[GHC] #7278: nonsensical kind variable ascription causes panic

[GHC]

#7278: nonsensical kind variable ascription causes panic
--------------------------------+-------------------------------------------
 Reporter:  nfrisby             |          Owner:                         
     Type:  bug                 |         Status:  new                    
 Priority:  normal              |      Component:  Compiler (Type checker)
  Version:  7.6.1               |       Keywords:                         
       Os:  Unknown/Multiple    |   Architecture:  Unknown/Multiple       
  Failure:  Compile-time crash  |       Testcase:                         
Blockedby:                      |       Blocking:                         
  Related:                      |  
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 {{{
 {-# LANGUAGE TypeFamilies, PolyKinds, MultiParamTypeClasses #-}

 module GHCBug where

 type family TF (t  :: k) :: * -> * -> *

 class C (t :: k) (dcs :: * -> * -> *)

 f :: (C (t :: k) (TF t)) => TF t p1 p0 -> t p1 p0
 f = undefined -- panic caused by (t :: k) in the signature's context
 }}}

 gives

 {{{
 [1 of 1] Compiling GHCBug           ( GHCPanic.hs, interpreted )
 ghc: panic! (the 'impossible' happened)
   (GHC version 7.6.1 for x86_64-apple-darwin):
         metaTvRef
 <<details unavailable>>
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7278>
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