Undef.golden

Singletons/Undef.hs:(0,0)-(0,0): Splicing declarations
    singletons
      [d| foo :: Bool -> Bool
          foo = undefined
          bar :: Bool -> Bool
          bar = error "urk" |]
  ======>
    foo :: Bool -> Bool
    foo = undefined
    bar :: Bool -> Bool
    bar = error "urk"
    type BarSym0 :: (~>) Bool Bool
    data BarSym0 :: (~>) Bool Bool
      where
        BarSym0KindInference :: SameKind (Apply BarSym0 arg) (BarSym1 arg) =>
                                BarSym0 a0123456789876543210
    type instance Apply BarSym0 a0123456789876543210 = Bar a0123456789876543210
    instance SuppressUnusedWarnings BarSym0 where
      suppressUnusedWarnings = snd (((,) BarSym0KindInference) ())
    type BarSym1 :: Bool -> Bool
    type family BarSym1 (a0123456789876543210 :: Bool) :: Bool where
      BarSym1 a0123456789876543210 = Bar a0123456789876543210
    type FooSym0 :: (~>) Bool Bool
    data FooSym0 :: (~>) Bool Bool
      where
        FooSym0KindInference :: SameKind (Apply FooSym0 arg) (FooSym1 arg) =>
                                FooSym0 a0123456789876543210
    type instance Apply FooSym0 a0123456789876543210 = Foo a0123456789876543210
    instance SuppressUnusedWarnings FooSym0 where
      suppressUnusedWarnings = snd (((,) FooSym0KindInference) ())
    type FooSym1 :: Bool -> Bool
    type family FooSym1 (a0123456789876543210 :: Bool) :: Bool where
      FooSym1 a0123456789876543210 = Foo a0123456789876543210
    type Bar :: Bool -> Bool
    type family Bar (a :: Bool) :: Bool where
      Bar a_0123456789876543210 = Apply (Apply ErrorSym0 "urk") a_0123456789876543210
    type Foo :: Bool -> Bool
    type family Foo (a :: Bool) :: Bool where
      Foo a_0123456789876543210 = Apply UndefinedSym0 a_0123456789876543210
    sBar ::
      forall (t :: Bool). Sing t -> Sing (Apply BarSym0 t :: Bool)
    sFoo ::
      forall (t :: Bool). Sing t -> Sing (Apply FooSym0 t :: Bool)
    sBar (sA_0123456789876543210 :: Sing a_0123456789876543210)
      = (sError (sing :: Sing "urk")) sA_0123456789876543210
    sFoo (sA_0123456789876543210 :: Sing a_0123456789876543210)
      = sUndefined sA_0123456789876543210
    instance SingI (BarSym0 :: (~>) Bool Bool) where
      sing = (singFun1 @BarSym0) sBar
    instance SingI (FooSym0 :: (~>) Bool Bool) where
      sing = (singFun1 @FooSym0) sFoo