[Hackage] #390: add cabal unpack command

[Hackage]

#390: add cabal unpack command
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  Reporter:  duncan              |        Owner:                 
      Type:  enhancement         |       Status:  new            
  Priority:  normal              |    Milestone:                 
 Component:  cabal-install tool  |      Version:                 
  Severity:  normal              |   Resolution:                 
  Keywords:                      |   Difficulty:  easy (<4 hours)
Ghcversion:  6.8.3               |     Platform:                 
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Comment (by Saizan):

 Replying to [comment:4 duncan]:
 > Replying to [comment:3 Saizan]:
 > [...]
 > > should we also take the packagePreferences field in consideration
 here?
 >
 > Hmm. Not sure actually.
 I decided to do so for the sake of consistency with cabal install/fetch.

 > > Currently it ignores exceptions (however if something goes wrong the
 functions involved still print error messages), summarizing failures at
 the end like in 'cabal install' is probably what we want.
 >
 > I'd suggest just failing on the first error. So I'd just remove the
 `try`. Since it does not do anything with dependencies the only time we
 can have multiple errors is if the user specifies multiple packages to
 unpack. If the first fails then they'd probably want to deal with that
 rather than having all the others unpack too (as possibly fail for the
 same reason).

 Right, it seems sensible.

 > What happens if the user specifies no packages? Getting a helpful error
 would be nice.

 same here.

 I've attached an amended patch with these edits.

-- 
Ticket URL: <http://hackage.haskell.org/trac/hackage/ticket/390#comment:5>
Hackage <http://haskell.org/cabal/>
Hackage: Cabal and related projects