Simplify build/use of builtin/system Eigen

- Make builtin "imported" target depend on Eigen external project.
- Subprojects only then need to link to the Eigen3::Eigen target
  whether builtin/external is used

FullSimLight/Plugins/Examples/UserActionPlugins/DummyUserActionPlugin/CMakeLists.txt

@@ -49,7 +49,6 @@ set(PROJECT_SOURCES ${SOURCES})
 # Set up the library.
 add_library(DummyUserActionPlugin SHARED ${SOURCES})
 
-#find_package (Eigen3 REQUIRED)
 find_package(Geant4 REQUIRED)
 #find_package(FullSimLight REQUIRED)
 find_package( HDF5 REQUIRED COMPONENTS CXX )

FullSimLight/Plugins/HitsPlugin/CMakeLists.txt

@@ -51,7 +51,6 @@ set(PROJECT_SOURCES ${SOURCES})
 # Set up the library.
 add_library(GenerateHitsPlugin SHARED ${SOURCES})
 
-#find_package (Eigen3 REQUIRED)
 find_package(Geant4 REQUIRED)
 #find_package(FullSimLight REQUIRED)
 find_package( HDF5 REQUIRED COMPONENTS CXX )

FullSimLight/Plugins/TracksPlugin/CMakeLists.txt

@@ -50,7 +50,6 @@ set(PROJECT_SOURCES ${HEADERS} ${SOURCES} TracksPlugin.cc)
 # Set up the library.
 add_library(GenerateTracksPlugin SHARED ${HEADERS} ${SOURCES} TracksPlugin.cc)
 
-#find_package (Eigen3 REQUIRED)
 find_package(Geant4 REQUIRED)
 #find_package(FullSimLight REQUIRED)
 find_package( HDF5 REQUIRED COMPONENTS CXX )

GeoModelCore/GeoModelKernel/CMakeLists.txt

@@ -13,9 +13,6 @@ target_include_directories( GeoModelKernel PUBLIC
    $<INSTALL_INTERFACE:include> )
 source_group( "GeoModelKernel" FILES ${HEADERS} )
 source_group( "src" FILES ${SOURCES} )
-if( GEOMODEL_USE_BUILTIN_EIGEN3 )
-   add_dependencies( GeoModelKernel Eigen3 )
-endif()
 set_target_properties( GeoModelKernel PROPERTIES
    VERSION ${PROJECT_VERSION}
    SOVERSION ${PROJECT_VERSION_MAJOR} )

cmake/SetupEigen3.cmake

@@ -5,60 +5,51 @@
 #
 
 # Make sure that this file is only included once.
-get_property( _eigenSetUp GLOBAL PROPERTY GEOMODEL_EIGEN_SET_UP SET )
-if( _eigenSetUp )
-   unset( _eigenSetUp )
-   return()
-endif()
-set_property( GLOBAL PROPERTY GEOMODEL_EIGEN_SET_UP TRUE )
+include_guard(GLOBAL)
 
 # Configuration option for how Eigen should be used.
-option( GEOMODEL_USE_BUILTIN_EIGEN3
-   "Download a version of Eigen3 during the build" FALSE )
+option(GEOMODEL_USE_BUILTIN_EIGEN3 "Download a version of Eigen3 during the build" OFF)
 
 # Now do what was requested.
 if( GEOMODEL_USE_BUILTIN_EIGEN3 )
-
-   # Tell the user what's happening.
-   message( STATUS "Building Eigen3 as part of the project" )
-
-   # Helper variables for the Eigen build.
-   set( Eigen3_INCLUDE_DIR
-      "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/Eigen3Install/include/eigen3" )
-   set( Eigen3_VERSION "3.2.9" )
-
-   # Create the include directory already, otherwise CMake refuses to
-   # create the imported target.
-   file( MAKE_DIRECTORY "${Eigen3_INCLUDE_DIR}" )
-
-   # Build/install Eigen3 using ExternalProject_Add(...).
-   include( ExternalProject )
-   ExternalProject_Add( Eigen3
-      PREFIX ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/Eigen3Build
-      INSTALL_DIR ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/Eigen3Install
-      URL "http://cern.ch/lcgpackages/tarFiles/sources/eigen-${Eigen3_VERSION}.tar.gz"
-      URL_MD5 "de04f424e6b86907ccc9737b5d3048e7"
-      CMAKE_CACHE_ARGS -DCMAKE_INSTALL_PREFIX:PATH=<INSTALL_DIR>
-      BUILD_BYPRODUCTS "${Eigen3_INCLUDE_DIR}" )
-   ExternalProject_Add_Step( Eigen3 removepc
-      COMMAND ${CMAKE_COMMAND} -E remove_directory <INSTALL_DIR>/share
-      COMMENT "Removing the pkgconfig file from Eigen"
-      DEPENDEES install )
-   install( DIRECTORY
-      ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/Eigen3Install/
-      DESTINATION .
-      COMPONENT Development
-      USE_SOURCE_PERMISSIONS )
-
-   # Set up an imported target that mimicks the one created by the exported
-   # CMake configuration of an Eigen installation.
-   add_library( Eigen3::Eigen INTERFACE IMPORTED )
-   set_target_properties( Eigen3::Eigen PROPERTIES
-      INTERFACE_INCLUDE_DIRECTORIES "${Eigen3_INCLUDE_DIR}" )
-
+  # Tell the user what's happening.
+  message( STATUS "Building Eigen3 as part of the project" )
+
+  # Helper variables for the Eigen build.
+  set( Eigen3_INCLUDE_DIR "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/Eigen3Install/include/eigen3" )
+  set( Eigen3_VERSION "3.2.9" )
+
+  # Create the include directory already, otherwise CMake refuses to
+  # create the imported target.
+  file( MAKE_DIRECTORY "${Eigen3_INCLUDE_DIR}" )
+
+  # Build/install Eigen3 using ExternalProject_Add(...).
+  include( ExternalProject )
+  ExternalProject_Add( Eigen3
+    PREFIX ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/Eigen3Build
+    INSTALL_DIR ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/Eigen3Install
+    URL "http://cern.ch/lcgpackages/tarFiles/sources/eigen-${Eigen3_VERSION}.tar.gz"
+    URL_MD5 "de04f424e6b86907ccc9737b5d3048e7"
+    CMAKE_CACHE_ARGS -DCMAKE_INSTALL_PREFIX:PATH=<INSTALL_DIR>
+    BUILD_BYPRODUCTS "${Eigen3_INCLUDE_DIR}" )
+  ExternalProject_Add_Step( Eigen3 removepc
+    COMMAND ${CMAKE_COMMAND} -E remove_directory <INSTALL_DIR>/share
+    COMMENT "Removing the pkgconfig file from Eigen"
+    DEPENDEES install )
+  install( DIRECTORY
+     ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/Eigen3Install/
+     DESTINATION .
+     COMPONENT Development
+     USE_SOURCE_PERMISSIONS )
+
+  # Set up an imported target that mimicks the one created by the exported
+  # CMake configuration of an Eigen installation.
+  add_library( Eigen3::Eigen INTERFACE IMPORTED )
+  set_target_properties( Eigen3::Eigen PROPERTIES INTERFACE_INCLUDE_DIRECTORIES "${Eigen3_INCLUDE_DIR}" )
+
+  # Add dependency to the underlying external project
+  add_dependencies(Eigen3::Eigen Eigen3)
 else()
-
-   # Just find an existing installation of Eigen3.
-   find_package( Eigen3 REQUIRED NO_MODULE )
-
+  # Just find an existing installation of Eigen3.
+  find_package( Eigen3 REQUIRED NO_MODULE )
 endif()