Bug#865313: haskell-dependent-sum FTBFS: Couldn't match type `(forall (a1 :: k1). x := a1 -> b0) -> b0'

[Adrian Bunk]

Source: haskell-dependent-sum
Version: 0.3.2.2-3
Severity: serious
Tags: buster sid

https://buildd.debian.org/status/package.php?p=haskell-dependent-sum&suite=sid

...
touch configure-ghc-stamp
. /usr/share/haskell-devscripts/Dh_Haskell.sh && \
build_recipe
Running debian/hlibrary.setup build --builddir=dist-ghc
Building dependent-sum-0.3.2.2...
Preprocessing library dependent-sum-0.3.2.2...
[1 of 4] Compiling Data.GADT.Show   ( src/Data/GADT/Show.hs, dist-ghc/build/Data/GADT/Show.o )
[2 of 4] Compiling Data.GADT.Compare ( src/Data/GADT/Compare.hs, dist-ghc/build/Data/GADT/Compare.o )

src/Data/GADT/Compare.hs:61:30: error:
    * Couldn't match type `(forall (a1 :: k1). x := a1 -> b0) -> b0'
                     with `forall b. (forall (a1 :: k1). x := a1 -> b) -> b'
      Expected type: [(forall b. (forall (a :: k1). x := a -> b) -> b,
                       String)]
        Actual type: [((forall (a :: k1). x := a -> b0) -> b0, String)]
    * In the expression:
        return
          ((\ x -> x Refl) :: forall b. (forall a. x := a -> b) -> b, rest)
      In an equation for `f':
          f (Refl, rest)
            = return
                ((\ x -> x Refl) :: forall b. (forall a. x := a -> b) -> b, rest)
      In an equation for `greadsPrec':
          greadsPrec p s
            = readsPrec p s >>= f
            where
                f ::
                  forall x.
                  (x := x, String)
                  -> [(forall b. (forall a. x := a -> b) -> b, String)]
                f (Refl, rest)
                  = return
                      ((\ x -> x Refl) :: forall b. (forall a. x := a -> b) -> b, rest)
    * Relevant bindings include
        f :: (x := x, String)
             -> [(forall b. (forall (a :: k1). x := a -> b) -> b, String)]
          (bound at src/Data/GADT/Compare.hs:61:13)
/usr/share/cdbs/1/class/hlibrary.mk:147: recipe for target 'build-ghc-stamp' failed
make: *** [build-ghc-stamp] Error 1