The stgit package is installing using make, which leaves the application in a state where it can not properly find the installed package stgit.
---
File "/run/current-system/sw/bin/stg", line 35, in <module>
from stgit.main import main
ImportError: No module named stgit.main
---
This is fixed by using buildPythonApplication instead of stdenv.mkDerivation.
e5f0d13a49