HEADS UP: change of default in `layer-basic`


As discussed in this PR there are some issues with the current pin-set for pip and setuptools in layer-basic. In essence, deploying a charm with dependencies built at deploy time currently fails on Python 3.7 systems.

A solution to the issue is to unpin pip and setuptools which allows a compatible combination of those tools to be distributed with the charm.

However this also mandates a change of the default value for the include_system_packages configuration option in layer-basic from True to False.

Without this change a charm being deployed will end up using incompatible pip or setuptools versions from what is installed on the system and subsequently fail.

Having the charms rely on their distributed dependencies only, without interference from system installed packages, is a safer default. It also prohibits charm authors from inadvertently making boundary violations by having the charm rely on the software it is installing or managing on a system.

Most charms should be OK with this change, and charm authors still have the option to explicitly set include_system_packages to True to restore the old default behaviour.

The Juju Show #51 - Juju + Open Source Mano : June 18 13:00 UTC

Just a reminder that this change is imminent and will most likely be merged today.

The final prerequisites have merged to charm-helpers and released in version v0.20.0.