[GHC] #14710: GHC 8.4.1-alpha allows the use of kind polymorphism without PolyKinds

[GHC]

#14710: GHC 8.4.1-alpha allows the use of kind polymorphism without PolyKinds
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler (Type    |              Version:  8.4.1-alpha1
  checker)                           |
      Resolution:                    |             Keywords:  PolyKinds
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC accepts       |  Unknown/Multiple
  invalid program                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by RyanGlScott):

 Well, I'd //like// to be able to fix this, but have no solid idea of where
 to start.

 My first inclination would be to insert a validity check into the
 `KindedTyVar` case of
 [http://git.haskell.org/ghc.git/blob/f00ddea96cc856654ac90fcf7d29556a758d6648:/compiler/rename/RnTypes.hs#l1033
 bindLHsTyVarBndrs]. I'd need to do roughly the following:

 * I'd need to figure out which variables are already bound in an enclosing
 scope (after all, those are the only sorts of type variables that exhibit
 this problem).
 * I'd need to partition them into type and kind variables (we only care
 about the kind variables).
 * Of those kind variables, I'd need to figure out which of them were
 originally bound as type variables.

 I'm afraid I don't know how to do any of those steps. Help?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14710#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler