[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
-------------------------------------+-------------------------------------
              Reporter:  mitar       |            Owner:
                  Type:  feature     |           Status:  infoneeded
  request                            |        Milestone:  7.10.1
              Priority:  low         |          Version:  7.0.1
             Component:  Compiler    |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by mitar):

 See [https://stackoverflow.com/questions/13794168/haskell-cant-find-
 package here an example] of exactly what I am talking about here and how
 it confuses users. So user here has issues using Haskell program and
 module is said to not exist: `Could not find module
 'Data.Vector'`.

 But then you can see such error:

 {{{
 package vector-0.10.0.1-3450daae3d9f2092020075d05481123c is unusable due
 to missing or recursive dependencies:
   base-4.5.1.0-81d626fb996bc7e140a3fd4481b338cd
 primitive-0.5.0.1-15cdc8c11a54a78809b647af0c2975b3
 }}}

 So instead of saying that that module is not found which make one think
 you just have to install it, something else should be said.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4806#comment:6>
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