Kind inference does not propagate annotations on associated types

Consider the following:

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

data Proxy a = Proxy

class C a where
  type F (a :: *) :: *
  op :: Proxy a -> Int

instance C [] where
  op _ = 5

When compiled, this code generates a warning saying that F [] is undefined. That's a good warning, but the problem is that the code is erroneous and should not compile. The problem is that the kind annotation on a in the declaration of the family F says that a should have kind *. However, I am permitted to write an instance for [], which does not have kind *.

After playing around with this, I was unable to find a way to cause a type safety error, but the behavior should probably be fixed.

Trac metadata

Trac field	Value
Version	7.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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