Associated type is accepted even without mentioning class parameters

The following module is accepted:

{-# LANGUAGE TypeFamilies #-}

module Bug where

class C a where
  type F b

Note that the associate type family F does not mention the class variable a. Because associated type families are somewhat thin sugar over non-associated type families, I doubt this causes any great disaster anywhere, but it should probably be fixed.

Trac metadata

Trac field	Value
Version	7.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	low
Resolution	Unresolved
Component	Compiler
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