This program compiles with 8.6.5 and 8.8.1 but not with HEAD.

{-# LANGUAGE
             MagicHash,
             FlexibleInstances,
             MultiParamTypeClasses,
             TypeFamilies,
             PolyKinds,
             DataKinds,
             FunctionalDependencies,
             TypeFamilyDependencies #-}
module A where

import GHC.Prim
import GHC.Exts


type family Rep rep where
  Rep Int = IntRep

type family Unboxed rep = (urep :: TYPE (Rep rep)) | urep -> rep where
  Unboxed Int = Int#

[1 of 1] Compiling A                ( A.hs, A.o )

A.hs:20:17: error:
    • Expected kind ‘TYPE (Rep rep)’,
        but ‘Int#’ has kind ‘TYPE 'IntRep’
    • In the type ‘Int#’
      In the type family declaration for ‘Unboxed’
   |
20 |   Unboxed Int = Int#
   |                 ^^^^