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'.
>>
>> 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.
> 
> Ken
> 
> 
> 0001-Implement-a-default-solution-for-SOLVER_RULE_PKG_REQ.patch
> 
> +      if (type == SOLVER_RULE_PKG_REQUIRES)
> +	{
> +	  packagemeta *pkg = db.findBinary(PackageSpecification(pool_dep2str(pool.pool, dep)));
> +	  if (!pkg->desired && pkg->installed < pkg->default_version)
> +	    // User chose to uninstall or skip a required package.
> +	    trans.push_back(SolverTransaction(pkg->default_version,
> +					      SolverTransaction::transInstall));

This isn't quite right.  We also need a transErase if the package is 
installed.  Revised patch attached.

Ken