COMP: Fix standalone extension build

CMakeLists.txt

@@ -34,6 +34,7 @@ mark_as_superbuild(PYTHON_LIBRARY)
 option(${EXTENSION_NAME}_SUPERBUILD "Build ${EXTENSION_NAME} and the projects it depends on." ON)
 mark_as_advanced(${EXTENSION_NAME}_SUPERBUILD)
 if(${EXTENSION_NAME}_SUPERBUILD)
+  include("${CMAKE_CURRENT_SOURCE_DIR}/SuperBuildPrerequisites.cmake")
   include("${CMAKE_CURRENT_SOURCE_DIR}/SuperBuild.cmake")
   return()
 endif()

SuperBuild/External_ITKBSplineGradient.cmake

@@ -5,7 +5,6 @@ set(proj ITKBSplineGradient)
 
 # Dependencies
 set(${proj}_DEPENDENCIES
-  ITK
   ITKMeshToPolyData
   )
 ExternalProject_Include_Dependencies(${proj} PROJECT_VAR proj DEPENDS_VAR ${proj}_DEPENDENCIES)

SuperBuild/External_ITKHigherOrderAccurateGradient.cmake

@@ -5,7 +5,6 @@ set(proj ITKHigherOrderAccurateGradient)
 
 # Dependencies
 set(${proj}_DEPENDENCIES
-  ITK
   )
 ExternalProject_Include_Dependencies(${proj} PROJECT_VAR proj DEPENDS_VAR ${proj}_DEPENDENCIES)
 

SuperBuild/External_ITKMeshToPolyData.cmake

@@ -5,7 +5,6 @@ set(proj ITKMeshToPolyData)
 
 # Dependencies
 set(${proj}_DEPENDENCIES
-  ITK
   )
 ExternalProject_Include_Dependencies(${proj} PROJECT_VAR proj DEPENDS_VAR ${proj}_DEPENDENCIES)
 

SuperBuild/External_ITKSplitComponents.cmake

@@ -5,7 +5,6 @@ set(proj ITKSplitComponents)
 
 # Dependencies
 set(${proj}_DEPENDENCIES
-  ITK
   )
 ExternalProject_Include_Dependencies(${proj} PROJECT_VAR proj DEPENDS_VAR ${proj}_DEPENDENCIES)
 

SuperBuild/External_ITKStrain.cmake

@@ -5,7 +5,6 @@ set(proj ITKStrain)
 
 # Dependencies
 set(${proj}_DEPENDENCIES
-  ITK
   )
 ExternalProject_Include_Dependencies(${proj} PROJECT_VAR proj DEPENDS_VAR ${proj}_DEPENDENCIES)
 

SuperBuild/External_ITKUltrasound.cmake

@@ -5,12 +5,10 @@ set(proj ITKUltrasound)
 
 # Dependencies
 set(${proj}_DEPENDENCIES
-  ITK
   ITKBSplineGradient
   ITKHigherOrderAccurateGradient
   ITKSplitComponents
   ITKStrain
-  VTK
   )
 ExternalProject_Include_Dependencies(${proj} PROJECT_VAR proj DEPENDS_VAR ${proj}_DEPENDENCIES)
 

SuperBuildPrerequisites.cmake

@@ -0,0 +1,40 @@
+if(DEFINED slicersources_SOURCE_DIR AND NOT DEFINED Slicer_SOURCE_DIR)
+  # Explicitly setting "Slicer_SOURCE_DIR" when only "slicersources_SOURCE_DIR"
+  # is defined is required to successfully complete configuration in an empty
+  # build directory
+  #
+  # Indeed, in that case, Slicer sources have been downloaded by they have not been
+  # added using "add_subdirectory()" and the variable "Slicer_SOURCE_DIR" is not yet in
+  # in the CACHE.
+  set(Slicer_SOURCE_DIR ${slicersources_SOURCE_DIR})
+endif()
+
+if(NOT DEFINED Slicer_SOURCE_DIR)
+  # Extension is built standalone
+
+  # NA
+
+else()
+  # Extension is bundled in a custom application
+
+  # Additional external project dependencies
+  foreach(itk_module IN ITEMS
+    ITKBSplineGradient
+    ITKHigherOrderAccurateGradient
+    ITKMeshToPolyData
+    ITKSplitComponents
+    ITKStrain
+    ITKUltrasound
+    )
+    ExternalProject_Add_Dependencies(${itk_module}
+      DEPENDS
+        ITK
+      )
+  endforeach()
+
+  ExternalProject_Add_Dependencies(ITKUltrasound
+    DEPENDS
+      VTK
+    )
+
+endif()