Instantiation of invisible type family arguments is too eager

This module looks, to me, like it should be accepted:

{-# LANGUAGE TypeInType, RankNTypes, TypeFamilies #-}

module Bug where

import Data.Kind

type family F :: forall k2. (k1, k2)

data T :: (forall k2. (Bool, k2)) -> Type

type S = T F

But it's not. The problem is that TcHsType.handle_tyfams eagerly instantiates all invisible arguments to a type family at every occurrence. Instead, it should instantiate only those that are counted in the TF's arity -- that is, those "before the colon".

Will fix.

Trac metadata

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