Re: [PATCH setup 00/14] Use libsolv, solve all our problems... (WIP)

[Jon Turney <jon dot turney at dronecode dot org dot uk>]

On 24/12/2017 15:00, Ken Brown wrote:
> On 12/13/2017 5:31 PM, Ken Brown wrote:
> > On 12/13/2017 1:05 PM, Achim Gratz wrote:
> > > Ken Brown writes:
> > > > 1. Uninstall A.
> > > > 2. Don't uninstall B.
> > > >
> > > > On the surface, it would seem that libsolv chose 2 by default, because
> > > > it returned an empty transaction list.  This was reflected in the log
> > > > and was also clear when I selected 'Back'.

Yeah, I think what is actually happening here is that the solver returns 
a partial solution, without the problematic transaction.

But yeah, there's no real concept of a default solution, so (lacking a 
UI to choose, which I think is a bit out of scope for the moment), it's 
up to us to define one.

> > > I don't think there is a default in this case.  I also see in zypper
> > > that the order of the proposed solutions (there can be way more than two
> > > if the dependencies are more complicated) is not always the same, so
> > > there is no preference implied by the order as well.
> > >
> > > > Maybe we have to deal with this situation ourselves.  Whenever a
> > > > problem involves a missing dependency, we could choose as default
> > > > solution the one that installs/keeps the dependent package, as is
> > > > currently done.
> > >
> > > That solution unfortunately isn't always the one that causes the least
> > > amount of transactions or even the least amount of breakage.
> >
> > That may be true, but I still think it's a reasonable default.  The 
> > user doesn't have to accept it.  Also, it's consistent with what setup 
> > currently does, so it won't surprise anyone.
> >
> > The attached patch attempts to implement my suggestion.

I came up with a slightly different solution of just picking the first 
solution as a default.

After solving problems we also need to consider the 'install source for 
everything I install' flag, which unfortunately requires quite a bit of 
refactoring.

See attached.

Attachment: 0001-Apply-default-solution-s.patch
Description: Text document