GHC 8.4.1 pretty-prints data family instances with redundant kind signatures using -ddump-splices

Consider this program:

{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}
{-# OPTIONS_GHC -ddump-splices #-}
module Bug where

$([d| data family Foo :: *
      data instance Foo :: * |])

On GHC 8.2.2, this gives the following -ddump-splices output:

$ /opt/ghc/8.2.2/bin/ghci Bug.hs
GHCi, version 8.2.2: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/rgscott/.ghci
[1 of 1] Compiling Bug              ( Bug.hs, interpreted )
Bug.hs:(6,3)-(7,31): Splicing declarations
    [d| data family Foo_a1sB :: *
        
        data instance :: * |]
  ======>
    data family Foo_a494 :: GHC.Types.Type
    data instance :: GHC.Types.Type

But on GHC 8.4.1, we have:

$ /opt/ghc/8.4.1/bin/ghci Bug.hs
GHCi, version 8.4.0.20180209: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/rgscott/.ghci
[1 of 1] Compiling Bug              ( Bug.hs, interpreted )
Bug.hs:(6,3)-(7,31): Splicing declarations
    [d| data family Foo_a1xd :: *
        
        data instance Foo_a1xd :: * :: * |]
  ======>
    data family Foo_a487 :: GHC.Types.Type
    data instance Foo_a487 :: GHC.Types.Type :: GHC.Types.Type

Notice how there is a redundant kind signature in data instance Foo_a1xd :: * :: *.

Trac metadata

Trac field	Value
Version	8.4.1-alpha3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	alanz
Operating system
Architecture