Re: Bug#501866: Missing dependancy - libpango1.0-common.prerm uses defoma-app in pkg defoma

[Raphael Hertzog <hertzog@debian.org>]

On Thu, 16 Oct 2008, Sven Joachim wrote:
> On 2008-10-15 17:20 +0200, Josselin Mouette wrote:
> 
> > Le mercredi 15 octobre 2008 à 10:37 -0400, Higgins, Paul a écrit :
> >> I'm not sure where the problem lies.  I saw that the packages that
> >> couldn't find File/Copy.pm seemed to have their dependencies correct,
> >> but apt and dpkg still allowed perl-modules to break it.  The one
> >> package I checked closely because it broke the install, libtiff4,
> >> doesn't seem to depend on doc-base as it should.  
> >> 
> >> It seems like there must be some way to make sure the unpack, etc. for
> >> package perl-modules 5.10.x either leaves the 5.8.x tree alone, or
> >> waits until it is no longer needed to remove it.
> >
> > Frankly, I’m tempted to reassign this to dpkg; Policy §7.2 is very clear
> > on the relationship between prerm scripts and Depends. 
> 
> I think reassigning would be OK.  Maybe also raising the severity to
> important.

I'm not quite sure this is the right thing to do, quoting policy:
    A Depends field takes effect only when a package is to be configured. It
    does not prevent a package being on the system in an unconfigured state
    while its dependencies are unsatisfied, and it is possible to replace a
    package whose dependencies are satisfied and which is properly
    installed with a different version whose dependencies are not and
    cannot be satisfied; 

So there's no guaranty in the prerm script. You can only rely on essential
packages being unpacked.

The fundamental problem here is that perl-modules/perl/perl-base are not
unpacked together. Unless you predepend on perl-modules/perl you can't ensure
that they are in sync. IMO any perl script that is called in a prerm
script should only rely on perl-base and not more.

> > Dpkg needs to ensure that all dependencies *and their own dependencies*
> > are in a clean, installed state when running the prerm script. It
> > correctly does it for postinst already.

I don't think this is reasonable. You are asking to change all Depends
into Pre-Depends.

Cheers,
-- 
Raphaël Hertzog

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