move to deb822 sources in ubuntu:lunar docker image

[Colin Watson]

On Mon, Jan 16, 2023 at 05:30:27PM +0100, Thomas Bechtold wrote:
> So my understanding is, that we would need to adjust live-build and/or
> livecd-rootfs to use the deb822 format. And if we do that, would
> we also need to adjust launchpad-buildd to handle the new format, too?

I don't think we can reasonably switch to writing out the new format
from launchpad-buildd in the short term; it would require some
not-quite-trivial changes to Launchpad as well, and we're short-staffed
at the moment with a lot of other stuff going on, so taking on more
refactoring work doesn't really appeal.  We've also recently dispatched
builds for trusty (though I didn't check exactly why), and I believe its
apt is too old to support the deb822 format, so we need to retain
compatibility with it for a while longer.

The simplest change might be to make launchpad-buildd ensure that the
new default sources.list path (/etc/apt/sources.list.d/ubuntu.sources?)
doesn't exist, and then just write out the old format to sources.list as
before.

I definitely anticipate lots of breakage from this change!  I hope all
the effort will be worth it.

-- 
Colin Watson (he/him)                              [cjwatson at ubuntu.com]