deb2snap transitional packages and channel tracking

[Julian Andres Klode]

I've been reviewing some of ack's changes for the maas deb2snap
transitional package, and in the latest merge request

- 
https://code.launchpad.net/~ack/ubuntu/+source/maas/+git/maas/+merge/383411
-

a topic came up that I don't think we've discussed before.

Currently, the maas deb installs maas 2.7/stable/ubuntu-$release
(or other versions of maas instead of 2.7). They'd like to add a
fallback that if the /ubuntu-$release channel is not there, it
would install 2.7/stable instead, and then maybe only have the
/ubuntu-$release channels for LTS releases.

Now, I don't think this makes a lot of sense. I'd argue that
the same policies as for seeded snaps should also apply to
deb2snap transitions, as the rationale is the same - we can,
if necessary, roll out fixes specific to an Ubuntu release.

It also creates less confusion if people install the Ubuntu devel
release while no such channel exists yet - people who install early
in the 22.04 cycle would track 2.7/stable, people who install
late would get 2.7/stable/ubuntu-22.04.


So I don't think we currently have a progress for deb2snap transitions
where the snap is not seeded. I think it should be the same as
for seeded snaps:

* deb2snap target snaps should always track /ubuntu-$release channels
* deb2snap target snaps should be notified to create such channels
  on archive opening

This ensures that people get a consistent experience for snaps
they get pre-installed, and snaps they get upgraded from debs,
or if they install a new deb that installs a snap.

-- 
debian developer - deb.li/jak | jak-linux.org - free software dev
ubuntu core developer                              i speak de, en