Updated GEANT4_TAG handling to new Geant4-srcs layout

note that the special tag HEAD maps to a hardcoded value

Geant4/G4config/CMakeLists.txt

@@ -21,27 +21,23 @@ else()
   set(G4DATA ../share)
 endif()
 
+# Geant4-srcs required version is by default the same as this project as
+# declared in the top level make file, with the special case "HEAD" (or empty
+# string) that maps to a special (hardcoded) branch.
 if (NOT GEANT4_TAG)
   if(DEFINED ENV{G4_NATIVE_VERSION})
     set(GEANT4_TAG $ENV{G4_NATIVE_VERSION})
-    if(NOT GEANT4_TAG MATCHES "^4\\.")
-      # G4_NATIVE_VERSION might not contain the initial '4.' that we need
-      # see https://its.cern.ch/jira/browse/LHCBGAUSS-43
-      set(GEANT4_TAG 4.${GEANT4_TAG})
-    endif()
-    if(NOT GEANT4_TAG MATCHES "^geant")
-      set(GEANT4_TAG geant${GEANT4_TAG})
-    endif()
+  elseif(CMAKE_PROJECT_VERSION STREQUAL "HEAD")
+    # Special mapping of version HEAD
+    # WARNING this must be kept up to date manually
+    set(GEANT4_TAG "lhcb/v9.6.4-branch")
   else()
-    set(GEANT4_TAG ${CMAKE_PROJECT_VERSION})
+    set(GEANT4_TAG lhcb/${CMAKE_PROJECT_VERSION})
   endif()
-  # Special mapping of version HEAD
-  if(GEANT4_TAG STREQUAL "HEAD")
-    set(GEANT4_TAG master)
-  endif()
-  set(GEANT4_TAG ${GEANT4_TAG} CACHE STRING "Tag of Geant4 to get from the Geant4-srcs repository")
 endif()
 
+set(GEANT4_TAG ${GEANT4_TAG} CACHE STRING "Tag of Geant4 to get from the Geant4-srcs repository")
+
 include(ExternalProject)
 
 ExternalProject_Add(Geant4