[Hackage] #512: Use a proper exception for the 'die' utility function

[Hackage]

#512: Use a proper exception for the 'die' utility function
----------------------------+-----------------------------------------------
  Reporter:  duncan         |        Owner:         
      Type:  defect         |       Status:  new    
  Priority:  normal         |    Milestone:         
 Component:  Cabal library  |      Version:  1.6.0.1
  Severity:  normal         |     Keywords:         
Difficulty:  unknown        |   Ghcversion:         
  Platform:                 |  
----------------------------+-----------------------------------------------
 Currently the `die` function prints the error message to stderror and
 throws an exit with exception. This is not a good approach for library
 code. Instead it should throw an user error exception with the string
 message. A top level handler in `Distribution.Simple.main` or `cabal-
 install` should catch this, print it as before and throw an exit
 exception.

 See also #510 for an example of how this causes problems. The
 `readPackageDescription` ends up throwing the exit exception when it would
 be more helpful to clients for it to throw an ordinary exception
 containing the error message.

-- 
Ticket URL: <http://hackage.haskell.org/trac/hackage/ticket/512>
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