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   step:cp copy1.txt copy2.txt

(file:orig.txt)
               state = MISSING
                sink   (step:cp orig.txt copy1.txt)

(step:cp orig.txt copy1.txt)
               state = PENDING
                need = DEFAULT
              source   (file:orig.txt)
             product   (file:copy1.txt)
                sink   (file:copy1.txt)

(file:copy1.txt)
               state = OUTDATED
             creator   (step:cp orig.txt copy1.txt)
              source   (step:cp orig.txt copy1.txt)
                sink   step:cp copy1.txt copy2.txt

step:cp copy1.txt copy2.txt
               state = PENDING
                need = DEFAULT
             creator   step:./plan.py
              source   (file:copy1.txt)
             product   file:copy2.txt
                sink   file:copy2.txt

file:copy2.txt
               state = OUTDATED
             creator   step:cp copy1.txt copy2.txt
              source   step:cp copy1.txt copy2.txt
