Sync from Piper @310858019

PROTOBUF_SYNC_PIPER

conformance/binary_json_conformance_suite.cc

@@ -1865,6 +1865,16 @@ void BinaryAndJsonConformanceSuite::RunJsonTestsForFieldNameConvention() {
       })",
       [](const Json::Value& value) { return !value.isMember("FieldName13"); },
       true);
+  RunValidJsonTestWithValidator(
+      "FieldNameExtension", RECOMMENDED,
+      R"({
+        "[protobuf_test_messages.proto2.extension_int32]": 1
+      })",
+      [](const Json::Value& value) {
+        return value.isMember(
+            "[protobuf_test_messages.proto2.extension_int32]");
+      },
+      false);
 }
 
 void BinaryAndJsonConformanceSuite::RunJsonTestsForNonRepeatedTypes() {

conformance/failure_list_cpp.txt

@@ -34,3 +34,4 @@ Recommended.Proto3.JsonInput.TrailingCommaInAnObject
 Recommended.Proto3.JsonInput.TrailingCommaInAnObjectWithNewlines
 Recommended.Proto3.JsonInput.TrailingCommaInAnObjectWithSpace
 Recommended.Proto3.JsonInput.TrailingCommaInAnObjectWithSpaceCommaSpace
+Recommended.Proto2.JsonInput.FieldNameExtension.Validator

conformance/failure_list_csharp.txt

@@ -1,2 +1,3 @@
 Recommended.Proto3.JsonInput.BytesFieldBase64Url.JsonOutput
 Recommended.Proto3.JsonInput.BytesFieldBase64Url.ProtobufOutput
+Required.Proto2.JsonInput.StoresDefaultPrimitive.Validator

conformance/failure_list_java.txt

@@ -34,6 +34,7 @@ Recommended.Proto3.JsonInput.StringFieldUnpairedHighSurrogate
 Recommended.Proto3.JsonInput.StringFieldUnpairedLowSurrogate
 Recommended.Proto3.JsonInput.Uint32MapFieldKeyNotQuoted
 Recommended.Proto3.JsonInput.Uint64MapFieldKeyNotQuoted
+Recommended.Proto2.JsonInput.FieldNameExtension.Validator
 Required.Proto3.JsonInput.EnumFieldNotQuoted
 Required.Proto3.JsonInput.Int32FieldLeadingZero
 Required.Proto3.JsonInput.Int32FieldNegativeWithLeadingZero

conformance/failure_list_php.txt

@@ -61,6 +61,7 @@ Recommended.Proto3.ProtobufInput.ValidDataRepeated.UINT64.PackedInput.DefaultOut
 Recommended.Proto3.ProtobufInput.ValidDataRepeated.UINT64.PackedInput.PackedOutput.ProtobufOutput
 Recommended.Proto3.ProtobufInput.ValidDataRepeated.UINT64.UnpackedInput.DefaultOutput.ProtobufOutput
 Recommended.Proto3.ProtobufInput.ValidDataRepeated.UINT64.UnpackedInput.PackedOutput.ProtobufOutput
+Required.Proto2.JsonInput.StoresDefaultPrimitive.Validator
 Required.Proto3.JsonInput.DoubleFieldTooSmall
 Required.Proto3.JsonInput.FloatFieldTooLarge
 Required.Proto3.JsonInput.FloatFieldTooSmall
@@ -75,8 +76,8 @@ Required.Proto3.JsonInput.Uint32FieldNotInteger
 Required.Proto3.JsonInput.Uint64FieldNotInteger
 Required.Proto3.ProtobufInput.RepeatedScalarMessageMerge.JsonOutput
 Required.Proto3.ProtobufInput.RepeatedScalarMessageMerge.ProtobufOutput
+Required.Proto3.ProtobufInput.ValidDataOneof.MESSAGE.Merge.JsonOutput
+Required.Proto3.ProtobufInput.ValidDataOneof.MESSAGE.Merge.ProtobufOutput
 Required.Proto3.ProtobufInput.ValidDataRepeated.FLOAT.PackedInput.JsonOutput
 Required.Proto3.ProtobufInput.ValidDataRepeated.FLOAT.UnpackedInput.JsonOutput
 Required.Proto3.ProtobufInput.ValidDataScalar.FLOAT[2].JsonOutput
-Required.Proto3.ProtobufInput.ValidDataOneof.MESSAGE.Merge.JsonOutput
-Required.Proto3.ProtobufInput.ValidDataOneof.MESSAGE.Merge.ProtobufOutput

conformance/failure_list_php_c.txt

@@ -79,6 +79,7 @@ Recommended.Proto3.ProtobufInput.ValidDataScalarBinary.ENUM[3].ProtobufOutput
 Recommended.Proto3.ProtobufInput.ValidDataScalarBinary.ENUM[4].ProtobufOutput
 Required.DurationProtoInputTooLarge.JsonOutput
 Required.DurationProtoInputTooSmall.JsonOutput
+Required.Proto2.JsonInput.StoresDefaultPrimitive.Validator
 Required.Proto3.JsonInput.DoubleFieldMaxNegativeValue.JsonOutput
 Required.Proto3.JsonInput.DoubleFieldMaxNegativeValue.ProtobufOutput
 Required.Proto3.JsonInput.DoubleFieldMinPositiveValue.JsonOutput

conformance/failure_list_php_c_32.txt

@@ -84,6 +84,7 @@ Recommended.Proto3.ProtobufInput.ValidDataScalarBinary.ENUM[3].ProtobufOutput
 Recommended.Proto3.ProtobufInput.ValidDataScalarBinary.ENUM[4].ProtobufOutput
 Required.DurationProtoInputTooLarge.JsonOutput
 Required.DurationProtoInputTooSmall.JsonOutput
+Required.Proto2.JsonInput.StoresDefaultPrimitive.Validator
 Required.Proto3.JsonInput.DoubleFieldMaxNegativeValue.JsonOutput
 Required.Proto3.JsonInput.DoubleFieldMaxNegativeValue.ProtobufOutput
 Required.Proto3.JsonInput.DoubleFieldMinPositiveValue.JsonOutput
@@ -99,13 +100,13 @@ Required.Proto3.JsonInput.FloatFieldInfinity.JsonOutput
 Required.Proto3.JsonInput.FloatFieldNan.JsonOutput
 Required.Proto3.JsonInput.FloatFieldNegativeInfinity.JsonOutput
 Required.Proto3.JsonInput.Int64FieldMaxValue.JsonOutput
-Required.Proto3.JsonInput.Int64FieldMaxValue.ProtobufOutput
 Required.Proto3.JsonInput.Int64FieldMaxValueNotQuoted.JsonOutput
 Required.Proto3.JsonInput.Int64FieldMaxValueNotQuoted.ProtobufOutput
+Required.Proto3.JsonInput.Int64FieldMaxValue.ProtobufOutput
 Required.Proto3.JsonInput.Int64FieldMinValue.JsonOutput
-Required.Proto3.JsonInput.Int64FieldMinValue.ProtobufOutput
 Required.Proto3.JsonInput.Int64FieldMinValueNotQuoted.JsonOutput
 Required.Proto3.JsonInput.Int64FieldMinValueNotQuoted.ProtobufOutput
+Required.Proto3.JsonInput.Int64FieldMinValue.ProtobufOutput
 Required.Proto3.JsonInput.OneofFieldDuplicate
 Required.Proto3.JsonInput.RejectTopLevelNull
 Required.Proto3.JsonInput.StringFieldSurrogatePair.JsonOutput
@@ -123,9 +124,9 @@ Required.Proto3.JsonInput.TimestampWithNegativeOffset.ProtobufOutput
 Required.Proto3.JsonInput.TimestampWithPositiveOffset.JsonOutput
 Required.Proto3.JsonInput.TimestampWithPositiveOffset.ProtobufOutput
 Required.Proto3.JsonInput.Uint64FieldMaxValue.JsonOutput
-Required.Proto3.JsonInput.Uint64FieldMaxValue.ProtobufOutput
 Required.Proto3.JsonInput.Uint64FieldMaxValueNotQuoted.JsonOutput
 Required.Proto3.JsonInput.Uint64FieldMaxValueNotQuoted.ProtobufOutput
+Required.Proto3.JsonInput.Uint64FieldMaxValue.ProtobufOutput
 Required.Proto3.ProtobufInput.DoubleFieldNormalizeQuietNan.JsonOutput
 Required.Proto3.ProtobufInput.DoubleFieldNormalizeSignalingNan.JsonOutput
 Required.Proto3.ProtobufInput.FloatFieldNormalizeQuietNan.JsonOutput

conformance/failure_list_ruby.txt

@@ -77,6 +77,7 @@ Recommended.Proto3.ProtobufInput.ValidDataScalarBinary.ENUM[3].ProtobufOutput
 Recommended.Proto3.ProtobufInput.ValidDataScalarBinary.ENUM[4].ProtobufOutput
 Required.DurationProtoInputTooLarge.JsonOutput
 Required.DurationProtoInputTooSmall.JsonOutput
+Required.Proto2.JsonInput.StoresDefaultPrimitive.Validator
 Required.Proto3.JsonInput.DoubleFieldMaxNegativeValue.JsonOutput
 Required.Proto3.JsonInput.DoubleFieldMaxNegativeValue.ProtobufOutput
 Required.Proto3.JsonInput.DoubleFieldMinPositiveValue.JsonOutput

csharp/src/Google.Protobuf.Test/Reflection/FieldAccessTest.cs

@@ -98,7 +98,48 @@ namespace Google.Protobuf.Reflection
         }
 
         [Test]
-        public void HasValue_Proto3()
+        public void HasValue_Proto3_Message()
+        {
+            var message = new TestAllTypes();
+            var accessor = ((IMessage) message).Descriptor.Fields[TestProtos.TestAllTypes.SingleForeignMessageFieldNumber].Accessor;
+            Assert.False(accessor.HasValue(message));
+            message.SingleForeignMessage = new ForeignMessage();
+            Assert.True(accessor.HasValue(message));
+            message.SingleForeignMessage = null;
+            Assert.False(accessor.HasValue(message));
+        }
+
+        [Test]
+        public void HasValue_Proto3_Oneof()
+        {
+            TestAllTypes message = new TestAllTypes();
+            var accessor = ((IMessage) message).Descriptor.Fields[TestProtos.TestAllTypes.OneofStringFieldNumber].Accessor;
+            Assert.False(accessor.HasValue(message));
+            // Even though it's the default value, we still have a value.
+            message.OneofString = "";
+            Assert.True(accessor.HasValue(message));
+            message.OneofString = "hello";
+            Assert.True(accessor.HasValue(message));
+            message.OneofUint32 = 10;
+            Assert.False(accessor.HasValue(message));
+        }
+
+        [Test]
+        public void HasValue_Proto3_Primitive_Optional()
+        {
+            var message = new TestProto3Optional();
+            var accessor = ((IMessage) message).Descriptor.Fields[TestProto3Optional.OptionalInt64FieldNumber].Accessor;
+            Assert.IsFalse(accessor.HasValue(message));
+            message.OptionalInt64 = 5L;
+            Assert.IsTrue(accessor.HasValue(message));
+            message.ClearOptionalInt64();
+            Assert.IsFalse(accessor.HasValue(message));
+            message.OptionalInt64 = 0L;
+            Assert.IsTrue(accessor.HasValue(message));
+        }
+
+        [Test]
+        public void HasValue_Proto3_Primitive_NotOptional()
         {
             IMessage message = SampleMessages.CreateFullTestAllTypes();
             var fields = message.Descriptor.Fields;
@@ -106,36 +147,63 @@ namespace Google.Protobuf.Reflection
         }
 
         [Test]
-        public void HasValue_Proto3Optional()
+        public void HasValue_Proto3_Repeated()
         {
-            IMessage message = new TestProto3Optional
-            {
-                OptionalInt32 = 0,
-                LazyNestedMessage = new TestProto3Optional.Types.NestedMessage()
-            };
-            var fields = message.Descriptor.Fields;
-            Assert.IsFalse(fields[TestProto3Optional.OptionalInt64FieldNumber].Accessor.HasValue(message));
-            Assert.IsFalse(fields[TestProto3Optional.OptionalNestedMessageFieldNumber].Accessor.HasValue(message));
-            Assert.IsTrue(fields[TestProto3Optional.LazyNestedMessageFieldNumber].Accessor.HasValue(message));
-            Assert.IsTrue(fields[TestProto3Optional.OptionalInt32FieldNumber].Accessor.HasValue(message));
+            var message = new TestAllTypes();
+            var accessor = ((IMessage) message).Descriptor.Fields[TestProtos.TestAllTypes.RepeatedBoolFieldNumber].Accessor;
+            Assert.Throws<InvalidOperationException>(() => accessor.HasValue(message));
         }
 
         [Test]
-        public void HasValue()
+        public void HasValue_Proto2_Primitive()
         {
-            IMessage message = new Proto2.TestAllTypes();
-            var fields = message.Descriptor.Fields;
-            var accessor = fields[Proto2.TestAllTypes.OptionalBoolFieldNumber].Accessor;
+            var message = new Proto2.TestAllTypes();
+            var accessor = ((IMessage) message).Descriptor.Fields[Proto2.TestAllTypes.OptionalInt64FieldNumber].Accessor;
+
+            Assert.IsFalse(accessor.HasValue(message));
+            message.OptionalInt64 = 5L;
+            Assert.IsTrue(accessor.HasValue(message));
+            message.ClearOptionalInt64();
+            Assert.IsFalse(accessor.HasValue(message));
+            message.OptionalInt64 = 0L;
+            Assert.IsTrue(accessor.HasValue(message));
+        }
 
-            Assert.False(accessor.HasValue(message));
+        [Test]
+        public void HasValue_Proto2_Message()
+        {
+            var message = new Proto2.TestAllTypes();
+            var field = ((IMessage) message).Descriptor.Fields[Proto2.TestAllTypes.OptionalForeignMessageFieldNumber];
+            Assert.False(field.Accessor.HasValue(message));
+            message.OptionalForeignMessage = new Proto2.ForeignMessage();
+            Assert.True(field.Accessor.HasValue(message));
+            message.OptionalForeignMessage = null;
+            Assert.False(field.Accessor.HasValue(message));
+        }
 
-            accessor.SetValue(message, true);
+        [Test]
+        public void HasValue_Proto2_Oneof()
+        {
+            var message = new Proto2.TestAllTypes();
+            var accessor = ((IMessage) message).Descriptor.Fields[Proto2.TestAllTypes.OneofStringFieldNumber].Accessor;
+            Assert.False(accessor.HasValue(message));
+            // Even though it's the default value, we still have a value.
+            message.OneofString = "";
             Assert.True(accessor.HasValue(message));
-
-            accessor.Clear(message);
+            message.OneofString = "hello";
+            Assert.True(accessor.HasValue(message));
+            message.OneofUint32 = 10;
             Assert.False(accessor.HasValue(message));
         }
 
+        [Test]
+        public void HasValue_Proto2_Repeated()
+        {
+            var message = new Proto2.TestAllTypes();
+            var accessor = ((IMessage) message).Descriptor.Fields[Proto2.TestAllTypes.RepeatedBoolFieldNumber].Accessor;
+            Assert.Throws<InvalidOperationException>(() => accessor.HasValue(message));
+        }
+
         [Test]
         public void SetValue_SingleFields()
         {
@@ -262,6 +330,42 @@ namespace Google.Protobuf.Reflection
             Assert.Null(message.OptionalNestedMessage);
         }
 
+        [Test]
+        public void Clear_Proto3_Oneof()
+        {
+            var message = new TestAllTypes();
+            var accessor = ((IMessage) message).Descriptor.Fields[TestProtos.TestAllTypes.OneofUint32FieldNumber].Accessor;
+
+            // The field accessor Clear method only affects a oneof if the current case is the one being cleared.
+            message.OneofString = "hello";
+            Assert.AreEqual(TestProtos.TestAllTypes.OneofFieldOneofCase.OneofString, message.OneofFieldCase);
+            accessor.Clear(message);
+            Assert.AreEqual(TestProtos.TestAllTypes.OneofFieldOneofCase.OneofString, message.OneofFieldCase);
+
+            message.OneofUint32 = 100;
+            Assert.AreEqual(TestProtos.TestAllTypes.OneofFieldOneofCase.OneofUint32, message.OneofFieldCase);
+            accessor.Clear(message);
+            Assert.AreEqual(TestProtos.TestAllTypes.OneofFieldOneofCase.None, message.OneofFieldCase);
+        }
+
+        [Test]
+        public void Clear_Proto2_Oneof()
+        {
+            var message = new Proto2.TestAllTypes();
+            var accessor = ((IMessage) message).Descriptor.Fields[Proto2.TestAllTypes.OneofUint32FieldNumber].Accessor;
+
+            // The field accessor Clear method only affects a oneof if the current case is the one being cleared.
+            message.OneofString = "hello";
+            Assert.AreEqual(Proto2.TestAllTypes.OneofFieldOneofCase.OneofString, message.OneofFieldCase);
+            accessor.Clear(message);
+            Assert.AreEqual(Proto2.TestAllTypes.OneofFieldOneofCase.OneofString, message.OneofFieldCase);
+
+            message.OneofUint32 = 100;
+            Assert.AreEqual(Proto2.TestAllTypes.OneofFieldOneofCase.OneofUint32, message.OneofFieldCase);
+            accessor.Clear(message);
+            Assert.AreEqual(Proto2.TestAllTypes.OneofFieldOneofCase.None, message.OneofFieldCase);
+        }
+
         [Test]
         public void FieldDescriptor_ByName()
         {
@@ -301,5 +405,32 @@ namespace Google.Protobuf.Reflection
             message.ClearExtension(RepeatedBoolExtension);
             Assert.IsNull(message.GetExtension(RepeatedBoolExtension));
         }
+
+        [Test]
+        public void HasPresence()
+        {
+            // Proto3
+            var fields = TestProtos.TestAllTypes.Descriptor.Fields;
+            Assert.IsFalse(fields[TestProtos.TestAllTypes.SingleBoolFieldNumber].HasPresence);
+            Assert.IsTrue(fields[TestProtos.TestAllTypes.OneofBytesFieldNumber].HasPresence);
+            Assert.IsTrue(fields[TestProtos.TestAllTypes.SingleForeignMessageFieldNumber].HasPresence);
+            Assert.IsFalse(fields[TestProtos.TestAllTypes.RepeatedBoolFieldNumber].HasPresence);
+
+            fields = TestMap.Descriptor.Fields;
+            Assert.IsFalse(fields[TestMap.MapBoolBoolFieldNumber].HasPresence);
+
+            fields = TestProto3Optional.Descriptor.Fields;
+            Assert.IsTrue(fields[TestProto3Optional.OptionalBoolFieldNumber].HasPresence);
+
+            // Proto2
+            fields = Proto2.TestAllTypes.Descriptor.Fields;
+            Assert.IsTrue(fields[Proto2.TestAllTypes.OptionalBoolFieldNumber].HasPresence);
+            Assert.IsTrue(fields[Proto2.TestAllTypes.OneofBytesFieldNumber].HasPresence);
+            Assert.IsTrue(fields[Proto2.TestAllTypes.OptionalForeignMessageFieldNumber].HasPresence);
+            Assert.IsFalse(fields[Proto2.TestAllTypes.RepeatedBoolFieldNumber].HasPresence);
+
+            fields = Proto2.TestRequired.Descriptor.Fields;
+            Assert.IsTrue(fields[Proto2.TestRequired.AFieldNumber].HasPresence);
+        }
     }
 }

csharp/src/Google.Protobuf/Extension.cs

@@ -55,6 +55,8 @@ namespace Google.Protobuf
         /// Gets the field number of this extension
         /// </summary>
         public int FieldNumber { get; }
+
+        internal abstract bool IsRepeated { get; }
     }
 
     /// <summary>
@@ -79,6 +81,8 @@ namespace Google.Protobuf
 
         internal override Type TargetType => typeof(TTarget);
 
+        internal override bool IsRepeated => false;
+
         internal override IExtensionValue CreateValue()
         {
             return new ExtensionValue<TValue>(codec);
@@ -105,6 +109,8 @@ namespace Google.Protobuf
 
         internal override Type TargetType => typeof(TTarget);
 
+        internal override bool IsRepeated => true;
+
         internal override IExtensionValue CreateValue()
         {
             return new RepeatedExtensionValue<TValue>(codec);

csharp/src/Google.Protobuf/Reflection/FieldDescriptor.cs

@@ -70,6 +70,21 @@ namespace Google.Protobuf.Reflection
         /// </summary>
         public string JsonName { get; }
 
+        /// <summary>
+        /// Indicates whether this field supports presence, either implicitly (e.g. due to it being a message
+        /// type field) or explicitly via Has/Clear members. If this returns true, it is safe to call
+        /// <see cref="IFieldAccessor.Clear(IMessage)"/> and <see cref="IFieldAccessor.HasValue(IMessage)"/>
+        /// on this field's accessor with a suitable message.
+        /// </summary>
+        public bool HasPresence =>
+            Extension != null ? !Extension.IsRepeated
+            : IsRepeated ? false
+            : IsMap ? false
+            : FieldType == FieldType.Message ? true
+            // This covers "real oneof members" and "proto3 optional fields"
+            : ContainingOneof != null ? true
+            : File.Syntax == Syntax.Proto2;
+
         internal FieldDescriptorProto Proto { get; }
 
         /// <summary>

csharp/src/Google.Protobuf/Reflection/SingleFieldAccessor.cs

@@ -57,63 +57,68 @@ namespace Google.Protobuf.Reflection
                 throw new ArgumentException("Not all required properties/methods available");
             }
             setValueDelegate = ReflectionUtil.CreateActionIMessageObject(property.GetSetMethod());
-            if (descriptor.File.Syntax == Syntax.Proto3 && !descriptor.Proto.Proto3Optional)
+
+            // Note: this looks worrying in that we access the containing oneof, which isn't valid until cross-linking
+            // is complete... but field accessors aren't created until after cross-linking.
+            // The oneof itself won't be cross-linked yet, but that's okay: the oneof accessor is created
+            // earlier.
+
+            // Message fields always support presence, via null checks.
+            if (descriptor.FieldType == FieldType.Message)
+            {
+                hasDelegate = message => GetValue(message) != null;
+                clearDelegate = message => SetValue(message, null);
+            }
+            // Oneof fields always support presence, via case checks.
+            // Note that clearing the field is a no-op unless that specific field is the current "case".
+            else if (descriptor.RealContainingOneof != null)
             {
-                hasDelegate = message =>
+                var oneofAccessor = descriptor.RealContainingOneof.Accessor;
+                hasDelegate = message => oneofAccessor.GetCaseFieldDescriptor(message) == descriptor;
+                clearDelegate = message =>
                 {
-                    throw new InvalidOperationException("HasValue is not implemented for non-optional proto3 fields");
+                    // Clear on a field only affects the oneof itself if the current case is the field we're accessing.
+                    if (oneofAccessor.GetCaseFieldDescriptor(message) == descriptor)
+                    {
+                        oneofAccessor.Clear(message);
+                    }
                 };
-                var clrType = property.PropertyType;
-
-                // TODO: Validate that this is a reasonable single field? (Should be a value type, a message type, or string/ByteString.)
-                object defaultValue =
-                    descriptor.FieldType == FieldType.Message ? null
-                    : clrType == typeof(string) ? ""
-                    : clrType == typeof(ByteString) ? ByteString.Empty
-                    : Activator.CreateInstance(clrType);
-                clearDelegate = message => SetValue(message, defaultValue);
             }
-            else
+            // Primitive fields always support presence in proto2, and support presence in proto3 for optional fields.
+            else if (descriptor.File.Syntax == Syntax.Proto2 || descriptor.Proto.Proto3Optional)
             {
-                // For message fields, just compare with null and set to null.
-                // For primitive fields, use the Has/Clear methods.
-
-                if (descriptor.FieldType == FieldType.Message)
+                MethodInfo hasMethod = property.DeclaringType.GetRuntimeProperty("Has" + property.Name).GetMethod;
+                if (hasMethod == null)
                 {
-                    hasDelegate = message => GetValue(message) != null;
-                    clearDelegate = message => SetValue(message, null);
+                    throw new ArgumentException("Not all required properties/methods are available");
                 }
-                else
+                hasDelegate = ReflectionUtil.CreateFuncIMessageBool(hasMethod);
+                MethodInfo clearMethod = property.DeclaringType.GetRuntimeMethod("Clear" + property.Name, ReflectionUtil.EmptyTypes);
+                if (clearMethod == null)
                 {
-                    MethodInfo hasMethod = property.DeclaringType.GetRuntimeProperty("Has" + property.Name).GetMethod;
-                    if (hasMethod == null)
-                    {
-                        throw new ArgumentException("Not all required properties/methods are available");
-                    }
-                    hasDelegate = ReflectionUtil.CreateFuncIMessageBool(hasMethod);
-                    MethodInfo clearMethod = property.DeclaringType.GetRuntimeMethod("Clear" + property.Name, ReflectionUtil.EmptyTypes);
-                    if (clearMethod == null)
-                    {
-                        throw new ArgumentException("Not all required properties/methods are available");
-                    }
-                    clearDelegate = ReflectionUtil.CreateActionIMessage(clearMethod);
+                    throw new ArgumentException("Not all required properties/methods are available");
                 }
+                clearDelegate = ReflectionUtil.CreateActionIMessage(clearMethod);
             }
-        }
+            // What's left?
+            // Primitive proto3 fields without the optional keyword, which aren't in oneofs.
+            else
+            {
+                hasDelegate = message => { throw new InvalidOperationException("Presence is not implemented for this field"); };
 
-        public override void Clear(IMessage message)
-        {
-            clearDelegate(message);
-        }
+                // While presence isn't supported, clearing still is; it's just setting to a default value.
+                var clrType = property.PropertyType;
 
-        public override bool HasValue(IMessage message)
-        {
-            return hasDelegate(message);
+                object defaultValue =
+                    clrType == typeof(string) ? ""
+                    : clrType == typeof(ByteString) ? ByteString.Empty
+                    : Activator.CreateInstance(clrType);
+                clearDelegate = message => SetValue(message, defaultValue);
+            }
         }
 
-        public override void SetValue(IMessage message, object value)
-        {
-            setValueDelegate(message, value);
-        }
+        public override void Clear(IMessage message) => clearDelegate(message);
+        public override bool HasValue(IMessage message) => hasDelegate(message);
+        public override void SetValue(IMessage message, object value) => setValueDelegate(message, value);
     }
 }

java/core/src/test/java/com/google/protobuf/FieldPresenceTest.java

@@ -38,6 +38,7 @@ import com.google.protobuf.Descriptors.OneofDescriptor;
 import com.google.protobuf.FieldPresenceTestProto.TestAllTypes;
 import com.google.protobuf.FieldPresenceTestProto.TestOptionalFieldsOnly;
 import com.google.protobuf.FieldPresenceTestProto.TestRepeatedFieldsOnly;
+import com.google.protobuf.testing.proto.TestProto3Optional;
 import protobuf_unittest.UnittestProto;
 import junit.framework.TestCase;
 
@@ -101,6 +102,113 @@ public class FieldPresenceTest extends TestCase {
         UnittestProto.TestAllTypes.Builder.class, TestAllTypes.Builder.class, "OneofBytes");
   }
 
+  public void testHasMethodForProto3Optional() throws Exception {
+    assertFalse(TestProto3Optional.getDefaultInstance().hasOptionalInt32());
+    assertFalse(TestProto3Optional.getDefaultInstance().hasOptionalInt64());
+    assertFalse(TestProto3Optional.getDefaultInstance().hasOptionalUint32());
+    assertFalse(TestProto3Optional.getDefaultInstance().hasOptionalUint64());
+    assertFalse(TestProto3Optional.getDefaultInstance().hasOptionalSint32());
+    assertFalse(TestProto3Optional.getDefaultInstance().hasOptionalSint64());
+    assertFalse(TestProto3Optional.getDefaultInstance().hasOptionalFixed32());
+    assertFalse(TestProto3Optional.getDefaultInstance().hasOptionalFixed64());
+    assertFalse(TestProto3Optional.getDefaultInstance().hasOptionalFloat());
+    assertFalse(TestProto3Optional.getDefaultInstance().hasOptionalDouble());
+    assertFalse(TestProto3Optional.getDefaultInstance().hasOptionalBool());
+    assertFalse(TestProto3Optional.getDefaultInstance().hasOptionalString());
+    assertFalse(TestProto3Optional.getDefaultInstance().hasOptionalBytes());
+
+    TestProto3Optional.Builder builder = TestProto3Optional.newBuilder().setOptionalInt32(0);
+    assertTrue(builder.hasOptionalInt32());
+    assertTrue(builder.build().hasOptionalInt32());
+
+    TestProto3Optional.Builder otherBuilder = TestProto3Optional.newBuilder().setOptionalInt32(1);
+    otherBuilder.mergeFrom(builder.build());
+    assertTrue(otherBuilder.hasOptionalInt32());
+    assertEquals(0, otherBuilder.getOptionalInt32());
+
+    TestProto3Optional.Builder builder3 =
+        TestProto3Optional.newBuilder().setOptionalNestedEnumValue(5);
+    assertTrue(builder3.hasOptionalNestedEnum());
+
+    TestProto3Optional.Builder builder4 =
+        TestProto3Optional.newBuilder().setOptionalNestedEnum(TestProto3Optional.NestedEnum.FOO);
+    assertTrue(builder4.hasOptionalNestedEnum());
+
+    TestProto3Optional proto = TestProto3Optional.parseFrom(builder.build().toByteArray());
+    assertTrue(proto.hasOptionalInt32());
+    assertTrue(proto.toBuilder().hasOptionalInt32());
+  }
+
+  private static void assertProto3OptionalReflection(String name) throws Exception {
+    FieldDescriptor fieldDescriptor = TestProto3Optional.getDescriptor().findFieldByName(name);
+    OneofDescriptor oneofDescriptor = fieldDescriptor.getContainingOneof();
+    assertNotNull(fieldDescriptor.getContainingOneof());
+    assertTrue(fieldDescriptor.hasOptionalKeyword());
+    assertTrue(fieldDescriptor.hasPresence());
+
+    assertFalse(TestProto3Optional.getDefaultInstance().hasOneof(oneofDescriptor));
+    assertNull(TestProto3Optional.getDefaultInstance().getOneofFieldDescriptor(oneofDescriptor));
+
+    TestProto3Optional.Builder builder = TestProto3Optional.newBuilder();
+    builder.setField(fieldDescriptor, fieldDescriptor.getDefaultValue());
+    assertTrue(builder.hasField(fieldDescriptor));
+    assertEquals(fieldDescriptor.getDefaultValue(), builder.getField(fieldDescriptor));
+    assertTrue(builder.build().hasField(fieldDescriptor));
+    assertEquals(fieldDescriptor.getDefaultValue(), builder.build().getField(fieldDescriptor));
+    assertTrue(builder.hasOneof(oneofDescriptor));
+    assertEquals(fieldDescriptor, builder.getOneofFieldDescriptor(oneofDescriptor));
+    assertTrue(builder.build().hasOneof(oneofDescriptor));
+    assertEquals(fieldDescriptor, builder.build().getOneofFieldDescriptor(oneofDescriptor));
+
+    TestProto3Optional.Builder otherBuilder = TestProto3Optional.newBuilder();
+    otherBuilder.mergeFrom(builder.build());
+    assertTrue(otherBuilder.hasField(fieldDescriptor));
+    assertEquals(fieldDescriptor.getDefaultValue(), otherBuilder.getField(fieldDescriptor));
+
+    TestProto3Optional proto = TestProto3Optional.parseFrom(builder.build().toByteArray());
+    assertTrue(proto.hasField(fieldDescriptor));
+    assertTrue(proto.toBuilder().hasField(fieldDescriptor));
+
+    DynamicMessage.Builder dynamicBuilder =
+        DynamicMessage.newBuilder(TestProto3Optional.getDescriptor());
+    dynamicBuilder.setField(fieldDescriptor, fieldDescriptor.getDefaultValue());
+    assertTrue(dynamicBuilder.hasField(fieldDescriptor));
+    assertEquals(fieldDescriptor.getDefaultValue(), dynamicBuilder.getField(fieldDescriptor));
+    assertTrue(dynamicBuilder.build().hasField(fieldDescriptor));
+    assertEquals(
+        fieldDescriptor.getDefaultValue(), dynamicBuilder.build().getField(fieldDescriptor));
+    assertTrue(dynamicBuilder.hasOneof(oneofDescriptor));
+    assertEquals(fieldDescriptor, dynamicBuilder.getOneofFieldDescriptor(oneofDescriptor));
+    assertTrue(dynamicBuilder.build().hasOneof(oneofDescriptor));
+    assertEquals(fieldDescriptor, dynamicBuilder.build().getOneofFieldDescriptor(oneofDescriptor));
+
+    DynamicMessage.Builder otherDynamicBuilder =
+        DynamicMessage.newBuilder(TestProto3Optional.getDescriptor());
+    otherDynamicBuilder.mergeFrom(dynamicBuilder.build());
+    assertTrue(otherDynamicBuilder.hasField(fieldDescriptor));
+    assertEquals(fieldDescriptor.getDefaultValue(), otherDynamicBuilder.getField(fieldDescriptor));
+
+    DynamicMessage dynamicProto =
+        DynamicMessage.parseFrom(TestProto3Optional.getDescriptor(), builder.build().toByteArray());
+    assertTrue(dynamicProto.hasField(fieldDescriptor));
+    assertTrue(dynamicProto.toBuilder().hasField(fieldDescriptor));
+  }
+
+  public void testProto3Optional_reflection() throws Exception {
+    assertProto3OptionalReflection("optional_int32");
+    assertProto3OptionalReflection("optional_int64");
+    assertProto3OptionalReflection("optional_uint32");
+    assertProto3OptionalReflection("optional_uint64");
+    assertProto3OptionalReflection("optional_sint32");
+    assertProto3OptionalReflection("optional_sint64");
+    assertProto3OptionalReflection("optional_fixed32");
+    assertProto3OptionalReflection("optional_fixed64");
+    assertProto3OptionalReflection("optional_float");
+    assertProto3OptionalReflection("optional_double");
+    assertProto3OptionalReflection("optional_bool");
+    assertProto3OptionalReflection("optional_string");
+    assertProto3OptionalReflection("optional_bytes");
+  }
 
   public void testOneofEquals() throws Exception {
     TestAllTypes.Builder builder = TestAllTypes.newBuilder();

java/core/src/test/java/com/google/protobuf/TextFormatTest.java

@@ -40,6 +40,8 @@ import com.google.protobuf.Descriptors.Descriptor;
 import com.google.protobuf.Descriptors.FieldDescriptor;
 import com.google.protobuf.Descriptors.FileDescriptor;
 import com.google.protobuf.TextFormat.Parser.SingularOverwritePolicy;
+import com.google.protobuf.testing.proto.TestProto3Optional;
+import com.google.protobuf.testing.proto.TestProto3Optional.NestedEnum;
 import any_test.AnyTestProto.TestAny;
 import map_test.MapTestProto.TestMap;
 import protobuf_unittest.UnittestMset.TestMessageSetExtension1;
@@ -319,6 +321,24 @@ public class TextFormatTest extends TestCase {
     assertEquals(canonicalExoticText, message.toString());
   }
 
+  public void testRoundtripProto3Optional() throws Exception {
+    Message message =
+        TestProto3Optional.newBuilder()
+            .setOptionalInt32(1)
+            .setOptionalInt64(2)
+            .setOptionalNestedEnum(NestedEnum.BAZ)
+            .build();
+    TestProto3Optional.Builder message2 = TestProto3Optional.newBuilder();
+    TextFormat.merge(message.toString(), message2);
+
+    assertTrue(message2.hasOptionalInt32());
+    assertTrue(message2.hasOptionalInt64());
+    assertTrue(message2.hasOptionalNestedEnum());
+    assertEquals(1, message2.getOptionalInt32());
+    assertEquals(2, message2.getOptionalInt64());
+    assertEquals(NestedEnum.BAZ, message2.getOptionalNestedEnum());
+  }
+
   public void testPrintMessageSet() throws Exception {
     TestMessageSet messageSet =
         TestMessageSet.newBuilder()

js/experimental/runtime/kernel/conformance/conformance_testee.js

@@ -8,7 +8,8 @@ const BinaryStorage = goog.require('protobuf.runtime.BinaryStorage');
 const BufferDecoder = goog.require('protobuf.binary.BufferDecoder');
 const WireType = goog.require('protobuf.binary.WireType');
 const {Field} = goog.require('protobuf.binary.field');
-const {checkCriticalElementIndex, checkCriticalState} = goog.require('protobuf.internal.checks');
+const {checkCriticalState} = goog.require('protobuf.internal.checks');
+const {skipField, tagToFieldNumber, tagToWireType} = goog.require('protobuf.binary.tag');
 
 /**
  * Appends a new entry in the index array for the given field number.
@@ -26,26 +27,6 @@ function addIndexEntry(storage, fieldNumber, wireType, startIndex) {
   }
 }
 
-/**
- * Returns wire type stored in a tag.
- * Protos store the wire type as the first 3 bit of a tag.
- * @param {number} tag
- * @return {!WireType}
- */
-function tagToWireType(tag) {
-  return /** @type {!WireType} */ (tag & 0x07);
-}
-
-/**
- * Returns the field number stored in a tag.
- * Protos store the field number in the upper 29 bits of a 32 bit number.
- * @param {number} tag
- * @return {number}
- */
-function tagToFieldNumber(tag) {
-  return tag >>> 3;
-}
-
 /**
  * Creates an index of field locations in a given binary protobuf.
  * @param {!BufferDecoder} bufferDecoder
@@ -62,83 +43,13 @@ function buildIndex(bufferDecoder, pivot) {
     const wireType = tagToWireType(tag);
     const fieldNumber = tagToFieldNumber(tag);
     checkCriticalState(fieldNumber > 0, `Invalid field number ${fieldNumber}`);
-
     addIndexEntry(storage, fieldNumber, wireType, bufferDecoder.cursor());
-
-    checkCriticalState(
-        !skipField_(bufferDecoder, wireType, fieldNumber),
-        'Found unmatched stop group.');
+    skipField(bufferDecoder, wireType, fieldNumber);
   }
   return storage;
 }
 
-/**
- * Skips over fields until the next field of the message.
- * @param {!BufferDecoder} bufferDecoder
- * @param {!WireType} wireType
- * @param {number} fieldNumber
- * @return {boolean} Whether the field we skipped over was a stop group.
- * @private
- */
-function skipField_(bufferDecoder, wireType, fieldNumber) {
-  switch (wireType) {
-    case WireType.VARINT:
-      checkCriticalElementIndex(
-          bufferDecoder.cursor(), bufferDecoder.endIndex());
-      bufferDecoder.skipVarint();
-      return false;
-    case WireType.FIXED64:
-      bufferDecoder.skip(8);
-      return false;
-    case WireType.DELIMITED:
-      checkCriticalElementIndex(
-          bufferDecoder.cursor(), bufferDecoder.endIndex());
-      const length = bufferDecoder.getUnsignedVarint32();
-      bufferDecoder.skip(length);
-      return false;
-    case WireType.START_GROUP:
-      checkCriticalState(
-          skipGroup_(bufferDecoder, fieldNumber), 'No end group found.');
-      return false;
-    case WireType.END_GROUP:
-      // Signal that we found a stop group to the caller
-      return true;
-    case WireType.FIXED32:
-      bufferDecoder.skip(4);
-      return false;
-    default:
-      throw new Error(`Invalid wire type: ${wireType}`);
-  }
-}
-
-/**
- * Skips over fields until it finds the end of a given group.
- * @param {!BufferDecoder} bufferDecoder
- * @param {number} groupFieldNumber
- * @return {boolean} Returns true if an end was found.
- * @private
- */
-function skipGroup_(bufferDecoder, groupFieldNumber) {
-  // On a start group we need to keep skipping fields until we find a
-  // corresponding stop group
-  // Note: Since we are calling skipField from here nested groups will be
-  // handled by recursion of this method and thus we will not see a nested
-  // STOP GROUP here unless there is something wrong with the input data.
-  while (bufferDecoder.hasNext()) {
-    const tag = bufferDecoder.getUnsignedVarint32();
-    const wireType = tagToWireType(tag);
-    const fieldNumber = tagToFieldNumber(tag);
-
-    if (skipField_(bufferDecoder, wireType, fieldNumber)) {
-      checkCriticalState(
-          groupFieldNumber === fieldNumber,
-          `Expected stop group for fieldnumber ${groupFieldNumber} not found.`);
-      return true;
-    }
-  }
-  return false;
-}
-
 exports = {
   buildIndex,
+  tagToWireType,
 };

js/experimental/runtime/kernel/indexer_test.js

@@ -72,12 +72,12 @@ describe('Indexer does', () => {
 
   it('fail for invalid wire type (6)', () => {
     expect(() => buildIndex(createBufferDecoder(0x0E, 0x01), PIVOT))
-        .toThrowError('Invalid wire type: 6');
+        .toThrowError('Unexpected wire type: 6');
   });
 
   it('fail for invalid wire type (7)', () => {
     expect(() => buildIndex(createBufferDecoder(0x0F, 0x01), PIVOT))
-        .toThrowError('Invalid wire type: 7');
+        .toThrowError('Unexpected wire type: 7');
   });
 
   it('index varint', () => {
@@ -269,33 +269,8 @@ describe('Indexer does', () => {
 
   it('fail on unmatched stop group', () => {
     const data = createBufferDecoder(0x0C, 0x01);
-    if (CHECK_CRITICAL_STATE) {
-      expect(() => buildIndex(data, PIVOT))
-          .toThrowError('Found unmatched stop group.');
-    } else {
-      // Note in unchecked mode we produce invalid output for invalid inputs.
-      // This test just documents our behavior in those cases.
-      // These values might change at any point and are not considered
-      // what the implementation should be doing here.
-      const storage = buildIndex(data, PIVOT);
-
-      expect(getStorageSize(storage)).toBe(1);
-      const entryArray = storage.get(1).getIndexArray();
-      expect(entryArray).not.toBeUndefined();
-      expect(entryArray.length).toBe(1);
-      const entry = entryArray[0];
-
-      expect(Field.getWireType(entry)).toBe(WireType.END_GROUP);
-      expect(Field.getStartIndex(entry)).toBe(1);
-
-      const entryArray2 = storage.get(0).getIndexArray();
-      expect(entryArray2).not.toBeUndefined();
-      expect(entryArray2.length).toBe(1);
-      const entry2 = entryArray2[0];
-
-      expect(Field.getWireType(entry2)).toBe(WireType.FIXED64);
-      expect(Field.getStartIndex(entry2)).toBe(2);
-    }
+    expect(() => buildIndex(data, PIVOT))
+        .toThrowError('Unexpected wire type: 4');
   });
 
   it('fail for groups without matching stop group', () => {

js/experimental/runtime/kernel/kernel.js

@@ -26,6 +26,7 @@ const reader = goog.require('protobuf.binary.reader');
 const {CHECK_TYPE, checkCriticalElementIndex, checkCriticalState, checkCriticalType, checkCriticalTypeBool, checkCriticalTypeBoolArray, checkCriticalTypeByteString, checkCriticalTypeByteStringArray, checkCriticalTypeDouble, checkCriticalTypeDoubleArray, checkCriticalTypeFloat, checkCriticalTypeFloatIterable, checkCriticalTypeMessageArray, checkCriticalTypeSignedInt32, checkCriticalTypeSignedInt32Array, checkCriticalTypeSignedInt64, checkCriticalTypeSignedInt64Array, checkCriticalTypeString, checkCriticalTypeStringArray, checkCriticalTypeUnsignedInt32, checkCriticalTypeUnsignedInt32Array, checkDefAndNotNull, checkElementIndex, checkFieldNumber, checkFunctionExists, checkState, checkTypeDouble, checkTypeFloat, checkTypeSignedInt32, checkTypeSignedInt64, checkTypeUnsignedInt32} = goog.require('protobuf.internal.checks');
 const {Field, IndexEntry} = goog.require('protobuf.binary.field');
 const {buildIndex} = goog.require('protobuf.binary.indexer');
+const {createTag, get32BitVarintLength, getTagLength} = goog.require('protobuf.binary.tag');
 
 
 /**
@@ -139,6 +140,28 @@ function readRepeatedNonPrimitive(indexArray, bufferDecoder, singularReadFunc) {
   return result;
 }
 
+/**
+ * Converts all entries of the index array to the template type using the given
+ * read function and return an Array containing those converted values. This is
+ * used to implement parsing repeated non-primitive fields.
+ * @param {!Array<!IndexEntry>} indexArray
+ * @param {!BufferDecoder} bufferDecoder
+ * @param {number} fieldNumber
+ * @param {function(!Kernel):T} instanceCreator
+ * @param {number=} pivot
+ * @return {!Array<T>}
+ * @template T
+ */
+function readRepeatedGroup(
+    indexArray, bufferDecoder, fieldNumber, instanceCreator, pivot) {
+  const result = new Array(indexArray.length);
+  for (let i = 0; i < indexArray.length; i++) {
+    result[i] = doReadGroup(
+        bufferDecoder, indexArray[i], fieldNumber, instanceCreator, pivot);
+  }
+  return result;
+}
+
 /**
  * Creates a new bytes array to contain all data of a submessage.
  * When there are multiple entries, merge them together.
@@ -193,6 +216,51 @@ function readMessage(indexArray, bufferDecoder, instanceCreator, pivot) {
   return instanceCreator(accessor);
 }
 
+/**
+ * Merges all index entries of the index array using the given read function.
+ * This is used to implement parsing singular group fields.
+ * @param {!Array<!IndexEntry>} indexArray
+ * @param {!BufferDecoder} bufferDecoder
+ * @param {number} fieldNumber
+ * @param {function(!Kernel):T} instanceCreator
+ * @param {number=} pivot
+ * @return {T}
+ * @template T
+ */
+function readGroup(
+    indexArray, bufferDecoder, fieldNumber, instanceCreator, pivot) {
+  checkInstanceCreator(instanceCreator);
+  checkState(indexArray.length > 0);
+  return doReadGroup(
+      bufferDecoder, indexArray[indexArray.length - 1], fieldNumber,
+      instanceCreator, pivot);
+}
+
+/**
+ * Merges all index entries of the index array using the given read function.
+ * This is used to implement parsing singular message fields.
+ * @param {!BufferDecoder} bufferDecoder
+ * @param {!IndexEntry} indexEntry
+ * @param {number} fieldNumber
+ * @param {function(!Kernel):T} instanceCreator
+ * @param {number=} pivot
+ * @return {T}
+ * @template T
+ */
+function doReadGroup(
+    bufferDecoder, indexEntry, fieldNumber, instanceCreator, pivot) {
+  validateWireType(indexEntry, WireType.START_GROUP);
+  const fieldStartIndex = Field.getStartIndex(indexEntry);
+  const tag = createTag(WireType.START_GROUP, fieldNumber);
+  const groupTagLength = get32BitVarintLength(tag);
+  const groupLength = getTagLength(
+      bufferDecoder, fieldStartIndex, WireType.START_GROUP, fieldNumber);
+  const accessorBuffer = bufferDecoder.subBufferDecoder(
+      fieldStartIndex, groupLength - groupTagLength);
+  const kernel = Kernel.fromBufferDecoder_(accessorBuffer, pivot);
+  return instanceCreator(kernel);
+}
+
 /**
  * @param {!Writer} writer
  * @param {number} fieldNumber
@@ -203,6 +271,18 @@ function writeMessage(writer, fieldNumber, value) {
       fieldNumber, checkDefAndNotNull(value).internalGetKernel().serialize());
 }
 
+/**
+ * @param {!Writer} writer
+ * @param {number} fieldNumber
+ * @param {?InternalMessage} value
+ */
+function writeGroup(writer, fieldNumber, value) {
+  const kernel = checkDefAndNotNull(value).internalGetKernel();
+  writer.writeStartGroup(fieldNumber);
+  kernel.serializeToWriter(writer);
+  writer.writeEndGroup(fieldNumber);
+}
+
 /**
  * Writes the array of Messages into the writer for the given field number.
  * @param {!Writer} writer
@@ -215,6 +295,18 @@ function writeRepeatedMessage(writer, fieldNumber, values) {
   }
 }
 
+/**
+ * Writes the array of Messages into the writer for the given field number.
+ * @param {!Writer} writer
+ * @param {number} fieldNumber
+ * @param {!Array<!InternalMessage>} values
+ */
+function writeRepeatedGroup(writer, fieldNumber, values) {
+  for (const value of values) {
+    writeGroup(writer, fieldNumber, value);
+  }
+}
+
 /**
  * Array.from has a weird type definition in google3/javascript/externs/es6.js
  * and wants the mapping function accept strings.
@@ -406,7 +498,8 @@ class Kernel {
           writer.writeTag(fieldNumber, Field.getWireType(indexEntry));
           writer.writeBufferDecoder(
               checkDefAndNotNull(this.bufferDecoder_),
-              Field.getStartIndex(indexEntry), Field.getWireType(indexEntry));
+              Field.getStartIndex(indexEntry), Field.getWireType(indexEntry),
+              fieldNumber);
         }
       }
     });
@@ -690,6 +783,28 @@ class Kernel {
         writeMessage);
   }
 
+  /**
+   * Returns data as a mutable proto Message for the given field number.
+   * If no value has been set, return null.
+   * If hasFieldNumber(fieldNumber) == false before calling, it remains false.
+   *
+   * This method should not be used along with getMessage, since calling
+   * getMessageOrNull after getMessage will not register the encoder.
+   *
+   * @param {number} fieldNumber
+   * @param {function(!Kernel):T} instanceCreator
+   * @param {number=} pivot
+   * @return {?T}
+   * @template T
+   */
+  getGroupOrNull(fieldNumber, instanceCreator, pivot = undefined) {
+    return this.getFieldWithDefault_(
+        fieldNumber, null,
+        (indexArray, bytes) =>
+            readGroup(indexArray, bytes, fieldNumber, instanceCreator, pivot),
+        writeGroup);
+  }
+
   /**
    * Returns data as a mutable proto Message for the given field number.
    * If no value has been set previously, creates and attaches an instance.
@@ -714,6 +829,30 @@ class Kernel {
     return instance;
   }
 
+  /**
+   * Returns data as a mutable proto Message for the given field number.
+   * If no value has been set previously, creates and attaches an instance.
+   * Postcondition: hasFieldNumber(fieldNumber) == true.
+   *
+   * This method should not be used along with getMessage, since calling
+   * getMessageAttach after getMessage will not register the encoder.
+   *
+   * @param {number} fieldNumber
+   * @param {function(!Kernel):T} instanceCreator
+   * @param {number=} pivot
+   * @return {T}
+   * @template T
+   */
+  getGroupAttach(fieldNumber, instanceCreator, pivot = undefined) {
+    checkInstanceCreator(instanceCreator);
+    let instance = this.getGroupOrNull(fieldNumber, instanceCreator, pivot);
+    if (!instance) {
+      instance = instanceCreator(Kernel.createEmpty());
+      this.setField_(fieldNumber, instance, writeGroup);
+    }
+    return instance;
+  }
+
   /**
    * Returns data as a proto Message for the given field number.
    * If no value has been set, return a default instance.
@@ -744,6 +883,36 @@ class Kernel {
     return message === null ? instanceCreator(Kernel.createEmpty()) : message;
   }
 
+  /**
+   * Returns data as a proto Message for the given field number.
+   * If no value has been set, return a default instance.
+   * This default instance is guaranteed to be the same instance, unless this
+   * field is cleared.
+   * Does not register the encoder, so changes made to the returned
+   * sub-message will not be included when serializing the parent message.
+   * Use getMessageAttach() if the resulting sub-message should be mutable.
+   *
+   * This method should not be used along with getMessageOrNull or
+   * getMessageAttach, since these methods register the encoder.
+   *
+   * @param {number} fieldNumber
+   * @param {function(!Kernel):T} instanceCreator
+   * @param {number=} pivot
+   * @return {T}
+   * @template T
+   */
+  getGroup(fieldNumber, instanceCreator, pivot = undefined) {
+    checkInstanceCreator(instanceCreator);
+    const message = this.getFieldWithDefault_(
+        fieldNumber, null,
+        (indexArray, bytes) =>
+            readGroup(indexArray, bytes, fieldNumber, instanceCreator, pivot));
+    // Returns an empty message as the default value if the field doesn't exist.
+    // We don't pass the default value to getFieldWithDefault_ to reduce object
+    // allocation.
+    return message === null ? instanceCreator(Kernel.createEmpty()) : message;
+  }
+
   /**
    * Returns the accessor for the given singular message, or returns null if
    * it hasn't been set.
@@ -1614,6 +1783,71 @@ class Kernel {
         .length;
   }
 
+  /**
+   * Returns an Array instance containing boolean values for the given field
+   * number.
+   * @param {number} fieldNumber
+   * @param {function(!Kernel):T} instanceCreator
+   * @param {number|undefined} pivot
+   * @return {!Array<T>}
+   * @template T
+   * @private
+   */
+  getRepeatedGroupArray_(fieldNumber, instanceCreator, pivot) {
+    return this.getFieldWithDefault_(
+        fieldNumber, [],
+        (indexArray, bufferDecoder) => readRepeatedGroup(
+            indexArray, bufferDecoder, fieldNumber, instanceCreator, pivot),
+        writeRepeatedGroup);
+  }
+
+  /**
+   * Returns the element at index for the given field number as a group.
+   * @param {number} fieldNumber
+   * @param {function(!Kernel):T} instanceCreator
+   * @param {number} index
+   * @param {number=} pivot
+   * @return {T}
+   * @template T
+   */
+  getRepeatedGroupElement(
+      fieldNumber, instanceCreator, index, pivot = undefined) {
+    const array =
+        this.getRepeatedGroupArray_(fieldNumber, instanceCreator, pivot);
+    checkCriticalElementIndex(index, array.length);
+    return array[index];
+  }
+
+  /**
+   * Returns an Iterable instance containing group values for the given field
+   * number.
+   * @param {number} fieldNumber
+   * @param {function(!Kernel):T} instanceCreator
+   * @param {number=} pivot
+   * @return {!Iterable<T>}
+   * @template T
+   */
+  getRepeatedGroupIterable(fieldNumber, instanceCreator, pivot = undefined) {
+    // Don't split this statement unless needed. JS compiler thinks
+    // getRepeatedMessageArray_ might have side effects and doesn't inline the
+    // call in the compiled code. See cl/293894484 for details.
+    return new ArrayIterable(
+        this.getRepeatedGroupArray_(fieldNumber, instanceCreator, pivot));
+  }
+
+  /**
+   * Returns the size of the repeated field.
+   * @param {number} fieldNumber
+   * @param {function(!Kernel):T} instanceCreator
+   * @return {number}
+   * @param {number=} pivot
+   * @template T
+   */
+  getRepeatedGroupSize(fieldNumber, instanceCreator, pivot = undefined) {
+    return this.getRepeatedGroupArray_(fieldNumber, instanceCreator, pivot)
+        .length;
+  }
+
   /***************************************************************************
    *                        OPTIONAL SETTER METHODS
    ***************************************************************************/
@@ -1801,6 +2035,20 @@ class Kernel {
     this.setInt64(fieldNumber, value);
   }
 
+  /**
+   * Sets a proto Group to the field with the given field number.
+   * Instead of working with the Kernel inside of the message directly, we
+   * need the message instance to keep its reference equality for subsequent
+   * gettings.
+   * @param {number} fieldNumber
+   * @param {!InternalMessage} value
+   */
+  setGroup(fieldNumber, value) {
+    checkCriticalType(
+        value !== null, 'Given value is not a message instance: null');
+    this.setField_(fieldNumber, value, writeGroup);
+  }
+
   /**
    * Sets a proto Message to the field with the given field number.
    * Instead of working with the Kernel inside of the message directly, we
@@ -3806,6 +4054,69 @@ class Kernel {
     this.addRepeatedMessageIterable(
         fieldNumber, [value], instanceCreator, pivot);
   }
+
+  // Groups
+  /**
+   * Sets all message values into the field for the given field number.
+   * @param {number} fieldNumber
+   * @param {!Iterable<!InternalMessage>} values
+   */
+  setRepeatedGroupIterable(fieldNumber, values) {
+    const /** !Array<!InternalMessage> */ array = Array.from(values);
+    checkCriticalTypeMessageArray(array);
+    this.setField_(fieldNumber, array, writeRepeatedGroup);
+  }
+
+  /**
+   * Adds all message values into the field for the given field number.
+   * @param {number} fieldNumber
+   * @param {!Iterable<!InternalMessage>} values
+   * @param {function(!Kernel):!InternalMessage} instanceCreator
+   * @param {number=} pivot
+   */
+  addRepeatedGroupIterable(
+      fieldNumber, values, instanceCreator, pivot = undefined) {
+    const array = [
+      ...this.getRepeatedGroupArray_(fieldNumber, instanceCreator, pivot),
+      ...values,
+    ];
+    checkCriticalTypeMessageArray(array);
+    // Needs to set it back with the new array.
+    this.setField_(fieldNumber, array, writeRepeatedGroup);
+  }
+
+  /**
+   * Sets a single message value into the field for the given field number at
+   * the given index.
+   * @param {number} fieldNumber
+   * @param {!InternalMessage} value
+   * @param {function(!Kernel):!InternalMessage} instanceCreator
+   * @param {number} index
+   * @param {number=} pivot
+   * @throws {!Error} if index is out of range when check mode is critical
+   */
+  setRepeatedGroupElement(
+      fieldNumber, value, instanceCreator, index, pivot = undefined) {
+    checkInstanceCreator(instanceCreator);
+    checkCriticalType(
+        value !== null, 'Given value is not a message instance: null');
+    const array =
+        this.getRepeatedGroupArray_(fieldNumber, instanceCreator, pivot);
+    checkCriticalElementIndex(index, array.length);
+    array[index] = value;
+  }
+
+  /**
+   * Adds a single message value into the field for the given field number.
+   * @param {number} fieldNumber
+   * @param {!InternalMessage} value
+   * @param {function(!Kernel):!InternalMessage} instanceCreator
+   * @param {number=} pivot
+   */
+  addRepeatedGroupElement(
+      fieldNumber, value, instanceCreator, pivot = undefined) {
+    this.addRepeatedGroupIterable(fieldNumber, [value], instanceCreator, pivot);
+  }
 }
 
 exports = Kernel;

js/experimental/runtime/kernel/kernel_repeated_test.js

@@ -7425,3 +7425,383 @@ describe('Kernel for repeated message does', () => {
     }
   });
 });
+
+describe('Kernel for repeated groups does', () => {
+  it('return empty array for the empty input', () => {
+    const accessor = Kernel.createEmpty();
+    expectEqualToArray(
+        accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator), []);
+  });
+
+  it('ensure not the same instance returned for the empty input', () => {
+    const accessor = Kernel.createEmpty();
+    const list1 =
+        accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator);
+    const list2 =
+        accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator);
+    expect(list1).not.toBe(list2);
+  });
+
+  it('return size for the empty input', () => {
+    const accessor = Kernel.createEmpty();
+    expect(accessor.getRepeatedGroupSize(1, TestMessage.instanceCreator))
+        .toEqual(0);
+  });
+
+  it('return values from the input', () => {
+    const bytes1 = createArrayBuffer(0x08, 0x01);
+    const bytes2 = createArrayBuffer(0x08, 0x02);
+    const msg1 = new TestMessage(Kernel.fromArrayBuffer(bytes1));
+    const msg2 = new TestMessage(Kernel.fromArrayBuffer(bytes2));
+
+    const bytes =
+        createArrayBuffer(0x0B, 0x08, 0x01, 0x0C, 0x0B, 0x08, 0x02, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    expectEqualToMessageArray(
+        accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator),
+        [msg1, msg2]);
+  });
+
+  it('ensure not the same array instance returned', () => {
+    const bytes =
+        createArrayBuffer(0x0B, 0x08, 0x01, 0x0C, 0x0B, 0x08, 0x02, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    const list1 =
+        accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator);
+    const list2 =
+        accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator);
+    expect(list1).not.toBe(list2);
+  });
+
+  it('ensure the same array element returned for get iterable', () => {
+    const bytes =
+        createArrayBuffer(0x0B, 0x08, 0x01, 0x0C, 0x0B, 0x08, 0x02, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    const list1 =
+        accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator);
+    const list2 = accessor.getRepeatedGroupIterable(
+        1, TestMessage.instanceCreator, /* pivot= */ 0);
+    const array1 = Array.from(list1);
+    const array2 = Array.from(list2);
+    for (let i = 0; i < array1.length; i++) {
+      expect(array1[i]).toBe(array2[i]);
+    }
+  });
+
+  it('return accessors from the input', () => {
+    const bytes =
+        createArrayBuffer(0x0B, 0x08, 0x01, 0x0C, 0x0B, 0x08, 0x02, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    const [accessor1, accessor2] =
+        [...accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator)];
+    expect(accessor1.getInt32WithDefault(1)).toEqual(1);
+    expect(accessor2.getInt32WithDefault(1)).toEqual(2);
+  });
+
+  it('return accessors from the input when pivot is set', () => {
+    const bytes =
+        createArrayBuffer(0x0B, 0x08, 0x01, 0x0C, 0x0B, 0x08, 0x02, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    const [accessor1, accessor2] = [...accessor.getRepeatedGroupIterable(
+        1, TestMessage.instanceCreator, /* pivot= */ 0)];
+    expect(accessor1.getInt32WithDefault(1)).toEqual(1);
+    expect(accessor2.getInt32WithDefault(1)).toEqual(2);
+  });
+
+  it('return the repeated field element from the input', () => {
+    const bytes =
+        createArrayBuffer(0x0B, 0x08, 0x01, 0x0C, 0x0B, 0x08, 0x02, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    const msg1 = accessor.getRepeatedGroupElement(
+        /* fieldNumber= */ 1, TestMessage.instanceCreator,
+        /* index= */ 0);
+    const msg2 = accessor.getRepeatedGroupElement(
+        /* fieldNumber= */ 1, TestMessage.instanceCreator,
+        /* index= */ 1, /* pivot= */ 0);
+    expect(msg1.getInt32WithDefault(
+               /* fieldNumber= */ 1, /* default= */ 0))
+        .toEqual(1);
+    expect(msg2.getInt32WithDefault(
+               /* fieldNumber= */ 1, /* default= */ 0))
+        .toEqual(2);
+  });
+
+  it('ensure the same array element returned', () => {
+    const bytes =
+        createArrayBuffer(0x0B, 0x08, 0x01, 0x0C, 0x0B, 0x08, 0x02, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    const msg1 = accessor.getRepeatedGroupElement(
+        /* fieldNumber= */ 1, TestMessage.instanceCreator,
+        /* index= */ 0);
+    const msg2 = accessor.getRepeatedGroupElement(
+        /* fieldNumber= */ 1, TestMessage.instanceCreator,
+        /* index= */ 0);
+    expect(msg1).toBe(msg2);
+  });
+
+  it('return the size from the input', () => {
+    const bytes =
+        createArrayBuffer(0x0B, 0x08, 0x01, 0x0C, 0x0B, 0x08, 0x02, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    expect(accessor.getRepeatedGroupSize(1, TestMessage.instanceCreator))
+        .toEqual(2);
+  });
+
+  it('encode repeated message from the input', () => {
+    const bytes =
+        createArrayBuffer(0x0B, 0x08, 0x01, 0x0C, 0x0B, 0x08, 0x02, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    expect(accessor.serialize()).toEqual(bytes);
+  });
+
+  it('add a single value', () => {
+    const accessor = Kernel.createEmpty();
+    const bytes1 = createArrayBuffer(0x08, 0x01);
+    const msg1 = new TestMessage(Kernel.fromArrayBuffer(bytes1));
+    const bytes2 = createArrayBuffer(0x08, 0x02);
+    const msg2 = new TestMessage(Kernel.fromArrayBuffer(bytes2));
+
+    accessor.addRepeatedGroupElement(1, msg1, TestMessage.instanceCreator);
+    accessor.addRepeatedGroupElement(1, msg2, TestMessage.instanceCreator);
+    const result =
+        accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator);
+
+    expect(Array.from(result)).toEqual([msg1, msg2]);
+  });
+
+  it('add values', () => {
+    const accessor = Kernel.createEmpty();
+    const bytes1 = createArrayBuffer(0x08, 0x01);
+    const msg1 = new TestMessage(Kernel.fromArrayBuffer(bytes1));
+    const bytes2 = createArrayBuffer(0x08, 0x02);
+    const msg2 = new TestMessage(Kernel.fromArrayBuffer(bytes2));
+
+    accessor.addRepeatedGroupIterable(1, [msg1], TestMessage.instanceCreator);
+    accessor.addRepeatedGroupIterable(1, [msg2], TestMessage.instanceCreator);
+    const result =
+        accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator);
+
+    expect(Array.from(result)).toEqual([msg1, msg2]);
+  });
+
+  it('set a single value', () => {
+    const bytes = createArrayBuffer(0x0B, 0x08, 0x01, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    const subbytes = createArrayBuffer(0x08, 0x01);
+    const submsg = new TestMessage(Kernel.fromArrayBuffer(subbytes));
+
+    accessor.setRepeatedGroupElement(
+        /* fieldNumber= */ 1, submsg, TestMessage.instanceCreator,
+        /* index= */ 0);
+    const result =
+        accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator);
+
+    expect(Array.from(result)).toEqual([submsg]);
+  });
+
+  it('write submessage changes made via getRepeatedGroupElement', () => {
+    const bytes = createArrayBuffer(0x0B, 0x08, 0x05, 0x0C);
+    const expected = createArrayBuffer(0x0B, 0x08, 0x00, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    const submsg = accessor.getRepeatedGroupElement(
+        /* fieldNumber= */ 1, TestMessage.instanceCreator,
+        /* index= */ 0);
+    expect(submsg.getInt32WithDefault(1, 0)).toEqual(5);
+    submsg.setInt32(1, 0);
+
+    expect(accessor.serialize()).toEqual(expected);
+  });
+
+  it('set values', () => {
+    const accessor = Kernel.createEmpty();
+    const subbytes = createArrayBuffer(0x08, 0x01);
+    const submsg = new TestMessage(Kernel.fromArrayBuffer(subbytes));
+
+    accessor.setRepeatedGroupIterable(1, [submsg]);
+    const result =
+        accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator);
+
+    expect(Array.from(result)).toEqual([submsg]);
+  });
+
+  it('encode for adding single value', () => {
+    const accessor = Kernel.createEmpty();
+    const bytes1 = createArrayBuffer(0x08, 0x01);
+    const msg1 = new TestMessage(Kernel.fromArrayBuffer(bytes1));
+    const bytes2 = createArrayBuffer(0x08, 0x00);
+    const msg2 = new TestMessage(Kernel.fromArrayBuffer(bytes2));
+    const expected =
+        createArrayBuffer(0x0B, 0x08, 0x01, 0x0C, 0x0B, 0x08, 0x00, 0x0C);
+
+    accessor.addRepeatedGroupElement(1, msg1, TestMessage.instanceCreator);
+    accessor.addRepeatedGroupElement(1, msg2, TestMessage.instanceCreator);
+    const result = accessor.serialize();
+
+    expect(result).toEqual(expected);
+  });
+
+  it('encode for adding values', () => {
+    const accessor = Kernel.createEmpty();
+    const bytes1 = createArrayBuffer(0x08, 0x01);
+    const msg1 = new TestMessage(Kernel.fromArrayBuffer(bytes1));
+    const bytes2 = createArrayBuffer(0x08, 0x00);
+    const msg2 = new TestMessage(Kernel.fromArrayBuffer(bytes2));
+    const expected =
+        createArrayBuffer(0x0B, 0x08, 0x01, 0x0C, 0x0B, 0x08, 0x00, 0x0C);
+
+    accessor.addRepeatedGroupIterable(
+        1, [msg1, msg2], TestMessage.instanceCreator);
+    const result = accessor.serialize();
+
+    expect(result).toEqual(expected);
+  });
+
+  it('encode for setting single value', () => {
+    const bytes = createArrayBuffer(0x0B, 0x08, 0x00, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    const subbytes = createArrayBuffer(0x08, 0x01);
+    const submsg = new TestMessage(Kernel.fromArrayBuffer(subbytes));
+    const expected = createArrayBuffer(0x0B, 0x08, 0x01, 0x0C);
+
+    accessor.setRepeatedGroupElement(
+        /* fieldNumber= */ 1, submsg, TestMessage.instanceCreator,
+        /* index= */ 0);
+    const result = accessor.serialize();
+
+    expect(result).toEqual(expected);
+  });
+
+  it('encode for setting values', () => {
+    const accessor = Kernel.createEmpty();
+    const subbytes = createArrayBuffer(0x08, 0x01);
+    const submsg = new TestMessage(Kernel.fromArrayBuffer(subbytes));
+    const expected = createArrayBuffer(0x0B, 0x08, 0x01, 0x0C);
+
+    accessor.setRepeatedGroupIterable(1, [submsg]);
+    const result = accessor.serialize();
+
+    expect(result).toEqual(expected);
+  });
+
+  it('fail when getting groups value with other wire types', () => {
+    const accessor = Kernel.fromArrayBuffer(createArrayBuffer(
+        0x09, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00));
+
+    if (CHECK_CRITICAL_STATE) {
+      expect(() => {
+        accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator);
+      }).toThrow();
+    }
+  });
+
+  it('fail when adding group values with wrong type value', () => {
+    const accessor = Kernel.createEmpty();
+    const fakeValue = /** @type {!TestMessage} */ (/** @type {*} */ (null));
+    if (CHECK_CRITICAL_STATE) {
+      expect(
+          () => accessor.addRepeatedGroupIterable(
+              1, [fakeValue], TestMessage.instanceCreator))
+          .toThrowError('Given value is not a message instance: null');
+    } else {
+      // Note in unchecked mode we produce invalid output for invalid inputs.
+      // This test just documents our behavior in those cases.
+      // These values might change at any point and are not considered
+      // what the implementation should be doing here.
+      accessor.addRepeatedGroupIterable(
+          1, [fakeValue], TestMessage.instanceCreator);
+      const list =
+          accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator);
+      expect(Array.from(list)).toEqual([null]);
+    }
+  });
+
+  it('fail when adding single group value with wrong type value', () => {
+    const accessor = Kernel.createEmpty();
+    const fakeValue = /** @type {!TestMessage} */ (/** @type {*} */ (null));
+    if (CHECK_CRITICAL_STATE) {
+      expect(
+          () => accessor.addRepeatedGroupElement(
+              1, fakeValue, TestMessage.instanceCreator))
+          .toThrowError('Given value is not a message instance: null');
+    } else {
+      // Note in unchecked mode we produce invalid output for invalid inputs.
+      // This test just documents our behavior in those cases.
+      // These values might change at any point and are not considered
+      // what the implementation should be doing here.
+      accessor.addRepeatedGroupElement(
+          1, fakeValue, TestMessage.instanceCreator);
+      const list =
+          accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator);
+      expect(Array.from(list)).toEqual([null]);
+    }
+  });
+
+  it('fail when setting message values with wrong type value', () => {
+    const accessor = Kernel.createEmpty();
+    const fakeValue = /** @type {!TestMessage} */ (/** @type {*} */ (null));
+    if (CHECK_CRITICAL_STATE) {
+      expect(() => accessor.setRepeatedGroupIterable(1, [fakeValue]))
+          .toThrowError('Given value is not a message instance: null');
+    } else {
+      // Note in unchecked mode we produce invalid output for invalid inputs.
+      // This test just documents our behavior in those cases.
+      // These values might change at any point and are not considered
+      // what the implementation should be doing here.
+      accessor.setRepeatedGroupIterable(1, [fakeValue]);
+      const list =
+          accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator);
+      expect(Array.from(list)).toEqual([null]);
+    }
+  });
+
+  it('fail when setting single value with wrong type value', () => {
+    const accessor =
+        Kernel.fromArrayBuffer(createArrayBuffer(0x0B, 0x08, 0x00, 0x0C));
+    const fakeValue = /** @type {!TestMessage} */ (/** @type {*} */ (null));
+    if (CHECK_CRITICAL_STATE) {
+      expect(
+          () => accessor.setRepeatedGroupElement(
+              /* fieldNumber= */ 1, fakeValue, TestMessage.instanceCreator,
+              /* index= */ 0))
+          .toThrowError('Given value is not a message instance: null');
+    } else {
+      // Note in unchecked mode we produce invalid output for invalid inputs.
+      // This test just documents our behavior in those cases.
+      // These values might change at any point and are not considered
+      // what the implementation should be doing here.
+      accessor.setRepeatedGroupElement(
+          /* fieldNumber= */ 1, fakeValue, TestMessage.instanceCreator,
+          /* index= */ 0);
+      const list =
+          accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator);
+      expect(Array.from(list).length).toEqual(1);
+    }
+  });
+
+  it('fail when setting single value with out-of-bound index', () => {
+    const accessor =
+        Kernel.fromArrayBuffer(createArrayBuffer(0x0B, 0x08, 0x00, 0x0C));
+    const msg1 =
+        accessor.getRepeatedGroupElement(1, TestMessage.instanceCreator, 0);
+    const bytes2 = createArrayBuffer(0x08, 0x01);
+    const msg2 = new TestMessage(Kernel.fromArrayBuffer(bytes2));
+    if (CHECK_CRITICAL_STATE) {
+      expect(
+          () => accessor.setRepeatedGroupElement(
+              /* fieldNumber= */ 1, msg2, TestMessage.instanceCreator,
+              /* index= */ 1))
+          .toThrowError('Index out of bounds: index: 1 size: 1');
+    } else {
+      // Note in unchecked mode we produce invalid output for invalid inputs.
+      // This test just documents our behavior in those cases.
+      // These values might change at any point and are not considered
+      // what the implementation should be doing here.
+      accessor.setRepeatedGroupElement(
+          /* fieldNumber= */ 1, msg2, TestMessage.instanceCreator,
+          /* index= */ 1);
+      expectEqualToArray(
+          accessor.getRepeatedGroupIterable(1, TestMessage.instanceCreator),
+          [msg1, msg2]);
+    }
+  });
+});

js/experimental/runtime/kernel/kernel_test.js

@@ -2075,3 +2075,255 @@ describe('Double access', () => {
     }
   });
 });
+
+describe('Kernel for singular group does', () => {
+  it('return group from the input', () => {
+    const bytes = createArrayBuffer(0x0B, 0x08, 0x01, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    const msg = accessor.getGroupOrNull(1, TestMessage.instanceCreator);
+    expect(msg.getBoolWithDefault(1, false)).toBe(true);
+  });
+
+  it('return group from the input when pivot is set', () => {
+    const bytes = createArrayBuffer(0x0B, 0x08, 0x01, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    const msg = accessor.getGroupOrNull(1, TestMessage.instanceCreator, 0);
+    expect(msg.getBoolWithDefault(1, false)).toBe(true);
+  });
+
+  it('encode group from the input', () => {
+    const bytes = createArrayBuffer(0x0B, 0x08, 0x01, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    expect(accessor.serialize()).toEqual(bytes);
+  });
+
+  it('encode group from the input after read', () => {
+    const bytes = createArrayBuffer(0x0B, 0x08, 0x01, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    accessor.getGroupOrNull(1, TestMessage.instanceCreator);
+    expect(accessor.serialize()).toEqual(bytes);
+  });
+
+  it('return last group from multiple inputs', () => {
+    const bytes =
+        createArrayBuffer(0x0B, 0x08, 0x00, 0x0C, 0x0B, 0x08, 0x01, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    const msg = accessor.getGroupOrNull(1, TestMessage.instanceCreator);
+    expect(msg.getBoolWithDefault(1, false)).toBe(true);
+  });
+
+  it('removes duplicated group when serializing', () => {
+    const bytes =
+        createArrayBuffer(0x0B, 0x08, 0x00, 0x0C, 0x0B, 0x08, 0x01, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    accessor.getGroupOrNull(1, TestMessage.instanceCreator);
+    expect(accessor.serialize())
+        .toEqual(createArrayBuffer(0x0B, 0x08, 0x01, 0x0C));
+  });
+
+  it('encode group from multiple inputs', () => {
+    const bytes =
+        createArrayBuffer(0x0B, 0x08, 0x00, 0x0C, 0x0B, 0x08, 0x01, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    expect(accessor.serialize()).toEqual(bytes);
+  });
+
+  it('encode group after read', () => {
+    const bytes =
+        createArrayBuffer(0x0B, 0x08, 0x00, 0x0C, 0x0B, 0x08, 0x01, 0x0C);
+    const expected = createArrayBuffer(0x0B, 0x08, 0x01, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    accessor.getGroupOrNull(1, TestMessage.instanceCreator);
+    expect(accessor.serialize()).toEqual(expected);
+  });
+
+  it('return group from setter', () => {
+    const bytes = createArrayBuffer(0x08, 0x01);
+    const accessor = Kernel.fromArrayBuffer(new ArrayBuffer(0));
+    const subaccessor = Kernel.fromArrayBuffer(bytes);
+    const submsg1 = new TestMessage(subaccessor);
+    accessor.setGroup(1, submsg1);
+    const submsg2 = accessor.getGroup(1, TestMessage.instanceCreator);
+    expect(submsg1).toBe(submsg2);
+  });
+
+  it('encode group from setter', () => {
+    const accessor = Kernel.fromArrayBuffer(new ArrayBuffer(0));
+    const subaccessor = Kernel.fromArrayBuffer(createArrayBuffer(0x08, 0x01));
+    const submsg = new TestMessage(subaccessor);
+    accessor.setGroup(1, submsg);
+    const expected = createArrayBuffer(0x0B, 0x08, 0x01, 0x0C);
+    expect(accessor.serialize()).toEqual(expected);
+  });
+
+  it('leave hasFieldNumber unchanged after getGroupOrNull', () => {
+    const accessor = Kernel.createEmpty();
+    expect(accessor.hasFieldNumber(1)).toBe(false);
+    expect(accessor.getGroupOrNull(1, TestMessage.instanceCreator)).toBe(null);
+    expect(accessor.hasFieldNumber(1)).toBe(false);
+  });
+
+  it('serialize changes to subgroups made with getGroupsOrNull', () => {
+    const intTwoBytes = createArrayBuffer(0x0B, 0x08, 0x02, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(intTwoBytes);
+    const mutableSubMessage =
+        accessor.getGroupOrNull(1, TestMessage.instanceCreator);
+    mutableSubMessage.setInt32(1, 10);
+    const intTenBytes = createArrayBuffer(0x0B, 0x08, 0x0A, 0x0C);
+    expect(accessor.serialize()).toEqual(intTenBytes);
+  });
+
+  it('serialize additions to subgroups made with getGroupOrNull', () => {
+    const intTwoBytes = createArrayBuffer(0x0B, 0x08, 0x02, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(intTwoBytes);
+    const mutableSubMessage =
+        accessor.getGroupOrNull(1, TestMessage.instanceCreator);
+    mutableSubMessage.setInt32(2, 3);
+    // Sub group contains the original field, plus the new one.
+    expect(accessor.serialize())
+        .toEqual(createArrayBuffer(0x0B, 0x08, 0x02, 0x10, 0x03, 0x0C));
+  });
+
+  it('fail with getGroupOrNull if immutable group exist in cache', () => {
+    const intTwoBytes = createArrayBuffer(0x0B, 0x08, 0x02, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(intTwoBytes);
+
+    const readOnly = accessor.getGroup(1, TestMessage.instanceCreator);
+    if (CHECK_TYPE) {
+      expect(() => accessor.getGroupOrNull(1, TestMessage.instanceCreator))
+          .toThrow();
+    } else {
+      const mutableSubGropu =
+          accessor.getGroupOrNull(1, TestMessage.instanceCreator);
+      // The instance returned by getGroupOrNull is the exact same instance.
+      expect(mutableSubGropu).toBe(readOnly);
+
+      // Serializing the subgroup does not write the changes
+      mutableSubGropu.setInt32(1, 0);
+      expect(accessor.serialize()).toEqual(intTwoBytes);
+    }
+  });
+
+  it('change hasFieldNumber after getGroupAttach', () => {
+    const accessor = Kernel.createEmpty();
+    expect(accessor.hasFieldNumber(1)).toBe(false);
+    expect(accessor.getGroupAttach(1, TestMessage.instanceCreator))
+        .not.toBe(null);
+    expect(accessor.hasFieldNumber(1)).toBe(true);
+  });
+
+  it('change hasFieldNumber after getGroupAttach when pivot is set', () => {
+    const accessor = Kernel.createEmpty();
+    expect(accessor.hasFieldNumber(1)).toBe(false);
+    expect(
+        accessor.getGroupAttach(1, TestMessage.instanceCreator, /* pivot= */ 1))
+        .not.toBe(null);
+    expect(accessor.hasFieldNumber(1)).toBe(true);
+  });
+
+  it('serialize subgroups made with getGroupAttach', () => {
+    const accessor = Kernel.createEmpty();
+    const mutableSubGroup =
+        accessor.getGroupAttach(1, TestMessage.instanceCreator);
+    mutableSubGroup.setInt32(1, 10);
+    const intTenBytes = createArrayBuffer(0x0B, 0x08, 0x0A, 0x0C);
+    expect(accessor.serialize()).toEqual(intTenBytes);
+  });
+
+  it('serialize additions to subgroups using getMessageAttach', () => {
+    const intTwoBytes = createArrayBuffer(0x0B, 0x08, 0x02, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(intTwoBytes);
+    const mutableSubGroup =
+        accessor.getGroupAttach(1, TestMessage.instanceCreator);
+    mutableSubGroup.setInt32(2, 3);
+    // Sub message contains the original field, plus the new one.
+    expect(accessor.serialize())
+        .toEqual(createArrayBuffer(0x0B, 0x08, 0x02, 0x10, 0x03, 0x0C));
+  });
+
+  it('fail with getGroupAttach if immutable message exist in cache', () => {
+    const intTwoBytes = createArrayBuffer(0x0B, 0x08, 0x02, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(intTwoBytes);
+
+    const readOnly = accessor.getGroup(1, TestMessage.instanceCreator);
+    if (CHECK_TYPE) {
+      expect(() => accessor.getGroupAttach(1, TestMessage.instanceCreator))
+          .toThrow();
+    } else {
+      const mutableSubGroup =
+          accessor.getGroupAttach(1, TestMessage.instanceCreator);
+      // The instance returned by getMessageOrNull is the exact same instance.
+      expect(mutableSubGroup).toBe(readOnly);
+
+      // Serializing the submessage does not write the changes
+      mutableSubGroup.setInt32(1, 0);
+      expect(accessor.serialize()).toEqual(intTwoBytes);
+    }
+  });
+
+  it('read default group return empty group with getGroup', () => {
+    const bytes = new ArrayBuffer(0);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    expect(accessor.getGroup(1, TestMessage.instanceCreator)).toBeTruthy();
+    expect(accessor.getGroup(1, TestMessage.instanceCreator).serialize())
+        .toEqual(bytes);
+  });
+
+  it('read default group return null with getGroupOrNull', () => {
+    const bytes = new ArrayBuffer(0);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    expect(accessor.getGroupOrNull(1, TestMessage.instanceCreator)).toBe(null);
+  });
+
+  it('read group preserve reference equality', () => {
+    const bytes = createArrayBuffer(0x0B, 0x08, 0x02, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    const msg1 = accessor.getGroupOrNull(1, TestMessage.instanceCreator);
+    const msg2 = accessor.getGroupOrNull(1, TestMessage.instanceCreator);
+    const msg3 = accessor.getGroupAttach(1, TestMessage.instanceCreator);
+    expect(msg1).toBe(msg2);
+    expect(msg1).toBe(msg3);
+  });
+
+  it('fail when getting group with null instance constructor', () => {
+    const accessor =
+        Kernel.fromArrayBuffer(createArrayBuffer(0x0A, 0x02, 0x08, 0x01));
+    const nullMessage = /** @type {function(!Kernel):!TestMessage} */
+        (/** @type {*} */ (null));
+    expect(() => accessor.getGroupOrNull(1, nullMessage)).toThrow();
+  });
+
+  it('fail when setting group value with null value', () => {
+    const accessor = Kernel.fromArrayBuffer(new ArrayBuffer(0));
+    const fakeMessage = /** @type {!TestMessage} */ (/** @type {*} */ (null));
+    if (CHECK_CRITICAL_TYPE) {
+      expect(() => accessor.setGroup(1, fakeMessage))
+          .toThrowError('Given value is not a message instance: null');
+    } else {
+      // Note in unchecked mode we produce invalid output for invalid inputs.
+      // This test just documents our behavior in those cases.
+      // These values might change at any point and are not considered
+      // what the implementation should be doing here.
+      accessor.setMessage(1, fakeMessage);
+      expect(accessor.getGroupOrNull(
+                 /* fieldNumber= */ 1, TestMessage.instanceCreator))
+          .toBeNull();
+    }
+  });
+
+  it('reads group in a longer buffer', () => {
+    const bytes = createArrayBuffer(
+        0x12, 0x20,  // 32 length delimited
+        0x00,        // random values for padding start
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00,  // random values for padding end
+        0x0B,  // Group tag
+        0x08, 0x02, 0x0C);
+    const accessor = Kernel.fromArrayBuffer(bytes);
+    const msg1 = accessor.getGroupOrNull(1, TestMessage.instanceCreator);
+    const msg2 = accessor.getGroupOrNull(1, TestMessage.instanceCreator);
+    expect(msg1).toBe(msg2);
+  });
+});

js/experimental/runtime/kernel/message_set.js

@@ -0,0 +1,285 @@
+/*
+##########################################################
+#                                                        #
+#  __          __     _____  _   _ _____ _   _  _____    #
+#  \ \        / /\   |  __ \| \ | |_   _| \ | |/ ____|   #
+#   \ \  /\  / /  \  | |__) |  \| | | | |  \| | |  __    #
+#    \ \/  \/ / /\ \ |  _  /| . ` | | | | . ` | | |_ |   #
+#     \  /\  / ____ \| | \ \| |\  |_| |_| |\  | |__| |   #
+#      \/  \/_/    \_\_|  \_\_| \_|_____|_| \_|\_____|   #
+#                                                        #
+#                                                        #
+##########################################################
+# Do not use this class in your code. This class purely  #
+# exists to make proto code generation easier.           #
+##########################################################
+*/
+goog.module('protobuf.runtime.MessageSet');
+
+const InternalMessage = goog.require('protobuf.binary.InternalMessage');
+const Kernel = goog.require('protobuf.runtime.Kernel');
+
+// These are the tags for the old MessageSet format, which was defined as:
+//   message MessageSet {
+//     repeated group Item = 1 {
+//       required uint32 type_id = 2;
+//       optional bytes message = 3;
+//     }
+//   }
+/** @const {number} */
+const MSET_GROUP_FIELD_NUMBER = 1;
+/** @const {number} */
+const MSET_TYPE_ID_FIELD_NUMBER = 2;
+/** @const {number} */
+const MSET_MESSAGE_FIELD_NUMBER = 3;
+
+/**
+ * @param {!Kernel} kernel
+ * @return {!Map<number, !Item>}
+ */
+function createItemMap(kernel) {
+  const itemMap = new Map();
+  let totalCount = 0;
+  for (const item of kernel.getRepeatedGroupIterable(
+           MSET_GROUP_FIELD_NUMBER, Item.fromKernel)) {
+    itemMap.set(item.getTypeId(), item);
+    totalCount++;
+  }
+
+  // Normalize the entries.
+  if (totalCount > itemMap.size) {
+    writeItemMap(kernel, itemMap);
+  }
+  return itemMap;
+}
+
+/**
+ * @param {!Kernel} kernel
+ * @param {!Map<number, !Item>} itemMap
+ */
+function writeItemMap(kernel, itemMap) {
+  kernel.setRepeatedGroupIterable(MSET_GROUP_FIELD_NUMBER, itemMap.values());
+}
+
+/**
+ * @implements {InternalMessage}
+ * @final
+ */
+class MessageSet {
+  /**
+   * @param {!Kernel} kernel
+   * @return {!MessageSet}
+   */
+  static fromKernel(kernel) {
+    const itemMap = createItemMap(kernel);
+    return new MessageSet(kernel, itemMap);
+  }
+
+  /**
+   * @return {!MessageSet}
+   */
+  static createEmpty() {
+    return MessageSet.fromKernel(Kernel.createEmpty());
+  }
+
+  /**
+   * @param {!Kernel} kernel
+   * @param {!Map<number, !Item>} itemMap
+   * @private
+   */
+  constructor(kernel, itemMap) {
+    /** @const {!Kernel} @private */
+    this.kernel_ = kernel;
+    /** @const {!Map<number, !Item>} @private */
+    this.itemMap_ = itemMap;
+  }
+
+
+
+  // code helpers for code gen
+
+  /**
+   * @param {number} typeId
+   * @param {function(!Kernel):T} instanceCreator
+   * @param {number=} pivot
+   * @return {?T}
+   * @template T
+   */
+  getMessageOrNull(typeId, instanceCreator, pivot) {
+    const item = this.itemMap_.get(typeId);
+    return item ? item.getMessageOrNull(instanceCreator, pivot) : null;
+  }
+
+  /**
+   * @param {number} typeId
+   * @param {function(!Kernel):T} instanceCreator
+   * @param {number=} pivot
+   * @return {T}
+   * @template T
+   */
+  getMessageAttach(typeId, instanceCreator, pivot) {
+    let item = this.itemMap_.get(typeId);
+    if (item) {
+      return item.getMessageAttach(instanceCreator, pivot);
+    }
+    const message = instanceCreator(Kernel.createEmpty());
+    this.setMessage(typeId, message);
+    return message;
+  }
+
+  /**
+   * @param {number} typeId
+   * @param {number=} pivot
+   * @return {?Kernel}
+   */
+  getMessageAccessorOrNull(typeId, pivot) {
+    const item = this.itemMap_.get(typeId);
+    return item ? item.getMessageAccessorOrNull(pivot) : null;
+  }
+
+
+  /**
+   * @param {number} typeId
+   */
+  clearMessage(typeId) {
+    if (this.itemMap_.delete(typeId)) {
+      writeItemMap(this.kernel_, this.itemMap_);
+    }
+  }
+
+  /**
+   * @param {number} typeId
+   * @return {boolean}
+   */
+  hasMessage(typeId) {
+    return this.itemMap_.has(typeId);
+  }
+
+  /**
+   * @param {number} typeId
+   * @param {!InternalMessage} value
+   */
+  setMessage(typeId, value) {
+    const item = this.itemMap_.get(typeId);
+    if (item) {
+      item.setMessage(value);
+    } else {
+      this.itemMap_.set(typeId, Item.create(typeId, value));
+      writeItemMap(this.kernel_, this.itemMap_);
+    }
+  }
+
+  /**
+   * @return {!Kernel}
+   * @override
+   */
+  internalGetKernel() {
+    return this.kernel_;
+  }
+}
+
+/**
+ * @implements {InternalMessage}
+ * @final
+ */
+class Item {
+  /**
+   * @param {number} typeId
+   * @param {!InternalMessage} message
+   * @return {!Item}
+   */
+  static create(typeId, message) {
+    const messageSet = Item.fromKernel(Kernel.createEmpty());
+    messageSet.setTypeId_(typeId);
+    messageSet.setMessage(message);
+    return messageSet;
+  }
+
+
+  /**
+   * @param {!Kernel} kernel
+   * @return {!Item}
+   */
+  static fromKernel(kernel) {
+    return new Item(kernel);
+  }
+
+  /**
+   * @param {!Kernel} kernel
+   * @private
+   */
+  constructor(kernel) {
+    /** @const {!Kernel} @private */
+    this.kernel_ = kernel;
+  }
+
+  /**
+   * @param {function(!Kernel):T} instanceCreator
+   * @param {number=} pivot
+   * @return {T}
+   * @template T
+   */
+  getMessage(instanceCreator, pivot) {
+    return this.kernel_.getMessage(
+        MSET_MESSAGE_FIELD_NUMBER, instanceCreator, pivot);
+  }
+
+  /**
+   * @param {function(!Kernel):T} instanceCreator
+   * @param {number=} pivot
+   * @return {?T}
+   * @template T
+   */
+  getMessageOrNull(instanceCreator, pivot) {
+    return this.kernel_.getMessageOrNull(
+        MSET_MESSAGE_FIELD_NUMBER, instanceCreator, pivot);
+  }
+
+  /**
+   * @param {function(!Kernel):T} instanceCreator
+   * @param {number=} pivot
+   * @return {T}
+   * @template T
+   */
+  getMessageAttach(instanceCreator, pivot) {
+    return this.kernel_.getMessageAttach(
+        MSET_MESSAGE_FIELD_NUMBER, instanceCreator, pivot);
+  }
+
+  /**
+   * @param {number=} pivot
+   * @return {?Kernel}
+   */
+  getMessageAccessorOrNull(pivot) {
+    return this.kernel_.getMessageAccessorOrNull(
+        MSET_MESSAGE_FIELD_NUMBER, pivot);
+  }
+
+  /** @param {!InternalMessage} value */
+  setMessage(value) {
+    this.kernel_.setMessage(MSET_MESSAGE_FIELD_NUMBER, value);
+  }
+
+  /** @return {number} */
+  getTypeId() {
+    return this.kernel_.getUint32WithDefault(MSET_TYPE_ID_FIELD_NUMBER);
+  }
+
+  /**
+   * @param {number} value
+   * @private
+   */
+  setTypeId_(value) {
+    this.kernel_.setUint32(MSET_TYPE_ID_FIELD_NUMBER, value);
+  }
+
+  /**
+   * @return {!Kernel}
+   * @override
+   */
+  internalGetKernel() {
+    return this.kernel_;
+  }
+}
+
+exports = MessageSet;

js/experimental/runtime/kernel/message_set_test.js

@@ -0,0 +1,262 @@
+/**
+ * @fileoverview Tests for message_set.js.
+ */
+goog.module('protobuf.runtime.MessageSetTest');
+
+goog.setTestOnly();
+
+const Kernel = goog.require('protobuf.runtime.Kernel');
+const MessageSet = goog.require('protobuf.runtime.MessageSet');
+const TestMessage = goog.require('protobuf.testing.binary.TestMessage');
+
+/**
+ * @param {...number} bytes
+ * @return {!ArrayBuffer}
+ */
+function createArrayBuffer(...bytes) {
+  return new Uint8Array(bytes).buffer;
+}
+
+describe('MessageSet does', () => {
+  it('returns no messages for empty set', () => {
+    const messageSet = MessageSet.createEmpty();
+    expect(messageSet.getMessageOrNull(12345, TestMessage.instanceCreator))
+        .toBeNull();
+  });
+
+  it('returns no kernel for empty set', () => {
+    const messageSet = MessageSet.createEmpty();
+    expect(messageSet.getMessageAccessorOrNull(12345)).toBeNull();
+  });
+
+  it('returns message that has been set', () => {
+    const messageSet = MessageSet.createEmpty();
+    const message = TestMessage.createEmpty();
+    messageSet.setMessage(12345, message);
+    expect(messageSet.getMessageOrNull(12345, TestMessage.instanceCreator))
+        .toBe(message);
+  });
+
+  it('returns null for cleared message', () => {
+    const messageSet = MessageSet.createEmpty();
+    const message = TestMessage.createEmpty();
+    messageSet.setMessage(12345, message);
+    messageSet.clearMessage(12345);
+    expect(messageSet.getMessageAccessorOrNull(12345)).toBeNull();
+  });
+
+  it('returns false for not present message', () => {
+    const messageSet = MessageSet.createEmpty();
+    expect(messageSet.hasMessage(12345)).toBe(false);
+  });
+
+  it('returns true for present message', () => {
+    const messageSet = MessageSet.createEmpty();
+    const message = TestMessage.createEmpty();
+    messageSet.setMessage(12345, message);
+    expect(messageSet.hasMessage(12345)).toBe(true);
+  });
+
+  it('returns false for cleared message', () => {
+    const messageSet = MessageSet.createEmpty();
+    const message = TestMessage.createEmpty();
+    messageSet.setMessage(12345, message);
+    messageSet.clearMessage(12345);
+    expect(messageSet.hasMessage(12345)).toBe(false);
+  });
+
+  it('returns false for cleared message without it being present', () => {
+    const messageSet = MessageSet.createEmpty();
+    messageSet.clearMessage(12345);
+    expect(messageSet.hasMessage(12345)).toBe(false);
+  });
+
+  const createMessageSet = () => {
+    const messageSet = MessageSet.createEmpty();
+    const message = TestMessage.createEmpty();
+    message.setInt32(1, 2);
+    messageSet.setMessage(12345, message);
+
+
+    const parsedKernel =
+        Kernel.fromArrayBuffer(messageSet.internalGetKernel().serialize());
+    return MessageSet.fromKernel(parsedKernel);
+  };
+
+  it('pass through pivot for getMessageOrNull', () => {
+    const messageSet = createMessageSet();
+    const message =
+        messageSet.getMessageOrNull(12345, TestMessage.instanceCreator, 2);
+    expect(message.internalGetKernel().getPivot()).toBe(2);
+  });
+
+  it('pass through pivot for getMessageAttach', () => {
+    const messageSet = createMessageSet();
+    const message =
+        messageSet.getMessageAttach(12345, TestMessage.instanceCreator, 2);
+    expect(message.internalGetKernel().getPivot()).toBe(2);
+  });
+
+  it('pass through pivot for getMessageAccessorOrNull', () => {
+    const messageSet = createMessageSet();
+    const kernel = messageSet.getMessageAccessorOrNull(12345, 2);
+    expect(kernel.getPivot()).toBe(2);
+  });
+
+  it('pick the last value in the stream', () => {
+    const arrayBuffer = createArrayBuffer(
+        0x52,  // Tag (field:10, length delimited)
+        0x14,  // Length of 20 bytes
+        0x0B,  // Start group fieldnumber 1
+        0x10,  // Tag (field 2, varint)
+        0xB9,  // 12345
+        0x60,  // 12345
+        0x1A,  // Tag (field 3, length delimited)
+        0x03,  // length 3
+        0xA0,  // Tag (fieldnumber 20, varint)
+        0x01,  // Tag (fieldnumber 20, varint)
+        0x1E,  // 30
+        0x0C,  // Stop Group field number 1
+        // second group
+        0x0B,  // Start group fieldnumber 1
+        0x10,  // Tag (field 2, varint)
+        0xB9,  // 12345
+        0x60,  // 12345
+        0x1A,  // Tag (field 3, length delimited)
+        0x03,  // length 3
+        0xA0,  // Tag (fieldnumber 20, varint)
+        0x01,  // Tag (fieldnumber 20, varint)
+        0x01,  // 1
+        0x0C   // Stop Group field number 1
+    );
+
+    const outerMessage = Kernel.fromArrayBuffer(arrayBuffer);
+
+    const messageSet = outerMessage.getMessage(10, MessageSet.fromKernel);
+
+    const message =
+        messageSet.getMessageOrNull(12345, TestMessage.instanceCreator);
+    expect(message.getInt32WithDefault(20)).toBe(1);
+  });
+
+  it('removes duplicates when read', () => {
+    const arrayBuffer = createArrayBuffer(
+        0x52,  // Tag (field:10, length delimited)
+        0x14,  // Length of 20 bytes
+        0x0B,  // Start group fieldnumber 1
+        0x10,  // Tag (field 2, varint)
+        0xB9,  // 12345
+        0x60,  // 12345
+        0x1A,  // Tag (field 3, length delimited)
+        0x03,  // length 3
+        0xA0,  // Tag (fieldnumber 20, varint)
+        0x01,  // Tag (fieldnumber 20, varint)
+        0x1E,  // 30
+        0x0C,  // Stop Group field number 1
+        // second group
+        0x0B,  // Start group fieldnumber 1
+        0x10,  // Tag (field 2, varint)
+        0xB9,  // 12345
+        0x60,  // 12345
+        0x1A,  // Tag (field 3, length delimited)
+        0x03,  // length 3
+        0xA0,  // Tag (fieldnumber 20, varint)
+        0x01,  // Tag (fieldnumber 20, varint)
+        0x01,  // 1
+        0x0C   // Stop Group field number 1
+    );
+
+
+    const outerMessage = Kernel.fromArrayBuffer(arrayBuffer);
+    outerMessage.getMessageAttach(10, MessageSet.fromKernel);
+
+    expect(outerMessage.serialize())
+        .toEqual(createArrayBuffer(
+            0x52,  // Tag (field:10, length delimited)
+            0x0A,  // Length of 10 bytes
+            0x0B,  // Start group fieldnumber 1
+            0x10,  // Tag (field 2, varint)
+            0xB9,  // 12345
+            0x60,  // 12345
+            0x1A,  // Tag (field 3, length delimited)
+            0x03,  // length 3
+            0xA0,  // Tag (fieldnumber 20, varint)
+            0x01,  // Tag (fieldnumber 20, varint)
+            0x01,  // 1
+            0x0C   // Stop Group field number 1
+            ));
+  });
+
+  it('allow for large typeIds', () => {
+    const messageSet = MessageSet.createEmpty();
+    const message = TestMessage.createEmpty();
+    messageSet.setMessage(0xFFFFFFFE >>> 0, message);
+    expect(messageSet.hasMessage(0xFFFFFFFE >>> 0)).toBe(true);
+  });
+});
+
+describe('Optional MessageSet does', () => {
+  // message Bar {
+  //  optional MessageSet mset = 10;
+  //}
+  //
+  // message Foo {
+  //  extend proto2.bridge.MessageSet {
+  //    optional Foo message_set_extension = 12345;
+  //  }
+  //  optional int32 f20 = 20;
+  //}
+
+  it('encode as a field', () => {
+    const fooMessage = Kernel.createEmpty();
+    fooMessage.setInt32(20, 30);
+
+    const messageSet = MessageSet.createEmpty();
+    messageSet.setMessage(12345, TestMessage.instanceCreator(fooMessage));
+
+    const barMessage = Kernel.createEmpty();
+    barMessage.setMessage(10, messageSet);
+
+    expect(barMessage.serialize())
+        .toEqual(createArrayBuffer(
+            0x52,  // Tag (field:10, length delimited)
+            0x0A,  // Length of 10 bytes
+            0x0B,  // Start group fieldnumber 1
+            0x10,  // Tag (field 2, varint)
+            0xB9,  // 12345
+            0x60,  // 12345
+            0x1A,  // Tag (field 3, length delimited)
+            0x03,  // length 3
+            0xA0,  // Tag (fieldnumber 20, varint)
+            0x01,  // Tag (fieldnumber 20, varint)
+            0x1E,  // 30
+            0x0C   // Stop Group field number 1
+            ));
+  });
+
+  it('deserializes', () => {
+    const fooMessage = Kernel.createEmpty();
+    fooMessage.setInt32(20, 30);
+
+    const messageSet = MessageSet.createEmpty();
+    messageSet.setMessage(12345, TestMessage.instanceCreator(fooMessage));
+
+
+    const barMessage = Kernel.createEmpty();
+    barMessage.setMessage(10, messageSet);
+
+    const arrayBuffer = barMessage.serialize();
+
+    const barMessageParsed = Kernel.fromArrayBuffer(arrayBuffer);
+    expect(barMessageParsed.hasFieldNumber(10)).toBe(true);
+
+    const messageSetParsed =
+        barMessageParsed.getMessage(10, MessageSet.fromKernel);
+
+    const fooMessageParsed =
+        messageSetParsed.getMessageOrNull(12345, TestMessage.instanceCreator)
+            .internalGetKernel();
+
+    expect(fooMessageParsed.getInt32WithDefault(20)).toBe(30);
+  });
+});

js/experimental/runtime/kernel/tag.js

@@ -0,0 +1,144 @@
+goog.module('protobuf.binary.tag');
+
+const BufferDecoder = goog.require('protobuf.binary.BufferDecoder');
+const WireType = goog.require('protobuf.binary.WireType');
+const {checkCriticalElementIndex, checkCriticalState} = goog.require('protobuf.internal.checks');
+
+/**
+ * Returns wire type stored in a tag.
+ * Protos store the wire type as the first 3 bit of a tag.
+ * @param {number} tag
+ * @return {!WireType}
+ */
+function tagToWireType(tag) {
+  return /** @type {!WireType} */ (tag & 0x07);
+}
+
+/**
+ * Returns the field number stored in a tag.
+ * Protos store the field number in the upper 29 bits of a 32 bit number.
+ * @param {number} tag
+ * @return {number}
+ */
+function tagToFieldNumber(tag) {
+  return tag >>> 3;
+}
+
+/**
+ * Combines wireType and fieldNumber into a tag.
+ * @param {!WireType} wireType
+ * @param {number} fieldNumber
+ * @return {number}
+ */
+function createTag(wireType, fieldNumber) {
+  return (fieldNumber << 3 | wireType) >>> 0;
+}
+
+/**
+ * Returns the length, in bytes, of the field in the tag stream, less the tag
+ * itself.
+ * Note: This moves the cursor in the bufferDecoder.
+ * @param {!BufferDecoder} bufferDecoder
+ * @param {number} start
+ * @param {!WireType} wireType
+ * @param {number} fieldNumber
+ * @return {number}
+ * @private
+ */
+function getTagLength(bufferDecoder, start, wireType, fieldNumber) {
+  bufferDecoder.setCursor(start);
+  skipField(bufferDecoder, wireType, fieldNumber);
+  return bufferDecoder.cursor() - start;
+}
+
+/**
+ * @param {number} value
+ * @return {number}
+ */
+function get32BitVarintLength(value) {
+  if (value < 0) {
+    return 5;
+  }
+  let size = 1;
+  while (value >= 128) {
+    size++;
+    value >>>= 7;
+  }
+  return size;
+}
+
+/**
+ * Skips over a field.
+ * Note: If the field is a start group the entire group will be skipped, placing
+ * the cursor onto the next field.
+ * @param {!BufferDecoder} bufferDecoder
+ * @param {!WireType} wireType
+ * @param {number} fieldNumber
+ */
+function skipField(bufferDecoder, wireType, fieldNumber) {
+  switch (wireType) {
+    case WireType.VARINT:
+      checkCriticalElementIndex(
+          bufferDecoder.cursor(), bufferDecoder.endIndex());
+      bufferDecoder.skipVarint();
+      return;
+    case WireType.FIXED64:
+      bufferDecoder.skip(8);
+      return;
+    case WireType.DELIMITED:
+      checkCriticalElementIndex(
+          bufferDecoder.cursor(), bufferDecoder.endIndex());
+      const length = bufferDecoder.getUnsignedVarint32();
+      bufferDecoder.skip(length);
+      return;
+    case WireType.START_GROUP:
+      const foundGroup = skipGroup_(bufferDecoder, fieldNumber);
+      checkCriticalState(foundGroup, 'No end group found.');
+      return;
+    case WireType.FIXED32:
+      bufferDecoder.skip(4);
+      return;
+    default:
+      throw new Error(`Unexpected wire type: ${wireType}`);
+  }
+}
+
+/**
+ * Skips over fields until it finds the end of a given group consuming the stop
+ * group tag.
+ * @param {!BufferDecoder} bufferDecoder
+ * @param {number} groupFieldNumber
+ * @return {boolean} Whether the end group tag was found.
+ * @private
+ */
+function skipGroup_(bufferDecoder, groupFieldNumber) {
+  // On a start group we need to keep skipping fields until we find a
+  // corresponding stop group
+  // Note: Since we are calling skipField from here nested groups will be
+  // handled by recursion of this method and thus we will not see a nested
+  // STOP GROUP here unless there is something wrong with the input data.
+  while (bufferDecoder.hasNext()) {
+    const tag = bufferDecoder.getUnsignedVarint32();
+    const wireType = tagToWireType(tag);
+    const fieldNumber = tagToFieldNumber(tag);
+
+    if (wireType === WireType.END_GROUP) {
+      checkCriticalState(
+          groupFieldNumber === fieldNumber,
+          `Expected stop group for fieldnumber ${groupFieldNumber} not found.`);
+      return true;
+    } else {
+      skipField(bufferDecoder, wireType, fieldNumber);
+    }
+  }
+  return false;
+}
+
+exports = {
+  createTag,
+  get32BitVarintLength,
+  getTagLength,
+  skipField,
+  tagToWireType,
+  tagToFieldNumber,
+};

js/experimental/runtime/kernel/tag_test.js

@@ -0,0 +1,221 @@
+/**
+ * @fileoverview Tests for tag.js.
+ */
+goog.module('protobuf.binary.TagTests');
+
+const BufferDecoder = goog.require('protobuf.binary.BufferDecoder');
+const WireType = goog.require('protobuf.binary.WireType');
+const {CHECK_CRITICAL_STATE} = goog.require('protobuf.internal.checks');
+const {createTag, get32BitVarintLength, skipField, tagToFieldNumber, tagToWireType} = goog.require('protobuf.binary.tag');
+
+
+goog.setTestOnly();
+
+/**
+ * @param {...number} bytes
+ * @return {!ArrayBuffer}
+ */
+function createArrayBuffer(...bytes) {
+  return new Uint8Array(bytes).buffer;
+}
+
+describe('skipField', () => {
+  it('skips varints', () => {
+    const bufferDecoder =
+        BufferDecoder.fromArrayBuffer(createArrayBuffer(0x80, 0x00));
+    skipField(bufferDecoder, WireType.VARINT, 1);
+    expect(bufferDecoder.cursor()).toBe(2);
+  });
+
+  it('throws for out of bounds varints', () => {
+    const bufferDecoder =
+        BufferDecoder.fromArrayBuffer(createArrayBuffer(0x80, 0x00));
+    bufferDecoder.setCursor(2);
+    if (CHECK_CRITICAL_STATE) {
+      expect(() => skipField(bufferDecoder, WireType.VARINT, 1)).toThrowError();
+    }
+  });
+
+  it('skips fixed64', () => {
+    const bufferDecoder = BufferDecoder.fromArrayBuffer(
+        createArrayBuffer(0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00));
+    skipField(bufferDecoder, WireType.FIXED64, 1);
+    expect(bufferDecoder.cursor()).toBe(8);
+  });
+
+  it('throws for fixed64 if length is too short', () => {
+    const bufferDecoder =
+        BufferDecoder.fromArrayBuffer(createArrayBuffer(0x80, 0x00));
+    if (CHECK_CRITICAL_STATE) {
+      expect(() => skipField(bufferDecoder, WireType.FIXED64, 1))
+          .toThrowError();
+    }
+  });
+
+  it('skips fixed32', () => {
+    const bufferDecoder = BufferDecoder.fromArrayBuffer(
+        createArrayBuffer(0x80, 0x00, 0x00, 0x00));
+    skipField(bufferDecoder, WireType.FIXED32, 1);
+    expect(bufferDecoder.cursor()).toBe(4);
+  });
+
+  it('throws for fixed32 if length is too short', () => {
+    const bufferDecoder =
+        BufferDecoder.fromArrayBuffer(createArrayBuffer(0x80, 0x00));
+    if (CHECK_CRITICAL_STATE) {
+      expect(() => skipField(bufferDecoder, WireType.FIXED32, 1))
+          .toThrowError();
+    }
+  });
+
+
+  it('skips length delimited', () => {
+    const bufferDecoder = BufferDecoder.fromArrayBuffer(
+        createArrayBuffer(0x03, 0x00, 0x00, 0x00));
+    skipField(bufferDecoder, WireType.DELIMITED, 1);
+    expect(bufferDecoder.cursor()).toBe(4);
+  });
+
+  it('throws for length delimited if length is too short', () => {
+    const bufferDecoder =
+        BufferDecoder.fromArrayBuffer(createArrayBuffer(0x03, 0x00, 0x00));
+    if (CHECK_CRITICAL_STATE) {
+      expect(() => skipField(bufferDecoder, WireType.DELIMITED, 1))
+          .toThrowError();
+    }
+  });
+
+  it('skips groups', () => {
+    const bufferDecoder = BufferDecoder.fromArrayBuffer(
+        createArrayBuffer(0x0B, 0x08, 0x01, 0x0C));
+    bufferDecoder.setCursor(1);
+    skipField(bufferDecoder, WireType.START_GROUP, 1);
+    expect(bufferDecoder.cursor()).toBe(4);
+  });
+
+  it('skips group in group', () => {
+    const buffer = createArrayBuffer(
+        0x0B,        // start outter
+        0x10, 0x01,  // field: 2, value: 1
+        0x0B,        // start inner group
+        0x10, 0x01,  // payload inner group
+        0x0C,        // stop inner group
+        0x0C         // end outter
+    );
+    const bufferDecoder = BufferDecoder.fromArrayBuffer(buffer);
+    bufferDecoder.setCursor(1);
+    skipField(bufferDecoder, WireType.START_GROUP, 1);
+    expect(bufferDecoder.cursor()).toBe(8);
+  });
+
+  it('throws for group if length is too short', () => {
+    // no closing group
+    const bufferDecoder =
+        BufferDecoder.fromArrayBuffer(createArrayBuffer(0x0B, 0x00, 0x00));
+    if (CHECK_CRITICAL_STATE) {
+      expect(() => skipField(bufferDecoder, WireType.START_GROUP, 1))
+          .toThrowError();
+    }
+  });
+});
+
+
+describe('tagToWireType', () => {
+  it('decodes numbers ', () => {
+    // simple numbers
+    expect(tagToWireType(0x00)).toBe(WireType.VARINT);
+    expect(tagToWireType(0x01)).toBe(WireType.FIXED64);
+    expect(tagToWireType(0x02)).toBe(WireType.DELIMITED);
+    expect(tagToWireType(0x03)).toBe(WireType.START_GROUP);
+    expect(tagToWireType(0x04)).toBe(WireType.END_GROUP);
+    expect(tagToWireType(0x05)).toBe(WireType.FIXED32);
+
+    // upper bits should not matter
+    expect(tagToWireType(0x08)).toBe(WireType.VARINT);
+    expect(tagToWireType(0x09)).toBe(WireType.FIXED64);
+    expect(tagToWireType(0x0A)).toBe(WireType.DELIMITED);
+    expect(tagToWireType(0x0B)).toBe(WireType.START_GROUP);
+    expect(tagToWireType(0x0C)).toBe(WireType.END_GROUP);
+    expect(tagToWireType(0x0D)).toBe(WireType.FIXED32);
+
+    // upper bits should not matter
+    expect(tagToWireType(0xF8)).toBe(WireType.VARINT);
+    expect(tagToWireType(0xF9)).toBe(WireType.FIXED64);
+    expect(tagToWireType(0xFA)).toBe(WireType.DELIMITED);
+    expect(tagToWireType(0xFB)).toBe(WireType.START_GROUP);
+    expect(tagToWireType(0xFC)).toBe(WireType.END_GROUP);
+    expect(tagToWireType(0xFD)).toBe(WireType.FIXED32);
+
+    // negative numbers work
+    expect(tagToWireType(-8)).toBe(WireType.VARINT);
+    expect(tagToWireType(-7)).toBe(WireType.FIXED64);
+    expect(tagToWireType(-6)).toBe(WireType.DELIMITED);
+    expect(tagToWireType(-5)).toBe(WireType.START_GROUP);
+    expect(tagToWireType(-4)).toBe(WireType.END_GROUP);
+    expect(tagToWireType(-3)).toBe(WireType.FIXED32);
+  });
+});
+
+describe('tagToFieldNumber', () => {
+  it('returns fieldNumber', () => {
+    expect(tagToFieldNumber(0x08)).toBe(1);
+    expect(tagToFieldNumber(0x09)).toBe(1);
+    expect(tagToFieldNumber(0x10)).toBe(2);
+    expect(tagToFieldNumber(0x12)).toBe(2);
+  });
+});
+
+describe('createTag', () => {
+  it('combines fieldNumber and wireType', () => {
+    expect(createTag(WireType.VARINT, 1)).toBe(0x08);
+    expect(createTag(WireType.FIXED64, 1)).toBe(0x09);
+    expect(createTag(WireType.DELIMITED, 1)).toBe(0x0A);
+    expect(createTag(WireType.START_GROUP, 1)).toBe(0x0B);
+    expect(createTag(WireType.END_GROUP, 1)).toBe(0x0C);
+    expect(createTag(WireType.FIXED32, 1)).toBe(0x0D);
+
+    expect(createTag(WireType.VARINT, 2)).toBe(0x10);
+    expect(createTag(WireType.FIXED64, 2)).toBe(0x11);
+    expect(createTag(WireType.DELIMITED, 2)).toBe(0x12);
+    expect(createTag(WireType.START_GROUP, 2)).toBe(0x13);
+    expect(createTag(WireType.END_GROUP, 2)).toBe(0x14);
+    expect(createTag(WireType.FIXED32, 2)).toBe(0x15);
+
+    expect(createTag(WireType.VARINT, 0x1FFFFFFF)).toBe(0xFFFFFFF8 >>> 0);
+    expect(createTag(WireType.FIXED64, 0x1FFFFFFF)).toBe(0xFFFFFFF9 >>> 0);
+    expect(createTag(WireType.DELIMITED, 0x1FFFFFFF)).toBe(0xFFFFFFFA >>> 0);
+    expect(createTag(WireType.START_GROUP, 0x1FFFFFFF)).toBe(0xFFFFFFFB >>> 0);
+    expect(createTag(WireType.END_GROUP, 0x1FFFFFFF)).toBe(0xFFFFFFFC >>> 0);
+    expect(createTag(WireType.FIXED32, 0x1FFFFFFF)).toBe(0xFFFFFFFD >>> 0);
+  });
+});
+
+describe('get32BitVarintLength', () => {
+  it('length of tag', () => {
+    expect(get32BitVarintLength(0)).toBe(1);
+    expect(get32BitVarintLength(1)).toBe(1);
+    expect(get32BitVarintLength(1)).toBe(1);
+
+    expect(get32BitVarintLength(Math.pow(2, 7) - 1)).toBe(1);
+    expect(get32BitVarintLength(Math.pow(2, 7))).toBe(2);
+
+    expect(get32BitVarintLength(Math.pow(2, 14) - 1)).toBe(2);
+    expect(get32BitVarintLength(Math.pow(2, 14))).toBe(3);
+
+    expect(get32BitVarintLength(Math.pow(2, 21) - 1)).toBe(3);
+    expect(get32BitVarintLength(Math.pow(2, 21))).toBe(4);
+
+    expect(get32BitVarintLength(Math.pow(2, 28) - 1)).toBe(4);
+    expect(get32BitVarintLength(Math.pow(2, 28))).toBe(5);
+
+    expect(get32BitVarintLength(Math.pow(2, 31) - 1)).toBe(5);
+
+    expect(get32BitVarintLength(-1)).toBe(5);
+    expect(get32BitVarintLength(-Math.pow(2, 31))).toBe(5);
+
+    expect(get32BitVarintLength(createTag(WireType.VARINT, 0x1fffffff)))
+        .toBe(5);
+    expect(get32BitVarintLength(createTag(WireType.FIXED32, 0x1fffffff)))
+        .toBe(5);
+  });
+});

js/experimental/runtime/kernel/writer.js

@@ -10,6 +10,7 @@ const Int64 = goog.require('protobuf.Int64');
 const WireType = goog.require('protobuf.binary.WireType');
 const {POLYFILL_TEXT_ENCODING, checkFieldNumber, checkTypeUnsignedInt32, checkWireType} = goog.require('protobuf.internal.checks');
 const {concatenateByteArrays} = goog.require('protobuf.binary.uint8arrays');
+const {createTag, getTagLength} = goog.require('protobuf.binary.tag');
 const {encode} = goog.require('protobuf.binary.textencoding');
 
 /**
@@ -92,8 +93,8 @@ class Writer {
   writeTag(fieldNumber, wireType) {
     checkFieldNumber(fieldNumber);
     checkWireType(wireType);
-    const tag = fieldNumber << 3 | wireType;
-    this.writeUnsignedVarint32_(tag >>> 0);
+    const tag = createTag(wireType, fieldNumber);
+    this.writeUnsignedVarint32_(tag);
   }
 
   /**
@@ -299,6 +300,22 @@ class Writer {
     this.writeSfixed64Value_(value);
   }
 
+  /**
+   * Writes a sfixed64 value field to the buffer.
+   * @param {number} fieldNumber
+   */
+  writeStartGroup(fieldNumber) {
+    this.writeTag(fieldNumber, WireType.START_GROUP);
+  }
+
+  /**
+   * Writes a sfixed64 value field to the buffer.
+   * @param {number} fieldNumber
+   */
+  writeEndGroup(fieldNumber) {
+    this.writeTag(fieldNumber, WireType.END_GROUP);
+  }
+
   /**
    * Writes a uint32 value field to the buffer as a varint without tag.
    * @param {number} value
@@ -430,67 +447,17 @@ class Writer {
    * @param {!BufferDecoder} bufferDecoder
    * @param {number} start
    * @param {!WireType} wireType
+   * @param {number} fieldNumber
    * @package
    */
-  writeBufferDecoder(bufferDecoder, start, wireType) {
+  writeBufferDecoder(bufferDecoder, start, wireType, fieldNumber) {
     this.closeAndStartNewBuffer_();
-    const dataLength = this.getLength_(bufferDecoder, start, wireType);
+    const dataLength =
+        getTagLength(bufferDecoder, start, wireType, fieldNumber);
     this.blocks_.push(
         bufferDecoder.subBufferDecoder(start, dataLength).asUint8Array());
   }
 
-  /**
-   * Returns the length of the data to serialize. Returns -1 when a STOP GROUP
-   * is found.
-   * @param {!BufferDecoder} bufferDecoder
-   * @param {number} start
-   * @param {!WireType} wireType
-   * @return {number}
-   * @private
-   */
-  getLength_(bufferDecoder, start, wireType) {
-    switch (wireType) {
-      case WireType.VARINT:
-        bufferDecoder.setCursor(start);
-        bufferDecoder.skipVarint();
-        return bufferDecoder.cursor() - start;
-      case WireType.FIXED64:
-        return 8;
-      case WireType.DELIMITED:
-        const dataLength = bufferDecoder.getUnsignedVarint32At(start);
-        return dataLength + bufferDecoder.cursor() - start;
-      case WireType.START_GROUP:
-        return this.getGroupLength_(bufferDecoder, start);
-      case WireType.FIXED32:
-        return 4;
-      default:
-        throw new Error(`Invalid wire type: ${wireType}`);
-    }
-  }
-
-  /**
-   * Skips over fields until it finds the end of a given group.
-   * @param {!BufferDecoder} bufferDecoder
-   * @param {number} start
-   * @return {number}
-   * @private
-   */
-  getGroupLength_(bufferDecoder, start) {
-    // On a start group we need to keep skipping fields until we find a
-    // corresponding stop group
-    let cursor = start;
-    while (cursor < bufferDecoder.endIndex()) {
-      const tag = bufferDecoder.getUnsignedVarint32At(cursor);
-      const wireType = /** @type {!WireType} */ (tag & 0x07);
-      if (wireType === WireType.END_GROUP) {
-        return bufferDecoder.cursor() - start;
-      }
-      cursor = bufferDecoder.cursor() +
-          this.getLength_(bufferDecoder, bufferDecoder.cursor(), wireType);
-    }
-    throw new Error('No end group found');
-  }
-
   /**
    * Write the whole bytes as a length delimited field.
    * @param {number} fieldNumber

js/experimental/runtime/kernel/writer_test.js

@@ -148,7 +148,7 @@ describe('Writer.writeBufferDecoder does', () => {
     const expected = createArrayBuffer(
         0x08, /* varint start= */ 0xFF, /* varint end= */ 0x01, 0x08, 0x01);
     writer.writeBufferDecoder(
-        BufferDecoder.fromArrayBuffer(expected), 1, WireType.VARINT);
+        BufferDecoder.fromArrayBuffer(expected), 1, WireType.VARINT, 1);
     const result = writer.getAndResetResultBuffer();
     expect(result).toEqual(arrayBufferSlice(expected, 1, 3));
   });
@@ -159,7 +159,7 @@ describe('Writer.writeBufferDecoder does', () => {
         0x09, /* fixed64 start= */ 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
         /* fixed64 end= */ 0x08, 0x08, 0x01);
     writer.writeBufferDecoder(
-        BufferDecoder.fromArrayBuffer(expected), 1, WireType.FIXED64);
+        BufferDecoder.fromArrayBuffer(expected), 1, WireType.FIXED64, 1);
     const result = writer.getAndResetResultBuffer();
     expect(result).toEqual(arrayBufferSlice(expected, 1, 9));
   });
@@ -170,7 +170,7 @@ describe('Writer.writeBufferDecoder does', () => {
         0xA, /* length= */ 0x03, /* data start= */ 0x01, 0x02,
         /* data end= */ 0x03, 0x08, 0x01);
     writer.writeBufferDecoder(
-        BufferDecoder.fromArrayBuffer(expected), 1, WireType.DELIMITED);
+        BufferDecoder.fromArrayBuffer(expected), 1, WireType.DELIMITED, 1);
     const result = writer.getAndResetResultBuffer();
     expect(result).toEqual(arrayBufferSlice(expected, 1, 5));
   });
@@ -181,7 +181,7 @@ describe('Writer.writeBufferDecoder does', () => {
         0xB, /* group start= */ 0x08, 0x01, /* nested group start= */ 0x0B,
         /* nested group end= */ 0x0C, /* group end= */ 0x0C, 0x08, 0x01);
     writer.writeBufferDecoder(
-        BufferDecoder.fromArrayBuffer(expected), 1, WireType.START_GROUP);
+        BufferDecoder.fromArrayBuffer(expected), 1, WireType.START_GROUP, 1);
     const result = writer.getAndResetResultBuffer();
     expect(result).toEqual(arrayBufferSlice(expected, 1, 6));
   });
@@ -192,7 +192,7 @@ describe('Writer.writeBufferDecoder does', () => {
         0x09, /* fixed64 start= */ 0x01, 0x02, 0x03, /* fixed64 end= */ 0x04,
         0x08, 0x01);
     writer.writeBufferDecoder(
-        BufferDecoder.fromArrayBuffer(expected), 1, WireType.FIXED32);
+        BufferDecoder.fromArrayBuffer(expected), 1, WireType.FIXED32, 1);
     const result = writer.getAndResetResultBuffer();
     expect(result).toEqual(arrayBufferSlice(expected, 1, 5));
   });
@@ -203,7 +203,7 @@ describe('Writer.writeBufferDecoder does', () => {
     const subBuffer = arrayBufferSlice(buffer, 0, 2);
     expect(
         () => writer.writeBufferDecoder(
-            BufferDecoder.fromArrayBuffer(subBuffer), 0, WireType.DELIMITED))
+            BufferDecoder.fromArrayBuffer(subBuffer), 0, WireType.DELIMITED, 1))
         .toThrow();
   });
 });

js/experimental/runtime/testing/binary/test_message.js

@@ -13,6 +13,13 @@ const Kernel = goog.require('protobuf.runtime.Kernel');
  * @implements {InternalMessage}
  */
 class TestMessage {
+  /**
+   * @return {!TestMessage}
+   */
+  static createEmpty() {
+    return TestMessage.instanceCreator(Kernel.createEmpty());
+  }
+
   /**
    * @param {!Kernel} kernel
    * @return {!TestMessage}
@@ -31,7 +38,6 @@ class TestMessage {
 
   /**
    * @override
-   * @package
    * @return {!Kernel}
    */
   internalGetKernel() {
@@ -1760,4 +1766,4 @@ class TestMessage {
   }
 }
 
-exports = TestMessage;
+exports = TestMessage;

protobuf.bzl

@@ -432,7 +432,7 @@ def py_proto_library(
       protoc: the label of the protocol compiler to generate the sources.
       use_grpc_plugin: a flag to indicate whether to call the Python C++ plugin
           when processing the proto files.
-      **kargs: other keyword arguments that are passed to cc_library.
+      **kargs: other keyword arguments that are passed to py_library.
 
     """
     outs = _PyOuts(srcs, use_grpc_plugin)

python/google/protobuf/internal/test_proto3_optional.proto

@@ -30,10 +30,7 @@
 
 syntax = "proto3";
 
-package protobuf_unittest;
-
-option java_multiple_files = true;
-option java_package = "com.google.protobuf.testing.proto";
+package google.protobuf.python.internal;
 
 message TestProto3Optional {
   message NestedMessage {

src/google/protobuf/api.pb.h

@@ -1063,7 +1063,9 @@ inline void Api::unsafe_arena_set_allocated_source_context(
   // @@protoc_insertion_point(field_unsafe_arena_set_allocated:google.protobuf.Api.source_context)
 }
 inline PROTOBUF_NAMESPACE_ID::SourceContext* Api::release_source_context() {
-  auto temp = unsafe_arena_release_source_context();
+  
+  PROTOBUF_NAMESPACE_ID::SourceContext* temp = source_context_;
+  source_context_ = nullptr;
   if (GetArena() != nullptr) {
     temp = ::PROTOBUF_NAMESPACE_ID::internal::DuplicateIfNonNull(temp);
   }

src/google/protobuf/compiler/cpp/cpp_message.cc

@@ -614,7 +614,6 @@ MessageGenerator::MessageGenerator(
     }
   }
 
-
   if (!has_bit_indices_.empty()) {
     field_generators_.SetHasBitIndices(has_bit_indices_);
   }

src/google/protobuf/compiler/cpp/cpp_message_field.cc

@@ -199,7 +199,10 @@ void MessageFieldGenerator::GenerateInlineAccessorDefinitions(
         "}\n");
     format(
         "inline $type$* $classname$::$release_name$() {\n"
-        "  auto temp = unsafe_arena_release_$name$();\n"
+        "$type_reference_function$"
+        "  $clear_hasbit$\n"
+        "  $type$* temp = $casted_member$;\n"
+        "  $name$_ = nullptr;\n"
         "  if (GetArena() != nullptr) {\n"
         "    temp = ::$proto_ns$::internal::DuplicateIfNonNull(temp);\n"
         "  }\n"

src/google/protobuf/compiler/java/java_enum_field.cc

@@ -225,6 +225,7 @@ void ImmutableEnumFieldGenerator::GenerateBuilderMembers(
     printer->Print(variables_,
                    "$deprecation$public Builder "
                    "${$set$capitalized_name$Value$}$(int value) {\n"
+                   "  $set_has_field_bit_builder$\n"
                    "  $name$_ = value;\n"
                    "  $on_changed$\n"
                    "  return this;\n"

src/google/protobuf/compiler/plugin.pb.h

@@ -1441,7 +1441,9 @@ inline void CodeGeneratorRequest::unsafe_arena_set_allocated_compiler_version(
   // @@protoc_insertion_point(field_unsafe_arena_set_allocated:google.protobuf.compiler.CodeGeneratorRequest.compiler_version)
 }
 inline PROTOBUF_NAMESPACE_ID::compiler::Version* CodeGeneratorRequest::release_compiler_version() {
-  auto temp = unsafe_arena_release_compiler_version();
+  _has_bits_[0] &= ~0x00000002u;
+  PROTOBUF_NAMESPACE_ID::compiler::Version* temp = compiler_version_;
+  compiler_version_ = nullptr;
   if (GetArena() != nullptr) {
     temp = ::PROTOBUF_NAMESPACE_ID::internal::DuplicateIfNonNull(temp);
   }

src/google/protobuf/descriptor.pb.h

@@ -7484,7 +7484,9 @@ inline void FileDescriptorProto::unsafe_arena_set_allocated_options(
   // @@protoc_insertion_point(field_unsafe_arena_set_allocated:google.protobuf.FileDescriptorProto.options)
 }
 inline PROTOBUF_NAMESPACE_ID::FileOptions* FileDescriptorProto::release_options() {
-  auto temp = unsafe_arena_release_options();
+  _has_bits_[0] &= ~0x00000008u;
+  PROTOBUF_NAMESPACE_ID::FileOptions* temp = options_;
+  options_ = nullptr;
   if (GetArena() != nullptr) {
     temp = ::PROTOBUF_NAMESPACE_ID::internal::DuplicateIfNonNull(temp);
   }
@@ -7565,7 +7567,9 @@ inline void FileDescriptorProto::unsafe_arena_set_allocated_source_code_info(
   // @@protoc_insertion_point(field_unsafe_arena_set_allocated:google.protobuf.FileDescriptorProto.source_code_info)
 }
 inline PROTOBUF_NAMESPACE_ID::SourceCodeInfo* FileDescriptorProto::release_source_code_info() {
-  auto temp = unsafe_arena_release_source_code_info();
+  _has_bits_[0] &= ~0x00000010u;
+  PROTOBUF_NAMESPACE_ID::SourceCodeInfo* temp = source_code_info_;
+  source_code_info_ = nullptr;
   if (GetArena() != nullptr) {
     temp = ::PROTOBUF_NAMESPACE_ID::internal::DuplicateIfNonNull(temp);
   }
@@ -7799,7 +7803,9 @@ inline void DescriptorProto_ExtensionRange::unsafe_arena_set_allocated_options(
   // @@protoc_insertion_point(field_unsafe_arena_set_allocated:google.protobuf.DescriptorProto.ExtensionRange.options)
 }
 inline PROTOBUF_NAMESPACE_ID::ExtensionRangeOptions* DescriptorProto_ExtensionRange::release_options() {
-  auto temp = unsafe_arena_release_options();
+  _has_bits_[0] &= ~0x00000001u;
+  PROTOBUF_NAMESPACE_ID::ExtensionRangeOptions* temp = options_;
+  options_ = nullptr;
   if (GetArena() != nullptr) {
     temp = ::PROTOBUF_NAMESPACE_ID::internal::DuplicateIfNonNull(temp);
   }
@@ -8271,7 +8277,9 @@ inline void DescriptorProto::unsafe_arena_set_allocated_options(
   // @@protoc_insertion_point(field_unsafe_arena_set_allocated:google.protobuf.DescriptorProto.options)
 }
 inline PROTOBUF_NAMESPACE_ID::MessageOptions* DescriptorProto::release_options() {
-  auto temp = unsafe_arena_release_options();
+  _has_bits_[0] &= ~0x00000002u;
+  PROTOBUF_NAMESPACE_ID::MessageOptions* temp = options_;
+  options_ = nullptr;
   if (GetArena() != nullptr) {
     temp = ::PROTOBUF_NAMESPACE_ID::internal::DuplicateIfNonNull(temp);
   }
@@ -9091,7 +9099,9 @@ inline void FieldDescriptorProto::unsafe_arena_set_allocated_options(
   // @@protoc_insertion_point(field_unsafe_arena_set_allocated:google.protobuf.FieldDescriptorProto.options)
 }
 inline PROTOBUF_NAMESPACE_ID::FieldOptions* FieldDescriptorProto::release_options() {
-  auto temp = unsafe_arena_release_options();
+  _has_bits_[0] &= ~0x00000020u;
+  PROTOBUF_NAMESPACE_ID::FieldOptions* temp = options_;
+  options_ = nullptr;
   if (GetArena() != nullptr) {
     temp = ::PROTOBUF_NAMESPACE_ID::internal::DuplicateIfNonNull(temp);
   }
@@ -9297,7 +9307,9 @@ inline void OneofDescriptorProto::unsafe_arena_set_allocated_options(
   // @@protoc_insertion_point(field_unsafe_arena_set_allocated:google.protobuf.OneofDescriptorProto.options)
 }
 inline PROTOBUF_NAMESPACE_ID::OneofOptions* OneofDescriptorProto::release_options() {
-  auto temp = unsafe_arena_release_options();
+  _has_bits_[0] &= ~0x00000002u;
+  PROTOBUF_NAMESPACE_ID::OneofOptions* temp = options_;
+  options_ = nullptr;
   if (GetArena() != nullptr) {
     temp = ::PROTOBUF_NAMESPACE_ID::internal::DuplicateIfNonNull(temp);
   }
@@ -9574,7 +9586,9 @@ inline void EnumDescriptorProto::unsafe_arena_set_allocated_options(
   // @@protoc_insertion_point(field_unsafe_arena_set_allocated:google.protobuf.EnumDescriptorProto.options)
 }
 inline PROTOBUF_NAMESPACE_ID::EnumOptions* EnumDescriptorProto::release_options() {
-  auto temp = unsafe_arena_release_options();
+  _has_bits_[0] &= ~0x00000002u;
+  PROTOBUF_NAMESPACE_ID::EnumOptions* temp = options_;
+  options_ = nullptr;
   if (GetArena() != nullptr) {
     temp = ::PROTOBUF_NAMESPACE_ID::internal::DuplicateIfNonNull(temp);
   }
@@ -9893,7 +9907,9 @@ inline void EnumValueDescriptorProto::unsafe_arena_set_allocated_options(
   // @@protoc_insertion_point(field_unsafe_arena_set_allocated:google.protobuf.EnumValueDescriptorProto.options)
 }
 inline PROTOBUF_NAMESPACE_ID::EnumValueOptions* EnumValueDescriptorProto::release_options() {
-  auto temp = unsafe_arena_release_options();
+  _has_bits_[0] &= ~0x00000002u;
+  PROTOBUF_NAMESPACE_ID::EnumValueOptions* temp = options_;
+  options_ = nullptr;
   if (GetArena() != nullptr) {
     temp = ::PROTOBUF_NAMESPACE_ID::internal::DuplicateIfNonNull(temp);
   }
@@ -10110,7 +10126,9 @@ inline void ServiceDescriptorProto::unsafe_arena_set_allocated_options(
   // @@protoc_insertion_point(field_unsafe_arena_set_allocated:google.protobuf.ServiceDescriptorProto.options)
 }
 inline PROTOBUF_NAMESPACE_ID::ServiceOptions* ServiceDescriptorProto::release_options() {
-  auto temp = unsafe_arena_release_options();
+  _has_bits_[0] &= ~0x00000002u;
+  PROTOBUF_NAMESPACE_ID::ServiceOptions* temp = options_;
+  options_ = nullptr;
   if (GetArena() != nullptr) {
     temp = ::PROTOBUF_NAMESPACE_ID::internal::DuplicateIfNonNull(temp);
   }
@@ -10474,7 +10492,9 @@ inline void MethodDescriptorProto::unsafe_arena_set_allocated_options(
   // @@protoc_insertion_point(field_unsafe_arena_set_allocated:google.protobuf.MethodDescriptorProto.options)
 }
 inline PROTOBUF_NAMESPACE_ID::MethodOptions* MethodDescriptorProto::release_options() {
-  auto temp = unsafe_arena_release_options();
+  _has_bits_[0] &= ~0x00000008u;
+  PROTOBUF_NAMESPACE_ID::MethodOptions* temp = options_;
+  options_ = nullptr;
   if (GetArena() != nullptr) {
     temp = ::PROTOBUF_NAMESPACE_ID::internal::DuplicateIfNonNull(temp);
   }

src/google/protobuf/descriptor_database.cc

@@ -146,6 +146,53 @@ bool SimpleDescriptorDatabase::DescriptorIndex<Value>::AddFile(
   return true;
 }
 
+namespace {
+
+// Returns true if and only if all characters in the name are alphanumerics,
+// underscores, or periods.
+bool ValidateSymbolName(StringPiece name) {
+  for (char c : name) {
+    // I don't trust ctype.h due to locales.  :(
+    if (c != '.' && c != '_' && (c < '0' || c > '9') && (c < 'A' || c > 'Z') &&
+        (c < 'a' || c > 'z')) {
+      return false;
+    }
+  }
+  return true;
+}
+
+// Find the last key in the container which sorts less than or equal to the
+// symbol name.  Since upper_bound() returns the *first* key that sorts
+// *greater* than the input, we want the element immediately before that.
+template <typename Container, typename Key>
+typename Container::const_iterator FindLastLessOrEqual(Container* container,
+                                                       const Key& key) {
+  auto iter = container->upper_bound(key);
+  if (iter != container->begin()) --iter;
+  return iter;
+}
+
+// As above, but using std::upper_bound instead.
+template <typename Container, typename Key, typename Cmp>
+typename Container::const_iterator FindLastLessOrEqual(Container* container,
+                                                       const Key& key,
+                                                       const Cmp& cmp) {
+  auto iter = std::upper_bound(container->begin(), container->end(), key, cmp);
+  if (iter != container->begin()) --iter;
+  return iter;
+}
+
+// True if either the arguments are equal or super_symbol identifies a
+// parent symbol of sub_symbol (e.g. "foo.bar" is a parent of
+// "foo.bar.baz", but not a parent of "foo.barbaz").
+bool IsSubSymbol(StringPiece sub_symbol, StringPiece super_symbol) {
+  return sub_symbol == super_symbol ||
+         (HasPrefixString(super_symbol, sub_symbol) &&
+          super_symbol[sub_symbol.size()] == '.');
+}
+
+}  // namespace
+
 template <typename Value>
 bool SimpleDescriptorDatabase::DescriptorIndex<Value>::AddSymbol(
     const std::string& name, Value value) {
@@ -161,8 +208,7 @@ bool SimpleDescriptorDatabase::DescriptorIndex<Value>::AddSymbol(
 
   // Try to look up the symbol to make sure a super-symbol doesn't already
   // exist.
-  typename std::map<std::string, Value>::iterator iter =
-      FindLastLessOrEqual(name);
+  auto iter = FindLastLessOrEqual(&by_symbol_, name);
 
   if (iter == by_symbol_.end()) {
     // Apparently the map is currently empty.  Just insert and be done with it.
@@ -252,8 +298,7 @@ Value SimpleDescriptorDatabase::DescriptorIndex<Value>::FindFile(
 template <typename Value>
 Value SimpleDescriptorDatabase::DescriptorIndex<Value>::FindSymbol(
     const std::string& name) {
-  typename std::map<std::string, Value>::iterator iter =
-      FindLastLessOrEqual(name);
+  auto iter = FindLastLessOrEqual(&by_symbol_, name);
 
   return (iter != by_symbol_.end() && IsSubSymbol(iter->first, name))
              ? iter->second
@@ -294,40 +339,6 @@ void SimpleDescriptorDatabase::DescriptorIndex<Value>::FindAllFileNames(
   }
 }
 
-template <typename Value>
-typename std::map<std::string, Value>::iterator
-SimpleDescriptorDatabase::DescriptorIndex<Value>::FindLastLessOrEqual(
-    const std::string& name) {
-  // Find the last key in the map which sorts less than or equal to the
-  // symbol name.  Since upper_bound() returns the *first* key that sorts
-  // *greater* than the input, we want the element immediately before that.
-  typename std::map<std::string, Value>::iterator iter =
-      by_symbol_.upper_bound(name);
-  if (iter != by_symbol_.begin()) --iter;
-  return iter;
-}
-
-template <typename Value>
-bool SimpleDescriptorDatabase::DescriptorIndex<Value>::IsSubSymbol(
-    const std::string& sub_symbol, const std::string& super_symbol) {
-  return sub_symbol == super_symbol ||
-         (HasPrefixString(super_symbol, sub_symbol) &&
-          super_symbol[sub_symbol.size()] == '.');
-}
-
-template <typename Value>
-bool SimpleDescriptorDatabase::DescriptorIndex<Value>::ValidateSymbolName(
-    const std::string& name) {
-  for (int i = 0; i < name.size(); i++) {
-    // I don't trust ctype.h due to locales.  :(
-    if (name[i] != '.' && name[i] != '_' && (name[i] < '0' || name[i] > '9') &&
-        (name[i] < 'A' || name[i] > 'Z') && (name[i] < 'a' || name[i] > 'z')) {
-      return false;
-    }
-  }
-  return true;
-}
-
 // -------------------------------------------------------------------
 
 bool SimpleDescriptorDatabase::Add(const FileDescriptorProto& file) {
@@ -378,19 +389,88 @@ bool SimpleDescriptorDatabase::MaybeCopy(const FileDescriptorProto* file,
 
 // -------------------------------------------------------------------
 
-EncodedDescriptorDatabase::EncodedDescriptorDatabase() {}
-EncodedDescriptorDatabase::~EncodedDescriptorDatabase() {
-  for (int i = 0; i < files_to_delete_.size(); i++) {
-    operator delete(files_to_delete_[i]);
-  }
-}
+class EncodedDescriptorDatabase::DescriptorIndex {
+ public:
+  using Value = std::pair<const void*, int>;
+  // Helpers to recursively add particular descriptors and all their contents
+  // to the index.
+  bool AddFile(const FileDescriptorProto& file, Value value);
+
+  Value FindFile(StringPiece filename);
+  Value FindSymbol(StringPiece name);
+  Value FindSymbolOnlyFlat(StringPiece name) const;
+  Value FindExtension(StringPiece containing_type, int field_number);
+  bool FindAllExtensionNumbers(StringPiece containing_type,
+                               std::vector<int>* output);
+  void FindAllFileNames(std::vector<std::string>* output) const;
+
+ private:
+  friend class EncodedDescriptorDatabase;
+
+  bool AddSymbol(StringPiece name, Value value);
+  bool AddNestedExtensions(StringPiece filename,
+                           const DescriptorProto& message_type, Value value);
+  bool AddExtension(StringPiece filename,
+                    const FieldDescriptorProto& field, Value value);
+
+  // All the maps below have two representations:
+  //  - a std::set<> where we insert initially.
+  //  - a std::vector<> where we flatten the structure on demand.
+  // The initial tree helps avoid O(N) behavior of inserting into a sorted
+  // vector, while the vector reduces the heap requirements of the data
+  // structure.
+
+  void EnsureFlat();
+
+  struct Entry {
+    std::string name;
+    Value data;
+  };
+  struct Compare {
+    bool operator()(const Entry& a, const Entry& b) const {
+      return a.name < b.name;
+    }
+    bool operator()(const Entry& a, StringPiece b) const {
+      return a.name < b;
+    }
+    bool operator()(StringPiece a, const Entry& b) const {
+      return a < b.name;
+    }
+  };
+  std::set<Entry, Compare> by_name_;
+  std::vector<Entry> by_name_flat_;
+  std::set<Entry, Compare> by_symbol_;
+  std::vector<Entry> by_symbol_flat_;
+  struct ExtensionEntry {
+    std::string extendee;
+    int extension_number;
+    Value data;
+  };
+  struct ExtensionCompare {
+    bool operator()(const ExtensionEntry& a, const ExtensionEntry& b) const {
+      return std::tie(a.extendee, a.extension_number) <
+             std::tie(b.extendee, b.extension_number);
+    }
+    bool operator()(const ExtensionEntry& a,
+                    std::tuple<StringPiece, int> b) const {
+      return std::tie(a.extendee, a.extension_number) < b;
+    }
+    bool operator()(std::tuple<StringPiece, int> a,
+                    const ExtensionEntry& b) const {
+      return a < std::tie(b.extendee, b.extension_number);
+    }
+  };
+  std::set<ExtensionEntry, ExtensionCompare> by_extension_;
+  std::vector<ExtensionEntry> by_extension_flat_;
+};
 
 bool EncodedDescriptorDatabase::Add(const void* encoded_file_descriptor,
                                     int size) {
   google::protobuf::Arena arena;
   auto* file = google::protobuf::Arena::CreateMessage<FileDescriptorProto>(&arena);
   if (file->ParseFromArray(encoded_file_descriptor, size)) {
-    return index_.AddFile(*file, std::make_pair(encoded_file_descriptor, size));
+    return index_->AddFile(*file,
+                           std::make_pair(encoded_file_descriptor, size));
   } else {
     GOOGLE_LOG(ERROR) << "Invalid file descriptor data passed to "
                   "EncodedDescriptorDatabase::Add().";
@@ -408,22 +488,22 @@ bool EncodedDescriptorDatabase::AddCopy(const void* encoded_file_descriptor,
 
 bool EncodedDescriptorDatabase::FindFileByName(const std::string& filename,
                                                FileDescriptorProto* output) {
-  return MaybeParse(index_.FindFile(filename), output);
+  return MaybeParse(index_->FindFile(filename), output);
 }
 
 bool EncodedDescriptorDatabase::FindFileContainingSymbol(
     const std::string& symbol_name, FileDescriptorProto* output) {
-  return MaybeParse(index_.FindSymbol(symbol_name), output);
+  return MaybeParse(index_->FindSymbol(symbol_name), output);
 }
 
 bool EncodedDescriptorDatabase::FindNameOfFileContainingSymbol(
     const std::string& symbol_name, std::string* output) {
-  std::pair<const void*, int> encoded_file = index_.FindSymbol(symbol_name);
+  auto encoded_file = index_->FindSymbol(symbol_name);
   if (encoded_file.first == NULL) return false;
 
   // Optimization:  The name should be the first field in the encoded message.
   //   Try to just read it directly.
-  io::CodedInputStream input(reinterpret_cast<const uint8*>(encoded_file.first),
+  io::CodedInputStream input(static_cast<const uint8*>(encoded_file.first),
                              encoded_file.second);
 
   const uint32 kNameTag = internal::WireFormatLite::MakeTag(
@@ -447,18 +527,245 @@ bool EncodedDescriptorDatabase::FindNameOfFileContainingSymbol(
 bool EncodedDescriptorDatabase::FindFileContainingExtension(
     const std::string& containing_type, int field_number,
     FileDescriptorProto* output) {
-  return MaybeParse(index_.FindExtension(containing_type, field_number),
+  return MaybeParse(index_->FindExtension(containing_type, field_number),
                     output);
 }
 
 bool EncodedDescriptorDatabase::FindAllExtensionNumbers(
     const std::string& extendee_type, std::vector<int>* output) {
-  return index_.FindAllExtensionNumbers(extendee_type, output);
+  return index_->FindAllExtensionNumbers(extendee_type, output);
+}
+
+bool EncodedDescriptorDatabase::DescriptorIndex::AddFile(
+    const FileDescriptorProto& file, Value value) {
+  if (!InsertIfNotPresent(&by_name_, Entry{file.name(), value}) ||
+      std::binary_search(by_name_flat_.begin(), by_name_flat_.end(),
+                         file.name(), by_name_.key_comp())) {
+    GOOGLE_LOG(ERROR) << "File already exists in database: " << file.name();
+    return false;
+  }
+
+  // We must be careful here -- calling file.package() if file.has_package() is
+  // false could access an uninitialized static-storage variable if we are being
+  // run at startup time.
+  std::string path = file.has_package() ? file.package() : std::string();
+  if (!path.empty()) path += '.';
+
+  for (const auto& message_type : file.message_type()) {
+    if (!AddSymbol(path + message_type.name(), value)) return false;
+    if (!AddNestedExtensions(file.name(), message_type, value)) return false;
+  }
+  for (const auto& enum_type : file.enum_type()) {
+    if (!AddSymbol(path + enum_type.name(), value)) return false;
+  }
+  for (const auto& extension : file.extension()) {
+    if (!AddSymbol(path + extension.name(), value)) return false;
+    if (!AddExtension(file.name(), extension, value)) return false;
+  }
+  for (const auto& service : file.service()) {
+    if (!AddSymbol(path + service.name(), value)) return false;
+  }
+
+  return true;
 }
 
+template <typename Iter, typename Iter2>
+static bool CheckForMutualSubsymbols(StringPiece symbol_name, Iter* iter,
+                                     Iter2 end) {
+  if (*iter != end) {
+    if (IsSubSymbol((*iter)->name, symbol_name)) {
+      GOOGLE_LOG(ERROR) << "Symbol name \"" << symbol_name
+                 << "\" conflicts with the existing symbol \"" << (*iter)->name
+                 << "\".";
+      return false;
+    }
+
+    // OK, that worked.  Now we have to make sure that no symbol in the map is
+    // a sub-symbol of the one we are inserting.  The only symbol which could
+    // be so is the first symbol that is greater than the new symbol.  Since
+    // |iter| points at the last symbol that is less than or equal, we just have
+    // to increment it.
+    ++*iter;
+
+    if (*iter != end && IsSubSymbol(symbol_name, (*iter)->name)) {
+      GOOGLE_LOG(ERROR) << "Symbol name \"" << symbol_name
+                 << "\" conflicts with the existing symbol \"" << (*iter)->name
+                 << "\".";
+      return false;
+    }
+  }
+  return true;
+}
+
+bool EncodedDescriptorDatabase::DescriptorIndex::AddSymbol(
+    StringPiece name, Value value) {
+  // We need to make sure not to violate our map invariant.
+
+  // If the symbol name is invalid it could break our lookup algorithm (which
+  // relies on the fact that '.' sorts before all other characters that are
+  // valid in symbol names).
+  if (!ValidateSymbolName(name)) {
+    GOOGLE_LOG(ERROR) << "Invalid symbol name: " << name;
+    return false;
+  }
+
+  Entry entry = {std::string(name), value};
+
+  auto iter = FindLastLessOrEqual(&by_symbol_, entry);
+  if (!CheckForMutualSubsymbols(name, &iter, by_symbol_.end())) {
+    return false;
+  }
+
+  // Same, but on by_symbol_flat_
+  auto flat_iter =
+      FindLastLessOrEqual(&by_symbol_flat_, name, by_symbol_.key_comp());
+  if (!CheckForMutualSubsymbols(name, &flat_iter, by_symbol_flat_.end())) {
+    return false;
+  }
+
+  // OK, no conflicts.
+
+  // Insert the new symbol using the iterator as a hint, the new entry will
+  // appear immediately before the one the iterator is pointing at.
+  by_symbol_.insert(iter, std::move(entry));
+
+  return true;
+}
+
+bool EncodedDescriptorDatabase::DescriptorIndex::AddNestedExtensions(
+    StringPiece filename, const DescriptorProto& message_type,
+    Value value) {
+  for (const auto& nested_type : message_type.nested_type()) {
+    if (!AddNestedExtensions(filename, nested_type, value)) return false;
+  }
+  for (const auto& extension : message_type.extension()) {
+    if (!AddExtension(filename, extension, value)) return false;
+  }
+  return true;
+}
+
+bool EncodedDescriptorDatabase::DescriptorIndex::AddExtension(
+    StringPiece filename, const FieldDescriptorProto& field,
+    Value value) {
+  if (!field.extendee().empty() && field.extendee()[0] == '.') {
+    // The extension is fully-qualified.  We can use it as a lookup key in
+    // the by_symbol_ table.
+    if (!InsertIfNotPresent(&by_extension_,
+                                 ExtensionEntry{field.extendee().substr(1),
+                                                field.number(), value}) ||
+        std::binary_search(
+            by_extension_flat_.begin(), by_extension_flat_.end(),
+            std::make_pair(field.extendee().substr(1), field.number()),
+            by_extension_.key_comp())) {
+      GOOGLE_LOG(ERROR) << "Extension conflicts with extension already in database: "
+                    "extend "
+                 << field.extendee() << " { " << field.name() << " = "
+                 << field.number() << " } from:" << filename;
+      return false;
+    }
+  } else {
+    // Not fully-qualified.  We can't really do anything here, unfortunately.
+    // We don't consider this an error, though, because the descriptor is
+    // valid.
+  }
+  return true;
+}
+
+std::pair<const void*, int>
+EncodedDescriptorDatabase::DescriptorIndex::FindSymbol(StringPiece name) {
+  EnsureFlat();
+  return FindSymbolOnlyFlat(name);
+}
+
+std::pair<const void*, int>
+EncodedDescriptorDatabase::DescriptorIndex::FindSymbolOnlyFlat(
+    StringPiece name) const {
+  auto iter =
+      FindLastLessOrEqual(&by_symbol_flat_, name, by_symbol_.key_comp());
+
+  return iter != by_symbol_flat_.end() && IsSubSymbol(iter->name, name)
+             ? iter->data
+             : Value();
+}
+
+std::pair<const void*, int>
+EncodedDescriptorDatabase::DescriptorIndex::FindExtension(
+    StringPiece containing_type, int field_number) {
+  EnsureFlat();
+
+  auto it = std::lower_bound(
+      by_extension_flat_.begin(), by_extension_flat_.end(),
+      std::make_tuple(containing_type, field_number), by_extension_.key_comp());
+  return it == by_extension_flat_.end() || it->extendee != containing_type ||
+                 it->extension_number != field_number
+             ? std::make_pair(nullptr, 0)
+             : it->data;
+}
+
+template <typename T, typename Less>
+static void MergeIntoFlat(std::set<T, Less>* s, std::vector<T>* flat) {
+  if (s->empty()) return;
+  std::vector<T> new_flat(s->size() + flat->size());
+  std::merge(s->begin(), s->end(), flat->begin(), flat->end(), &new_flat[0],
+             s->key_comp());
+  *flat = std::move(new_flat);
+  s->clear();
+}
+
+void EncodedDescriptorDatabase::DescriptorIndex::EnsureFlat() {
+  // Merge each of the sets into their flat counterpart.
+  MergeIntoFlat(&by_name_, &by_name_flat_);
+  MergeIntoFlat(&by_symbol_, &by_symbol_flat_);
+  MergeIntoFlat(&by_extension_, &by_extension_flat_);
+}
+
+bool EncodedDescriptorDatabase::DescriptorIndex::FindAllExtensionNumbers(
+    StringPiece containing_type, std::vector<int>* output) {
+  EnsureFlat();
+
+  bool success = false;
+  auto it = std::lower_bound(
+      by_extension_flat_.begin(), by_extension_flat_.end(),
+      std::make_tuple(containing_type, 0), by_extension_.key_comp());
+  for (; it != by_extension_flat_.end() && it->extendee == containing_type;
+       ++it) {
+    output->push_back(it->extension_number);
+    success = true;
+  }
+
+  return success;
+}
+
+void EncodedDescriptorDatabase::DescriptorIndex::FindAllFileNames(
+    std::vector<std::string>* output) const {
+  output->resize(by_name_.size() + by_name_flat_.size());
+  int i = 0;
+  for (const auto& entry : by_name_) {
+    (*output)[i] = entry.name;
+    i++;
+  }
+  for (const auto& entry : by_name_flat_) {
+    (*output)[i] = entry.name;
+    i++;
+  }
+}
+
+std::pair<const void*, int>
+EncodedDescriptorDatabase::DescriptorIndex::FindFile(
+    StringPiece filename) {
+  EnsureFlat();
+
+  auto it = std::lower_bound(by_name_flat_.begin(), by_name_flat_.end(),
+                             filename, by_name_.key_comp());
+  return it == by_name_flat_.end() || it->name != filename
+             ? std::make_pair(nullptr, 0)
+             : it->data;
+}
+
+
 bool EncodedDescriptorDatabase::FindAllFileNames(
     std::vector<std::string>* output) {
-  index_.FindAllFileNames(output);
+  index_->FindAllFileNames(output);
   return true;
 }
 
@@ -468,6 +775,15 @@ bool EncodedDescriptorDatabase::MaybeParse(
   return output->ParseFromArray(encoded_file.first, encoded_file.second);
 }
 
+EncodedDescriptorDatabase::EncodedDescriptorDatabase()
+    : index_(new DescriptorIndex()) {}
+
+EncodedDescriptorDatabase::~EncodedDescriptorDatabase() {
+  for (void* p : files_to_delete_) {
+    operator delete(p);
+  }
+}
+
 // ===================================================================
 
 DescriptorPoolDatabase::DescriptorPoolDatabase(const DescriptorPool& pool)

src/google/protobuf/descriptor_database.h

@@ -266,21 +266,6 @@ class PROTOBUF_EXPORT SimpleDescriptorDatabase : public DescriptorDatabase {
     // That symbol cannot be a super-symbol of the search key since if it were,
     // then it would be a match, and we're assuming the match key doesn't exist.
     // Therefore, step 2 will correctly return no match.
-
-    // Find the last entry in the by_symbol_ map whose key is less than or
-    // equal to the given name.
-    typename std::map<std::string, Value>::iterator FindLastLessOrEqual(
-        const std::string& name);
-
-    // True if either the arguments are equal or super_symbol identifies a
-    // parent symbol of sub_symbol (e.g. "foo.bar" is a parent of
-    // "foo.bar.baz", but not a parent of "foo.barbaz").
-    bool IsSubSymbol(const std::string& sub_symbol,
-                     const std::string& super_symbol);
-
-    // Returns true if and only if all characters in the name are alphanumerics,
-    // underscores, or periods.
-    bool ValidateSymbolName(const std::string& name);
   };
 
   DescriptorIndex<const FileDescriptorProto*> index_;
@@ -332,8 +317,10 @@ class PROTOBUF_EXPORT EncodedDescriptorDatabase : public DescriptorDatabase {
   bool FindAllFileNames(std::vector<std::string>* output) override;
 
  private:
-  SimpleDescriptorDatabase::DescriptorIndex<std::pair<const void*, int> >
-      index_;
+  class DescriptorIndex;
+  // Keep DescriptorIndex by pointer to hide the implementation to keep a
+  // cleaner header.
+  std::unique_ptr<DescriptorIndex> index_;
   std::vector<void*> files_to_delete_;
 
   // If encoded_file.first is non-NULL, parse the data into *output and return

src/google/protobuf/io/printer.cc

@@ -305,7 +305,7 @@ void Printer::FormatInternal(const std::vector<std::string>& args,
 }
 
 const char* Printer::WriteVariable(
-    const std::vector<string>& args,
+    const std::vector<std::string>& args,
     const std::map<std::string, std::string>& vars, const char* format,
     int* arg_index, std::vector<AnnotationCollector::Annotation>* annotations) {
   auto start = format;

src/google/protobuf/io/printer_unittest.cc

@@ -573,7 +573,7 @@ TEST(Printer, WriteFailurePartial) {
   EXPECT_TRUE(printer.failed());
 
   // Buffer should contain the first 17 bytes written.
-  EXPECT_EQ("0123456789abcdef<", string(buffer, sizeof(buffer)));
+  EXPECT_EQ("0123456789abcdef<", std::string(buffer, sizeof(buffer)));
 }
 
 TEST(Printer, WriteFailureExact) {
@@ -595,7 +595,7 @@ TEST(Printer, WriteFailureExact) {
   EXPECT_TRUE(printer.failed());
 
   // Buffer should contain the first 16 bytes written.
-  EXPECT_EQ("0123456789abcdef", string(buffer, sizeof(buffer)));
+  EXPECT_EQ("0123456789abcdef", std::string(buffer, sizeof(buffer)));
 }
 
 TEST(Printer, FormatInternal) {

src/google/protobuf/type.pb.h

@@ -1689,7 +1689,9 @@ inline void Type::unsafe_arena_set_allocated_source_context(
   // @@protoc_insertion_point(field_unsafe_arena_set_allocated:google.protobuf.Type.source_context)
 }
 inline PROTOBUF_NAMESPACE_ID::SourceContext* Type::release_source_context() {
-  auto temp = unsafe_arena_release_source_context();
+  
+  PROTOBUF_NAMESPACE_ID::SourceContext* temp = source_context_;
+  source_context_ = nullptr;
   if (GetArena() != nullptr) {
     temp = ::PROTOBUF_NAMESPACE_ID::internal::DuplicateIfNonNull(temp);
   }
@@ -2414,7 +2416,9 @@ inline void Enum::unsafe_arena_set_allocated_source_context(
   // @@protoc_insertion_point(field_unsafe_arena_set_allocated:google.protobuf.Enum.source_context)
 }
 inline PROTOBUF_NAMESPACE_ID::SourceContext* Enum::release_source_context() {
-  auto temp = unsafe_arena_release_source_context();
+  
+  PROTOBUF_NAMESPACE_ID::SourceContext* temp = source_context_;
+  source_context_ = nullptr;
   if (GetArena() != nullptr) {
     temp = ::PROTOBUF_NAMESPACE_ID::internal::DuplicateIfNonNull(temp);
   }
@@ -2738,7 +2742,9 @@ inline void Option::unsafe_arena_set_allocated_value(
   // @@protoc_insertion_point(field_unsafe_arena_set_allocated:google.protobuf.Option.value)
 }
 inline PROTOBUF_NAMESPACE_ID::Any* Option::release_value() {
-  auto temp = unsafe_arena_release_value();
+  
+  PROTOBUF_NAMESPACE_ID::Any* temp = value_;
+  value_ = nullptr;
   if (GetArena() != nullptr) {
     temp = ::PROTOBUF_NAMESPACE_ID::internal::DuplicateIfNonNull(temp);
   }

src/google/protobuf/unittest_lite.proto

@@ -38,7 +38,7 @@ package protobuf_unittest;
 
 import "google/protobuf/unittest_import_lite.proto";
 
-option cc_enable_arenas = false;
+option cc_enable_arenas = true;
 option optimize_for = LITE_RUNTIME;
 option java_package = "com.google.protobuf";