[GHC] #13512: GHC incorrectly warns that a variable used in a type application is unused

[GHC]

#13512: GHC incorrectly warns that a variable used in a type application is unused
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |             Keywords:
      Resolution:                    |  TypeApplications
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by ulysses4ever):

 @RyanGlScott How did you trace usage of `bindLHsTyVarBndrs` to
 `rnValBindsLHS`? I was only able to trace it to `rnValBindsRHS` as
 @simonpj told:

 {{{

 -- RnTypes.hs

 warnUnusedForAll  ←
 bindLHsTyVarBndrs ←
 rnHsTyKi          ←
 rnLHsType         ←
 rnHsSigType       ←

 -- RnBinds.hs

 renameSig         ←
 rnValBindsRHS
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13512#comment:5>
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