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:work.py
             product   step:./work.py
             product   step:echo ping > ping.txt

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

step:./work.py
               state = PENDING
                need = DEFAULT
           using_env = STEPUP_PATH_FILTER [dynamic]
             creator   step:./plan.py
              source   file:ping.txt [dynamic]
              source   (file:pong.txt) [dynamic]
              source   file:work.py
             product   file:work.txt
                sink   file:work.txt

file:work.txt
               state = PLANNED
             creator   step:./work.py
              source   step:./work.py

step:echo ping > ping.txt
               state = SUCCEEDED
                need = DEFAULT
             creator   step:./plan.py
             product   file:ping.txt
                sink   file:ping.txt

file:ping.txt
               state = BUILT
             creator   step:echo ping > ping.txt
              source   step:echo ping > ping.txt
                sink   step:./work.py

(file:pong.txt)
               state = UNDECLARED
                sink   step:./work.py
