Support custom options in C#

This consists of:
- Changing the codegen for the fixed set of options protos, to parse unknown fields instead of skipping them
- Add a new CustomOptions type in the C# support library
- Expose CustomOptions properties from the immutable proto wrappers in the support library

Only single-value options are currently supported, and fetching options values requires getting the type right
and knowing the field number. Both of these can be addressed at a later time.

Fixes #2143, at least as a first pass.

Makefile.am

@@ -60,6 +60,7 @@ csharp_EXTRA_DIST=                                                           \
   csharp/keys/Google.Protobuf.public.snk                                     \
   csharp/keys/Google.Protobuf.snk                                            \
   csharp/keys/README.md                                                      \
+  csharp/protos/unittest_custom_options_proto3.proto                         \
   csharp/protos/unittest_issues.proto                                        \
   csharp/src/AddressBook/AddPerson.cs                                        \
   csharp/src/AddressBook/Addressbook.cs                                      \
@@ -92,6 +93,7 @@ csharp_EXTRA_DIST=                                                           \
   csharp/src/Google.Protobuf.Test/JsonFormatterTest.cs                       \
   csharp/src/Google.Protobuf.Test/JsonParserTest.cs                          \
   csharp/src/Google.Protobuf.Test/JsonTokenizerTest.cs                       \
+  csharp/src/Google.Protobuf.Test/Reflection/CustomOptionsTest.cs            \
   csharp/src/Google.Protobuf.Test/Reflection/DescriptorsTest.cs              \
   csharp/src/Google.Protobuf.Test/Reflection/FieldAccessTest.cs              \
   csharp/src/Google.Protobuf.Test/Reflection/TypeRegistryTest.cs             \
@@ -101,6 +103,7 @@ csharp_EXTRA_DIST=                                                           \
   csharp/src/Google.Protobuf.Test/TestProtos/ForeignMessagePartial.cs        \
   csharp/src/Google.Protobuf.Test/TestProtos/MapUnittestProto3.cs            \
   csharp/src/Google.Protobuf.Test/TestProtos/TestMessagesProto3.cs           \
+  csharp/src/Google.Protobuf.Test/TestProtos/UnittestCustomOptionsProto3.cs  \
   csharp/src/Google.Protobuf.Test/TestProtos/UnittestImportProto3.cs         \
   csharp/src/Google.Protobuf.Test/TestProtos/UnittestImportPublicProto3.cs   \
   csharp/src/Google.Protobuf.Test/TestProtos/UnittestIssues.cs               \
@@ -140,6 +143,7 @@ csharp_EXTRA_DIST=                                                           \
   csharp/src/Google.Protobuf/MessageParser.cs                                \
   csharp/src/Google.Protobuf/ProtoPreconditions.cs                           \
   csharp/src/Google.Protobuf/Properties/AssemblyInfo.cs                      \
+  csharp/src/Google.Protobuf/Reflection/CustomOptions.cs                     \
   csharp/src/Google.Protobuf/Reflection/Descriptor.cs                        \
   csharp/src/Google.Protobuf/Reflection/DescriptorBase.cs                    \
   csharp/src/Google.Protobuf/Reflection/DescriptorPool.cs                    \

csharp/generate_protos.sh

@@ -50,9 +50,10 @@ $PROTOC -Isrc --csharp_out=csharp/src/Google.Protobuf.Test \
     src/google/protobuf/unittest_well_known_types.proto
 
 # Different base namespace to the protos above
-$PROTOC -Icsharp/protos --csharp_out=csharp/src/Google.Protobuf.Test \
+$PROTOC -Isrc -Icsharp/protos --csharp_out=csharp/src/Google.Protobuf.Test \
     --csharp_opt=base_namespace=UnitTest.Issues \
-    csharp/protos/unittest_issues.proto
+    csharp/protos/unittest_issues.proto \
+    csharp/protos/unittest_custom_options_proto3.proto
 
 # Don't specify a base namespace at all; we just want to make sure the
 # results end up in TestProtos.

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

@@ -2779,6 +2779,8 @@ namespace Google.Protobuf.Reflection {
       get { return Descriptor; }
     }
 
+    internal CustomOptions CustomOptions{ get; private set; } = CustomOptions.Empty;
+
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public FileOptions() {
       OnConstruction();
@@ -3299,7 +3301,7 @@ namespace Google.Protobuf.Reflection {
       while ((tag = input.ReadTag()) != 0) {
         switch(tag) {
           default:
-            input.SkipLastField();
+            CustomOptions = CustomOptions.ReadOrSkipUnknownField(input);
             break;
           case 10: {
             JavaPackage = input.ReadString();
@@ -3411,6 +3413,8 @@ namespace Google.Protobuf.Reflection {
       get { return Descriptor; }
     }
 
+    internal CustomOptions CustomOptions{ get; private set; } = CustomOptions.Empty;
+
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public MessageOptions() {
       OnConstruction();
@@ -3646,7 +3650,7 @@ namespace Google.Protobuf.Reflection {
       while ((tag = input.ReadTag()) != 0) {
         switch(tag) {
           default:
-            input.SkipLastField();
+            CustomOptions = CustomOptions.ReadOrSkipUnknownField(input);
             break;
           case 8: {
             MessageSetWireFormat = input.ReadBool();
@@ -3689,6 +3693,8 @@ namespace Google.Protobuf.Reflection {
       get { return Descriptor; }
     }
 
+    internal CustomOptions CustomOptions{ get; private set; } = CustomOptions.Empty;
+
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public FieldOptions() {
       OnConstruction();
@@ -3980,7 +3986,7 @@ namespace Google.Protobuf.Reflection {
       while ((tag = input.ReadTag()) != 0) {
         switch(tag) {
           default:
-            input.SkipLastField();
+            CustomOptions = CustomOptions.ReadOrSkipUnknownField(input);
             break;
           case 8: {
             ctype_ = (global::Google.Protobuf.Reflection.FieldOptions.Types.CType) input.ReadEnum();
@@ -4062,6 +4068,8 @@ namespace Google.Protobuf.Reflection {
       get { return Descriptor; }
     }
 
+    internal CustomOptions CustomOptions{ get; private set; } = CustomOptions.Empty;
+
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public OneofOptions() {
       OnConstruction();
@@ -4147,7 +4155,7 @@ namespace Google.Protobuf.Reflection {
       while ((tag = input.ReadTag()) != 0) {
         switch(tag) {
           default:
-            input.SkipLastField();
+            CustomOptions = CustomOptions.ReadOrSkipUnknownField(input);
             break;
           case 7994: {
             uninterpretedOption_.AddEntriesFrom(input, _repeated_uninterpretedOption_codec);
@@ -4174,6 +4182,8 @@ namespace Google.Protobuf.Reflection {
       get { return Descriptor; }
     }
 
+    internal CustomOptions CustomOptions{ get; private set; } = CustomOptions.Empty;
+
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public EnumOptions() {
       OnConstruction();
@@ -4317,7 +4327,7 @@ namespace Google.Protobuf.Reflection {
       while ((tag = input.ReadTag()) != 0) {
         switch(tag) {
           default:
-            input.SkipLastField();
+            CustomOptions = CustomOptions.ReadOrSkipUnknownField(input);
             break;
           case 16: {
             AllowAlias = input.ReadBool();
@@ -4352,6 +4362,8 @@ namespace Google.Protobuf.Reflection {
       get { return Descriptor; }
     }
 
+    internal CustomOptions CustomOptions{ get; private set; } = CustomOptions.Empty;
+
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public EnumValueOptions() {
       OnConstruction();
@@ -4467,7 +4479,7 @@ namespace Google.Protobuf.Reflection {
       while ((tag = input.ReadTag()) != 0) {
         switch(tag) {
           default:
-            input.SkipLastField();
+            CustomOptions = CustomOptions.ReadOrSkipUnknownField(input);
             break;
           case 8: {
             Deprecated = input.ReadBool();
@@ -4498,6 +4510,8 @@ namespace Google.Protobuf.Reflection {
       get { return Descriptor; }
     }
 
+    internal CustomOptions CustomOptions{ get; private set; } = CustomOptions.Empty;
+
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public ServiceOptions() {
       OnConstruction();
@@ -4613,7 +4627,7 @@ namespace Google.Protobuf.Reflection {
       while ((tag = input.ReadTag()) != 0) {
         switch(tag) {
           default:
-            input.SkipLastField();
+            CustomOptions = CustomOptions.ReadOrSkipUnknownField(input);
             break;
           case 264: {
             Deprecated = input.ReadBool();
@@ -4644,6 +4658,8 @@ namespace Google.Protobuf.Reflection {
       get { return Descriptor; }
     }
 
+    internal CustomOptions CustomOptions{ get; private set; } = CustomOptions.Empty;
+
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public MethodOptions() {
       OnConstruction();
@@ -4783,7 +4799,7 @@ namespace Google.Protobuf.Reflection {
       while ((tag = input.ReadTag()) != 0) {
         switch(tag) {
           default:
-            input.SkipLastField();
+            CustomOptions = CustomOptions.ReadOrSkipUnknownField(input);
             break;
           case 264: {
             Deprecated = input.ReadBool();

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

@@ -112,5 +112,10 @@ namespace Google.Protobuf.Reflection
         {
             return File.DescriptorPool.FindSymbol<EnumValueDescriptor>(FullName + "." + name);
         }
+
+        /// <summary>
+        /// The (possibly empty) set of custom options for this enum.
+        /// </summary>
+        public CustomOptions CustomOptions => Proto.Options?.CustomOptions ?? CustomOptions.Empty;
     }
 }
\ No newline at end of file

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

@@ -66,5 +66,10 @@ namespace Google.Protobuf.Reflection
         /// Returns the enum descriptor that this value is part of.
         /// </summary>
         public EnumDescriptor EnumDescriptor { get { return enumDescriptor; } }
+
+        /// <summary>
+        /// The (possibly empty) set of custom options for this enum value.
+        /// </summary>
+        public CustomOptions CustomOptions => Proto.Options?.CustomOptions ?? CustomOptions.Empty;
     }
 }
\ No newline at end of file

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

@@ -250,6 +250,11 @@ namespace Google.Protobuf.Reflection
             }
         }
 
+        /// <summary>
+        /// The (possibly empty) set of custom options for this field.
+        /// </summary>
+        public CustomOptions CustomOptions => Proto.Options?.CustomOptions ?? CustomOptions.Empty;
+
         /// <summary>
         /// Look up and cross-link all field types etc.
         /// </summary>

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

@@ -329,5 +329,10 @@ namespace Google.Protobuf.Reflection
         /// The file descriptor for <c>descriptor.proto</c>.
         /// </value>
         public static FileDescriptor DescriptorProtoFileDescriptor { get { return DescriptorReflection.Descriptor; } }
+
+        /// <summary>
+        /// The (possibly empty) set of custom options for this file.
+        /// </summary>
+        public CustomOptions CustomOptions => Proto.Options?.CustomOptions ?? CustomOptions.Empty;
     }
 }

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

@@ -220,6 +220,11 @@ namespace Google.Protobuf.Reflection
         public T FindDescriptor<T>(string name)  where T : class, IDescriptor =>
             File.DescriptorPool.FindSymbol<T>(FullName + "." + name);
 
+        /// <summary>
+        /// The (possibly empty) set of custom options for this message.
+        /// </summary>
+        public CustomOptions CustomOptions => Proto.Options?.CustomOptions ?? CustomOptions.Empty;
+
         /// <summary>
         /// Looks up and cross-links all fields and nested types.
         /// </summary>

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

@@ -67,6 +67,11 @@ namespace Google.Protobuf.Reflection
         /// </value>
         public bool IsServerStreaming { get { return proto.ServerStreaming; } }
 
+        /// <summary>
+        /// The (possibly empty) set of custom options for this method.
+        /// </summary>
+        public CustomOptions CustomOptions => Proto.Options?.CustomOptions ?? CustomOptions.Empty;
+
         internal MethodDescriptor(MethodDescriptorProto proto, FileDescriptor file,
                                   ServiceDescriptor parent, int index)
             : base(file, parent.FullName + "." + proto.Name, index)

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

@@ -90,6 +90,11 @@ namespace Google.Protobuf.Reflection
         /// </value>
         public OneofAccessor Accessor { get { return accessor; } }
 
+        /// <summary>
+        /// The (possibly empty) set of custom options for this oneof.
+        /// </summary>
+        public CustomOptions CustomOptions => proto.Options?.CustomOptions ?? CustomOptions.Empty;
+
         internal void CrossLink()
         {
             List<FieldDescriptor> fieldCollection = new List<FieldDescriptor>();

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

@@ -78,6 +78,11 @@ namespace Google.Protobuf.Reflection
             return File.DescriptorPool.FindSymbol<MethodDescriptor>(FullName + "." + name);
         }
 
+        /// <summary>
+        /// The (possibly empty) set of custom options for this service.
+        /// </summary>
+        public CustomOptions CustomOptions => Proto.Options?.CustomOptions ?? CustomOptions.Empty;
+
         internal void CrossLink()
         {
             foreach (MethodDescriptor method in methods)

src/google/protobuf/compiler/csharp/csharp_helpers.h

@@ -120,6 +120,22 @@ inline bool IsDescriptorProto(const FileDescriptor* descriptor) {
   return descriptor->name() == "google/protobuf/descriptor.proto";
 }
 
+// Determines whether the given message is an options message within descriptor.proto.
+inline bool IsDescriptorOptionMessage(const Descriptor* descriptor) {
+  if (!IsDescriptorProto(descriptor->file())) {
+    return false;
+  }
+  const string name = descriptor->full_name();
+  return name == "google.protobuf.FileOptions" ||
+      name == "google.protobuf.MessageOptions" ||
+      name == "google.protobuf.FieldOptions" ||
+      name == "google.protobuf.OneofOptions" ||
+      name == "google.protobuf.EnumOptions" ||
+      name == "google.protobuf.EnumValueOptions" ||
+      name == "google.protobuf.ServiceOptions" ||
+      name == "google.protobuf.MethodOptions";
+}
+
 inline bool IsWrapperType(const FieldDescriptor* descriptor) {
   return descriptor->type() == FieldDescriptor::TYPE_MESSAGE &&
       descriptor->message_type()->file()->name() == "google/protobuf/wrappers.proto";

src/google/protobuf/compiler/csharp/csharp_message.cc

@@ -151,6 +151,12 @@ void MessageGenerator::Generate(io::Printer* printer) {
     "  get { return Descriptor; }\n"
     "}\n"
     "\n");
+  // CustomOptions property, only for options messages
+  if (IsDescriptorOptionMessage(descriptor_)) {
+    printer->Print(
+      "internal CustomOptions CustomOptions{ get; private set; } = CustomOptions.Empty;\n"
+       "\n");
+  }
 
   // Parameterless constructor and partial OnConstruction method.
   WriteGeneratedCodeAttributes(printer);
@@ -475,10 +481,18 @@ void MessageGenerator::GenerateMergingMethods(io::Printer* printer) {
     "  switch(tag) {\n");
   printer->Indent();
   printer->Indent();
+  // Option messages need to store unknown fields so that options can be parsed later.
+  if (IsDescriptorOptionMessage(descriptor_)) {
+	printer->Print(
+      "default:\n"
+      "  CustomOptions = CustomOptions.ReadOrSkipUnknownField(input);\n"
+      "  break;\n");
+  } else {
     printer->Print(
       "default:\n"
       "  input.SkipLastField();\n" // We're not storing the data, but we still need to consume it.
       "  break;\n");
+  }
   for (int i = 0; i < fields_by_number().size(); i++) {
     const FieldDescriptor* field = fields_by_number()[i];
     internal::WireFormatLite::WireType wt =