Add a AUTHOR_WARNING if the source file does not exist.

Installation/cmake/modules/CGAL_CreateSingleSourceCGALProgram.cmake

@@ -1,35 +1,37 @@
-function(create_single_source_cgal_program firstfile )
-
-  if(NOT IS_ABSOLUTE "${firstfile}")
-    set(firstfile "${CMAKE_CURRENT_SOURCE_DIR}/${firstfile}")
-  endif()
-
-  if(EXISTS "${firstfile}")
-  
-    set( all "${firstfile}" )
-    
-    # remaining files
-    foreach( i ${ARGN} )
-      set( all ${all} ${CMAKE_CURRENT_SOURCE_DIR}/${i} ) 
-    endforeach()
-    
-
-    get_filename_component(exe_name ${firstfile} NAME_WE)
-    add_executable(${exe_name} ${all})
-    
-    add_to_cached_list( CGAL_EXECUTABLE_TARGETS ${exe_name} )
-    
-    # Link the executable to CGAL and third-party libraries
-    if ( CGAL_AUTO_LINK_ENABLED )    
-
-      target_link_libraries(${exe_name} ${CGAL_3RD_PARTY_LIBRARIES} )
-
-    else()
-
-      target_link_libraries(${exe_name} ${CGAL_LIBRARIES} ${CGAL_3RD_PARTY_LIBRARIES} )
-
-    endif()
-  
-  endif()
-    
-endfunction()
+function(create_single_source_cgal_program firstfile )
+
+  if(NOT IS_ABSOLUTE "${firstfile}")
+    set(firstfile "${CMAKE_CURRENT_SOURCE_DIR}/${firstfile}")
+  endif()
+
+  get_filename_component(exe_name ${firstfile} NAME_WE)
+
+  if(EXISTS "${firstfile}")
+
+    set( all "${firstfile}" )
+
+    # remaining files
+    foreach( i ${ARGN} )
+      set( all ${all} ${CMAKE_CURRENT_SOURCE_DIR}/${i} )
+    endforeach()
+
+
+    add_executable(${exe_name} ${all})
+
+    add_to_cached_list( CGAL_EXECUTABLE_TARGETS ${exe_name} )
+
+    # Link the executable to CGAL and third-party libraries
+    if ( CGAL_AUTO_LINK_ENABLED )
+
+      target_link_libraries(${exe_name} ${CGAL_3RD_PARTY_LIBRARIES} )
+
+    else()
+
+      target_link_libraries(${exe_name} ${CGAL_LIBRARIES} ${CGAL_3RD_PARTY_LIBRARIES} )
+
+    endif()
+  else()
+    message(AUTHOR_WARNING "The executable ${exe_name} will not be created because the source file ${firstfile} does not exist.")
+  endif()
+
+endfunction()