[Hackage] #951: Incorrect error messages for non-existing dependencies

Hackage cvs-ghc at haskell.org
Tue May 15 14:05:15 CEST 2012

#951: Incorrect error messages for non-existing dependencies
  Reporter:  guest               |        Owner:                    
      Type:  enhancement         |       Status:  new               
  Priority:  normal              |    Milestone:  cabal-install-0.16
 Component:  cabal-install tool  |      Version:  1.14.0            
  Severity:  normal              |     Keywords:  message, solver   
Difficulty:  unknown             |   Ghcversion:  7.4.1             
  Platform:  Linux               |  
Changes (by kosmikus):

  * keywords:  message solver => message, solver
  * type:  defect => enhancement
  * milestone:  => cabal-install-0.16


 Thanks for the report.

 I'm not sure what you would actually expect here. The solver has some
 freedom in which order to try to resolve the goals. And the problem it
 reports is the first problem it hits. The presence of the bogus dependency
 in this case prevents the solver from successfully backtracking. So yes,
 there's more than one problem in this case, and in general, it's difficult
 to judge which one's the one you want to hear about.

 If you remove the bogus dependency, it will still run into the problem you
 show above at first, but continue backtracking, and will ultimately find a
 solution (probably by picking an older version of transformers).

 So I agree that this might not be the error message you expect, and I see
 it as a valid enhancement request. But the error message given isn't
 "incorrect", and I unfortunately don't see a clear heuristics to apply

Ticket URL: <http://hackage.haskell.org/trac/hackage/ticket/951#comment:1>
Hackage <http://haskell.org/cabal/>
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