To hack on snapcraft, the first thing I want to do is reproduce the problem I'm trying to fix while running snapcraft straight from the source tree. Expected: after following HACKING.md, I can modify any part of snapcraft's source in my checked out VCS tree, immediately run snapcraft, and see the code changes in effect. Actual: HACKING.md does not appear to explain how to do this. If I run snapcraft, it seems to run out of the virtualenv set up by tools/environment-setup.sh (hacked to work around bug 1847774). Changes I make to the source tree do not seem to have any effect. I tried running: PYTHONPATH=$VCS_CHECKOUT python3 -m snapcraft.cli ... This appears to work superficially, but various changes I make to the source tree seem to not have effect, so I think it's incomplete.