[GHC] #2135: Warn if functions are exported whose types cannot be written

[GHC]

#2135: Warn if functions are exported whose types cannot be written
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 Reporter:  dons             |          Owner:         
     Type:  feature request  |         Status:  new    
 Priority:  normal           |      Milestone:         
Component:  Compiler         |        Version:  6.8.2  
 Severity:  normal           |     Resolution:         
 Keywords:  warnings         |     Difficulty:  Unknown
 Testcase:                   |   Architecture:  Unknown
       Os:  Unknown          |  
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Changes (by igloo):

  * difficulty:  => Unknown

Comment:

 Type synonyms make this trickier, e.g.:
 {{{
 module Q (TypeSyn, v) where

 v :: RealType
 v = Val

 type TypeSyn = RealType

 data RealType = Val
 }}}
 Perhaps this warning should only be used for values which have explicit
 type signatures, and should warn if the types in the explicit type
 signature aren't exported?

 I think we'd also have to ignore types that aren't defined in the current
 module, as we don't want to have to re-export all the types we use in our
 type signatures. But if we do that then we can be tripped up by modules
 hidden at the package level.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2135#comment:1>
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