Update TGeo keyname handling

Don't assume any keyname (-->"") when loading geometry in
MCReplayGenericApplication. TGeo will take first key in file where it
can find a valid geometry

Author: Benedikt Volkel

MCReplay/src/MCReplayEngine.cxx

@@ -728,7 +728,7 @@ int MCReplayEngine::getMediumId(int volId) const
         mCurrentLookups->volidtomedium[volId]->size() != 0) {
       // extract medium name, from that the TGeoMedium and from that finally the ID
       auto mediumName{*(mCurrentLookups->volidtomedium[volId])};
-      auto medium{gGeoManager->GetMedium(mediumName.c_str())};
+      auto medium{mGeoManager->GetMedium(mediumName.c_str())};
       if (medium) {
         return medium->GetId();
       }

MCReplay/src/MCReplayGenericApplication.cxx

@@ -27,11 +27,17 @@ MCReplayGenericApplication::MCReplayGenericApplication(const std::string& geoFil
     mStack{nullptr},
     mPrimGen{nullptr}
 {
-  if (mGeoFilename.empty() || mGeoKeyname.empty()) {
-    // Otherwise assume that the geometry was constructed already by the user
+  if (mGeoFilename.empty()) {
+    // we only require the file name to be non-empty. In that case the geo manager would take the first key
+    // under which a geometry can be found
     ::Fatal("MCReplayGenericApplication::ctor", "Need file and key name where to find TGeo geometry");
   }
+
   mGeoManager = TGeoManager::Import(mGeoFilename.c_str(), mGeoKeyname.c_str());
+
+  if (!mGeoManager) {
+    ::Fatal("MCReplayGenericApplication::ctor", "Could not load geometry from path %s under key %s", mGeoFilename.c_str(), mGeoKeyname.c_str());
+  }
 }
 
 void MCReplayGenericApplication::ConstructGeometry()

MCReplay/src/replay.cxx

@@ -24,7 +24,7 @@ int main(int argc, char* argv[])
 {
   // prepare reading cmd options and store them
   bpo::options_description desc("Replaying a previously recorded particle transport step-by-step. Mainly meant for checking and performance measurements/optimisation of the transport");
-  desc.add_options()("help", "show this help message and exit")("stepfilename", bpo::value<std::string>()->default_value("MCStepLoggerOutput.root"), "MCStepLogger filename")("steptreename", bpo::value<std::string>()->default_value("StepLoggerTree"), "treename inside file where to find step tree")("geofilename", bpo::value<std::string>()->default_value("o2sim_geometry.root"), "ROOT geometry filename")("geokeyname", bpo::value<std::string>()->default_value("FAIRGeom"), "key name inside geo file where to find geometry tree")("nevents,n", bpo::value<int>()->default_value(-1), "number of events to replay")("energycut,e", bpo::value<float>()->default_value(-1.), "energy cut to be applied [GeV]");
+  desc.add_options()("help", "show this help message and exit")("stepfilename", bpo::value<std::string>()->default_value("MCStepLoggerOutput.root"), "MCStepLogger filename")("steptreename", bpo::value<std::string>()->default_value("StepLoggerTree"), "treename inside file where to find step tree")("geofilename", bpo::value<std::string>()->default_value("o2sim_geometry.root"), "ROOT geometry filename")("geokeyname", bpo::value<std::string>()->default_value(""), "key name inside geo file where to find geometry tree")("nevents,n", bpo::value<int>()->default_value(-1), "number of events to replay")("energycut,e", bpo::value<float>()->default_value(-1.), "energy cut to be applied [GeV]");
 
   bpo::variables_map vm;
   bpo::store(bpo::parse_command_line(argc, argv, desc), vm);