[GHC] #4983: Warning about redundant import is wrong when hiding identifiers in order to avoid export ambiguities

[GHC]

#4983: Warning about redundant import is wrong when hiding identifiers in order to
avoid export ambiguities
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  Reporter:  Lemming                            |          Owner:                  
      Type:  bug                                |         Status:  closed          
  Priority:  normal                             |      Milestone:                  
 Component:  Compiler                           |        Version:  7.0.1           
Resolution:  wontfix                            |       Keywords:                  
  Testcase:                                     |      Blockedby:                  
Difficulty:                                     |             Os:  Unknown/Multiple
  Blocking:                                     |   Architecture:  Unknown/Multiple
   Failure:  Incorrect warning at compile-time  |  
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Comment(by Lemming):

 Replying to [comment:2 simonpj]:
 > I think Lemming's complaint is that the error message isn't right.  We
 don't want to import instances, but we still need `import Prelude ()`.  So
 the suggestion is right but the reason is wrong.

 Maybe this confused me and let me think that GHC is broken.
 My problem was, that I was not aware, that I did not use something from
 Prelude.
 Usually I use variables from Prelude without noting it.
 Maybe you can just alter the warning to:

 {{{
 src/Data/Monoid/HT.hs:6:1:
     Warning: You imported `Prelude', but used nothing of it,
                except perhaps instances from `Prelude'
              To import instances alone, use: import Prelude()
 }}}

 I remember that I have already seen such warnings from GHC (I mean: "used
 nothing of it"), but I do not know in what cases GHC emits them.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4983#comment:3>
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