o2-sim: Apply dynamic detector lib loading to all detectors

* code reduction:
- automatic factory method via DetImpl base class
- helper macro to implement extern "C" hooks

* application of dynamic loading during geometry construction
  and in the HitMerger

* removal of detector linking to o2-sim in CMakeFile

The benefit is ~60MB of memory reduction when only simulating
single detectors `o2-sim-serial -m TPC` and a faster load time in general.

Detectors/Base/include/DetectorsBase/Detector.h

@@ -41,6 +41,16 @@
 
 #include <fairmq/FwdDecls.h>
 
+// macro implementation helper to code unmanged "C" function
+// constructing a detector
+#define O2DetectorCreatorImpl(creatorfuncname, detname)      \
+  extern "C" {                                               \
+  o2::base::Detector* create_detector_##detname(bool active) \
+  {                                                          \
+    return creatorfuncname(active);                          \
+  }                                                          \
+  }
+
 namespace o2::base
 {
 
@@ -302,6 +312,19 @@ class DetImpl : public o2::base::Detector
   // offer same constructors as base
   using Detector::Detector;
 
+  /// automatic implementation of static Detector factory functions
+  template <typename... Args>
+  static o2::base::Detector* create(Args&&... args)
+  {
+    if constexpr (std::is_constructible_v<Det, Args...>) {
+      return new Det(std::forward<Args>(args)...);
+    } else {
+      static_assert(std::is_constructible_v<Det, Args...>,
+                    "No matching constructor found in Derived class.");
+      return nullptr;
+    }
+  }
+
   // default implementation for getHitBranchNames
   std::string getHitBranchNames(int probe) const override
   {

Detectors/CPV/simulation/src/Detector.cxx

@@ -37,6 +37,7 @@
 using namespace o2::cpv;
 
 ClassImp(Detector);
+O2DetectorCreatorImpl(o2::cpv::Detector::create, cpv);
 
 Detector::Detector(Bool_t active)
   : o2::base::DetImpl<Detector>("CPV", active),

Detectors/EMCAL/simulation/src/Detector.cxx

@@ -38,6 +38,7 @@
 using namespace o2::emcal;
 
 ClassImp(Detector);
+O2DetectorCreatorImpl(o2::emcal::Detector::create, emc);
 
 Detector::Detector(Bool_t active)
   : o2::base::DetImpl<Detector>("EMC", active),

Detectors/FIT/FDD/simulation/src/Detector.cxx

@@ -39,6 +39,7 @@ using o2::fdd::Geometry;
 using o2::fdd::Hit;
 
 ClassImp(o2::fdd::Detector);
+O2DetectorCreatorImpl(o2::fdd::Detector::create, fdd);
 
 //_____________________________________________________________________________
 Detector::Detector(Bool_t Active)

Detectors/FIT/FT0/simulation/src/Detector.cxx

@@ -42,6 +42,7 @@ using namespace o2::ft0;
 using o2::ft0::Geometry;
 
 ClassImp(Detector);
+O2DetectorCreatorImpl(o2::ft0::Detector::create, ft0);
 
 Detector::Detector(Bool_t Active)
   : o2::base::DetImpl<Detector>("FT0", Active), mIdSens1(0), mPMTeff(nullptr), mHits(o2::utils::createSimVector<o2::ft0::HitType>()), mTrackIdTop(-1), mTrackIdMCPtop(-1)

Detectors/FIT/FV0/simulation/src/Detector.cxx

@@ -30,6 +30,7 @@ using namespace o2::fv0;
 using o2::fv0::Geometry;
 
 ClassImp(Detector);
+O2DetectorCreatorImpl(o2::fv0::Detector::create, fv0);
 
 Detector::Detector()
   : o2::base::DetImpl<Detector>("FV0", kTRUE),

Detectors/HMPID/simulation/src/Detector.cxx

@@ -1379,3 +1379,4 @@ void Detector::defineOpticalProperties()
 } // end namespace o2
 
 ClassImp(o2::hmpid::Detector);
+O2DetectorCreatorImpl(o2::hmpid::Detector::create, hmp);

Detectors/ITSMFT/ITS/simulation/include/ITSSimulation/Detector.h

@@ -79,12 +79,6 @@ class Detector : public o2::base::DetImpl<Detector>
   ///         kFALSE for inactive detectors
   Detector(Bool_t active, TString name = "ITS");
 
-  // Factory method
-  static o2::base::Detector* create(const char* name, bool active)
-  {
-    return new Detector(active, name);
-  }
-
   /// Default constructor
   Detector();
 

Detectors/ITSMFT/ITS/simulation/src/Detector.cxx

@@ -1318,10 +1318,9 @@ Hit* Detector::addHit(int trackID, int detID, const TVector3& startPos, const TV
 
 ClassImp(o2::its::Detector);
 
-// Define Factory method for calling from the outside
 extern "C" {
 o2::base::Detector* create_detector_its(const char* name, bool active)
 {
-  return o2::its::Detector::create(name, active);
-}
+  return o2::its::Detector::create(active, name);
 }
+}

Detectors/ITSMFT/MFT/simulation/src/Detector.cxx

@@ -38,6 +38,7 @@ using o2::itsmft::Hit;
 using namespace o2::mft;
 
 ClassImp(o2::mft::Detector);
+O2DetectorCreatorImpl(o2::mft::Detector::create, mft);
 
 //_____________________________________________________________________________
 Detector::Detector()

Detectors/MUON/MCH/Simulation/src/Detector.cxx

@@ -20,6 +20,7 @@
 #include "TGeoManager.h"
 
 ClassImp(o2::mch::Detector);
+O2DetectorCreatorImpl(o2::mch::Detector::create, mch);
 
 namespace o2
 {

Detectors/MUON/MID/Simulation/src/Detector.cxx

@@ -17,6 +17,7 @@
 #include "FairVolume.h"
 
 ClassImp(o2::mid::Detector);
+O2DetectorCreatorImpl(o2::mid::Detector::create, mid);
 
 namespace o2
 {

Detectors/PHOS/simulation/src/Detector.cxx

@@ -37,6 +37,7 @@
 using namespace o2::phos;
 
 ClassImp(Detector);
+O2DetectorCreatorImpl(o2::phos::Detector::create, phs);
 
 Detector::Detector(Bool_t active)
   : o2::base::DetImpl<Detector>("PHS", active),

Detectors/TOF/simulation/src/Detector.cxx

@@ -26,6 +26,7 @@
 using namespace o2::tof;
 
 ClassImp(Detector);
+O2DetectorCreatorImpl(o2::tof::Detector::create, tof);
 
 Detector::Detector(Bool_t active)
   : o2::base::DetImpl<Detector>("TOF", active), mEventNr(0), mTOFHoles(kTRUE), mHits(o2::utils::createSimVector<HitType>())

Detectors/TPC/simulation/include/TPCSimulation/Detector.h

@@ -68,12 +68,6 @@ class Detector : public o2::base::DetImpl<Detector>
    */
   Detector(Bool_t Active);
 
-  // Factory method
-  static o2::base::Detector* create(bool active)
-  {
-    return new Detector(active);
-  }
-
   /**      default constructor    */
   Detector();
 

Detectors/TPC/simulation/src/Detector.cxx

@@ -3217,10 +3217,4 @@ std::string Detector::getHitBranchNames(int probe) const
 
 ClassImp(o2::tpc::Detector);
 
-// Define Factory method for calling from the outside
-extern "C" {
-o2::base::Detector* create_detector_tpc(bool active)
-{
-  return o2::tpc::Detector::create(active);
-}
-}
+O2DetectorCreatorImpl(o2::tpc::Detector::create, tpc)

Detectors/TRD/simulation/src/Detector.cxx

@@ -526,3 +526,4 @@ void Detector::addAlignableVolumes() const
 }
 
 ClassImp(Detector);
+O2DetectorCreatorImpl(o2::trd::Detector::create, trd)

Detectors/Upgrades/ALICE3/ECal/simulation/src/Detector.cxx

@@ -241,4 +241,5 @@ o2::itsmft::Hit* Detector::addHit(int trackID, int detID, const TVector3& startP
 } // namespace ecal
 } // namespace o2
 
-ClassImp(o2::ecal::Detector);
+ClassImp(o2::ecal::Detector);
+O2DetectorCreatorImpl(o2::ecal::Detector::create, ecl);

Detectors/Upgrades/ALICE3/FCT/simulation/src/Detector.cxx

@@ -575,3 +575,4 @@ Hit* Detector::addHit(int trackID, int detID, const TVector3& startPos, const TV
 }
 
 ClassImp(o2::fct::Detector);
+O2DetectorCreatorImpl(o2::fct::Detector::create, fct);

Detectors/Upgrades/ALICE3/FT3/simulation/src/Detector.cxx

@@ -761,3 +761,4 @@ Hit* Detector::addHit(int trackID, int detID, const TVector3& startPos, const TV
 }
 
 ClassImp(o2::ft3::Detector);
+O2DetectorCreatorImpl(o2::ft3::Detector::create, ft3);

Detectors/Upgrades/ALICE3/MID/simulation/src/Detector.cxx

@@ -233,4 +233,5 @@ o2::itsmft::Hit* Detector::addHit(int trackID, int detID, const TVector3& startP
   return &(mHits->back());
 }
 } // namespace o2::mi3
-ClassImp(o2::mi3::Detector);
+ClassImp(o2::mi3::Detector);
+O2DetectorCreatorImpl(o2::mi3::Detector::create, mi3);

Detectors/Upgrades/ALICE3/RICH/simulation/src/Detector.cxx

@@ -428,4 +428,5 @@ void Detector::prepareLayout()
 } // namespace rich
 } // namespace o2
 
-ClassImp(o2::rich::Detector);
+ClassImp(o2::rich::Detector);
+O2DetectorCreatorImpl(o2::rich::Detector::create, rch);

Detectors/Upgrades/ALICE3/TRK/simulation/include/TRKSimulation/Detector.h

@@ -34,12 +34,6 @@ class Detector : public o2::base::DetImpl<Detector>
   Detector();
   ~Detector();
 
-  // Factory method
-  static o2::base::Detector* create(bool active)
-  {
-    return new Detector(active);
-  }
-
   void ConstructGeometry() override;
 
   o2::itsmft::Hit* addHit(int trackID, int detID, const TVector3& startPos, const TVector3& endPos,

Detectors/Upgrades/ALICE3/TRK/simulation/src/Detector.cxx

@@ -366,11 +366,4 @@ o2::itsmft::Hit* Detector::addHit(int trackID, int detID, const TVector3& startP
 } // namespace o2
 
 ClassImp(o2::trk::Detector);
-
-// Define Factory method for calling from the outside
-extern "C" {
-o2::base::Detector* create_detector_trk(bool active)
-{
-  return o2::trk::Detector::create(active);
-}
-}
+O2DetectorCreatorImpl(o2::trk::Detector::create, trk);

Detectors/ZDC/simulation/src/Detector.cxx

@@ -39,6 +39,7 @@
 using namespace o2::zdc;
 
 ClassImp(o2::zdc::Detector);
+O2DetectorCreatorImpl(o2::zdc::Detector::create, zdc);
 #define kRaddeg TMath::RadToDeg()
 
 //_____________________________________________________________________________