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 -p missing.txt hello.txt

step:cp -p missing.txt hello.txt
               state = PENDING
                need = DEFAULT
             creator   step:./plan.py
              source   (file:missing.txt)
             product   file:hello.txt
                sink   file:hello.txt

(file:missing.txt)
               state = UNDECLARED
                sink   step:cp -p missing.txt hello.txt

file:hello.txt
               state = PLANNED
             creator   step:cp -p missing.txt hello.txt
              source   step:cp -p missing.txt hello.txt
