snapctl seem to cache values even if snap is removed and then installed again

[Ondrej Kubik]

preconditions:
$ snap install <snap>
$ snap set <snap> KEY1="VALUE"
$ snap set <snap> KEY2="VALUE"
$ snap remove <snap>
$ snap install <snap>
$ snap set <snap> KEY1="VALUE"

expected result:
when calling last $ snap set, configure hook associated to this "snap set" I'd expect snapctl only to return value for KEY1

actual result:
snapctl return values for both, KEY1 and KEY2

Are we cleaning snapctl cache when we remove snap?

tested on Ubuntu 16.04 classing
snapd version:
snap 2.16ubuntu3
snapd 2.16ubuntu3
series 16
ubuntu 16.04

[Kyle Fazzari (kyrofa)]

Indeed, even after `snap remove` is completed, the snap's configuration settings are still held in /var/lib/snapd/state.json. They should probably be purged, or if this behavior is desired, add a --purge option to `snap remove`.

[Gustavo Niemeyer (niemeyer)]

We should just clear config up from the state when the last revision from the snap is going away.

That needs to be done in a careful way to take undoing into account.

Eventually we should actually migrate to a model where configuration is keyed by (snap, revision) instead of simply (snap), so that reverts work properly. But that's a separate issue besides the need to clear configuration up on removals.

[Manik Taneja (manik)]

This affects me as well. In the previous iteration of the snap, I manually/explicitly changed the port numbers on which it should be working. After removal, and re-installation, those values are being used by the hooks to re-provision the snap, even though its a fresh install.

[Paweł Stołowski (stolowski)]

The PR: https://github.com/snapcore/snapd/pull/3052

[Kyle Fazzari (kyrofa)]

According to the changelog, it seems this was released in v2.24.