Panic repSplitTyConApp_maybe

This definition panics!

{-# LANGUAGE TypeFamilies, TypeInType #-}

module Whoops where
import Data.Kind

type family PComp (k :: j -> Type) (x :: k) :: ()

ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 8.3.20170828 for x86_64-unknown-linux):
        repSplitTyConApp_maybe
  j_aon[sk:1]
  *
  *
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/utils/Outputable.hs:1138:37 in ghc:Outputable
        pprPanic, called at compiler/types/Type.hs:1123:5 in ghc:Type

If I make it a type synonym instead, I get a proper error as expected.

Trac metadata

Trac field	Value
Version	8.2.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	goldfire
Operating system
Architecture