Status of weak dependencies support in Fedora 21+

[Jan Zelený]

On 10. 11. 2014 at 10:31:55, Kevin Fenzi wrote:
> On Mon, 10 Nov 2014 10:34:16 +0100
> 
> Jan Zelený <jzeleny at redhat.com> wrote:
> > Dnf should already have full support of this feature, at least that
> > is the plan. Some people already tested it and so far it seems it
> > works as expected. The semantics is described here:
> > 
> > http://rpm.org/wiki/PackagerDocs/Dependencies
> 
> Well, if things are fully implemented then...
> 
> 1. If there's a weak dep (reccomends or supplants) that generates a
> solving error, dnf drops that weak dep and goes on with no error?
> (I guess this case would be two packages recommending things that
> conflict or one recommending something and another package with a
> supplants for a different package)
> 
> 2. For 'very weak' deps (suggests, enhances) does dnf "show the
> matching packages as option to the user" ?
> 
> 3. The page says "The depsolver may offer to treat the weak like very
> weak relations or the other way round" does dnf do that? or not?

I will defer these three to Jan (CCed) to answer

> > However, as people already pointed out, there are no guidelines how
> > to use this feature and we don't have this fully tested (kind of
> > chicken-egg problem, we can't fully test it unless it's used in
> > Fedora).
> 
> Well, you could test with copr? Or a side repo?
> It should be pretty easy to create a repo with packages showing all the
> cases?

Some testing was already done, not on a large scale though. That was my 
original point.

> > We invite anyone to start using this feature to help us sand off the
> > rough edges. Any contribution (documentation, bug reports,
> > patches, ...) will help us. We would just like to ask you for
> > patience, as the state is what it is - before F22, this is more of a
> > tech preview than production ready feature.
> 
> I'd personally say people shouldn't start using this... we should be
> able to work up the cases or whatever... it just means that in f21
> people using yum (the default) will get sometimes different behavior
> from dnf (not yet the default).

I would like to emphasize that using this in Fedora will not do any damage, 
yum will continue to work exactly the same way it always has been working. 
Also, people using dnf already do experience different behavior than that of 
yum from time to time due to different dependency solvers so I don't see how 
this would be any different.

> Perhaps some folks would like to step up to help out with this?
> Make a wiki page or document of various cases people might use it, make
> a test copr with those cases? Draft a FPC guideline for using them?

That would be really appreciated. All those can be done simultaneously with 
the progressing adoption. I'm convinced we should use the test run in F21 to 
actually know what we need to regulate/control. Writing guidelines without any 
prior experience with the technology in Fedora is highly unlikely to do any 
good (remember SCLs?).

Thanks
Jan