[GHC] #16347: GHC HEAD regression: piResultTys1

[GHC]

#16347: GHC HEAD regression: piResultTys1
-------------------------------------+-------------------------------------
           Reporter:  RyanGlScott    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  highest        |         Milestone:
          Component:  Compiler       |           Version:  8.7
  (Type checker)                     |
           Keywords:  TypeInType     |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Compile-time
  Unknown/Multiple                   |  crash or panic
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 The following program typechecks on GHC 8.0.2 through 8.6.3, but panics on
 HEAD:

 {{{#!hs
 {-# LANGUAGE GADTs      #-}
 {-# LANGUAGE TypeInType #-}
 module Bug where

 import Data.Kind
 import Data.Proxy

 data T f :: f Type -> Type where
   MkT :: T f a
 }}}
 {{{
 $ ~/Software/ghc4/inplace/bin/ghc-stage2 Bug.hs
 [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )
 ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 8.7.20190219 for x86_64-unknown-linux):
         piResultTys1
   k_a10k[tau:1]
   [*]
   Call stack:
       CallStack (from HasCallStack):
         callStackDoc, called at compiler/utils/Outputable.hs:1159:37 in
 ghc:Outputable
         pprPanic, called at compiler/types/Type.hs:1063:5 in ghc:Type
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16347>
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