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]
           explained = yes
             creator   root:
              source   file:plan.py
             product   file:inner.py
             product   file:outer.py
             product   step:./outer.py foo

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

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

step:./outer.py foo
               state = SUCCEEDED
                need = DEFAULT
           using_env = STEPUP_PATH_FILTER [dynamic]
           explained = yes
             creator   step:./plan.py
              source   file:outer.py
             product   step:./inner.py

step:./inner.py
               state = SUCCEEDED
                need = DEFAULT
           using_env = STEPUP_PATH_FILTER [dynamic]
           explained = yes
             creator   step:./outer.py foo
              source   file:inner.py
             product   file:out.txt
                sink   file:out.txt

file:out.txt
               state = BUILT
             creator   step:./inner.py
              source   step:./inner.py
