Type family not reduced

Andres pointed out that the following fails to compile with GHC 8.0.1 but succeeds with master (f53d761d),

{-# LANGUAGE TypeInType, TypeFamilies #-}
module Kinds where

import GHC.Types

type family G (a :: Type) :: Type
type instance G Int = Bool

type family F (a :: Type) :: G a
type instance F Int = True

Error:

Hi.hs:10:23: error:
    • Expected kind ‘G Int’, but ‘'True’ has kind ‘Bool’
    • In the type ‘True’
      In the type instance declaration for ‘F’

We should figure out what fixed this so it can hopefully be merged for 8.0.2. I initially suspected the patch cited in #12175 (closed) but sadly this doesn't seem to be the case.

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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