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Re: [p2-dev] Planner explanation question 
The resolver computes *one* explanation only, so even if you have
multiple missing requirements, only one will be returned in a minimal
explanation, because it is sufficient to explain the failure.

We might have a trick to manage missing requirements and report all of
them, but we would still have an issue in case of multiple singleton
violations.

Daniel

Le 12/05/2011 21:18, Pascal Rapicault a écrit :
> What is returned by the slicer is not an explanation, but just a "bunch
> of notes" collected along the way as it was slicing. The information
> collected is very vague and here is an example why. I have the following IUs
> A requires B [0, 3.0)
> B-1 requires C 
> B-1.1 requires E
> B-2 requires D
> D
> When the slicer is slicing for A, it will include B-1, B-1.1 and B-2  in
> the slice. Now when it slices B-1 it will fail at finding a C and will
> create a log. Same will go for B-1.1 with E. When it comes to B-2 it
> will find D. In this case, the resolution of A will have a solution. Now
> if I take B-2 out of the set of available IUs, then the slicer will
> return 2 warnings but really only one of those warnings would have to be
> "fixed" for a solution to be found. Of course this is a small example,
> if you follow all the possibilities of all the versions you can get a
> lot of noise from which it may be hard for you to figure out what is
> really missing.
> 
> Computing an explanation is done by the core SAT solver and will sort
> through the noise to figure out something that you can act upon.
> I will let Daniel explain if more can actually be done.
> 
> I have released the test you provided, but it is not enabled as part of
> the global test suite.
> 
> PaScaL
> 
> On 2011-05-12, at 2:45 PM, Todorova, Katya wrote:
> 
>> The Slicer returns all missing requirements properly but if there's an
>> attempt to calculate the minimal explanation, some of these
>> reqirements are cut off and only the first one is returned to the end
>> user.
>>  
>> Here's the part of code that calculates the explanation:
>> ** 
>> *if*(s.getCode() != /UNSATISFIABLE/|| (context != *null*&&
>> !(context.getProperty(/EXPLANATION/) == *null*||
>> Boolean./TRUE/.toString().equalsIgnoreCase(context.getProperty(/EXPLANATION/))))) {
>>     ...
>>
>> *    return* plan;                          //that plan
>> status contains all problematic requirements though all substatus
>> codes are "Warning"
>>
>> }
>>
>>
>> //Extract the explanation
>>
>> Set<Explanation> explanation =
>> projector.getExplanation(sub.newChild(/_ExpandWork_/________/ 4));    
>> //here some of missing requirements are removed and the only one
>> remaining is marked as Error.
>>
>> Test case attached.
>>  
>> What is the minimal explanation supposed to contain?
>>  
>> Thanks,
>> Katya
>>
>>     ------------------------------------------------------------------------
>>     *From:* p2-dev-bounces@xxxxxxxxxxx
>>     <mailto:p2-dev-bounces@xxxxxxxxxxx>
>>     [mailto:p2-dev-bounces@xxxxxxxxxxx] *On Behalf Of *Pascal Rapicault
>>     *Sent:* Thursday, May 12, 2011 8:56 PM
>>     *To:* P2 developer discussions
>>     *Subject:* Re: [p2-dev] Planner explanation question
>>
>>     From a quick code inspection to SimplePlanner, setting explanation
>>     to false will completely disable the explanation support (this is
>>     used in the case of the dropins to avoid computing the explanation
>>     since there is no one to read it).
>>     Some of the missing requirements are filtered as part of the
>>     Slicer (but this is expected and filter out the noise), but after
>>     that the explanation is constructed by the solver and it tries to
>>     return the minimal explanation between what you have installed and
>>     what you are trying to install.
>>
>>     However if you have several missing requirements I think it will
>>     stop at the first one. Is that the pb you are seeing?
>>
>>     If you can provide an automated test case, we could see what can
>>     be done.
>>
>>     On 2011-05-12, at 1:40 PM, Todorova, Katya wrote:
>>
>>>     Hi guys,
>>>      
>>>     I came across a strange behavior of p2 planner - it hides
>>>     information when trying to resolve an IU and resolution fails
>>>     (due to missing requirements for example).
>>>     If there are more than one missing requirements the final
>>>     explanation (and corresponding MultiStatus) will contain only the
>>>     first one found. This default behavior
>>>     could be avoided if "org.eclipse.equinox.p2.director.explain"
>>>     property is set to "false" in the provisioning context used by
>>>     the planner.
>>>      
>>>     I thought that the explanation is supposed to contain more
>>>     details than the "ordinary" status but it turned out it's not the
>>>     case and it contains even less. Is that expected?
>>>     If yes, any idea why?
>>>      
>>>     Thanks in advance,
>>>     Katya
>>>      
>>>     _______________________________________________
>>>     p2-dev mailing list
>>>     p2-dev@xxxxxxxxxxx <mailto:p2-dev@xxxxxxxxxxx>
>>>     https://dev.eclipse.org/mailman/listinfo/p2-dev
>>
>> <ExplanationHidesRequirementsTest.txt>_______________________________________________
>> p2-dev mailing list
>> p2-dev@xxxxxxxxxxx <mailto:p2-dev@xxxxxxxxxxx>
>> https://dev.eclipse.org/mailman/listinfo/p2-dev
> 
> 
> 
> _______________________________________________
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> p2-dev@xxxxxxxxxxx
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-- 
             Daniel Le Berre             mailto:leberre@xxxxxxx
             MCF-HDR,  CRIL-CNRS UMR 8188,  Universite d'Artois
             http://www.cril.univ-artois.fr/~leberre

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