Bug#758234: transitive dependencies

[Santiago Vila <sanvila@unex.es>]

On Sat, Nov 15, 2014 at 09:09:06AM +0100, Matthias Urlichs wrote:
> If I read #759260 correctly, Gerrit Pape <pape@dbnbgs.smarden.org> objected
> to allowing depending on lower-priority packages and said that the current
> "file a bug and raise the priority" process is just fine. However, IMHO it
> clearly is, not because
> 
> * there's no technical reason (any more) to require this fix-override-file
>   business
> * it installs superfluous libraries when you exclude something when
>   debootstrap-ing
> * we forget to de-prioritize libraries when they're no longer needed in
>   the high-priority set

If those are the real reasons, then let's drop the rule only for
*libraries*, but not for every other package.

I would propose something like this:

 Packages must not depend on packages with lower priority values
 (excluding build-time dependencies).  In order to ensure this, the
 priorities of one or more packages may need to be adjusted.

 The previous rule is waived for libraries, which will generally be of
 "optional" priority, even if packages required, important or standard
 depend on them.

In fact, I'm not sure that making libc6 optional is a good idea.

BTW: A lot of years ago I tried to make the override file to follow
the rules without success. What about automating this procedure first?

> so I'd like to specifically invite arguments against this change here,
> instead of digging through archives and inferring any opponent's reasoning.
> 
> > Regarding your proposed change, I wonder what is the practical case for
> > forbidding conflicts with higher-priority packages.  Could you give an example
> > showing that it is strictly necessary ?
> 
> I do not know of a concrete example. I did infer, from previous discussion,
> that debootstrap et al. can't handle such conflicts. It seems prudent to
> proactively forbid such dependencies, rather than deal with a last-minute
> nonfixable bug filed on debootstrap.

The rule about conflicts, AFAIK, has nothing to do with debootstrap.

It is a rule that, when followed, makes the archive to have a very
good property: You can install as many optional packages as you want
without fear of conflicts. In fact, you could in theory install every
package which is >= optional (however, actually doing this[*] is not a
requisite for the rule to be useful).

I think this rule is useful and we should keep it.

[*] If I remember well, Dale Scheetz once managed to do that, but it
    was a lot of time ago and the number of packages was a lot lower.