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Regression around quantified constraints and superclasses

GHC 9.2 (and HEAD) reject the following, despite the fact that GHC 8.10.5 accepts:

{-# LANGUAGE QuantifiedConstraints #-}

module Bug2 where

f :: (forall a. Ord (m a), forall a. Semigroup a => Eq (m a)) => m Int
f = f

The problem is that, in the ambiguity check, GHC has [W] Eq (m a). But it has two ways to solve an [W] Eq (m a) constraint: either from the quantified constraint for Eq (m a) or from the superclass of the quantified constraint for Ord (m a). And so GHC, when presented with a fork in the road, crashes.

The Semigroup a => constraint is necessary to trigger the problem.

I don't know how GHC 8.10.5 accepted this program, and I have not yet explored further.

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