[Hackage] #597: non-exhaustive patterns when trying to install base

[Hackage]

#597: non-exhaustive patterns when trying to install base
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  Reporter:  guest               |        Owner:         
      Type:  defect              |       Status:  new    
  Priority:  normal              |    Milestone:         
 Component:  cabal-install tool  |      Version:  1.6.0.2
  Severity:  minor               |     Keywords:         
Difficulty:  normal              |   Ghcversion:  6.10.1 
  Platform:                      |  
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Comment(by duncan):

 If someone wants to fix this, the other thing to check is with and older
 or newer GHC that does not have two versions of base. A user reported that
 with ghc-6.6 they get an "impossible" internal error in this situation.

 The general fix here is to have a per-compiler list of packages that are
 impossible to upgrade. If the user explicitly asks to install one then
 they should get a sensible error. For all other cases it should use a
 constraint on picking an installed instance of these packages.

-- 
Ticket URL: <http://hackage.haskell.org/trac/hackage/ticket/597#comment:3>
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