[Hackage] #474: cabal-install needlessly reinstalls an existing package

[Hackage]

#474: cabal-install needlessly reinstalls an existing package
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  Reporter:  judah               |        Owner:         
      Type:  defect              |       Status:  new    
  Priority:  normal              |    Milestone:         
 Component:  cabal-install tool  |      Version:  1.6.0.1
  Severity:  normal              |   Resolution:         
  Keywords:                      |   Difficulty:  unknown
Ghcversion:                      |     Platform:         
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Comment (by duncan):

 Yes you're quite right. I can reproduce it. It's not the same as #470
 though it does lead to that situation as you say.

 So we pick Cabal and then process. We have not committed to picking the
 installed version of either yet. We end up picking the highest version of
 process. That then forces the choice of Cabal, we have to pick the
 available version because the installed version uses an older version of
 process.

 We already try to pick the installed versions of packages however that
 heuristic is not enough here because there are multiple installed versions
 of process. To pick between them we should pick the one that would let us
 use the installed version of another package that we have already picked
 where we still have the choice of installed or available.

-- 
Ticket URL: <http://hackage.haskell.org/trac/hackage/ticket/474#comment:4>
Hackage <http://haskell.org/cabal/>
Hackage: Cabal and related projects