proposed-migration, "SMOOTH_UPDATES", and NBS reports

[Steve Langasek]

As part of getting openssl 3 to migrate into the release pocket without
waiting for everything in the world to be rebuilt to drop its dependency on
libssl1.1, I've made a change to the config of britney to enable what are
called "smooth updates": explicitly telling britney that it's ok to keep old
(no-longer-built) binary packages around in the release pocket when updating
a source package.  In fact, the way britney interfaces with launchpad, it's
always the case that old binary packages are left behind in the release
pocket and have to be cleaned up by hand; so by explicitly instructing
britney that it's ok for them to be left around, britney will more quickly
calculate that a source package is ready to go to the release pocket,
improving development velocity overall.

The flipside is that this now means more packages will make it to the
release pocket while there are still reverse-dependencies of an old library
name; so when folks are working on proposed-migration, such as for +1
Maintenance, more attention will need to be paid to cleaning up these
stragglers.  We have always had an "NBS" (not built from source) report
showing us when this is the case, it's just that with the new configuration
there are going to be more such packages needing more attention to clear the
reverse-dependencies:

    https://people.canonical.com/~ubuntu-archive/nbs.html

In some cases these are packages that simply need no-change reuploads in
order to build against the new library package name, but in other cases the
packages have been rebuilt but are stuck for one reason or another in
-proposed.

So please pay attention to this list when you're working on -proposed; you
should find that the change makes proposed-migration run faster overall, but
we still need to make sure we're following through on cleaning up old
binaries afterwards.

Thanks,
-- 
Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                   https://www.debian.org/
slangasek at ubuntu.com                                     vorlon at debian.org
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