WIP: Refactor third-party Eigen3 CMake code

Remove Eigen3 external project, use itk module macros to install and
export eigen_internal target. Remove the CMake code to install
auxiliary cmake and configuration file for target. This target is now
imported through ITKTargets, and not a separate export and
configuration file.

Preserve Eigen3::Eigen project exports.

Author: blowekamp

CMake/itkExternal_Eigen3.cmake

@@ -736,11 +736,6 @@ if(BUILD_TESTING OR ITK_BUILD_DOCUMENTATION OR ITK_WRAP_PYTHON)
   endif()
 endif()
 
-#-----------------------------------------------------------------------------
-# Configure Eigen3 before ITKModuleEnablement
-# No download or build is performed. Generates Targets and Config.cmake files for Eigen
-include(itkExternal_Eigen3)
-
 #----------------------------------------------------------------------
 # Make sure remote modules are downloaded before sorting out the module
 # dependencies.

CMakeLists.txt

@@ -11,7 +11,7 @@ mark_as_advanced(ITK_USE_SYSTEM_EIGEN)
 if(ITK_USE_SYSTEM_EIGEN)
   set(_eigen_itk_target Eigen3::Eigen)
 else()
-  set(_eigen_itk_target ITKInternalEigen3::Eigen)
+  set(_eigen_itk_target eigen_internal)
 endif()
 set(ITKEigen3_LIBRARIES ${_eigen_itk_target})
 # Assume that Eigen generates a Eigen3Config.cmake
@@ -57,60 +57,51 @@ set(_Eigen3_min_version 3.3)
 if(ITK_USE_SYSTEM_EIGEN)
   set(_Eigen3_SYSTEM_OR_INTERNAL "Eigen3")
   find_package(${_Eigen3_SYSTEM_OR_INTERNAL} REQUIRED CONFIG)
-  set(Eigen3_DIR_INSTALL ${Eigen3_DIR})
-  set(Eigen3_DIR_BUILD ${Eigen3_DIR})
-else()
-  set(_Eigen3_SYSTEM_OR_INTERNAL "ITKInternalEigen3")
-  find_package(${_Eigen3_SYSTEM_OR_INTERNAL} REQUIRED CONFIG)
-  set(Eigen3_DIR_INSTALL "\${ITK_MODULES_DIR}")
-  set(_eigen3_build_dir "${ITK_BINARY_DIR}/ITKInternalEigen3-build")
-  set(Eigen3_DIR_BUILD "${_eigen3_build_dir}")
-endif()
-if(${_Eigen3_SYSTEM_OR_INTERNAL}_VERSION VERSION_LESS ${_Eigen3_min_version})
-  message(
-    FATAL_ERROR
-    "Eigen3 version ${_Eigen3_min_version} or later is required."
-  )
-endif()
 
-# Eigen3 is header only, but there are compile definitions that we want to provide
-# to enforce use of MPL only code, and to disable warnings.
-# We only need to add the location of the header itk_eigen.h used internally.
-get_target_property(
-  Eigen_INCLUDE_DIRS
-  ${_eigen_itk_target}
-  INTERFACE_INCLUDE_DIRECTORIES
-)
-set(
-  ITKEigen3_INCLUDE_DIRS
-  ${Eigen_INCLUDE_DIRS}
-  ${ITKEigen3_BINARY_DIR}/src # For the generated itk_eigen.h
-)
+  set(ITKEigen3_NO_SRC 1)
 
-# When this module is loaded by an app, load Eigen too.
-# Load ITKInternalEigen3 or Eigen3 depending on ITK_USE_SYSTEM_EIGEN
-set(
-  ITKEigen3_EXPORT_CODE_INSTALL
-  "
-set(ITK_USE_SYSTEM_EIGEN \"${ITK_USE_SYSTEM_EIGEN}\")
-set(${_Eigen3_SYSTEM_OR_INTERNAL}_DIR \"${Eigen3_DIR_INSTALL}\")
-find_package(${_Eigen3_SYSTEM_OR_INTERNAL} REQUIRED CONFIG)
-if(${_Eigen3_SYSTEM_OR_INTERNAL}_VERSION VERSION_LESS ${_Eigen3_min_version})
+  if(${_Eigen3_SYSTEM_OR_INTERNAL}_VERSION VERSION_LESS ${_Eigen3_min_version})
+    message(
+      FATAL_ERROR
+      "Eigen3 version ${_Eigen3_min_version} or later is required."
+    )
+  endif()
+
+  # When this module is loaded by an app, load Eigen too.
+  # Load ITKInternalEigen3 or Eigen3 depending on ITK_USE_SYSTEM_EIGEN
+  set(
+    ITKEigen3_EXPORT_CODE_INSTALL
+    "
+find_package(\"Eigen3\" REQUIRED CONFIG)
+if(Eigen3_VERSION VERSION_LESS ${_Eigen3_min_version})
   message(FATAL_ERROR \"Eigen3 version ${_Eigen3_min_version} or later is required.\")
 endif()
 "
-)
-set(
-  ITKEigen3_EXPORT_CODE_BUILD
-  "
-set(ITK_USE_SYSTEM_EIGEN \"${ITK_USE_SYSTEM_EIGEN}\")
-set(${_Eigen3_SYSTEM_OR_INTERNAL}_DIR \"${Eigen3_DIR_BUILD}\")
-find_package(${_Eigen3_SYSTEM_OR_INTERNAL} REQUIRED CONFIG)
-if(${_Eigen3_SYSTEM_OR_INTERNAL}_VERSION VERSION_LESS ${_Eigen3_min_version})
+  )
+  set(
+    ITKEigen3_EXPORT_CODE_BUILD
+    "
+    if(NOT ITK_BINARY_DIR)
+
+find_package(\"Eigen3\" REQUIRED CONFIG)
+if(Eigen3_VERSION VERSION_LESS ${_Eigen3_min_version})
   message(FATAL_ERROR \"Eigen3 version ${_Eigen3_min_version} or later is required.\")
 endif()
+endif()
 "
-)
+  )
+else()
+  set(_Eigen3_SYSTEM_OR_INTERNAL "ITKInternalEigen3")
+
+  set(ITKEigen3_INCLUDE_DIRS ${ITKEigen3_SOURCE_DIR}/src)
+
+  set(Eigen3_DIR_INSTALL "\${ITK_MODULES_DIR}")
+  set(_eigen3_build_dir "${ITK_BINARY_DIR}/ITKInternalEigen3-build")
+  set(Eigen3_DIR_BUILD "${_eigen3_build_dir}")
+endif()
+
+# For the generated itk_eigen.h
+list(APPEND ITKEigen3_INCLUDE_DIRS ${ITKEigen3_BINARY_DIR}/src)
 
 # Eigen3 targets are not installed if ITK_USE_SYSTEM_EIGEN==True
 itk_module_impl()

Modules/ThirdParty/Eigen3/CMakeLists.txt

@@ -882,7 +882,7 @@ install ( FILES ${CMAKE_CURRENT_BINARY_DIR}/Eigen3Config.cmake
 # Install files (used for both eigen_external and eigen_internal)
 install(
   DIRECTORY   "${CMAKE_CURRENT_SOURCE_DIR}/Eigen/"
-  DESTINATION "${INCLUDE_INSTALL_DIR}/itkeigen/Eigen"
+  DESTINATION "${ITK3P_INSTALL_INCLUDE_DIR}/itkeigen/Eigen"
   PATTERN "*.txt" EXCLUDE)
 
 ######################### eigen_internal #####################################
@@ -896,8 +896,6 @@ add_library (ITKInternalEigen3::Eigen ALIAS eigen_internal)
 # This would wrongly enforce EIGEN_MPL2_ONLY to other libraries using Eigen.
 # We wrap this definition in ITK_USE_EIGEN_MPL2_ONLY, and only enabling it internally in the dashboards and CI,
 # to avoid introducing GPL code from Eigen3 internally in ITK.
-option(ITK_USE_EIGEN_MPL2_ONLY "Set compile definition EIGEN_MPL2_ONLY for ITKInternalEigen3." OFF)
-mark_as_advanced(ITK_USE_EIGEN_MPL2_ONLY)
 
 if(ITK_USE_EIGEN_MPL2_ONLY)
   target_compile_definitions (eigen_internal INTERFACE "EIGEN_MPL2_ONLY")
@@ -908,40 +906,9 @@ endif()
 # INSTALL: headers require pre-prend itkeigen/Eigen/X.
 target_include_directories (eigen_internal SYSTEM INTERFACE
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/..>
-  # $<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}/..>
-  $<INSTALL_INTERFACE:${INCLUDE_INSTALL_DIR}>
+  "$<INSTALL_INTERFACE:$<INSTALL_PREFIX>/${ITK3P_INSTALL_INCLUDE_DIR}/itkeigen>;"
   )
 
 # Export as title case Eigen
-set_target_properties (eigen_internal PROPERTIES EXPORT_NAME Eigen)
-install (TARGETS eigen_internal EXPORT ITKInternalEigen3Targets)
+install (TARGETS eigen_internal EXPORT ${ITK3P_INSTALL_EXPORT_NAME})
 
-set(EIGEN3_TARGETS_FILE ITKInternalEigen3Targets.cmake)
-configure_package_config_file (
-  ${CMAKE_CURRENT_SOURCE_DIR}/cmake/Eigen3Config.cmake.in
-  ${CMAKE_CURRENT_BINARY_DIR}/ITKInternalEigen3Config.cmake
-  INSTALL_DESTINATION ${CMAKEPACKAGE_INSTALL_DIR}
-  NO_CHECK_REQUIRED_COMPONENTS_MACRO # Eigen does not provide components
-  )
-# Remove CMAKE_SIZEOF_VOID_P from Eigen3ConfigVersion.cmake since Eigen does
-# not depend on architecture specific settings or libraries. More
-# specifically, an Eigen3Config.cmake generated from a 64 bit target can be
-# used for 32 bit targets as well (and vice versa).
-set (_Eigen3_CMAKE_SIZEOF_VOID_P ${CMAKE_SIZEOF_VOID_P})
-unset (CMAKE_SIZEOF_VOID_P)
-write_basic_package_version_file (ITKInternalEigen3ConfigVersion.cmake
-  VERSION ${EIGEN_VERSION_NUMBER}
-  COMPATIBILITY SameMajorVersion)
-set (CMAKE_SIZEOF_VOID_P ${_Eigen3_CMAKE_SIZEOF_VOID_P})
-# The Eigen target will be located in the Eigen3 namespace. Other CMake
-# targets can refer to it using Eigen3::Eigen.
-export (TARGETS eigen_internal NAMESPACE ITKInternalEigen3:: FILE ITKInternalEigen3Targets.cmake)
-install (EXPORT ITKInternalEigen3Targets NAMESPACE ITKInternalEigen3:: DESTINATION ${CMAKEPACKAGE_INSTALL_DIR})
-# Files already installed in eigen_external
-# install(
-#   DIRECTORY   "${CMAKE_CURRENT_SOURCE_DIR}/Eigen/"
-#   DESTINATION "${INCLUDE_INSTALL_DIR}/itkeigen/Eigen"
-#   PATTERN "*.txt" EXCLUDE)
-install ( FILES ${CMAKE_CURRENT_BINARY_DIR}/ITKInternalEigen3Config.cmake
-  ${CMAKE_CURRENT_BINARY_DIR}/ITKInternalEigen3ConfigVersion.cmake
-  DESTINATION ${CMAKEPACKAGE_INSTALL_DIR} )