Re: new pre-dependency: perl{,-base,-modules} -> dpkg (>= 1.17.17)

[Ian Jackson <ijackson@chiark.greenend.org.uk>]

Guillem Jover writes ("Re: new pre-dependency: perl{,-base,-modules} -> dpkg (>= 1.17.17)"):
> On Sun, 2015-01-18 at 20:12:55 +0200, Niko Tyni wrote:
> > In order to fix trigger related wheezy->jessie upgrade failures in
> > xfonts-traditional (#774844, cc'd), I intend to make the main perl
> > binary packages (perl, perl-base, and perl-modules) Pre-Depend on dpkg
> > (>= 1.17.17), which has this change:
> > 
> >   * Defer trigger processing if the package does not fulfill dependencies.
> >     Closes: #671711
> > 
> > Together with making the jessie perl-modules and perl-base Break the
> > wheezy perl, this should ensure that the xfonts-traditional trigger will
> > not run when perl is in a broken state during upgrades.
> > 
> > Please see the #774844 bug log for details, and let me know if you have
> > objections or other suggestions.

Thanks, Niko, I think you have the correct fix.  I was meaning to
follow up suggesting a Pre-Depends.

> I've not looked into the details yet, but just to comment that there's
> been talk about possibly reverting that fix, because in some error
> situations it can get apt into an unrecoverable state (#774124). :(
> 
> Of course reverting that fix brings back all upgrade issues related
> to trigger processing w/o the required dependencies. Which are
> probably more, and easier to get into.

Yes.

> (I guess this just calls for both a fixed apt, and a dpkg that
> workarounds any such situation.)

Do we know what change is needed to apt ?

Thanks,
Ian.