Add ToProto() method to all C# descriptor classes

Fixes #9425.

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

@@ -124,6 +124,7 @@ private void TestFileDescriptor(FileDescriptor file, FileDescriptor importedFile
             }
 
             Assert.AreEqual(10, file.SerializedData[0]);
+            TestDescriptorToProto(file.ToProto, file.Proto);
         }
 
         [Test]
@@ -231,6 +232,7 @@ public void MessageDescriptor()
             {
                 Assert.AreEqual(i, messageType.EnumTypes[i].Index);
             }
+            TestDescriptorToProto(messageType.ToProto, messageType.Proto);
         }
 
         [Test]
@@ -294,6 +296,11 @@ public void FieldDescriptor_BuildFromByteStrings()
             // 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]
@@ -338,6 +345,8 @@ public void EnumDescriptor()
             {
                 Assert.AreEqual(i, enumType.Values[i].Index);
             }
+            TestDescriptorToProto(enumType.ToProto, enumType.Proto);
+            TestDescriptorToProto(nestedType.ToProto, nestedType.Proto);
         }
 
         [Test]
@@ -361,6 +370,7 @@ public void OneofDescriptor()
             }
 
             CollectionAssert.AreEquivalent(expectedFields, descriptor.Fields);
+            TestDescriptorToProto(descriptor.ToProto, descriptor.Proto);
         }
 
         [Test]
@@ -370,6 +380,7 @@ public void MapEntryMessageDescriptor()
             Assert.IsNull(descriptor.Parser);
             Assert.IsNull(descriptor.ClrType);
             Assert.IsNull(descriptor.Fields[1].Accessor);
+            TestDescriptorToProto(descriptor.ToProto, descriptor.Proto);
         }
 
         // From TestFieldOrdering:
@@ -391,6 +402,7 @@ public void DescriptorProtoFileDescriptor()
         {
             var descriptor = Google.Protobuf.Reflection.FileDescriptor.DescriptorProtoFileDescriptor;
             Assert.AreEqual("google/protobuf/descriptor.proto", descriptor.Name);
+            TestDescriptorToProto(descriptor.ToProto, descriptor.Proto);
         }
 
         [Test]
@@ -453,5 +465,17 @@ public void SyntheticOneofReflection()
                 }
             }
         }
+
+        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);
+        }
     }
 }

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

@@ -68,6 +68,14 @@ internal EnumDescriptor(EnumDescriptorProto proto, FileDescriptor file, MessageD
 
         internal EnumDescriptorProto Proto { get { return proto; } }
 
+        /// <summary>
+        /// Returns a clone of the underlying <see cref="EnumDescriptorProto"/> describing this enum.
+        /// Note that a copy is taken every time this method is called, so clients using it frequently
+        /// (and not modifying it) may want to cache the returned value.
+        /// </summary>
+        /// <returns>A protobuf representation of this enum descriptor.</returns>
+        public EnumDescriptorProto ToProto() => Proto.Clone();
+
         /// <summary>
         /// The brief name of the descriptor's target.
         /// </summary>

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

@@ -55,6 +55,14 @@ public sealed class EnumValueDescriptor : DescriptorBase
 
         internal EnumValueDescriptorProto Proto { get { return proto; } }
 
+        /// <summary>
+        /// Returns a clone of the underlying <see cref="EnumValueDescriptorProto"/> describing this enum value.
+        /// Note that a copy is taken every time this method is called, so clients using it frequently
+        /// (and not modifying it) may want to cache the returned value.
+        /// </summary>
+        /// <returns>A protobuf representation of this enum value descriptor.</returns>
+        public EnumValueDescriptorProto ToProto() => Proto.Clone();
+
         /// <summary>
         /// Returns the name of the enum value described by this object.
         /// </summary>

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

@@ -91,6 +91,14 @@ public sealed class FieldDescriptor : DescriptorBase, IComparable<FieldDescripto
 
         internal FieldDescriptorProto Proto { get; }
 
+        /// <summary>
+        /// Returns a clone of the underlying <see cref="FieldDescriptorProto"/> describing this field.
+        /// Note that a copy is taken every time this method is called, so clients using it frequently
+        /// (and not modifying it) may want to cache the returned value.
+        /// </summary>
+        /// <returns>A protobuf representation of this field descriptor.</returns>
+        public FieldDescriptorProto ToProto() => Proto.Clone();
+
         /// <summary>
         /// An extension identifier for this field, or <c>null</c> if this field isn't an extension.
         /// </summary>

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

@@ -249,6 +249,14 @@ private static IList<FileDescriptor> DeterminePublicDependencies(FileDescriptor
         /// </value>
         internal FileDescriptorProto Proto { get; }
 
+        /// <summary>
+        /// Returns a clone of the underlying <see cref="FileDescriptorProto"/> describing this file.
+        /// Note that a copy is taken every time this method is called, so clients using it frequently
+        /// (and not modifying it) may want to cache the returned value.
+        /// </summary>
+        /// <returns>A protobuf representation of this file descriptor.</returns>
+        public FileDescriptorProto ToProto() => Proto.Clone();
+
         /// <summary>
         /// The syntax of the file
         /// </summary>

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

@@ -151,6 +151,14 @@ internal override IReadOnlyList<DescriptorBase> GetNestedDescriptorListForField(
 
         internal DescriptorProto Proto { get; }
 
+        /// <summary>
+        /// Returns a clone of the underlying <see cref="DescriptorProto"/> describing this message.
+        /// Note that a copy is taken every time this method is called, so clients using it frequently
+        /// (and not modifying it) may want to cache the returned value.
+        /// </summary>
+        /// <returns>A protobuf representation of this message descriptor.</returns>
+        public DescriptorProto ToProto() => Proto.Clone();
+
         internal bool IsExtensionsInitialized(IMessage message)
         {
             if (Proto.ExtensionRange.Count == 0)

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

@@ -114,6 +114,14 @@ public RepeatedField<T> GetOption<T>(RepeatedExtension<MethodOptions, T> extensi
 
         internal MethodDescriptorProto Proto { get { return proto; } }
 
+        /// <summary>
+        /// Returns a clone of the underlying <see cref="MethodDescriptorProto"/> describing this method.
+        /// Note that a copy is taken every time this method is called, so clients using it frequently
+        /// (and not modifying it) may want to cache the returned value.
+        /// </summary>
+        /// <returns>A protobuf representation of this method descriptor.</returns>
+        public MethodDescriptorProto ToProto() => Proto.Clone();
+
         /// <summary>
         /// The brief name of the descriptor's target.
         /// </summary>

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

@@ -45,15 +45,14 @@ namespace Google.Protobuf.Reflection
     /// </summary>
     public sealed class OneofDescriptor : DescriptorBase
     {
-        private readonly OneofDescriptorProto proto;
         private MessageDescriptor containingType;
         private IList<FieldDescriptor> fields;
         private readonly OneofAccessor accessor;
 
         internal OneofDescriptor(OneofDescriptorProto proto, FileDescriptor file, MessageDescriptor parent, int index, string clrName)
             : base(file, file.ComputeFullName(parent, proto.Name), index)
         {
-            this.proto = proto;
+            this.Proto = proto;
             containingType = parent;
             file.DescriptorPool.AddSymbol(this);
 
@@ -68,7 +67,18 @@ internal OneofDescriptor(OneofDescriptorProto proto, FileDescriptor file, Messag
         /// <summary>
         /// The brief name of the descriptor's target.
         /// </summary>
-        public override string Name { get { return proto.Name; } }
+        public override string Name => Proto.Name;
+
+        // Visible for testing
+        internal OneofDescriptorProto Proto { get; }
+
+        /// <summary>
+        /// Returns a clone of the underlying <see cref="OneofDescriptorProto"/> describing this oneof.
+        /// Note that a copy is taken every time this method is called, so clients using it frequently
+        /// (and not modifying it) may want to cache the returned value.
+        /// </summary>
+        /// <returns>A protobuf representation of this oneof descriptor.</returns>
+        public OneofDescriptorProto ToProto() => Proto.Clone();
 
         /// <summary>
         /// Gets the message type containing this oneof.
@@ -118,23 +128,23 @@ public MessageDescriptor ContainingType
         /// The (possibly empty) set of custom options for this oneof.
         /// </summary>
         [Obsolete("CustomOptions are obsolete. Use the GetOptions method.")]
-        public CustomOptions CustomOptions => new CustomOptions(proto.Options?._extensions?.ValuesByNumber);
+        public CustomOptions CustomOptions => new CustomOptions(Proto.Options?._extensions?.ValuesByNumber);
 
         /// <summary>
         /// The <c>OneofOptions</c>, defined in <c>descriptor.proto</c>.
         /// If the options message is not present (i.e. there are no options), <c>null</c> is returned.
         /// Custom options can be retrieved as extensions of the returned message.
         /// NOTE: A defensive copy is created each time this property is retrieved.
         /// </summary>
-        public OneofOptions GetOptions() => proto.Options?.Clone();
+        public OneofOptions GetOptions() => Proto.Options?.Clone();
 
         /// <summary>
         /// Gets a single value oneof option for this descriptor
         /// </summary>
         [Obsolete("GetOption is obsolete. Use the GetOptions() method.")]
         public T GetOption<T>(Extension<OneofOptions, T> extension)
         {
-            var value = proto.Options.GetExtension(extension);
+            var value = Proto.Options.GetExtension(extension);
             return value is IDeepCloneable<T> ? (value as IDeepCloneable<T>).Clone() : value;
         }
 
@@ -144,7 +154,7 @@ public T GetOption<T>(Extension<OneofOptions, T> extension)
         [Obsolete("GetOption is obsolete. Use the GetOptions() method.")]
         public RepeatedField<T> GetOption<T>(RepeatedExtension<OneofOptions, T> extension)
         {
-            return proto.Options.GetExtension(extension).Clone();
+            return Proto.Options.GetExtension(extension).Clone();
         }
 
         internal void CrossLink()

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

@@ -73,6 +73,14 @@ internal override IReadOnlyList<DescriptorBase> GetNestedDescriptorListForField(
 
         internal ServiceDescriptorProto Proto { get { return proto; } }
 
+        /// <summary>
+        /// Returns a clone of the underlying <see cref="ServiceDescriptorProto"/> describing this service.
+        /// Note that a copy is taken every time this method is called, so clients using it frequently
+        /// (and not modifying it) may want to cache the returned value.
+        /// </summary>
+        /// <returns>A protobuf representation of this service descriptor.</returns>
+        public ServiceDescriptorProto ToProto() => Proto.Clone();
+
         /// <value>
         /// An unmodifiable list of methods in this service.
         /// </value>