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

Hackage cvs-ghc at haskell.org
Tue May 15 15:58:32 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               |  

Comment(by kosmikus):

 It's really a question about which error message to choose. If you scan up
 in your log, you will see another "fail (backjumping ..." line before the
 one you've just shown. Currently, the solver tries backtracking to a
 limit, and if it fails, it will print the *first* error it encountered.
 This is based on the heuristic that usually, the first choices involve the
 least compromises, and are most likely to point to the actual problem. In
 this case, it actually points at a real problem (namely "transformers-3"
 being incompatible with your package), but that's not the main problem
 you're interested in.

 I do have something in mind that might fix this. I am planning to use the
 backtracking solver to generate several install plans and pick a "best"
 one according to heuristics. We could do the same for error messages.
 However, it's less clear to me how to define heuristics for what
 constitutes the best among several error messages.

Ticket URL: <http://hackage.haskell.org/trac/hackage/ticket/951#comment:3>
Hackage <http://haskell.org/cabal/>
Hackage: Cabal and related projects

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