[GHC] #5610: Improve "Unacceptable argument type in foreign declaration" error message

[GHC]

#5610: Improve "Unacceptable argument type in foreign declaration" error message
-------------------------------------------------+-------------------------
        Reporter:  bgamari                       |            Owner:
            Type:  feature request               |           Status:  new
        Priority:  high                          |        Milestone:
       Component:  Compiler (Type checker)       |          Version:
      Resolution:                                |  7.6.1-rc1
Operating System:  Unknown/Multiple              |         Keywords:
 Type of failure:  Incorrect warning at          |     Architecture:
  compile-time                                   |  Unknown/Multiple
       Test Case:                                |       Difficulty:
        Blocking:                                |  Unknown
                                                 |       Blocked By:
                                                 |  Related Tickets:
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Comment (by mietek):

 With 7.8.2, using `import Foreign.C.Types (CInt)` still results in the
 unclear error message:
 {{{
 Unacceptable argument type in foreign declaration: CInt
 }}}

 Using `import Foreign.C.Types (CInt (..))` helps, but should this be
 required?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5610#comment:23>
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