[GHC] #15804: GHC panic (Visible kind application diff): data T :: (a :: k) -> *

[GHC]

#15804: GHC panic (Visible kind application diff): data T :: (a :: k) -> *
-------------------------------------+-------------------------------------
           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 [https://phabricator.haskell.org/D5229 Visual Kind Application
 (D5229)])

 This might be the root cause of some of my previous

 {{{#!hs
 {-# Language PolyKinds #-}

 data T :: (a :: k) -> *
 }}}
 {{{
 $ ghci -ignore-dot-ghci 580.hs
 GHCi, version 8.7.20181017: http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling Main             ( 580.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_a1xI}
   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

 >
 }}}

 on 8.6.1 this gives

 {{{
 $ ~/.stack/programs/x86_64-linux/ghc-8.6.1/bin/ghci -ignore-dot-ghci
 580.hs
 GHCi, version 8.6.1: http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling Main             ( /home/baldur/hs/580.hs, interpreted
 )

 /home/baldur/hs/580.hs:3:11: error:
     • Expected a type, but ‘(a :: k)’ has kind ‘k’
     • In the kind ‘(a :: k) -> *’
   |
 3 | data T :: (a :: k) -> *
   |           ^^^^^^^^
 Failed, no modules loaded.
 Prelude>
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15804>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler