Add std::monostate to represent null field and add Ipc::Shutdown

Fixes #265

// FIXME lsRequestId should be number | string | null (std::variant<std::monostate, double, string>

src/ipc.cc

@@ -10,6 +10,8 @@ const char* IpcIdToString(IpcId id) {
       return "initialize";
     case IpcId::Initialized:
       return "initialized";
+    case IpcId::Shutdown:
+      return "shutdown";
     case IpcId::Exit:
       return "exit";
     case IpcId::TextDocumentDidOpen:

src/ipc.h

@@ -10,6 +10,7 @@ enum class IpcId : int {
   CancelRequest = 0,
   Initialize,
   Initialized,
+  Shutdown,
   Exit,
   TextDocumentDidOpen,
   TextDocumentDidChange,

src/messages/shutdown.cc

@@ -0,0 +1,27 @@
+#include "message_handler.h"
+#include "queue_manager.h"
+
+namespace {
+struct Ipc_Shutdown : public IpcMessage<Ipc_Shutdown> {
+  static const IpcId kIpcId = IpcId::Shutdown;
+};
+MAKE_REFLECT_EMPTY_STRUCT(Ipc_Shutdown);
+REGISTER_IPC_MESSAGE(Ipc_Shutdown);
+
+struct Out_Shutdown
+    : public lsOutMessage<Out_Shutdown> {
+  lsRequestId id;
+  std::monostate result;
+};
+MAKE_REFLECT_STRUCT(Out_Shutdown, jsonrpc, id, result);
+
+struct ShutdownHandler : BaseMessageHandler<Ipc_Shutdown> {
+  void Run(Ipc_Shutdown* request) override {
+    Out_Shutdown out;
+    // FIXME lsRequestId should be number | string | null
+    out.id.id0 = 0;
+    QueueManager::WriteStdout(IpcId::TextDocumentDefinition, out);
+  }
+};
+REGISTER_MESSAGE_HANDLER(ShutdownHandler);
+}  // namespace

src/serializer.cc

@@ -201,6 +201,14 @@ void Reflect(TVisitor& visitor, IndexFile& value) {
   REFLECT_MEMBER_END();
 }
 
+void Reflect(Reader& visitor, std::monostate&) {
+  visitor.GetNull();
+}
+
+void Reflect(Writer& visitor, std::monostate&) {
+  visitor.Null();
+}
+
 void Reflect(Reader& visitor, SerializeFormat& value) {
   std::string fmt = visitor.GetString();
   value = fmt[0] == 'm' ? SerializeFormat::MessagePack : SerializeFormat::Json;

src/serializer.h

@@ -255,6 +255,9 @@ void ReflectMember(Reader& visitor, const char* name, T& value) {
 
 // Specializations
 
+void Reflect(Reader& visitor, std::monostate&);
+void Reflect(Writer& visitor, std::monostate&);
+
 void Reflect(Reader& visitor, SerializeFormat& value);
 void Reflect(Writer& visitor, SerializeFormat& value);