[Hackage] #490: cabal unpack gives bad error message for unsatisfiable constraints

[Hackage]

#490: cabal unpack gives bad error message for unsatisfiable constraints
---------------------------------+------------------------------------------
  Reporter:  duncan              |        Owner:                     
      Type:  defect              |       Status:  new                
  Priority:  normal              |    Milestone:  cabal-install-0.6  
 Component:  cabal-install tool  |      Version:  1.6.0.1            
  Severity:  normal              |   Resolution:                     
  Keywords:                      |   Difficulty:  very easy (<1 hour)
Ghcversion:                      |     Platform:                     
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Comment (by Saizan):

 With the attached patch we have:
 {{{
 $ cabal unpack haxml-1.20
 cabal: There is no available version of HaXml that satisfies ==1.20
 }}}
 {{{
 $ cabal unpack containers haxml-1.20 array
 'containers-0.2.0.0' is cached.
 Unpacking containers-0.2.0.0...
 cabal: There is no available version of HaXml that satisfies ==1.20
 }}}
 {{{
 $ cabal unpack containers nonexistant
 cabal: There is no package named nonexistant
 }}}

 So, non-existant package names make unpack die early, while non-resolvable
 deps for existing packages make it die on the first one encountered while
 fetching, like other fetching-related problems (e.g. downloading or
 extracting).

-- 
Ticket URL: <http://hackage.haskell.org/trac/hackage/ticket/490#comment:1>
Hackage <http://haskell.org/cabal/>
Hackage: Cabal and related projects