How to assume packaging downgrade in hard case ?

[rperrot@debian.org]

I'm packaging Bugzilla but at now I don't know how to
make downgrade possible.

After installing the last package version (not public at now), it
will not be possible to downgrade while there is major change in
the data structure. I've try to resolve some by making the prerm
script change back the data structure, but after all there were
left some inconsistency.

For example on last Bugzilla cvs version clear password have squeeze
out, so you imaging in what trouble we are if we downgrade after that!

In this case I have a solution, that is, regenerate random password
for all user. But I think this is only the visible part of the iceberg,
and indeed, that breaks other where.

The mainstream is very active, so for upgrade they maintain a script
to update database structure. As I call this script in postinst
upgrade work well. Unfortunately this script isn't done for downgrade.

It would be very boring to closely fallow upstream change and make
prerm trying to regenerate old database structure, at least on
CVS snapshot.

So how to deal with this?

Rémi Perrot