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@songzh reported to me via email that

{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}

import Language.Haskell.TH

data Proxy a = Proxy

yields

> $(reifyRoles ''Proxy >>= stringE.show)
"[PhantomR]"

while adding {-# LANGUAGE PolyKinds #-} to the module above will lead to

$(reifyRoles ''Proxy >>= stringE.show)
"[NominalR,PhantomR]"

This is confusing.

Given that (non-degenerate) invisible parameters are always nominal, we might imagine changing reifyRoles to skip invisible parameters. But this would be backward-incompatible and needlessly disruptive -- especially if we ever decide to allow non-nominal invisible parameters. So I argument for simply documenting this.

Patch coming very shortly.