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Re: Full install/removal/upgrade test results available

On ven., 2010-11-19 at 23:49 +0100, David Kalnischkies wrote:

> And i am usually not offended by someone blaming APT to be too dumb.
> APT is all about dependency resolution, so saying you are not to deep
> into it, but blaming APT to be wrong isn't the best tone either.
> Draw i would say…

Hey, please don't put words in my mouth, I never said apt was too dumb.
I said it looked to me like it was doing the wrong thing. And you don't
have to take that personally either.
> >> > By the way, adding a Breaks: xfce4-mcs-manager in xfce4-settings doesn't
> >> > work either, apt will still prefer to hold xfce4-session and keep
> >> > xfce4-mcs-*.
> >>
> >> You have way more information than APT - for example:
> >> Is it communicated that xfce4-mcs-manager and xfce4-mcs-plugin are
> >> now obsolete? No. All which is said is that the new xfce4-session doesn't
> >> work with them (it breaks them).
> >
> > No, xfce4-session depends on xfce4-settings. And xfce4-settings
> > *replaces* xfce4-mcs-*.
> >
> >>  So, for APT its clear that we loose two
> >> packages just to get another one upgraded… that doesn't feel right.
> >
> > Even with the Replaces: bit?
> Great, just that Replaces: only says that some files will be replaced,
> not the complete package… (so its mostly only used by dpkg).

Hmh, I missed that. I thought Replaces was package wide for apt.

> They ship common files => Replaces
> Or is xfce4-mcs-plugins broken now that you replaces some of its files?
> (or better as footnote 46 suggests: Does it hurt if the files are gone?)
> Then it really also Breaks:, but you also give the indication that
> something in xfce4-mcs-plugins is left which can be broken and
> therefore functionality is lost by removing it… (or allowing the other
> package to replace files of it in the first place).
> So you might want to provide a new xfce4-mcs-plugins without
> these files (by depending on them) which still provides this functionality
> (or nothing as a dummy package).
> > and xfce4-settings replaces
> > the functionality provided by xfce4-mcs-manager.
> dummy xfce4-mcs-manager depending on xfce4-settings if it is
> a package rename. If its not, but they do not conflict just leave
> xfce4-mcs-manager alone. If they conflict as they use the same files,
> its the same as with the other package…

xfce4-settings replaces (functionnalities) xfce4-mcs-manager and
xfce4-mcs-plugins, and ships files contained in those two packages.

So Conflicts/Replaces is necessary, but indeed not enough. So I guess
I'll have to version them, and add dummy packages back (yeah, NEW!).
> >> Or in short: either make empty dummy packages out of them or
> >> just leave them alone.
> >
> > Which would then need to Depends on xfce4-settings in order to provide
> > the same set of functionality, adding complexity to the dependencies.
> In general positive dependencies are easier to satisfy than negative
> as it is easier to install another package than to remove an installed.
> If we install a new package we have a relatively low probability that a
> negative dependency will effect it later. If we remove a package we can be
> nearly sure that another package depends on it and is now broken.
> (why would it be installed otherwise?)

In this case, I thought apt would use the Replaces: field for that.

> Also, a user normally doesn't complain too much if new functionality
> is added, but heavily if some functionality is gone without good reason…
> And the "good reason" is why APT doesn't remove the package on the
> breaks - the 'Considering' line in the output shows the scores the packages
> have. 0 vs 0 isn't a strong thing. If more packages would depend on
> one of the packages the decision will follow the highest scoring package.

Good point. In that case it's a simple package upgrade, while usually
the whole Xfce stack is installed. I've tried with the xfce4 metapackage
and the upgrade correctly picks xfce4-settings and wants to remove MCS.
So while the partial upgrade for only xfce4-session is a bit broken
(well, if you ask for xfce4-session install it works too), in general it
won't be a problem.

Thanks for your help and your time.


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