Foldable cannot be derived by GND due to redundant contexts

If GND is enabled, and roles don't permit a Foldable instance to be derived, it won't fall back on DeriveFoldable; instead it just produces an error. I think ideally I'd want to use a pragma to state explicitly that I want to use DeriveFoldable-style deriving for this specific instance, but an implicit fallback would be acceptable.

{-# LANGUAGE
--  GeneralizedNewtypeDeriving,
  DeriveFoldable #-}
module Derive where
import qualified Data.IntMap as M

newtype UniqFM ele = UFM {unUFM :: M.IntMap ele}
  deriving (Foldable)

Trac metadata

Trac field	Value
Version	7.9
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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