[GHC] #15787: GHC panic using kind application

[GHC]

#15787: GHC panic using kind application
-------------------------------------+-------------------------------------
           Reporter:  Iceland_jack   |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.6.1
           Keywords:                 |  Operating System:  Unknown/Multiple
  TypeApplications                   |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Using GHC head at diff [https://phabricator.haskell.org/D5229 Visible kind
 application D5229] (#12045),

 bug goes away if you remove `@ob`.

 {{{#!hs
 {-# Language RankNTypes #-}
 {-# Language TypeApplications #-}
 {-# Language DataKinds        #-}
 {-# Language PolyKinds        #-}
 {-# Language GADTs            #-}
 {-# Language TypeFamilies     #-}

 import Data.Kind

 class Ríki (ob :: Type) where
  type Hom :: ob -> ob -> Type

 data
   Kl_kind :: forall ob . (ob -> ob) -> ob -> Type where
   Kl      :: k -> Kl_kind @ob (m) k

 type family
   UnKl (kl :: Kl_kind m k) = (res :: k) where
   UnKl (Kl a) = a
 }}}

 {{{
 $ ghci -ignore-dot-ghci 543_bug.hs
 GHCi, version 8.7.20181017: http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling Main             ( 543_bug.hs, interpreted )
 ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 8.7.20181017 for x86_64-unknown-linux):
         ASSERT failed!
   Type-correct unfilled coercion hole {co_a1yH}
   Call stack:
       CallStack (from HasCallStack):
         callStackDoc, called at compiler/utils/Outputable.hs:1160:37 in
 ghc:Outputable
         pprPanic, called at compiler/utils/Outputable.hs:1219:5 in
 ghc:Outputable
         assertPprPanic, called at compiler/typecheck/TcHsSyn.hs:1805:99 in
 ghc:TcHsSyn

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

 >
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15787>
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