GHC.Prim does not export Constraint

This code from the effect-monad library worked in ghc-7.10, but fails with ghc-8.0.1-rc1:

{-# LANGUAGE TypeFamilies, ConstraintKinds, PolyKinds #-}

module Control.Effect.Cond where

import GHC.Prim

class Cond (m :: k -> * -> *) where
    type AltInv m (s :: k) (t :: k) :: Constraint

It seems one now needs to import Constraint from GHC.Exts.

This should be mentioned in the migration guide (https://ghc.haskell.org/trac/ghc/wiki/Migration/8.0), together with any other breaking changes there might be from the kind equalities patch (67465497).

Trac metadata

Trac field	Value
Version	8.0.1-rc1
Type	Bug
TypeOfFailure	OtherFailure
Priority	highest
Resolution	Unresolved
Component	Compiler
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