Use the GenEvent event_number in HepMcParticleLink constructors where it is known

Use the GenEvent event_number in HepMcParticleLink constructors where it is known

InnerDetector/InDetValidation/InDetRecStatistics/src/TrackStatHelper.cxx

 /*
-  Copyright (C) 2002-2023 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration
 */
 
 //////////////////////////////////////////////////////////////////
@@ -426,7 +426,7 @@ void InDet::TrackStatHelper::addEvent(const TrackCollection              * recTr
     bool matched = false;
     int nmatched = 0;
     
-    HepMcParticleLink hmpl2(particle,truth->second,HepMcParticleLink::IS_EVENTNUM); // FIXME truth->second is actually the position of the GenEvent in the McEventCollection!! See InDetRecStatisticsAlg::selectGenSignal(...) method (only client of TrackStatsHelper)
+    HepMcParticleLink hmpl2(particle,particle->parent_event()->event_number(),HepMcParticleLink::IS_EVENTNUM);
     recoToTruthMap::iterator rttIter=rttMap.find(hmpl2);
     if(rttIter != rttMap.end()){
       for(imap = rttMap.lower_bound(hmpl2); imap !=rttMap.upper_bound(hmpl2); ++imap){

MuonSpectrometer/MuonTruthAlgs/src/MuonDecayTruthTrajectoryBuilder.cxx

 /*
-  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration
 */
 
 // Niels van Eldik 2010
@@ -41,18 +41,19 @@ namespace Muon {
 
             // copy the outer half to result
             while (!tmp.empty()) {
-                ATH_MSG_DEBUG(" Adding daughter: " << current);
-                result->emplace_back(tmp.top(),0,HepMcParticleLink::IS_EVENTNUM); // FIXME should not be using eventIndex=0 with IS_EVENTNUM either obtain event number from GenParticlePtr or use IS_POSITION
+                ATH_MSG_DEBUG(" Adding daughter: " << current); // FIXME "current" is not changed in this loop - it might make sense to print tmp.top() instead here?
+                result->emplace_back(tmp.top(),tmp.top()->parent_event()->event_number(),HepMcParticleLink::IS_EVENTNUM);
                 tmp.pop();
             }
 
             // The input particle itself
-            result->emplace_back(input,0,HepMcParticleLink::IS_EVENTNUM); // FIXME should not be using eventIndex=0 with IS_EVENTNUM either obtain event number from GenParticlePtr or use IS_POSITION
+            result->emplace_back(input,input->parent_event()->event_number(),HepMcParticleLink::IS_EVENTNUM);
 
             // Now continue towards the interaction point
             while ((next = getMother(current))) {
-                ATH_MSG_DEBUG(" Adding mother:  " << current);
-                result->emplace_back(current = next,0,HepMcParticleLink::IS_EVENTNUM); // FIXME should not be using eventIndex=0 with IS_EVENTNUM either obtain event number from GenParticlePtr or use IS_POSITION
+                ATH_MSG_DEBUG(" Adding mother:  " << current); // FIXME "current" here refers to the child particle rather than the mother? Consider moving this after "current = next"
+                current = next;
+                result->emplace_back(current,current->parent_event()->event_number(),HepMcParticleLink::IS_EVENTNUM);
             }
 
             ATH_MSG_DEBUG(" Final TruthTrajectory: ");

Simulation/ISF/ISF_Core/ISF_Services/test/InputConverter_test.cxx

@@ -40,8 +40,7 @@ ATLAS_NO_CHECK_FILE_THREAD_SAFETY;
 #include "GeoPrimitives/GeoPrimitives.h"
 
 // HepMC
-#include "AtlasHepMC/GenParticle.h"
-#include "AtlasHepMC/GenVertex.h"
+#include "AtlasHepMC/GenEvent.h"
 #include "AtlasHepMC/Operators.h"
 #include "GeneratorObjects/HepMcParticleLink.h"
 #include "GeneratorObjects/McEventCollection.h"
@@ -205,13 +204,15 @@ TEST_F(InputConverter_test, convertParticle_using_generated_mass) {
   // create dummy input McEventCollection containing a dummy GenEvent
   SG::WriteHandle<McEventCollection> inputTestDataHandle{"GEN_EVENT"};
   inputTestDataHandle = std::make_unique<McEventCollection>();
-  inputTestDataHandle->push_back(new HepMC::GenEvent());
+  const int signal_process_id{1};
+  const int event_number{1};
+  inputTestDataHandle->push_back(HepMC::newGenEvent(signal_process_id, event_number));
   HepMC::GenEvent& ge = *(inputTestDataHandle->at(0));
   ge.add_vertex( prodVtx );
   //AV: we set barcode here because only here the particle in HepMC3 enters event and can have a meaningful barcode.
   HepMC::suggest_barcode(genPart,particleBarcode);
   HepMC::fillBarcodesAttribute(&ge);
-  HepMcParticleLink* trackLink = new HepMcParticleLink(particleBarcode, 0, HepMcParticleLink::IS_EVENTNUM, HepMcParticleLink::IS_BARCODE); // FIXME barcode-based syntax
+  HepMcParticleLink* trackLink = new HepMcParticleLink(particleBarcode, event_number, HepMcParticleLink::IS_EVENTNUM, HepMcParticleLink::IS_BARCODE); // FIXME barcode-based syntax
 
   Amg::Vector3D expectedPos(9.8, 7.65, 4.3);
   Amg::Vector3D expectedMom(12.3, 45.6, 78.9);
@@ -261,13 +262,15 @@ TEST_F(InputConverter_test, convertParticle_using_particleDataTable_photon) {
   // create dummy input McEventCollection containing a dummy GenEvent
   SG::WriteHandle<McEventCollection> inputTestDataHandle{"GEN_EVENT"};
   inputTestDataHandle = std::make_unique<McEventCollection>();
-  inputTestDataHandle->push_back(new HepMC::GenEvent());
+  const int signal_process_id{1};
+  const int event_number{1};
+  inputTestDataHandle->push_back(HepMC::newGenEvent(signal_process_id, event_number));
   HepMC::GenEvent& ge = *(inputTestDataHandle->at(0));
   ge.add_vertex( prodVtx );
   //AV: we set barcode here because only here the particle in HepMC3 enters event and can have a meaningful barcode.
   HepMC::suggest_barcode(genPart,particleBarcode);
   HepMC::fillBarcodesAttribute(&ge);
-  HepMcParticleLink* trackLink = new HepMcParticleLink(particleBarcode, 0, HepMcParticleLink::IS_EVENTNUM, HepMcParticleLink::IS_BARCODE);
+  HepMcParticleLink* trackLink = new HepMcParticleLink(particleBarcode, event_number, HepMcParticleLink::IS_EVENTNUM, HepMcParticleLink::IS_BARCODE);
 
   Amg::Vector3D expectedPos(9.8, 7.65, 4.3);
   Amg::Vector3D expectedMom(12.3, 45.6, 78.9);
@@ -317,11 +320,13 @@ TEST_F(InputConverter_test, convertParticle_using_particleDataTable_electron) {
   // create dummy input McEventCollection containing a dummy GenEvent
   SG::WriteHandle<McEventCollection> inputTestDataHandle{"GEN_EVENT"};
   inputTestDataHandle = std::make_unique<McEventCollection>();
-  inputTestDataHandle->push_back(new HepMC::GenEvent());
+  const int signal_process_id{1};
+  const int event_number{1};
+  inputTestDataHandle->push_back(HepMC::newGenEvent(signal_process_id, event_number));
   HepMC::GenEvent& ge = *(inputTestDataHandle->at(0));
   ge.add_vertex( prodVtx );
   HepMC::suggest_barcode(genPart,particleBarcode);
-  HepMcParticleLink* trackLink = new HepMcParticleLink(particleBarcode, 0, HepMcParticleLink::IS_EVENTNUM, HepMcParticleLink::IS_BARCODE);
+  HepMcParticleLink* trackLink = new HepMcParticleLink(particleBarcode, event_number, HepMcParticleLink::IS_EVENTNUM, HepMcParticleLink::IS_BARCODE);
 
   Amg::Vector3D expectedPos(9.8, 7.65, 4.3);
   Amg::Vector3D expectedMom(12.3, 45.6, 78.9);