[GHC] #7022: Kind variable scoping problem in Iface file when using Template Haskell

[GHC]

#7022: Kind variable scoping problem in Iface file when using Template Haskell
------------------------------+---------------------------------------------
 Reporter:  goldfire          |          Owner:                           
     Type:  bug               |         Status:  new                      
 Priority:  normal            |      Component:  Compiler                 
  Version:  7.5               |       Keywords:  TemplateHaskell PolyKinds
       Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple         
  Failure:  None/Unknown      |       Testcase:                           
Blockedby:                    |       Blocking:                           
  Related:                    |  
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 Consider the following modules:

 {{{
 module PolykindTH where

 import Language.Haskell.TH

 makeSList :: Q [Dec]
 makeSList = do
   a <- newName "a"
   k <- newName "k"
   return [TySynD (mkName "SList") [KindedTV a (AppT ListT (VarT k))]
                  (AppT (ConT (mkName "Sing")) (VarT a))]
 -- makes "type SList (a :: [k]) = Sing a"
 }}}

 {{{
 {-# LANGUAGE PolyKinds, TypeFamilies, DataKinds, TemplateHaskell #-}

 module Polykind where

 import PolykindTH

 data family Sing (a :: k)

 $( makeSList )
 }}}

 When these modules are compiled, the resultant Iface file fails to load
 when code attempts to use the modules. To check this, I packaged this up
 with a cabal file, registered the package with my GHC (7.5.20120620), and
 then attempted to compile the following:

 {{{
 import Polykind

 foo :: SList a -> Bool
 foo = undefined
 }}}

 Here is the error:

 {{{
 Declaration for SList:
   Iface type variable out of scope:  k
 Cannot continue after interface file error
 }}}

 I have attached a tarball of my cabal package for ease of testing.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7022>
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