Added option pythia6_nolink (CMake) to postpone linking with pythia6 library. Fixes ROOT-5802

cmake/modules/FindPythia6.cmake

-# Find the Pythia6 includes and library.
-# 
-# This module defines
-# PYTHIA6_LIBRARIES, the libraries to link against to use Pythia6
-# PYTHIA6_FOUND.  If false, you cannot build anything that requires Pythia6.
-# PYTHIA6_LIBRARY, where to find the libPythia6 library.
+# - Locate pythia6 library
+# Defines:
+#
+#  PYTHIA6_FOUND
+#  PYTHIA6_INCLUDE_DIR
+#  PYTHIA6_INCLUDE_DIRS (not cached)
+#  PYTHIA6_LIBRARY
+#  PYTHIA6_LIBRARY_DIR (not cached)
+#  PYTHIA6_LIBRARIES (not cached)
 
-set(PYTHIA6_FOUND 0)
-
-
-find_library(PYTHIA6_LIBRARY NAMES pythia6 Pythia6 PATHS
-  $ENV{PYTHIA6_DIR}/lib
-  /cern/pro/lib 
+set(CMAKE_LIBRARY_PATH
+  /cern/pro/lib
   /opt/pythia 
   /opt/pythia6
   /usr/lib/pythia
@@ -18,16 +17,19 @@ find_library(PYTHIA6_LIBRARY NAMES pythia6 Pythia6 PATHS
   /usr/lib/pythia6
   /usr/local/lib/pythia6
   /usr/lib
-  /usr/local/lib
-  DOC "Specify the Pythia6 library here."
-)
+  /usr/local/lib)
 
-if(PYTHIA6_LIBRARY)
-  message(STATUS "Found Pythia6 library at ${PYTHIA6_LIBRARY}")
-  set(PYTHIA6_FOUND 1 )
-endif()
 
+find_library(PYTHIA6_LIBRARY NAMES pythia6 Pythia6
+             HINTS $ENV{PYTHIA6_DIR}/lib ${PYTHIA6_DIR}/lib)
 
 set(PYTHIA6_LIBRARIES ${PYTHIA6_LIBRARY})
+get_filename_component(PYTHIA6_LIBRARY_DIR ${PYTHIA6_LIBRARY} PATH)
+
+# handle the QUIETLY and REQUIRED arguments and set PHOTOS_FOUND to TRUE if
+# all listed variables are TRUE
+
+INCLUDE(FindPackageHandleStandardArgs)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(Pythia6 DEFAULT_MSG PYTHIA6_LIBRARY)
 
-MARK_AS_ADVANCED( PYTHIA6_FOUND PYTHIA6_LIBRARY)
+mark_as_advanced(PYTHIA6_FOUND PYTHIA6_LIBRARY)

cmake/modules/RootBuildOptions.cmake

@@ -116,6 +116,7 @@ ROOT_BUILD_OPTION(pch ON)
 ROOT_BUILD_OPTION(peac ON "PEAC, PROOF Enabled Analysis Center, requires Clarens")
 ROOT_BUILD_OPTION(pgsql ON "PostgreSQL support, requires libpq")
 ROOT_BUILD_OPTION(pythia6 ON "Pythia6 EG support, requires libPythia6")
+ROOT_BUILD_OPTION(pythia6_nolink OFF "Delayed linking of Pythia6 library")
 ROOT_BUILD_OPTION(pythia8 ON "Pythia8 EG support, requires libPythia8")
 ROOT_BUILD_OPTION(python ON "Python ROOT bindings, requires python >= 2.2")
 ROOT_BUILD_OPTION(qt OFF "Qt graphics backend, requires libqt >= 4.x")

cmake/modules/SearchInstalledSoftware.cmake

@@ -450,8 +450,8 @@ endif()
 #---Check for Pythia6-------------------------------------------------------------------
 if(pythia6)
   message(STATUS "Looking for Pythia6")
-  find_package(Pythia6)
-  if(NOT PYTHIA6_FOUND)
+  find_package(Pythia6 QUIET)
+  if(NOT PYTHIA6_FOUND AND NOT pythia6_nolink)
     if(fail-on-missing)
       message(FATAL_ERROR "Pythia6 libraries not found and they are required (pythia6 option enabled)")
     else()

montecarlo/pythia6/CMakeLists.txt

@@ -9,5 +9,11 @@ ROOT_USE_PACKAGE(math/physics)
 
 ROOT_GENERATE_DICTIONARY(G__Pythia6 *.h  LINKDEF LinkDef.h)
 ROOT_GENERATE_ROOTMAP(EGPythia6 LINKDEF LinkDef.h DEPENDENCIES EG Graf VMC Physics )
-ROOT_LINKER_LIBRARY(EGPythia6 *.cxx G__Pythia6.cxx LIBRARIES Core ${PYTHIA6_LIBRARIES} DEPENDENCIES EG Graf VMC Physics)
+if(pythia6_nolink)
+  string(REGEX REPLACE "-Wl,--no-undefined" "" CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS}")
+  ROOT_LINKER_LIBRARY(EGPythia6 *.cxx G__Pythia6.cxx LIBRARIES Core  DEPENDENCIES EG Graf VMC Physics)
+else()
+  ROOT_LINKER_LIBRARY(EGPythia6 *.cxx G__Pythia6.cxx LIBRARIES Core ${PYTHIA6_LIBRARIES} DEPENDENCIES EG Graf VMC Physics)
+endif()
+
 ROOT_INSTALL_HEADERS()