Regression around pattern synonyms and higher-rank types

GHC 8.0.1 accepts, but HEAD rejects:

{-# LANGUAGE PatternSynonyms, RankNTypes, ViewPatterns #-}

module Bug where

pattern P :: (forall a. a -> a) -> String
pattern P x <- (\ _ -> id -> x)

(Sidenote: kudos to the parser on figuring out my view pattern.)

HEAD gives this error:

Bug.hs:6:30: error:
    • Couldn't match expected type ‘forall a. a -> a’
                  with actual type ‘a0 -> a0’
    • In the declaration for pattern synonym ‘P’
    • Relevant bindings include x :: a0 -> a0 (bound at Bug.hs:6:30)

The code looks correct to me.

Trac metadata

Trac field	Value
Version	8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
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