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Bug#592610: 7.3/7.4/7.6: Usage of Breaks and Conflicts unclear and contradictive

On Wed, Aug 18, 2010 at 07:07:35PM +0300, Eugene V. Lyubimkin wrote:
> Steve Langasek wrote:
> > Breaks and Replaces are both asymmetric relationships.

> and

> >> If I unpack two packages, one having Breaks+Replaces, in the other order, I
> >> will have a file conflict.

> > No, you won't.  Why would you think so?

> By logic. I didn't see anything to prevent them. However, as dpkg disagree
> with me too, I started to wonder if policy in 'Packages can declare in their
> control file that they should overwrite files in certain other packages, or
> completely replace other packages' actually means two-way dependency? And is
> it obvious to anyone but me?

It's not a "two-way dependency"; the relationship is still asymmetric, the
files from the package /declaring/ Replaces always takes precedence.  But
the Replaces operation is invariant with respect to package unpack order -
perhaps that's what you mean?

I wouldn't say this is obvious.  I would say it's the /correct/ way to
implement it, and I know this is how it's implemented because I remember
back to when dpkg *didn't* do this correctly.  But it's possible that this
should be clarified in Policy.

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                                    http://www.debian.org/
slangasek@ubuntu.com                                     vorlon@debian.org

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