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

using Google.Protobuf.TestProtos;
using LegacyFeaturesUnittest;
using NUnit.Framework;
using ProtobufUnittest;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Reflection;
using UnitTest.Issues.TestProtos;
using static Google.Protobuf.Reflection.FeatureSet.Types;
using proto2 = Google.Protobuf.TestProtos.Proto2;

namespace Google.Protobuf.Reflection
{
    /// <summary>
    /// Tests for descriptors. (Not in its own namespace or broken up into individual classes as the
    /// size doesn't warrant it. On the other hand, this makes me feel a bit dirty...)
    /// </summary>
    public class DescriptorsTest
    {
        [Test]
        public void FileDescriptor_GeneratedCode()
        {
            TestFileDescriptor(
                UnittestProto3Reflection.Descriptor,
                UnittestImportProto3Reflection.Descriptor,
                UnittestImportPublicProto3Reflection.Descriptor);
        }

        /// <summary>
        /// Performance test comparing descriptor loading WITH vs WITHOUT extension caching.
        /// 
        /// This test uses TWO separate proto sets to measure both scenarios in a single execution:
        /// - unittest_deep_dependencies_cached: Example message (WITH caching - default)
        /// - unittest_deep_dependencies_notcached: ExampleNotcached message (WITHOUT caching)
        /// 
        /// Both proto sets have identical structure (WIDTH=6, DEPTH=6, 33 files total) but different
        /// package names, allowing accurate measurement of caching performance in one test run.
        /// </summary>
        [Test]
        public void FileDescriptor_ExtensionCachingPerformance()
        {
            // ========== Part 1: Test WITH caching (default behavior) ==========
#if DEBUG
            FileDescriptor.ResetCounters();
#endif

            var stopwatchWithCache = Stopwatch.StartNew();
            // Access the Descriptor property to trigger static initialization if not already done.
            // The first access to any member of the generated Reflection class triggers the static
            // constructor which calls FileDescriptor.FromGeneratedCode(), and that's when traversal happens.
            var descriptor = UnittestDeepDependenciesCached.Example.Descriptor;
            var exampleWithCache = new UnittestDeepDependenciesCached.Example();
            stopwatchWithCache.Stop();

#if DEBUG
            var traversalsWithCache = FileDescriptor.GetAllDependedExtensionsCount;

            // Verify caching is working: should have minimal redundant traversals
            Assert.Less(traversalsWithCache, 100, 
                $"Should have very few redundant traversals with cache, but got {traversalsWithCache}");
#endif

            // ========== Part 2: Test WITHOUT caching ==========
            FileDescriptor.DisableExtensionCaching();
#if DEBUG
            FileDescriptor.ResetCounters();
#endif

            var stopwatchNoCache = Stopwatch.StartNew();
            // Force descriptor initialization by accessing it - this is when extension traversal happens
            var descriptorNoCache = UnittestDeepDependenciesNotCached.ExampleNotCached.Descriptor;
            var exampleNoCache = new UnittestDeepDependenciesNotCached.ExampleNotCached();
            stopwatchNoCache.Stop();

#if DEBUG
            var traversalsWithoutCache = FileDescriptor.GetAllDependedExtensionsCount;
            
            // Verify the problem: massive redundant traversals
            Assert.Greater(traversalsWithoutCache, 8000, 
                $"Should have thousands of redundant traversals without cache, but got {traversalsWithoutCache}");

            var improvement = (double) traversalsWithoutCache / Math.Max(1, traversalsWithCache);
 
            Assert.Greater(improvement, 1000, $"Traversals Improvement = WITHOUT cache: {traversalsWithoutCache:N0} / WITH cache: {traversalsWithCache:N0} = {improvement:F0}x should be > 1000x !");
#endif
            Assert.Greater(stopwatchNoCache.Elapsed, stopwatchWithCache.Elapsed, $"Traversals time: WITHOUT cache: {stopwatchNoCache.Elapsed} should be > WITH cache: {stopwatchWithCache.Elapsed} !");

        }

        [Test]
        public void FileDescriptor_BuildFromByteStrings()
        {
            // The descriptors have to be supplied in an order such that all the
            // dependencies come before the descriptors depending on them.
            var descriptorData = new List<ByteString>
            {
                UnittestImportPublicProto3Reflection.Descriptor.SerializedData,
                UnittestImportProto3Reflection.Descriptor.SerializedData,
                UnittestProto3Reflection.Descriptor.SerializedData
            };
            var converted = FileDescriptor.BuildFromByteStrings(descriptorData);
            Assert.AreEqual(3, converted.Count);
            TestFileDescriptor(converted[2], converted[1], converted[0]);
        }

        [Test]
        public void FileDescriptor_BuildFromByteStrings_WithExtensionRegistry()
        {
            var extension = UnittestCustomOptionsProto3Extensions.MessageOpt1;

            var byteStrings = new[]
            {
                DescriptorReflection.Descriptor.Proto.ToByteString(),
                UnittestCustomOptionsProto3Reflection.Descriptor.Proto.ToByteString()
            };
            var registry = new ExtensionRegistry { extension };

            var descriptor = FileDescriptor.BuildFromByteStrings(byteStrings, registry).Last();
            var message = descriptor.MessageTypes.Single(t => t.Name == nameof(TestMessageWithCustomOptions));
            var extensionValue = message.GetOptions().GetExtension(extension);
            Assert.AreEqual(-56, extensionValue);
        }

        private void TestFileDescriptor(FileDescriptor file, FileDescriptor importedFile, FileDescriptor importedPublicFile)
        {
            Assert.AreEqual("csharp/protos/unittest_proto3.proto", file.Name);
            Assert.AreEqual("protobuf_unittest3", file.Package);

            Assert.AreEqual("UnittestProto", file.Proto.Options.JavaOuterClassname);
            Assert.AreEqual("csharp/protos/unittest_proto3.proto", file.Proto.Name);

            // unittest_proto3.proto doesn't have any public imports, but unittest_import_proto3.proto does.
            Assert.AreEqual(0, file.PublicDependencies.Count);
            Assert.AreEqual(1, importedFile.PublicDependencies.Count);
            Assert.AreEqual(importedPublicFile, importedFile.PublicDependencies[0]);

            Assert.AreEqual(1, file.Dependencies.Count);
            Assert.AreEqual(importedFile, file.Dependencies[0]);

            Assert.Null(file.FindTypeByName<MessageDescriptor>("NoSuchType"));
            Assert.Null(file.FindTypeByName<MessageDescriptor>("protobuf_unittest3.TestAllTypes"));
            for (int i = 0; i < file.MessageTypes.Count; i++)
            {
                Assert.AreEqual(i, file.MessageTypes[i].Index);
            }

            Assert.AreEqual(file.EnumTypes[0], file.FindTypeByName<EnumDescriptor>("ForeignEnum"));
            Assert.Null(file.FindTypeByName<EnumDescriptor>("NoSuchType"));
            Assert.Null(file.FindTypeByName<EnumDescriptor>("protobuf_unittest3.ForeignEnum"));
            Assert.AreEqual(1, importedFile.EnumTypes.Count);
            Assert.AreEqual("ImportEnum", importedFile.EnumTypes[0].Name);
            for (int i = 0; i < file.EnumTypes.Count; i++)
            {
                Assert.AreEqual(i, file.EnumTypes[i].Index);
            }

            Assert.AreEqual(10, file.SerializedData[0]);
            TestDescriptorToProto(file.ToProto, file.Proto);
        }

        [Test]
        public void FileDescriptor_BuildFromByteStrings_MissingDependency()
        {
            var descriptorData = new List<ByteString>
            {
                UnittestImportProto3Reflection.Descriptor.SerializedData,
                UnittestProto3Reflection.Descriptor.SerializedData,
            };
            // This will fail, because we're missing UnittestImportPublicProto3Reflection
            Assert.Throws<ArgumentException>(() => FileDescriptor.BuildFromByteStrings(descriptorData));
        }

        [Test]
        public void FileDescriptor_BuildFromByteStrings_DuplicateNames()
        {
            var descriptorData = new List<ByteString>
            {
                UnittestImportPublicProto3Reflection.Descriptor.SerializedData,
                UnittestImportPublicProto3Reflection.Descriptor.SerializedData,
            };
            // This will fail due to the same name being used twice
            Assert.Throws<ArgumentException>(() => FileDescriptor.BuildFromByteStrings(descriptorData));
        }

        [Test]
        public void FileDescriptor_BuildFromByteStrings_IncorrectOrder()
        {
            var descriptorData = new List<ByteString>
            {
                UnittestProto3Reflection.Descriptor.SerializedData,
                UnittestImportPublicProto3Reflection.Descriptor.SerializedData,
                UnittestImportProto3Reflection.Descriptor.SerializedData
            };
            // This will fail, because the dependencies should come first
            Assert.Throws<ArgumentException>(() => FileDescriptor.BuildFromByteStrings(descriptorData));

        }

        [Test]
        public void MessageDescriptorFromGeneratedCodeFileDescriptor()
        {
            var file = UnittestProto3Reflection.Descriptor;

            MessageDescriptor messageType = TestAllTypes.Descriptor;
            Assert.AreSame(typeof(TestAllTypes), messageType.ClrType);
            Assert.AreSame(TestAllTypes.Parser, messageType.Parser);
            Assert.AreEqual(messageType, file.MessageTypes[0]);
            Assert.AreEqual(messageType, file.FindTypeByName<MessageDescriptor>("TestAllTypes"));
        }

        [Test]
        public void MessageDescriptor()
        {
            MessageDescriptor messageType = TestAllTypes.Descriptor;
            MessageDescriptor nestedType = TestAllTypes.Types.NestedMessage.Descriptor;

            Assert.AreEqual("TestAllTypes", messageType.Name);
            Assert.AreEqual("protobuf_unittest3.TestAllTypes", messageType.FullName);
            Assert.AreEqual(UnittestProto3Reflection.Descriptor, messageType.File);
            Assert.IsNull(messageType.ContainingType);
            Assert.IsNull(messageType.Proto.Options);

            Assert.AreEqual("TestAllTypes", messageType.Name);

            Assert.AreEqual("NestedMessage", nestedType.Name);
            Assert.AreEqual("protobuf_unittest3.TestAllTypes.NestedMessage", nestedType.FullName);
            Assert.AreEqual(UnittestProto3Reflection.Descriptor, nestedType.File);
            Assert.AreEqual(messageType, nestedType.ContainingType);

            FieldDescriptor field = messageType.Fields.InDeclarationOrder()[0];
            Assert.AreEqual("single_int32", field.Name);
            Assert.AreEqual(field, messageType.FindDescriptor<FieldDescriptor>("single_int32"));
            Assert.Null(messageType.FindDescriptor<FieldDescriptor>("no_such_field"));
            Assert.AreEqual(field, messageType.FindFieldByNumber(1));
            Assert.Null(messageType.FindFieldByNumber(571283));
            var fieldsInDeclarationOrder = messageType.Fields.InDeclarationOrder();
            for (int i = 0; i < fieldsInDeclarationOrder.Count; i++)
            {
                Assert.AreEqual(i, fieldsInDeclarationOrder[i].Index);
            }

            Assert.AreEqual(nestedType, messageType.NestedTypes[0]);
            Assert.AreEqual(nestedType, messageType.FindDescriptor<MessageDescriptor>("NestedMessage"));
            Assert.Null(messageType.FindDescriptor<MessageDescriptor>("NoSuchType"));
            for (int i = 0; i < messageType.NestedTypes.Count; i++)
            {
                Assert.AreEqual(i, messageType.NestedTypes[i].Index);
            }

            Assert.AreEqual(messageType.EnumTypes[0], messageType.FindDescriptor<EnumDescriptor>("NestedEnum"));
            Assert.Null(messageType.FindDescriptor<EnumDescriptor>("NoSuchType"));
            for (int i = 0; i < messageType.EnumTypes.Count; i++)
            {
                Assert.AreEqual(i, messageType.EnumTypes[i].Index);
            }
            TestDescriptorToProto(messageType.ToProto, messageType.Proto);
        }

        [Test]
        public void MessageDescriptor_IsMapEntry()
        {
            var testMapMessage = TestMap.Descriptor;
            Assert.False(testMapMessage.IsMapEntry);
            Assert.True(testMapMessage.Fields[1].MessageType.IsMapEntry);
        }

        [Test]
        public void FieldDescriptor_GeneratedCode()
        {
            TestFieldDescriptor(UnittestProto3Reflection.Descriptor, TestAllTypes.Descriptor, ForeignMessage.Descriptor, ImportMessage.Descriptor);
        }

        [Test]
        public void FieldDescriptor_BuildFromByteStrings()
        {
            // The descriptors have to be supplied in an order such that all the
            // dependencies come before the descriptors depending on them.
            var descriptorData = new List<ByteString>
            {
                UnittestImportPublicProto3Reflection.Descriptor.SerializedData,
                UnittestImportProto3Reflection.Descriptor.SerializedData,
                UnittestProto3Reflection.Descriptor.SerializedData
            };
            var converted = FileDescriptor.BuildFromByteStrings(descriptorData);
            TestFieldDescriptor(
                converted[2],
                converted[2].FindTypeByName<MessageDescriptor>("TestAllTypes"),
                converted[2].FindTypeByName<MessageDescriptor>("ForeignMessage"),
                converted[1].FindTypeByName<MessageDescriptor>("ImportMessage"));
        }

        public void TestFieldDescriptor(
            FileDescriptor unitTestProto3Descriptor,
            MessageDescriptor testAllTypesDescriptor,
            MessageDescriptor foreignMessageDescriptor,
            MessageDescriptor importMessageDescriptor)
        {
            FieldDescriptor primitiveField = testAllTypesDescriptor.FindDescriptor<FieldDescriptor>("single_int32");
            FieldDescriptor enumField = testAllTypesDescriptor.FindDescriptor<FieldDescriptor>("single_nested_enum");
            FieldDescriptor foreignMessageField = testAllTypesDescriptor.FindDescriptor<FieldDescriptor>("single_foreign_message");
            FieldDescriptor importMessageField = testAllTypesDescriptor.FindDescriptor<FieldDescriptor>("single_import_message");
            FieldDescriptor fieldInOneof = testAllTypesDescriptor.FindDescriptor<FieldDescriptor>("oneof_string");

            Assert.AreEqual("single_int32", primitiveField.Name);
            Assert.AreEqual("protobuf_unittest3.TestAllTypes.single_int32",
                            primitiveField.FullName);
            Assert.AreEqual(1, primitiveField.FieldNumber);
            Assert.AreEqual(testAllTypesDescriptor, primitiveField.ContainingType);
            Assert.AreEqual(unitTestProto3Descriptor, primitiveField.File);
            Assert.AreEqual(FieldType.Int32, primitiveField.FieldType);
            Assert.IsNull(primitiveField.Proto.Options);

            Assert.AreEqual("single_nested_enum", enumField.Name);
            Assert.AreEqual(FieldType.Enum, enumField.FieldType);
            Assert.AreEqual(testAllTypesDescriptor.EnumTypes[0], enumField.EnumType);

            Assert.AreEqual("single_foreign_message", foreignMessageField.Name);
            Assert.AreEqual(FieldType.Message, foreignMessageField.FieldType);
            Assert.AreEqual(foreignMessageDescriptor, foreignMessageField.MessageType);

            Assert.AreEqual("single_import_message", importMessageField.Name);
            Assert.AreEqual(FieldType.Message, importMessageField.FieldType);
            Assert.AreEqual(importMessageDescriptor, importMessageField.MessageType);

            // For a field in a regular onoef, ContainingOneof and RealContainingOneof should be the same.
            Assert.AreEqual("oneof_field", fieldInOneof.ContainingOneof.Name);
            Assert.AreSame(fieldInOneof.ContainingOneof, fieldInOneof.RealContainingOneof);

            TestDescriptorToProto(primitiveField.ToProto, primitiveField.Proto);
            TestDescriptorToProto(enumField.ToProto, enumField.Proto);
            TestDescriptorToProto(foreignMessageField.ToProto, foreignMessageField.Proto);
            TestDescriptorToProto(fieldInOneof.ToProto, fieldInOneof.Proto);
        }

        [Test]
        public void FieldDescriptorLabel()
        {
            FieldDescriptor singleField =
                TestAllTypes.Descriptor.FindDescriptor<FieldDescriptor>("single_int32");
            FieldDescriptor repeatedField =
                TestAllTypes.Descriptor.FindDescriptor<FieldDescriptor>("repeated_int32");

            Assert.IsFalse(singleField.IsRepeated);
            Assert.IsTrue(repeatedField.IsRepeated);
        }

        [Test]
        public void EnumDescriptor()
        {
            // Note: this test is a bit different to the Java version because there's no static way of getting to the descriptor
            EnumDescriptor enumType = UnittestProto3Reflection.Descriptor.FindTypeByName<EnumDescriptor>("ForeignEnum");
            EnumDescriptor nestedType = TestAllTypes.Descriptor.FindDescriptor<EnumDescriptor>("NestedEnum");

            Assert.AreEqual("ForeignEnum", enumType.Name);
            Assert.AreEqual("protobuf_unittest3.ForeignEnum", enumType.FullName);
            Assert.AreEqual(UnittestProto3Reflection.Descriptor, enumType.File);
            Assert.Null(enumType.ContainingType);
            Assert.Null(enumType.Proto.Options);

            Assert.AreEqual("NestedEnum", nestedType.Name);
            Assert.AreEqual("protobuf_unittest3.TestAllTypes.NestedEnum",
                            nestedType.FullName);
            Assert.AreEqual(UnittestProto3Reflection.Descriptor, nestedType.File);
            Assert.AreEqual(TestAllTypes.Descriptor, nestedType.ContainingType);

            EnumValueDescriptor value = enumType.FindValueByName("FOREIGN_FOO");
            Assert.AreEqual(value, enumType.Values[1]);
            Assert.AreEqual("FOREIGN_FOO", value.Name);
            Assert.AreEqual(4, value.Number);
            Assert.AreEqual((int) ForeignEnum.ForeignFoo, value.Number);
            Assert.AreEqual(value, enumType.FindValueByNumber(4));
            Assert.Null(enumType.FindValueByName("NO_SUCH_VALUE"));
            for (int i = 0; i < enumType.Values.Count; i++)
            {
                Assert.AreEqual(i, enumType.Values[i].Index);
            }
            TestDescriptorToProto(enumType.ToProto, enumType.Proto);
            TestDescriptorToProto(nestedType.ToProto, nestedType.Proto);
        }

        [Test]
        public void OneofDescriptor()
        {
            OneofDescriptor descriptor = TestAllTypes.Descriptor.FindDescriptor<OneofDescriptor>("oneof_field");
            Assert.IsFalse(descriptor.IsSynthetic);
            Assert.AreEqual("oneof_field", descriptor.Name);
            Assert.AreEqual("protobuf_unittest3.TestAllTypes.oneof_field", descriptor.FullName);

            var expectedFields = new[] {
                TestAllTypes.OneofBytesFieldNumber,
                TestAllTypes.OneofNestedMessageFieldNumber,
                TestAllTypes.OneofStringFieldNumber,
                TestAllTypes.OneofUint32FieldNumber }
                .Select(fieldNumber => TestAllTypes.Descriptor.FindFieldByNumber(fieldNumber))
                .ToList();
            foreach (var field in expectedFields)
            {
                Assert.AreSame(descriptor, field.ContainingOneof);
            }

            CollectionAssert.AreEquivalent(expectedFields, descriptor.Fields);
            TestDescriptorToProto(descriptor.ToProto, descriptor.Proto);
        }

        [Test]
        public void MapEntryMessageDescriptor()
        {
            var descriptor = MapWellKnownTypes.Descriptor.NestedTypes[0];
            Assert.IsNull(descriptor.Parser);
            Assert.IsNull(descriptor.ClrType);
            Assert.IsNull(descriptor.Fields[1].Accessor);
            TestDescriptorToProto(descriptor.ToProto, descriptor.Proto);
        }

        // From TestFieldOrdering:
        // string my_string = 11;
        // int64 my_int = 1;
        // float my_float = 101;
        // NestedMessage single_nested_message = 200;
        [Test]
        public void FieldListOrderings()
        {
            var fields = TestFieldOrderings.Descriptor.Fields;
            Assert.AreEqual(new[] { 11, 1, 101, 200 }, fields.InDeclarationOrder().Select(x => x.FieldNumber));
            Assert.AreEqual(new[] { 1, 11, 101, 200 }, fields.InFieldNumberOrder().Select(x => x.FieldNumber));
        }


        [Test]
        public void DescriptorProtoFileDescriptor()
        {
            var descriptor = Google.Protobuf.Reflection.FileDescriptor.DescriptorProtoFileDescriptor;
            Assert.AreEqual("google/protobuf/descriptor.proto", descriptor.Name);
            TestDescriptorToProto(descriptor.ToProto, descriptor.Proto);
        }

        [Test]
        public void DescriptorImportingExtensionsFromOldCodeGen()
        {
            if (MethodOptions.Descriptor.FullName != "google.protobuf.MethodOptions")
            {
                Assert.Ignore("Embedded descriptor for OldExtensions expects google.protobuf reflection package.");
            }

            // The extension collection includes a null extension. There's not a lot we can do about that
            // in itself, as the old generator didn't provide us the extension information.
            var extensions = TestProtos.OldGenerator.OldExtensions2Reflection.Descriptor.Extensions;
            Assert.AreEqual(1, extensions.UnorderedExtensions.Count);
            // Note: this assertion is present so that it will fail if OldExtensions2 is regenerated
            // with a new generator.
            Assert.Null(extensions.UnorderedExtensions[0].Extension);

            // ... but we can make sure we at least don't cause a failure when retrieving descriptors.
            // In particular, old_extensions1.proto imports old_extensions2.proto, and this used to cause
            // an execution-time failure.
            var importingDescriptor = TestProtos.OldGenerator.OldExtensions1Reflection.Descriptor;
            Assert.NotNull(importingDescriptor);
        }

        [Test]
        public void Proto3OptionalDescriptors()
        {
            var descriptor = TestProto3Optional.Descriptor;
            var field = descriptor.Fields[TestProto3Optional.OptionalInt32FieldNumber];
            Assert.NotNull(field.ContainingOneof);
            Assert.IsTrue(field.ContainingOneof.IsSynthetic);
            Assert.Null(field.RealContainingOneof);
        }


        [Test]
        public void SyntheticOneofReflection()
        {
            // Expect every oneof in TestProto3Optional to be synthetic
            var proto3OptionalDescriptor = TestProto3Optional.Descriptor;
            Assert.AreEqual(0, proto3OptionalDescriptor.RealOneofCount);
            foreach (var oneof in proto3OptionalDescriptor.Oneofs)
            {
                Assert.True(oneof.IsSynthetic);
            }

            // Expect no oneof in the original proto3 unit test file to be synthetic.
            // (This excludes oneofs with "lazy" in the name, due to internal differences.)
            foreach (var descriptor in ProtobufTestMessages.Proto3.TestMessagesProto3Reflection.Descriptor.MessageTypes)
            {
                var nonLazyOneofs = descriptor.Oneofs.Where(d => !d.Name.Contains("lazy")).ToList();
                Assert.AreEqual(nonLazyOneofs.Count, descriptor.RealOneofCount);
                foreach (var oneof in nonLazyOneofs)
                {
                    Assert.False(oneof.IsSynthetic);
                }
            }

            // Expect no oneof in the original proto2 unit test file to be synthetic.
            foreach (var descriptor in ProtobufTestMessages.Proto2.TestMessagesProto2Reflection.Descriptor.MessageTypes)
            {
                Assert.AreEqual(descriptor.Oneofs.Count, descriptor.RealOneofCount);
                foreach (var oneof in descriptor.Oneofs)
                {
                    Assert.False(oneof.IsSynthetic);
                }
            }
        }

        [Test]
        public void OptionRetention()
        {
          var proto = UnittestRetentionReflection.Descriptor.Proto;
          Assert.AreEqual(1, proto.Options.GetExtension(
              UnittestRetentionExtensions.PlainOption));
          Assert.AreEqual(2, proto.Options.GetExtension(
              UnittestRetentionExtensions.RuntimeRetentionOption));
          // This option has a value of 3 in the .proto file, but we expect it
          // to be zeroed out in the generated descriptor since it has source
          // retention.
          Assert.AreEqual(0, proto.Options.GetExtension(
              UnittestRetentionExtensions.SourceRetentionOption));
        }

        [Test]
        public void GetOptionsStripsFeatures()
        {
            var messageDescriptor = TestEditionsMessage.Descriptor;
            var fieldDescriptor = messageDescriptor.FindFieldByName("required_field");
            // Note: ideally we'd test GetOptions() for other descriptor types as well, but that requires
            // non-fields with features applied.
            Assert.Null(fieldDescriptor.GetOptions().Features);
        }

        [Test]
        public void LegacyRequiredTransform()
        {
            var messageDescriptor = TestEditionsMessage.Descriptor;
            var fieldDescriptor = messageDescriptor.FindFieldByName("required_field");
            Assert.True(fieldDescriptor.IsRequired);
        }

        [Test]
        public void LegacyGroupTransform()
        {
            var messageDescriptor = TestEditionsMessage.Descriptor;
            var fieldDescriptor = messageDescriptor.FindFieldByName("delimited_field");
            Assert.AreEqual(FieldType.Group, fieldDescriptor.FieldType);
        }

        [Test]
        public void LegacyInferRequired()
        {
            var messageDescriptor = proto2::TestRequired.Descriptor;
            var fieldDescriptor = messageDescriptor.FindFieldByName("a");
            Assert.AreEqual(FieldPresence.LegacyRequired, fieldDescriptor.Features.FieldPresence);
        }

        [Test]
        public void LegacyInferGroup()
        {
            var messageDescriptor = proto2::TestAllTypes.Descriptor;
            var fieldDescriptor = messageDescriptor.FindFieldByName("optionalgroup");
            Assert.AreEqual(MessageEncoding.Delimited, fieldDescriptor.Features.MessageEncoding);
        }

        [Test]
        public void LegacyInferProto2Packed()
        {
            var messageDescriptor = proto2::TestPackedTypes.Descriptor;
            var fieldDescriptor = messageDescriptor.FindFieldByName("packed_int32");
            Assert.AreEqual(RepeatedFieldEncoding.Packed, fieldDescriptor.Features.RepeatedFieldEncoding);
        }

        [Test]
        public void LegacyInferProto3Expanded()
        {
            var messageDescriptor = TestUnpackedTypes.Descriptor;
            var fieldDescriptor = messageDescriptor.FindFieldByName("unpacked_int32");
            Assert.NotNull(fieldDescriptor);
            Assert.AreEqual(RepeatedFieldEncoding.Expanded, fieldDescriptor.Features.RepeatedFieldEncoding);
        }

        private static void TestDescriptorToProto(Func<IMessage> toProtoFunction, IMessage expectedProto)
        {
            var clone1 = toProtoFunction();
            var clone2 = toProtoFunction();
            Assert.AreNotSame(clone1, clone2);
            Assert.AreNotSame(clone1, expectedProto);
            Assert.AreNotSame(clone2, expectedProto);

            Assert.AreEqual(clone1, clone2);
            Assert.AreEqual(clone1, expectedProto);
        }
    }
}