[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 (Type    |              Version:  8.7
  checker)                           |
      Resolution:                    |             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:                    |
-------------------------------------+-------------------------------------
Description changed by RyanGlScott:

Old description:

> 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
> }}}

New description:

 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

 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#comment:1>
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