Test Trac #7176

testsuite/tests/polykinds/T7176.hs

+{-# LANGUAGE TypeFamilies, DataKinds, PolyKinds, GADTs, RankNTypes #-}
+
+module T7176 where
+
+type family Sing (a :: b)
+
+data SMaybe (a :: Maybe c) where
+   SNothing :: SMaybe Nothing
+   SJust :: Sing a -> SMaybe (Just a)
+type instance Sing (a :: Maybe d) = SMaybe a
+
+sIsJust :: forall (a :: Maybe e). Sing a -> ()
+sIsJust SNothing = ()
+sIsJust (SJust _) = ()
+

testsuite/tests/polykinds/all.T

@@ -62,4 +62,5 @@ test('T7073', normal, compile,[''])
 test('T7128', normal, compile,[''])
 test('T7151', normal, compile_fail,[''])
 test('T7095', normal, compile,[''])
+test('T7176', normal, compile,[''])