Scoped kind variables in standalone kind signatures

Summary

StandaloneKindSignatures and ScopedTypeVariables currently do not interact, contrary to users' expectations. See e.g. #19498 (closed)

Term-level type signatures bring forall-bound type variables into scope in the definition. For consistency, standalone kind signatures should too. This change in behavior is the subject of the accepted proposal amendment #592 Scoped kind variables in standalone kind signatures.

Steps to reproduce

type T :: forall k. k -> Type
data T a = MkT (Proxy (a :: k))

This code fails with

Test.hs:5:29: error: [GHC-76037]
    Not in scope: type variable ‘k’
  |
5 | data T a = MkT (Proxy (a :: k))
  | 

Expected behavior

The example should compile and behave identically to

type T :: forall k. k -> Type
data T @k a = MkT (Proxy (a :: k))

Environment

• GHC version used: 9.10.1