[GHC] #4806: Make error message more user friendly when module is not found because package is unusable

[GHC]

#4806: Make error message more user friendly when module is not found because
package is unusable
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        Reporter:  mitar             |                Owner:  bollu
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.0.1
      Resolution:                    |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Phyx-):

 Would the sandbox (I'm fuzzy on the details of it) also sandbox the actual
 package registration? e.g. does the sandbox copy the installed packages or
 just links to the ones already installed?

 I must admit to not having used sandboxes before :)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4806#comment:19>
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