ(&arena,
-            internal::Proto3ArenaTestHelper::GetOwningArena(*submessage2));
   EXPECT_EQ(nullptr, repeated_submessage2->GetArena());
-  EXPECT_EQ(&arena, internal::Proto3ArenaTestHelper::GetOwningArena(
-                        *repeated_submessage2));
 }
 
 TEST(Proto3ArenaTest, Swap) {
diff --git a/src/google/protobuf/repeated_field.h b/src/google/protobuf/repeated_field.h
index 58190e3..ebccf18 100644
--- a/src/google/protobuf/repeated_field.h
+++ b/src/google/protobuf/repeated_field.h
@@ -688,7 +688,7 @@
   void UnsafeArenaAddAllocated(typename TypeHandler::Type* value);
 
   template <typename TypeHandler>
-  typename TypeHandler::Type* ReleaseLast() {
+  PROTOBUF_FUTURE_MUST_USE_RESULT typename TypeHandler::Type* ReleaseLast() {
     typename TypeImplementsMergeBehavior<typename TypeHandler::Type>::type t;
     return ReleaseLastInternal<TypeHandler>(t);
   }
@@ -702,7 +702,7 @@
   template <typename TypeHandler>
   void AddCleared(typename TypeHandler::Type* value);
   template <typename TypeHandler>
-  typename TypeHandler::Type* ReleaseCleared();
+  PROTOBUF_FUTURE_MUST_USE_RESULT typename TypeHandler::Type* ReleaseCleared();
 
   template <typename TypeHandler>
   void AddAllocatedInternal(typename TypeHandler::Type* value, std::true_type);
@@ -1084,7 +1084,7 @@
   // If this RepeatedPtrField is on an arena, an object copy is required to pass
   // ownership back to the user (for compatible semantics). Use
   // UnsafeArenaReleaseLast() if this behavior is undesired.
-  Element* ReleaseLast();
+  PROTOBUF_FUTURE_MUST_USE_RESULT Element* ReleaseLast();
 
   // Add an already-allocated object, skipping arena-ownership checks. The user
   // must guarantee that the given object is in the same arena as this
@@ -1154,7 +1154,7 @@
   //
   // This method cannot be called when the repeated field is on an arena; doing
   // so will trigger a GOOGLE_DCHECK-failure.
-  Element* ReleaseCleared();
+  PROTOBUF_FUTURE_MUST_USE_RESULT Element* ReleaseCleared();
 
   // Removes the element referenced by position.
   //
diff --git a/src/google/protobuf/repeated_field_unittest.cc b/src/google/protobuf/repeated_field_unittest.cc
index f3e8c2d..b270885 100644
--- a/src/google/protobuf/repeated_field_unittest.cc
+++ b/src/google/protobuf/repeated_field_unittest.cc
@@ -333,7 +333,7 @@
   EXPECT_GE(huge_field.Capacity(), min_clamping_size);
   ASSERT_LT(huge_field.Capacity(), std::numeric_limits<int>::max() - 1);
 
-#ifndef ADDRESS_SANITIZER
+#ifndef PROTOBUF_ASAN
   // The array containing all the fields is, in theory, up to MAXINT-1 in size.
   // However, some compilers can't handle a struct whose size is larger
   // than 2GB, and the protocol buffer format doesn't handle more than 2GB of
@@ -344,7 +344,7 @@
   // size must still be clamped to a valid range.
   huge_field.Reserve(huge_field.Capacity() + 1);
   EXPECT_EQ(huge_field.Capacity(), std::numeric_limits<int>::max());
-#endif
+#endif  // PROTOBUF_ASAN
 #endif  // PROTOBUF_TEST_ALLOW_LARGE_ALLOC
 }
 
diff --git a/src/google/protobuf/source_context.pb.cc b/src/google/protobuf/source_context.pb.cc
index 3994ceb..4dae936 100644
--- a/src/google/protobuf/source_context.pb.cc
+++ b/src/google/protobuf/source_context.pb.cc
@@ -264,7 +264,7 @@
 
 void SourceContext::InternalSwap(SourceContext* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   file_name_.Swap(&other->file_name_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
 }
 
diff --git a/src/google/protobuf/struct.pb.cc b/src/google/protobuf/struct.pb.cc
index fbe98e7..1b2fbc7 100644
--- a/src/google/protobuf/struct.pb.cc
+++ b/src/google/protobuf/struct.pb.cc
@@ -403,8 +403,8 @@
 
 void Struct::InternalSwap(Struct* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
-  fields_.Swap(&other->fields_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
+  fields_.InternalSwap(&other->fields_);
 }
 
 ::PROTOBUF_NAMESPACE_ID::Metadata Struct::GetMetadata() const {
@@ -842,7 +842,7 @@
 
 void Value::InternalSwap(Value* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(kind_, other->kind_);
   swap(_oneof_case_[0], other->_oneof_case_[0]);
 }
@@ -1038,7 +1038,7 @@
 
 void ListValue::InternalSwap(ListValue* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   values_.InternalSwap(&other->values_);
 }
 
diff --git a/src/google/protobuf/struct.pb.h b/src/google/protobuf/struct.pb.h
index 56df12e..a6f5e78 100644
--- a/src/google/protobuf/struct.pb.h
+++ b/src/google/protobuf/struct.pb.h
@@ -462,7 +462,7 @@
   public:
   void clear_struct_value();
   const PROTOBUF_NAMESPACE_ID::Struct& struct_value() const;
-  PROTOBUF_NAMESPACE_ID::Struct* release_struct_value();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::Struct* release_struct_value();
   PROTOBUF_NAMESPACE_ID::Struct* mutable_struct_value();
   void set_allocated_struct_value(PROTOBUF_NAMESPACE_ID::Struct* struct_value);
   private:
@@ -480,7 +480,7 @@
   public:
   void clear_list_value();
   const PROTOBUF_NAMESPACE_ID::ListValue& list_value() const;
-  PROTOBUF_NAMESPACE_ID::ListValue* release_list_value();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::ListValue* release_list_value();
   PROTOBUF_NAMESPACE_ID::ListValue* mutable_list_value();
   void set_allocated_list_value(PROTOBUF_NAMESPACE_ID::ListValue* list_value);
   private:
diff --git a/src/google/protobuf/text_format.cc b/src/google/protobuf/text_format.cc
index 2abd927..449a5a6 100644
--- a/src/google/protobuf/text_format.cc
+++ b/src/google/protobuf/text_format.cc
@@ -65,6 +65,7 @@
 // Must be included last.
 #include <google/protobuf/port_def.inc>
 
+#define DEBUG_STRING_SILENT_MARKER "\t "
 
 namespace google {
 namespace protobuf {
@@ -1247,6 +1248,18 @@
         buffer_size_(0),
         at_start_of_line_(true),
         failed_(false),
+        insert_silent_marker_(false),
+        indent_level_(initial_indent_level),
+        initial_indent_level_(initial_indent_level) {}
+
+  explicit TextGenerator(io::ZeroCopyOutputStream* output,
+                         bool insert_silent_marker, int initial_indent_level)
+      : output_(output),
+        buffer_(nullptr),
+        buffer_size_(0),
+        at_start_of_line_(true),
+        failed_(false),
+        insert_silent_marker_(insert_silent_marker),
         indent_level_(initial_indent_level),
         initial_indent_level_(initial_indent_level) {}
 
@@ -1309,6 +1322,22 @@
   // error.)
   bool failed() const { return failed_; }
 
+  void PrintMaybeWithMarker(StringPiece text) {
+    Print(text.data(), text.size());
+    if (ConsumeInsertSilentMarker()) {
+      PrintLiteral(DEBUG_STRING_SILENT_MARKER);
+    }
+  }
+
+  void PrintMaybeWithMarker(StringPiece text_head,
+                            StringPiece text_tail) {
+    Print(text_head.data(), text_head.size());
+    if (ConsumeInsertSilentMarker()) {
+      PrintLiteral(DEBUG_STRING_SILENT_MARKER);
+    }
+    Print(text_tail.data(), text_tail.size());
+  }
+
  private:
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(TextGenerator);
 
@@ -1369,17 +1398,68 @@
     buffer_size_ -= size;
   }
 
+  // Return the current value of insert_silent_marker_. If it is true, set it
+  // to false as we assume that a silent marker is inserted after a call to this
+  // function.
+  bool ConsumeInsertSilentMarker() {
+    if (insert_silent_marker_) {
+      insert_silent_marker_ = false;
+      return true;
+    }
+    return false;
+  }
+
   io::ZeroCopyOutputStream* const output_;
   char* buffer_;
   int buffer_size_;
   bool at_start_of_line_;
   bool failed_;
+  // This flag is false when inserting silent marker is disabled or a silent
+  // marker has been inserted.
+  bool insert_silent_marker_;
 
   int indent_level_;
   int initial_indent_level_;
 };
 
 // ===========================================================================
+//  An internal field value printer that may insert a silent marker in
+//  DebugStrings.
+class TextFormat::Printer::DebugStringFieldValuePrinter
+    : public TextFormat::FastFieldValuePrinter {
+ public:
+  void PrintMessageStart(const Message& message, int field_index,
+                         int field_count, bool single_line_mode,
+                         BaseTextGenerator* generator) const override {
+    // This is safe as only TextGenerator is used with
+    // DebugStringFieldValuePrinter.
+    TextGenerator* text_generator = static_cast<TextGenerator*>(generator);
+    if (single_line_mode) {
+      text_generator->PrintMaybeWithMarker(" ", "{ ");
+    } else {
+      text_generator->PrintMaybeWithMarker(" ", "{\n");
+    }
+  }
+};
+
+// ===========================================================================
+//  An internal field value printer that escape UTF8 strings.
+class TextFormat::Printer::FastFieldValuePrinterUtf8Escaping
+    : public TextFormat::Printer::DebugStringFieldValuePrinter {
+ public:
+  void PrintString(const std::string& val,
+                   TextFormat::BaseTextGenerator* generator) const override {
+    generator->PrintLiteral("\"");
+    generator->PrintString(strings::Utf8SafeCEscape(val));
+    generator->PrintLiteral("\"");
+  }
+  void PrintBytes(const std::string& val,
+                  TextFormat::BaseTextGenerator* generator) const override {
+    return FastFieldValuePrinter::PrintString(val, generator);
+  }
+};
+
+// ===========================================================================
 // Implementation of the default Finder for extensions.
 TextFormat::Finder::~Finder() {}
 
@@ -1808,22 +1888,6 @@
   std::unique_ptr<const TextFormat::FieldValuePrinter> delegate_;
 };
 
-// Our own specialization: for UTF8 escaped strings.
-class FastFieldValuePrinterUtf8Escaping
-    : public TextFormat::FastFieldValuePrinter {
- public:
-  void PrintString(const std::string& val,
-                   TextFormat::BaseTextGenerator* generator) const override {
-    generator->PrintLiteral("\"");
-    generator->PrintString(strings::Utf8SafeCEscape(val));
-    generator->PrintLiteral("\"");
-  }
-  void PrintBytes(const std::string& val,
-                  TextFormat::BaseTextGenerator* generator) const override {
-    return FastFieldValuePrinter::PrintString(val, generator);
-  }
-};
-
 }  // namespace
 
 const char* const TextFormat::Printer::kDoNotParse =
@@ -1834,6 +1898,7 @@
       single_line_mode_(false),
       use_field_number_(false),
       use_short_repeated_primitives_(false),
+      insert_silent_marker_(false),
       hide_unknown_fields_(false),
       print_message_fields_in_index_order_(false),
       expand_any_(false),
@@ -1844,7 +1909,7 @@
 
 void TextFormat::Printer::SetUseUtf8StringEscaping(bool as_utf8) {
   SetDefaultFieldValuePrinter(as_utf8 ? new FastFieldValuePrinterUtf8Escaping()
-                                      : new FastFieldValuePrinter());
+                                      : new DebugStringFieldValuePrinter());
 }
 
 void TextFormat::Printer::SetDefaultFieldValuePrinter(
@@ -1924,7 +1989,7 @@
 
 bool TextFormat::Printer::Print(const Message& message,
                                 io::ZeroCopyOutputStream* output) const {
-  TextGenerator generator(output, initial_indent_level_);
+  TextGenerator generator(output, insert_silent_marker_, initial_indent_level_);
 
   Print(message, &generator);
 
@@ -2302,7 +2367,7 @@
       printer->PrintMessageEnd(sub_message, field_index, count,
                                single_line_mode_, generator);
     } else {
-      generator->PrintLiteral(": ");
+      generator->PrintMaybeWithMarker(": ");
       // Write the field value.
       PrintFieldValue(message, reflection, field, field_index, generator);
       if (single_line_mode_) {
@@ -2327,7 +2392,7 @@
   int size = reflection->FieldSize(message, field);
   PrintFieldName(message, /*field_index=*/-1, /*field_count=*/size, reflection,
                  field, generator);
-  generator->PrintLiteral(": [");
+  generator->PrintMaybeWithMarker(": ", "[");
   for (int i = 0; i < size; i++) {
     if (i > 0) generator->PrintLiteral(", ");
     PrintFieldValue(message, reflection, field, i, generator);
@@ -2481,7 +2546,7 @@
     switch (field.type()) {
       case UnknownField::TYPE_VARINT:
         generator->PrintString(field_number);
-        generator->PrintLiteral(": ");
+        generator->PrintMaybeWithMarker(": ");
         generator->PrintString(StrCat(field.varint()));
         if (single_line_mode_) {
           generator->PrintLiteral(" ");
@@ -2491,7 +2556,7 @@
         break;
       case UnknownField::TYPE_FIXED32: {
         generator->PrintString(field_number);
-        generator->PrintLiteral(": 0x");
+        generator->PrintMaybeWithMarker(": ", "0x");
         generator->PrintString(
             StrCat(strings::Hex(field.fixed32(), strings::ZERO_PAD_8)));
         if (single_line_mode_) {
@@ -2503,7 +2568,7 @@
       }
       case UnknownField::TYPE_FIXED64: {
         generator->PrintString(field_number);
-        generator->PrintLiteral(": 0x");
+        generator->PrintMaybeWithMarker(": ", "0x");
         generator->PrintString(
             StrCat(strings::Hex(field.fixed64(), strings::ZERO_PAD_16)));
         if (single_line_mode_) {
@@ -2528,9 +2593,9 @@
           // This field is parseable as a Message.
           // So it is probably an embedded message.
           if (single_line_mode_) {
-            generator->PrintLiteral(" { ");
+            generator->PrintMaybeWithMarker(" ", "{ ");
           } else {
-            generator->PrintLiteral(" {\n");
+            generator->PrintMaybeWithMarker(" ", "{\n");
             generator->Indent();
           }
           PrintUnknownFields(embedded_unknown_fields, generator,
@@ -2544,7 +2609,7 @@
         } else {
           // This field is not parseable as a Message (or we ran out of
           // recursion budget). So it is probably just a plain string.
-          generator->PrintLiteral(": \"");
+          generator->PrintMaybeWithMarker(": ", "\"");
           generator->PrintString(CEscape(value));
           if (single_line_mode_) {
             generator->PrintLiteral("\" ");
@@ -2557,9 +2622,9 @@
       case UnknownField::TYPE_GROUP:
         generator->PrintString(field_number);
         if (single_line_mode_) {
-          generator->PrintLiteral(" { ");
+          generator->PrintMaybeWithMarker(" ", "{ ");
         } else {
-          generator->PrintLiteral(" {\n");
+          generator->PrintMaybeWithMarker(" ", "{\n");
           generator->Indent();
         }
         // For groups, we recurse without checking the budget. This is OK,
diff --git a/src/google/protobuf/text_format.h b/src/google/protobuf/text_format.h
index 3a3ee15..ce4d1f4 100644
--- a/src/google/protobuf/text_format.h
+++ b/src/google/protobuf/text_format.h
@@ -62,9 +62,9 @@
 class ErrorCollector;  // tokenizer.h
 }
 
-// This class implements protocol buffer text format.  Printing and parsing
-// protocol messages in text format is useful for debugging and human editing
-// of messages.
+// This class implements protocol buffer text format, colloquially known as text
+// proto.  Printing and parsing protocol messages in text format is useful for
+// debugging and human editing of messages.
 //
 // This class is really a namespace that contains only static methods.
 class PROTOBUF_EXPORT TextFormat {
@@ -369,6 +369,14 @@
     // output to the OutputStream (see text_format.cc for implementation).
     class TextGenerator;
 
+    // Forward declaration of an internal class used to print field values for
+    // DebugString APIs (see text_format.cc for implementation).
+    class DebugStringFieldValuePrinter;
+
+    // Forward declaration of an internal class used to print UTF-8 escaped
+    // strings (see text_format.cc for implementation).
+    class FastFieldValuePrinterUtf8Escaping;
+
     static const char* const kDoNotParse;
 
     // Internal Print method, used for writing to the OutputStream via
@@ -419,6 +427,7 @@
     bool single_line_mode_;
     bool use_field_number_;
     bool use_short_repeated_primitives_;
+    bool insert_silent_marker_;
     bool hide_unknown_fields_;
     bool print_message_fields_in_index_order_;
     bool expand_any_;
diff --git a/src/google/protobuf/timestamp.pb.cc b/src/google/protobuf/timestamp.pb.cc
index a3040a6..1828f83 100644
--- a/src/google/protobuf/timestamp.pb.cc
+++ b/src/google/protobuf/timestamp.pb.cc
@@ -285,7 +285,7 @@
 
 void Timestamp::InternalSwap(Timestamp* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   ::PROTOBUF_NAMESPACE_ID::internal::memswap<
       PROTOBUF_FIELD_OFFSET(Timestamp, nanos_)
       + sizeof(Timestamp::nanos_)
diff --git a/src/google/protobuf/type.pb.cc b/src/google/protobuf/type.pb.cc
index 024b277..214d205 100644
--- a/src/google/protobuf/type.pb.cc
+++ b/src/google/protobuf/type.pb.cc
@@ -696,7 +696,7 @@
 
 void Type::InternalSwap(Type* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   fields_.InternalSwap(&other->fields_);
   oneofs_.InternalSwap(&other->oneofs_);
   options_.InternalSwap(&other->options_);
@@ -1173,7 +1173,7 @@
 
 void Field::InternalSwap(Field* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   options_.InternalSwap(&other->options_);
   name_.Swap(&other->name_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
   type_url_.Swap(&other->type_url_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
@@ -1522,7 +1522,7 @@
 
 void Enum::InternalSwap(Enum* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   enumvalue_.InternalSwap(&other->enumvalue_);
   options_.InternalSwap(&other->options_);
   name_.Swap(&other->name_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
@@ -1788,7 +1788,7 @@
 
 void EnumValue::InternalSwap(EnumValue* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   options_.InternalSwap(&other->options_);
   name_.Swap(&other->name_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
   swap(number_, other->number_);
@@ -2038,7 +2038,7 @@
 
 void Option::InternalSwap(Option* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   name_.Swap(&other->name_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
   swap(value_, other->value_);
 }
diff --git a/src/google/protobuf/type.pb.h b/src/google/protobuf/type.pb.h
index acc86ed..e6a93f1 100644
--- a/src/google/protobuf/type.pb.h
+++ b/src/google/protobuf/type.pb.h
@@ -373,7 +373,7 @@
   public:
   void clear_source_context();
   const PROTOBUF_NAMESPACE_ID::SourceContext& source_context() const;
-  PROTOBUF_NAMESPACE_ID::SourceContext* release_source_context();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::SourceContext* release_source_context();
   PROTOBUF_NAMESPACE_ID::SourceContext* mutable_source_context();
   void set_allocated_source_context(PROTOBUF_NAMESPACE_ID::SourceContext* source_context);
   private:
@@ -938,7 +938,7 @@
   public:
   void clear_source_context();
   const PROTOBUF_NAMESPACE_ID::SourceContext& source_context() const;
-  PROTOBUF_NAMESPACE_ID::SourceContext* release_source_context();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::SourceContext* release_source_context();
   PROTOBUF_NAMESPACE_ID::SourceContext* mutable_source_context();
   void set_allocated_source_context(PROTOBUF_NAMESPACE_ID::SourceContext* source_context);
   private:
@@ -1273,7 +1273,7 @@
   public:
   void clear_value();
   const PROTOBUF_NAMESPACE_ID::Any& value() const;
-  PROTOBUF_NAMESPACE_ID::Any* release_value();
+  PROTOBUF_FUTURE_MUST_USE_RESULT PROTOBUF_NAMESPACE_ID::Any* release_value();
   PROTOBUF_NAMESPACE_ID::Any* mutable_value();
   void set_allocated_value(PROTOBUF_NAMESPACE_ID::Any* value);
   private:
diff --git a/src/google/protobuf/unittest_proto3_arena.proto b/src/google/protobuf/unittest_proto3_arena.proto
index fa26488..1752939 100644
--- a/src/google/protobuf/unittest_proto3_arena.proto
+++ b/src/google/protobuf/unittest_proto3_arena.proto
@@ -116,6 +116,23 @@
   repeated   string repeated_string   = 44;
   repeated    bytes repeated_bytes    = 45;
 
+  // Optional
+  optional    int32 proto3_optional_int32    = 116;
+  optional    int64 proto3_optional_int64    = 117;
+  optional   uint32 proto3_optional_uint32   = 118;
+  optional   uint64 proto3_optional_uint64   = 119;
+  optional   sint32 proto3_optional_sint32   = 120;
+  optional   sint64 proto3_optional_sint64   = 121;
+  optional  fixed32 proto3_optional_fixed32  = 122;
+  optional  fixed64 proto3_optional_fixed64  = 123;
+  optional sfixed32 proto3_optional_sfixed32 = 124;
+  optional sfixed64 proto3_optional_sfixed64 = 125;
+  optional    float proto3_optional_float    = 126;
+  optional   double proto3_optional_double   = 127;
+  optional     bool proto3_optional_bool     = 128;
+  optional   string proto3_optional_string   = 129;
+  optional    bytes proto3_optional_bytes    = 130;
+
   // Groups are not allowed in proto3.
   // repeated group RepeatedGroup = 46 {
   //   optional int32 a = 47;
diff --git a/src/google/protobuf/util/message_differencer.cc b/src/google/protobuf/util/message_differencer.cc
index 4815178..88e01df 100644
--- a/src/google/protobuf/util/message_differencer.cc
+++ b/src/google/protobuf/util/message_differencer.cc
@@ -266,7 +266,6 @@
 
 MessageDifferencer::MessageDifferencer()
     : reporter_(NULL),
-      field_comparator_(NULL),
       message_field_comparison_(EQUAL),
       scope_(FULL),
       repeated_field_comparison_(AS_LIST),
@@ -289,9 +288,19 @@
 
 void MessageDifferencer::set_field_comparator(FieldComparator* comparator) {
   GOOGLE_CHECK(comparator) << "Field comparator can't be NULL.";
-  field_comparator_ = comparator;
+  field_comparator_kind_ = kFCBase;
+  field_comparator_.base = comparator;
 }
 
+#ifdef PROTOBUF_FUTURE_BREAKING_CHANGES
+void MessageDifferencer::set_field_comparator(
+    DefaultFieldComparator* comparator) {
+  GOOGLE_CHECK(comparator) << "Field comparator can't be NULL.";
+  field_comparator_kind_ = kFCDefault;
+  field_comparator_.default_impl = comparator;
+}
+#endif  // PROTOBUF_FUTURE_BREAKING_CHANGES
+
 void MessageDifferencer::set_message_field_comparison(
     MessageFieldComparison comparison) {
   message_field_comparison_ = comparison;
@@ -1008,44 +1017,29 @@
   const Reflection* reflection2 = message2.GetReflection();
 
   // When both map fields are on map, do not sync to repeated field.
-  // TODO(jieluo): Add support for reporter
-  if (reporter_ == nullptr &&
+  if (reflection1->GetMapData(message1, repeated_field)->IsMapValid() &&
+      reflection2->GetMapData(message2, repeated_field)->IsMapValid() &&
+      // TODO(jieluo): Add support for reporter
+      reporter_ == nullptr &&
       // Users didn't set custom map field key comparator
       map_field_key_comparator_.find(repeated_field) ==
           map_field_key_comparator_.end() &&
       // Users didn't set repeated field comparison
-      repeated_field_comparison_ == AS_LIST) {
-    DefaultFieldComparator* map_field_comparator =
-        field_comparator_ ? nullptr : &default_field_comparator_;
-#if PROTOBUF_RTTI
-    // Inherit class from DefaultFieldComparator can not get the benefit
-    // because DefaultFieldComparator::Compare() method might be overwrote.
-    if (field_comparator_ &&
-        typeid(*field_comparator_) == typeid(default_field_comparator_)) {
-      map_field_comparator =
-          static_cast<DefaultFieldComparator*>(field_comparator_);
-    }
-#endif
-    if (map_field_comparator) {
-      const FieldDescriptor* key_des =
-          repeated_field->message_type()->map_key();
-      const FieldDescriptor* val_des =
-          repeated_field->message_type()->map_value();
-      const internal::MapFieldBase* map_field1 =
-          reflection1->GetMapData(message1, repeated_field);
-      const internal::MapFieldBase* map_field2 =
-          reflection2->GetMapData(message2, repeated_field);
-      std::vector<SpecificField> current_parent_fields(*parent_fields);
-      SpecificField specific_field;
-      specific_field.field = repeated_field;
-      current_parent_fields.push_back(specific_field);
-      if (map_field1->IsMapValid() && map_field2->IsMapValid() &&
-          !IsIgnored(message1, message2, key_des, current_parent_fields) &&
-          !IsIgnored(message1, message2, val_des, current_parent_fields)) {
-        return CompareMapFieldByMapReflection(
-            message1, message2, repeated_field, &current_parent_fields,
-            map_field_comparator);
-      }
+      repeated_field_comparison_ == AS_LIST &&
+      // Users didn't set their own FieldComparator implementation
+      field_comparator_kind_ == kFCDefault) {
+    const FieldDescriptor* key_des = repeated_field->message_type()->map_key();
+    const FieldDescriptor* val_des =
+        repeated_field->message_type()->map_value();
+    std::vector<SpecificField> current_parent_fields(*parent_fields);
+    SpecificField specific_field;
+    specific_field.field = repeated_field;
+    current_parent_fields.push_back(specific_field);
+    if (!IsIgnored(message1, message2, key_des, current_parent_fields) &&
+        !IsIgnored(message1, message2, val_des, current_parent_fields)) {
+      return CompareMapFieldByMapReflection(message1, message2, repeated_field,
+                                            &current_parent_fields,
+                                            field_comparator_.default_impl);
     }
   }
 
@@ -1869,9 +1863,9 @@
     const Message& message1, const Message& message2,
     const FieldDescriptor* field, int index1, int index2,
     const FieldContext* field_context) {
-  FieldComparator* comparator = field_comparator_ != NULL
-                                    ? field_comparator_
-                                    : &default_field_comparator_;
+  FieldComparator* comparator = field_comparator_kind_ == kFCBase
+                                    ? field_comparator_.base
+                                    : field_comparator_.default_impl;
   return comparator->Compare(message1, message2, field, index1, index2,
                              field_context);
 }
diff --git a/src/google/protobuf/util/message_differencer.h b/src/google/protobuf/util/message_differencer.h
index 943a0db..4cdb817 100644
--- a/src/google/protobuf/util/message_differencer.h
+++ b/src/google/protobuf/util/message_differencer.h
@@ -533,6 +533,9 @@
   // Note that this method must be called before Compare for the comparator to
   // be used.
   void set_field_comparator(FieldComparator* comparator);
+#ifdef PROTOBUF_FUTURE_BREAKING_CHANGES
+  void set_field_comparator(DefaultFieldComparator* comparator);
+#endif  // PROTOBUF_FUTURE_BREAKING_CHANGES
 
   // DEPRECATED. Pass a DefaultFieldComparator instance instead.
   // Sets the fraction and margin for the float comparison of a given field.
@@ -904,7 +907,6 @@
 
   Reporter* reporter_;
   DefaultFieldComparator default_field_comparator_;
-  FieldComparator* field_comparator_;
   MessageFieldComparison message_field_comparison_;
   Scope scope_;
   RepeatedFieldComparison repeated_field_comparison_;
@@ -925,6 +927,12 @@
 
   FieldSet ignored_fields_;
 
+  union {
+    DefaultFieldComparator* default_impl;
+    FieldComparator* base;
+  } field_comparator_ = {&default_field_comparator_};
+  enum { kFCDefault, kFCBase } field_comparator_kind_ = kFCDefault;
+
   bool report_matches_;
   bool report_moves_;
   bool report_ignores_;
diff --git a/src/google/protobuf/wrappers.pb.cc b/src/google/protobuf/wrappers.pb.cc
index c791d05..0f16f66 100644
--- a/src/google/protobuf/wrappers.pb.cc
+++ b/src/google/protobuf/wrappers.pb.cc
@@ -417,7 +417,7 @@
 
 void DoubleValue::InternalSwap(DoubleValue* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(value_, other->value_);
 }
 
@@ -605,7 +605,7 @@
 
 void FloatValue::InternalSwap(FloatValue* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(value_, other->value_);
 }
 
@@ -795,7 +795,7 @@
 
 void Int64Value::InternalSwap(Int64Value* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(value_, other->value_);
 }
 
@@ -985,7 +985,7 @@
 
 void UInt64Value::InternalSwap(UInt64Value* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(value_, other->value_);
 }
 
@@ -1175,7 +1175,7 @@
 
 void Int32Value::InternalSwap(Int32Value* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(value_, other->value_);
 }
 
@@ -1365,7 +1365,7 @@
 
 void UInt32Value::InternalSwap(UInt32Value* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(value_, other->value_);
 }
 
@@ -1553,7 +1553,7 @@
 
 void BoolValue::InternalSwap(BoolValue* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   swap(value_, other->value_);
 }
 
@@ -1754,7 +1754,7 @@
 
 void StringValue::InternalSwap(StringValue* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   value_.Swap(&other->value_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
 }
 
@@ -1950,7 +1950,7 @@
 
 void BytesValue::InternalSwap(BytesValue* other) {
   using std::swap;
-  _internal_metadata_.Swap<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(&other->_internal_metadata_);
+  _internal_metadata_.InternalSwap(&other->_internal_metadata_);
   value_.Swap(&other->value_, &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
 }