ghc 8.0rc4 treats INLINE pragmas for methods with default (implicit) definitions as errors

I was getting around to testing some of my maths code with ghc 8.0 and i noticed that whereas in ghc 7.10 and earlier i could have an INLINE pragma for a method of a type class method that has a default implementation (whether this did anything or not is another question), in ghc 8.0 this now gives an ERROR (with not even a warning in ghc 7.10)

is this a deliberate design change or an accident? I dont see it in the release notes!

heres a small program that illustrates the differences (builds fine with no mention of the INLINE pragma matter under -Wall for 7.10, errors during build in 8.0)

{-# LANGUAGE NoImplicitPrelude #-}

module Main where
import Prelude (putStrLn)
import qualified Data.Functor as Fun
import qualified  Data.Foldable as F
import Prelude hiding  (map,foldl,foldr,init,scanl,scanr,scanl1,scanr1,foldl1,foldr1)


newtype ListWrap a = ListWrap  { unListWrap  :: [a] } deriving (Eq, Show)

instance Foldable ListWrap where
  {-# INLINE foldMap #-}
  {-# INLINE foldr #-}
  foldMap f (ListWrap ls)=   (F.foldMap f ls )


main = putStrLn "hello"

this may be a *valid* design change, but i've not seen it documented anywhere, such as the release notes in the RC or in https://ghc.haskell.org/trac/ghc/wiki/Migration/8.0 ... so i'm assuming its a regression pending dicussion ;)

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	high
Resolution	Unresolved
Component	Compiler
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