T14289b.hs:11:3-46: Splicing declarations
    [d| data Foo a
          = Foo a
          deriving (y `C` z) |]
  ======>
    data Foo a
      = Foo a
      deriving (C y z)
T14289b.ppr.hs:(8,3)-(10,29): Splicing declarations
    [d| data Foo a
          = Foo a
          deriving (y `C` z) |]
  ======>
    data Foo a
      = Foo a
      deriving (C y z)