COMP: Fix macOS packaging ensuring extension has a superbuild layout

This commit is a follow-up of 70d5a3b (Fix extension build on macOS by
replacing real Virtual Reality module by a placeholder).

Since the extension build-system expects an inner-build directory
on all platform, this commit keeps the SuperBuild structure by:
- updating "SuperBuildPrerequisites" to list no external project dependencies.
- include "VirtualRealityStub" module source in the inner build

Author: jcfr

CMakeLists.txt

@@ -13,19 +13,6 @@ set(EXTENSION_SCREENSHOTURLS "https://www.slicer.org/w/images/4/49/SlicerVirtual
 set(EXTENSION_DEPENDS "NA") # Specified as a space separated string, a list or 'NA' if any
 
 #-----------------------------------------------------------------------------
-if(APPLE)
-  # Virtual Reality is not supported on macOS, create an extension that contains a stub module
-  # that just displays the message that Virtual Reality is not supported. This avoids having
-  # a build error on the extension build dashboard.
-  find_package(Slicer REQUIRED)
-  include(${Slicer_USE_FILE})
-  add_subdirectory(VirtualRealityStub)
-  include(${Slicer_EXTENSION_GENERATE_CONFIG})
-  include(${Slicer_EXTENSION_CPACK}) 
-  return()
-endif()
-#-----------------------------------------------------------------------------
-
 set(EXTENSION_BUILD_SUBDIRECTORY inner-build)
 
 set(SUPERBUILD_TOPLEVEL_PROJECT inner)
@@ -49,6 +36,24 @@ if(${EXTENSION_NAME}_SUPERBUILD)
   return()
 endif()
 
+#-----------------------------------------------------------------------------
+# Virtual Reality is not supported on macOS, create an extension that contains a stub module
+# that just displays the message that Virtual Reality is not supported.
+# This avoids having a build error on the extension build dashboard.
+if(APPLE)
+  add_subdirectory(VirtualRealityStub)
+
+  include(${Slicer_EXTENSION_GENERATE_CONFIG})
+
+  set(EXTENSION_CPACK_INSTALL_CMAKE_PROJECTS)
+  set(${EXTENSION_NAME}_CPACK_INSTALL_CMAKE_PROJECTS "${EXTENSION_CPACK_INSTALL_CMAKE_PROJECTS}" CACHE STRING "List of external projects to install" FORCE)
+
+  list(APPEND CPACK_INSTALL_CMAKE_PROJECTS "${CMAKE_BINARY_DIR};${EXTENSION_NAME};ALL;/")
+  list(APPEND CPACK_INSTALL_CMAKE_PROJECTS "${${EXTENSION_NAME}_CPACK_INSTALL_CMAKE_PROJECTS}")
+  include(${Slicer_EXTENSION_CPACK})
+  return()
+endif()
+
 #-----------------------------------------------------------------------------
 # Extension modules
 add_subdirectory(VirtualReality)

SuperBuildPrerequisites.cmake

@@ -9,6 +9,12 @@ if(DEFINED slicersources_SOURCE_DIR AND NOT DEFINED Slicer_SOURCE_DIR)
   set(Slicer_SOURCE_DIR ${slicersources_SOURCE_DIR})
 endif()
 
+if(APPLE)
+  set(SlicerVirtualReality_EXTERNAL_PROJECT_DEPENDENCIES "")
+  message(STATUS "SlicerVirtualReality_EXTERNAL_PROJECT_DEPENDENCIES:${SlicerVirtualReality_EXTERNAL_PROJECT_DEPENDENCIES}")
+  return()
+endif()
+
 # Set list of dependencies to ensure the custom application bundling this
 # extension does NOT automatically collect the project list and attempt to
 # build external projects associated with VTK modules enabled below.