Override of the upstream DD4hep_GdmlDetector to provide gdmlFile name

This is a copy of create_detector in https://github.com/AIDASoft/DD4hep/blob/master/DDCore/src/gdml/GdmlPlugins.cpp but with support for name in the gdml tag to only load the volume with that name (required to be at top level).

• make gdmlFile attribute name optional for backwards compatibility

src/DD4hep_GdmlDetector.cpp

+//==========================================================================
+//  AIDA Detector description implementation 
+//--------------------------------------------------------------------------
+// Copyright (C) Organisation europeenne pour la Recherche nucleaire (CERN)
+// All rights reserved.
+//
+// For the licensing terms see $DD4hepINSTALL/LICENSE.
+// For the list of contributors see $DD4hepINSTALL/doc/CREDITS.
+//
+// Author     : M.Frank
+//
+//==========================================================================
+
+// Framework include files
+#include "DD4hep/Detector.h"
+#include "DD4hep/Memory.h"
+#include "DD4hep/DD4hepUI.h"
+#include "DD4hep/Factories.h"
+#include "DD4hep/Printout.h"
+#include "DD4hep/DetectorTools.h"
+#include "DD4hep/DetFactoryHelper.h"
+#include "XML/DocumentHandler.h"
+#include "XML/Utilities.h"
+
+// ROOT includes
+#include "TInterpreter.h"
+#include "TGeoElement.h"
+#include "TGeoManager.h"
+#include "TGDMLParse.h"
+#include "TGDMLWrite.h"
+#include "TUri.h"
+
+using namespace std;
+using namespace dd4hep;
+
+#if ROOT_VERSION_CODE >= ROOT_VERSION(6,13,0)
+
+/// Factory to import subdetectors from GDML fragment
+static Ref_t create_detector(Detector& description, xml_h e, Ref_t /* sens_det */)  {
+  using namespace dd4hep::detail;
+  xml_det_t   x_det = e;
+  int         id    = x_det.hasAttr(_U(id)) ? x_det.id() : 0;
+  xml_dim_t   x_pos  (x_det.child(_U(position),false));
+  xml_dim_t   x_rot  (x_det.child(_U(rotation),false));
+  xml_dim_t   x_gdml (x_det.child(_U(gdmlFile)));
+  xml_dim_t   x_par  (x_det.child(_U(parent)));
+  string      name    = x_det.nameStr();
+  string      par_nam = x_par.nameStr();
+  string      gdml    = x_gdml.attr<string>(_U(ref));
+  string      gdml_physvol = dd4hep::getAttrOrDefault<string>(x_gdml, _Unicode(physvol), "");
+  DetElement  det_parent = description.detector(par_nam);
+  TGDMLParse parser;
+  if ( !gdml.empty() && gdml[0] == '/' )  {
+    TUri uri(gdml.c_str());
+    gdml = uri.GetRelativePart();
+  }
+  else {
+    string path = xml::DocumentHandler::system_path(e, gdml);
+    TUri uri(path.c_str());
+    gdml = uri.GetRelativePart();
+  }
+  if ( !det_parent.isValid() )  {
+    except(name,"+++ Cannot access detector parent: %s",par_nam.c_str());
+  }
+  DetElement  sdet(name, id);
+  Volume volume = parser.GDMLReadFile(gdml.c_str());
+  if ( !volume.isValid() )   {
+    except("ROOTGDMLParse","+++ Failed to parse GDML file:%s",gdml.c_str());
+  }
+  volume.import(); // We require the extensions in dd4hep.
+  printout(INFO,"ROOTGDMLParse","+++ Attach GDML volume %s", volume.name());
+  Volume mother = det_parent.volume();
+  PlacedVolume pv;
+
+  if ( !gdml_physvol.empty() ) {
+    PlacedVolume node = volume->FindNode(gdml_physvol.c_str());
+    if ( !node.isValid() ) {
+      printout(ERROR,"ROOTGDMLParse","+++ Invalid gdml placed volume %s", gdml_physvol.c_str());
+      printout(ERROR,"ROOTGDMLParse","+++ Valid top-level nodes are:");
+      volume->PrintNodes();
+      except("ROOTGDMLParse","+++ Failed to parse GDML file:%s for node:%s",
+        gdml.c_str(), gdml_physvol.c_str());
+    }
+    volume = node.volume();
+  }
+
+  if ( x_pos && x_rot )   {
+    Rotation3D rot(RotationZYX(x_rot.z(),x_rot.y(),x_rot.x()));
+    Transform3D transform(rot,Position(x_pos.x(),x_pos.y(),x_pos.z()));
+    pv = mother.placeVolume(volume,transform);
+  }
+  else if ( x_rot )  {
+    Rotation3D rot(RotationZYX(x_rot.z(),x_rot.y(),x_rot.x()));
+    Transform3D transform(rot,Position(0,0,0));
+    pv = mother.placeVolume(volume,transform);
+  }
+  else if ( x_pos )   {
+    pv = mother.placeVolume(volume,Position(x_pos.x(),x_pos.y(),x_pos.z()));
+  }
+  else  {
+    pv = mother.placeVolume(volume);
+  }
+  volume.setVisAttributes(description, x_det.visStr());
+  volume.setLimitSet(description, x_det.limitsStr());
+  volume.setRegion(description, x_det.regionStr());
+  if ( id != 0 )  {
+    pv.addPhysVolID("system", id);
+  }
+  sdet.setPlacement(pv);
+  return sdet;
+}
+
+// first argument is the type from the xml file
+DECLARE_DETELEMENT(DD4hep_GdmlDetector,create_detector)
+
+#endif