Deriving Bifunctor falls over on sufficiently higher-rank field types

[RyanGlScott]

It turns out that Data.Bifunctor.TH suffers from the same bug that caused GHC#17880. Here is a minimal demonstration of the bug:

{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE TemplateHaskell #-}
module Bug where

import Data.Bifunctor.TH

data T a b = MkT (forall c. c -> (forall d. a -> d) -> a)
$(deriveBifunctor ''T)

This should compile, but fails with the following error:

``` Bug.hs:8:3: error: • Couldn't match type ‘forall d1. a -> d1’ with ‘a -> p0’ Expected type: c1 -> (a -> p0) -> a Actual type: c1 -> (forall d. a -> d) -> a • In the first argument of ‘\ x_ajqV b_ajqW -> (\ x_ajqX b_ajqY -> f_ajqR (x_ajqX ((\ x_ajqZ b_ajr0 -> (\ x_ajr1 -> x_ajr1) (x_ajqZ (f_ajqR b_ajr0))) b_ajqY))) (x_ajqV ((\ x_ajr2 -> x_ajr2) b_ajqW))’, namely ‘_arg1_ajqU’ In the first argument of ‘MkT’, namely ‘((\ x_ajqV b_ajqW -> (\ x_ajqX b_ajqY -> f_ajqR (x_ajqX ((\ x_ajqZ b_ajr0 -> (\ x_ajr1 -> x_ajr1) (x_ajqZ (f_ajqR b_ajr0))) b_ajqY))) (x_ajqV ((\ x_ajr2 -> x_ajr2) b_ajqW))) _arg1_ajqU)’ In the expression: MkT ((\ x_ajqV b_ajqW -> (\ x_ajqX b_ajqY -> f_ajqR (x_ajqX ((\ x_ajqZ b_ajr0 -> (\ x_ajr1 -> x_ajr1) (x_ajqZ (f_ajqR b_ajr0))) b_ajqY))) (x_ajqV ((\ x_ajr2 -> x_ajr2) b_ajqW))) _arg1_ajqU) • Relevant bindings include _arg1_ajqU :: forall c. c -> (forall d. a -> d) -> a (bound at Bug.hs:8:3) value_ajqT :: T a c (bound at Bug.hs:8:3) f_ajqR :: a -> b (bound at Bug.hs:8:3) bimap :: (a -> b) -> (c -> d) -> T a c -> T b d (bound at Bug.hs:8:3) | 8 | $(deriveBifunctor ''T) | ^^^^^^^^^^^^^^^^^^^ ```

GHC has fixed this bug upstream, and it should be possible to apply a similar fix in Data.Bifunctor.TH.