An unwritten kind variable is "specified", when it shouldn't be.

This fails:

{-# LANGUAGE PolyKinds, TypeApplications, ScopedTypeVariables #-}

module Bug where

import Data.Proxy

class C a where
  foo :: Proxy a

bar :: forall a. C a => Proxy a
bar = foo @a

But it really should work, because the invisible kind variable to class C should not be available for type application. On the last line, foo @_ @a works, when you explicitly instantiate the kind variable. Also, saying :t foo in GHCi shows the specified kind variable.

Will fix. At some point.

Trac metadata

Trac field	Value
Version	8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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