Modernize ITK Module System with CMake Interface Libraries

CMake/ITKConfig.cmake.in

@@ -59,6 +59,9 @@ set(ITK_BUILD_DOCUMENTATION "@ITK_BUILD_DOCUMENTATION@")
 # List of available ITK modules.
 set(ITK_MODULES_ENABLED "@ITK_CONFIG_MODULES_ENABLED@")
 
+# Define the ITK library namespace for CMake targets, without the trailing ::.
+set(ITK_LIBRARY_NAMESPACE "@ITK_LIBRARY_NAMESPACE@")
+
 # Import ITK targets.
 set(ITK_CONFIG_TARGETS_FILE "@ITK_CONFIG_TARGETS_FILE@")
 if(NOT ITK_TARGETS_IMPORTED@ITK_CONFIG_TARGETS_CONDITION@)

CMake/ITKFactoryRegistration.cmake

@@ -136,10 +136,11 @@
 # Caveats
 # -------
 #
-# Since the both include directory containing the registration manager headers
-# and the `ITK_IO_FACTORY_REGISTER_MANAGER` COMPILE_DEFINITIONS are set as
-# directory properties, including external project (themselves including ITK)
-# after including ITK can have unintended side effects.
+# The include directory containing the registration manager headers and the
+# `ITK_<FACTORY_NAME>_FACTORY_REGISTER_MANAGER` COMPILE_DEFINITIONS are set as
+# target interface properties on the factory meta-module targets (ITKImageIO,
+# ITKMeshIO, ITKTransformIO, ITKFFTImageFilterInit). This ensures proper propagation
+# to dependent targets through modern CMake usage requirements.
 #
 
 # _itk_configure_FactoryRegisterManager(<factory_type> <formats>)
@@ -148,6 +149,8 @@
 # `<CMAKE_CURRENT_BINARY_DIR>/ITKFactoryRegistration/`.
 #
 # Header is named using the template `itk<factory_type>FactoryRegisterManager.h`
+# The include directory and compile definitions are added to the corresponding
+# factory meta-module target's INTERFACE properties.
 #
 function(_itk_configure_FactoryRegisterManager factory_type formats)
   set(LIST_OF_FACTORIES_REGISTRATION "")
@@ -169,6 +172,30 @@ function(_itk_configure_FactoryRegisterManager factory_type formats)
     "${CMAKE_CURRENT_BINARY_DIR}/ITKFactoryRegistration/itk${factory_type}FactoryRegisterManager.h"
     @ONLY
   )
+
+  # These functions may be called in the ITK source ( or a fetch content sub-project ),
+  # so support is needed when the namespaced meta-module target is an alias to the real target.
+  set(_meta_module ITK${factory_type})
+  if(ITK_LIBRARY_NAMESPACE)
+    set(_meta_module ${ITK_LIBRARY_NAMESPACE}::ITK${factory_type})
+  endif()
+  get_property(
+    aliased_target_name
+    TARGET ${_meta_module}
+    PROPERTY ALIASED_TARGET
+  )
+  if(aliased_target_name)
+    set(_meta_module ${aliased_target_name})
+  endif()
+  # Override the include directories to the current generated FactoryRegistration path.
+  # Enables multiple calls to adding factories with different sets of factories, in a project.
+  set_property(
+    TARGET
+      ${_meta_module}
+    PROPERTY
+      INTERFACE_INCLUDE_DIRECTORIES
+        "$<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}/ITKFactoryRegistration>"
+  )
 endfunction()
 
 # _itk_ADD_FACTORY_REGISTRATION(<registration_list_var> <names_list_var> <module_name> <factory_name>)

CMake/ITKModuleAPI.cmake

@@ -30,6 +30,7 @@ macro(_itk_module_config_recurse ns mod)
     list(APPEND _${ns}_USED_MODULES ${mod})
     itk_module_load("${mod}")
     list(APPEND ${ns}_LIBRARIES ${${mod}_LIBRARIES})
+    list(APPEND ${ns}_INTERFACE_LIBRARIES ${${mod}_INTERFACE_LIBRARY})
     list(APPEND ${ns}_INCLUDE_DIRS ${${mod}_INCLUDE_DIRS})
     list(APPEND ${ns}_LIBRARY_DIRS ${${mod}_LIBRARY_DIRS})
     list(APPEND ${ns}_RUNTIME_LIBRARY_DIRS ${${mod}_RUNTIME_LIBRARY_DIRS})
@@ -75,6 +76,7 @@ endmacro()
 #  <module>_TRANSITIVE_DEPENDS = List of dependencies on other modules (public link, compile)
 #  <module>_PRIVATE_DEPENDS    = List of dependencies on other modules (private link)
 #  <module>_LIBRARIES          = Libraries to link
+#  <module>_INTERFACE_LIBRARY  = Interface library for module
 #  <module>_INCLUDE_DIRS       = Header search path
 #  <module>_LIBRARY_DIRS       = Library search path (for outside dependencies)
 #  <module>_RUNTIME_LIBRARY_DIRS = Runtime linker search path
@@ -88,7 +90,15 @@ macro(itk_module_load mod)
     # than ITKTargets.cmake are created when modules are built externally. Do not
     # include the targets file inside the module itself -- which occurs in a module's
     # test configuration.
-    if(EXISTS "${${mod}_TARGETS_FILE}" AND NOT itk-module STREQUAL mod)
+    if(
+      EXISTS
+        "${${mod}_TARGETS_FILE}"
+      AND
+        NOT
+          "${itk-module}"
+            STREQUAL
+            "${mod}"
+    )
       include("${${mod}_TARGETS_FILE}")
     endif()
   endif()
@@ -97,7 +107,8 @@ endmacro()
 # itk_module_config(<namespace> [modules...])
 #
 # Configures variables describing the given modules and their dependencies:
-#  <namespace>_LIBRARIES    = Libraries to link
+#  <namespace>_LIBRARIES    = Libraries
+#  <namespace>_INTERFACE_LIBRARIES = Interface libraries to link with public interfaces
 #  <namespace>_INCLUDE_DIRS = Header search path
 #  <namespace>_LIBRARY_DIRS = Library search path (for outside dependencies)
 #  <namespace>_RUNTIME_LIBRARY_DIRS = Runtime linker search path
@@ -123,6 +134,7 @@ endmacro()
 # future. For more details, read documentation in CMake/UseITK.cmake.
 macro(itk_module_config ns)
   set(${ns}_LIBRARIES "")
+  set(${ns}_INTERFACE_LIBRARIES "")
   set(${ns}_INCLUDE_DIRS "")
   set(${ns}_LIBRARY_DIRS "")
   set(${ns}_RUNTIME_LIBRARY_DIRS "")
@@ -143,6 +155,7 @@ macro(itk_module_config ns)
   foreach(
     v
     ${ns}_LIBRARIES
+    ${ns}_INTERFACE_LIBRARIES
     ${ns}_INCLUDE_DIRS
     ${ns}_LIBRARY_DIRS
     ${ns}_RUNTIME_LIBRARY_DIRS
@@ -153,6 +166,7 @@ macro(itk_module_config ns)
       list(REMOVE_DUPLICATES ${v})
     endif()
   endforeach()
+
   foreach(_factory ${${ns}_FACTORY_LIST})
     list(SORT ${ns}_${_factory}) # Sort to ensure a deterministic order
   endforeach()

CMake/ITKModuleEnablement.cmake

@@ -428,6 +428,46 @@ macro(init_module_vars)
   set(${itk-module}-targets-build "${ITK_BINARY_DIR}/ITKTargets.cmake")
 endmacro()
 
+#----------------------------------------------------------------------
+# Create factory meta-module interface libraries
+# These are created for ITKImageIO, ITKMeshIO, ITKTransformIO and FFTImageFilterInit factories
+foreach(_factory_name IN ITEMS ImageIO MeshIO TransformIO FFTImageFilterInit)
+  set(itk-module ITK${_factory_name})
+  if(NOT TARGET ${itk-module})
+    add_library(${itk-module} INTERFACE)
+
+    init_module_vars(${itk-module})
+    set(ITK_MODULE_${itk-module}_DECLARED 1)
+
+    # Factory modules will be added as dependencies to this meta-module.
+    # When itk_generate_factory_registration() is called, it adds the include
+    # directory containing the generated FactoryRegisterManager header file.
+    #
+    # Note: Compilation errors like "itkImageIOFactoryRegisterManager.h: No such file or directory"
+    # indicate that itk_generate_factory_registration() has not been called to generate the header files.
+
+    # Add factory registration compile definition
+    string(TOUPPER ${_factory_name} _factory_uc)
+    target_compile_definitions(
+      ${itk-module}
+      INTERFACE
+        ITK_${_factory_uc}_FACTORY_REGISTER_MANAGER
+    )
+
+    set(ITK_MODULE_${itk-module}_TARGETS_NAMESPACE "")
+    if(ITK_LIBRARY_NAMESPACE)
+      set(
+        ITK_MODULE_${itk-module}_TARGETS_NAMESPACE
+        "${ITK_LIBRARY_NAMESPACE}::"
+      )
+    endif()
+
+    # Export and install the factory interface library
+    itk_module_target_export(${itk-module})
+    itk_module_target_install(${itk-module})
+  endif()
+endforeach()
+
 # Build all modules.
 foreach(itk-module ${ITK_MODULES_ENABLED})
   if(NOT ${itk-module}_IS_TEST)

CMake/ITKModuleExternal.cmake

@@ -197,6 +197,8 @@ set(
 set(${itk-module}_TARGETS_FILE_BUILD "${${itk-module}-targets-build}")
 file(WRITE "${${itk-module}_TARGETS_FILE_BUILD}" "") # Clear targets
 set(${itk-module}_ENABLE_SHARED "${ITK_MODULE_${itk-module}_ENABLE_SHARED}")
+set(${itk-module}-targets-namespace "")
+
 itk_module_impl()
 
 if(

CMake/ITKModuleHeaderTest.cmake

@@ -122,10 +122,11 @@ macro(itk_module_headertest _name)
       add_executable(${_test_name} ${_header_test_src})
       target_link_libraries(
         ${_test_name}
-        PUBLIC
-          ${${_name}_LIBRARIES}
-          itksys
+        PRIVATE
+          ${ITK_MODULE_${_name}_TARGETS_NAMESPACE}${_name}Module
+          ${ITK_MODULE_${_name}_TARGETS_NAMESPACE}ITKKWSysModule
       )
+
       target_link_options(
         ${_test_name}
         PRIVATE

CMake/ITKModuleInfo.cmake.in

@@ -5,9 +5,11 @@ set(@itk-module@_PUBLIC_DEPENDS "@itk-module-PUBLIC_DEPENDS@")
 set(@itk-module@_TRANSITIVE_DEPENDS "@itk-module-TRANSITIVE_DEPENDS@")
 set(@itk-module@_PRIVATE_DEPENDS "@itk-module-PRIVATE_DEPENDS@")
 set(@itk-module@_LIBRARIES "@itk-module-LIBRARIES@")
+set(@itk-module@_INTERFACE_LIBRARY "@itk-module-INTERFACE_LIBRARY@")
 set(@itk-module@_INCLUDE_DIRS "@itk-module-INCLUDE_DIRS@")
 set(@itk-module@_LIBRARY_DIRS "@itk-module-LIBRARY_DIRS@")
 set(@itk-module@_RUNTIME_LIBRARY_DIRS "@itk-module-RUNTIME_LIBRARY_DIRS@")
 set(@itk-module@_TARGETS_FILE "@itk-module-TARGETS_FILE@")
 set(@itk-module@_FACTORY_NAMES "@itk-module-FACTORY_NAMES@")
+
 @itk-module-EXPORT_CODE@