Re: [gentoo-dev] Portage dependency solving algorithm

[hasufell]

On 11/08/2014 10:30 PM, Rich Freeman wrote:
> On Sat, Nov 8, 2014 at 2:48 PM, hasufell <hasufell@g.o> wrote:
>> On 11/08/2014 08:32 PM, hasufell wrote:
>>> On 11/08/2014 08:01 PM, Matthias Dahl wrote:
>>>> Hello Ciaran...
>>>>
>>>> On 08/11/14 19:26, Ciaran McCreesh wrote:
>>>>
>>>>> No. It would make sense to introduce a cultural change, where
>>>>> developers stop writing dependencies that seem to work with some
>>>>> particular version of Portage if you don't look very closely, and start
>>>>> writing good dependencies.
>>>>
>>>> Sorry to chime in like that but if you don't mind, I'd like to ask for a
>>>> real-life example for badly declared dependencies with a few words why
>>>> those are bad and how to make them actually better?
>>>>
>>>
>>> from dev-haskell/hashtables (note "hashtables" != "hashable"):
>>> || ( ( >=dev-haskell/hashable-1.1:=[profile?]
>>>        <dev-haskell/hashable-1.2:=[profile?] )
>>>      ( >=dev-haskell/hashable-1.2.1:=[profile?]
>>>        <dev-haskell/hashable-1.3:=[profile?] )
>>>    )
>>>
>>> Latest stable version of dev-haskell/hashable is 1.2.1.0.
>>> On a stable system (arch) the paludis dep-solver will try to match the
>>> first group first and realize that there is also a stable version
>>> 1.1.2.5 that matches that group. At that point there is a correct
>>> solution, but since that involves downgrading a package, it will require
>>> user-intervention, because it may not be what the user wants.
>>> (this is the easy scenario... if downgrading causes blockers, you get
>>> much more interesting output)
>>>
>>
>> To be more specific... it is assumed that hashable-1.2.1.0 is already
>> installed. Every time the dep solver runs through those packages without
>> specifying what you want, you will hit the downgrade-problem.
>
> I'm missing the problem.  The package requires one of two ranges of
> hashable versions.  One of them is already installed.  The dependency
> is satisfied.
>

The one that is installed (1.2.1.0) is *excluded* by the first group,
but there is a valid version that fits instead (1.1.2.5).

That's the point where the assumptions start about what the depstring
means and what the user wants.