## Summary I'm working on [`lift-type`](https://hackage.haskell.org/package/lift-type), which provides a function `liftType :: Typeable a => TemplateHaskell.Type`, as part of working on `discover-instances`. I ran into a bug in `discover-instances` where polykinded classes (ie `class TypeScript (a :: k) where ...` break the library. I determined that I can't discover all kinds of instances, but I can pick a single kind. `$$(discoverInstances @(TypeScript :: Type -> Constraint))` works fine, for example. In chasing it down, I determined that I needed to use `lift-type` to turn the provided kind into a `Type` so I can pass it to `discoverInstances`. Instead of providing `[VarT (mkName "a")]`, I need to provide `reifyInstances cls [SigT (VarT (mkName "a")) (liftType @Data.Kind.Type)]`. When I do that, however, I get a GHC error: ``` /home/matt/Projects/lift-type/test/Spec.hs:12:34: error: • Can't find interface-file declaration for data constructor ghc-prim-0.6.1:GHC.Prim.LiftedRep Probable cause: bug in .hi-boot file, or inconsistent .hi file Use -ddump-if-trace to get an idea of which file caused the error • In the first argument of ‘TYPE’, namely ‘'ghc-prim-0.6.1:GHC.Prim.LiftedRep’ In the first argument of ‘Proxy’, namely ‘(TYPE 'ghc-prim-0.6.1:GHC.Prim.LiftedRep)’ In an expression type signature: Proxy (TYPE 'ghc-prim-0.6.1:GHC.Prim.LiftedRep) | 12 | type_ = Proxy :: Proxy $(liftTypeQ @Type) | ^^^^^^^^^^^^^^^ ``` With `-ddump-splices`, I get this: ``` /home/matt/Projects/lift-type/test/Spec.hs:14:34-48: Splicing type liftTypeQ @Type ======> TYPE 'ghc-prim-0.6.1:GHC.Prim.LiftedRep ``` The code that produces it is here: ```haskell mk :: TyCon -> Type mk tyCon = let tcName = tyConName tyCon trySymbol = case tcName of '"' : cs -> Just $ LitT (StrTyLit (zipWith const cs (drop 1 cs))) _ -> Nothing tryTicked = case tcName of '\'' : dcName -> let nameBase = mkOccName dcName flavor = NameG DataName (mkPkgName $ tyConPackage tyCon) (mkModName $ tyConModule tyCon) name = Name nameBase flavor in Just (PromotedT name) _ -> Nothing tryNat = LitT . NumTyLit <$> readMaybe tcName plainType = let nameBase = mkOccName tcName flavor = NameG TcClsName (mkPkgName $ tyConPackage tyCon) (mkModName $ tyConModule tyCon) name = Name nameBase flavor in ConT name in fromMaybe plainType $ asum [tryTicked, trySymbol, tryNat] ``` It's taking the `tryTicked` path, which constructs the `NameG DataName pkgName modName` for `TemplateHaskell` to work with non-imported terms. I've worked around this by introducing this case: ```haskell go :: forall k (a :: k). TypeRep a -> Type go tr | Just HRefl <- eqTypeRep (typeRep @Kind.Type) tr = ConT ''Kind.Type | otherwise = ``` However, that's brittle, and won't work for other kinds than just `Type`, and it introduces a performance impact. ## Steps to reproduce ``` git clone git@github.com:parsonsmatt/lift-type cd lift-type git checkout mattp/demonstrate-interface-bug cabal test ``` ## Expected behavior I would expect the built-in types to work as well as the regular ones. For what it's worth, `liftType @Word#` works fine, so it's not only an issue wiht built-in types ## Environment * GHC version used: 8.10 and 9.4 (but CI shows it break in many ghcs: https://github.com/parsonsmatt/lift-type/pull/10) Optional: * Operating System: Ubuntu * System Architecture: x86-64