fix --database.check-version on an empty directory

arangod/RestServer/CheckVersionFeature.cpp

@@ -97,6 +97,10 @@ void CheckVersionFeature::start() {
 
   // and force shutdown
   server()->beginShutdown();
+  
+  LOG(DEBUG) << "checking version on an empty database";
+  usleep(1 * 1000 * 1000);  
+  TRI_EXIT_FUNCTION(EXIT_SUCCESS, nullptr);
 }
 
 void CheckVersionFeature::checkVersion() {

arangod/RestServer/DatabaseFeature.cpp

@@ -341,7 +341,7 @@ void DatabaseFeature::start() {
   }
 
   // TODO: handle _upgrade and _checkVersion here
-
+  
   // activate deadlock detection in case we're not running in cluster mode
   if (!arangodb::ServerState::instance()->isRunningInCluster()) {
     enableDeadlockDetection();

arangod/RestServer/DatabaseFeature.h

@@ -119,6 +119,7 @@ class DatabaseFeature final : public application_features::ApplicationFeature {
   bool throwCollectionNotLoadedError() const { return _throwCollectionNotLoadedError.load(std::memory_order_relaxed); }
   void throwCollectionNotLoadedError(bool value) { _throwCollectionNotLoadedError.store(value); }
   bool check30Revisions() const { return _check30Revisions; }
+  void isInitiallyEmpty(bool value) { _isInitiallyEmpty = value; }
 
  private:
   void closeDatabases();

arangod/RestServer/ServerIdFeature.cpp

@@ -51,9 +51,18 @@ void ServerIdFeature::start() {
   auto database = application_features::ApplicationServer::getFeature<DatabaseFeature>("Database");
   
   // read the server id or create a new one
-  int res = determineId(database->checkVersion());
+  bool const checkVersion = database->checkVersion();
+  int res = determineId(checkVersion);
 
   if (res == TRI_ERROR_ARANGO_EMPTY_DATADIR) {
+    if (checkVersion) {
+      // when we are version checking, we will not fail here
+      // additionally notify the database feature that we had no VERSION file
+      database->isInitiallyEmpty(true);
+      return;
+    }
+
+    // otherwise fail
     THROW_ARANGO_EXCEPTION(res);
   }