[Rpm-ecosystem] Rich deps syntax finalization

[Neal Gompa]

On Wed, Aug 26, 2015 at 8:00 AM, Florian Festi <ffesti at redhat.com> wrote:

> On 08/26/2015 10:47 AM, Florian Festi wrote:
> > Right now libsolv does not distinguish between different orders of the
> > operands. But we have already discussed making the OR operator
> > preferring the left most operand. This is something RPM does not really
> > care about but of cause has implications for packaging if implemented in
> > libsolv.
>
> May be I should append to this slightly:
>
> AFAIK libsolv uses the Suggests: and Enhances: to pick one of *equally
> adequate* packages. But we stil need to gain more experience on how well
> this works.
>
> But my feeling is that people are too much concerned with preference for
> packages. I understand that it is a topic in Fedora with the change of
> depsolvers and all the hidden assumptions breaking. But... outside of
> installing fixed groups during installation package preferences are
> pretty weak. They stand against a raging sea of other dependencies and
> present, past and future user commands -  waiting to be washed away.
>
> So if one of multiple providers should be chosen the right way is to add
> an hard Requires to the package, meta package or comps group that cares.
>
> Rich dependencies are at first not a tool to express package preferences
> or to allow more flexibility (although they might be used for this).
> They are primarily a tool to get Requires right in more complicated
> cases that cannot be solved with the Requires we already have.
>
> Florian
>
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>
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​The preferential ordering of dependencies doesn't have to necessarily be
in Requires. It could be in Recommends or Suggests as well.

That said, rich dependencies provide interesting opportunities to solve all
kinds of complex dependency resolution conditions. Of course, it is up to
the distribution on how they wish to utilize the functionality. But if it
is within the bounds of reason, we should consider supporting the
capability.


-- 
真実はいつも一つ！/ Always, there's only one truth!
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