root:
             product   file:plan.py
             product   step:./plan.py

file:plan.py
               state = CONFIRMED
             creator   root:
                sink   step:./plan.py

step:./plan.py
               state = SUCCEEDED
                need = PLAN
           using_env = STEPUP_PATH_FILTER [dynamic]
             creator   root:
              source   file:plan.py
             product   file:paths.txt
                sink   file:paths.txt [dynamic]

file:paths.txt
               state = VOLATILE
             creator   step:./plan.py
              source   step:./plan.py
