add wildcards testcase for T25647a

testsuite/tests/typecheck/should_compile/T25647a.hs

@@ -72,3 +72,21 @@ newtype instance Dix5 f = DIn5 (f (Dix5 f))
 data family Dix7 :: (k -> TYPE 'IntRep) -> k
 newtype instance Dix7 f = DIn7 (f (Dix7 f))
 
+
+
+-- anonymous wildcards
+type Dix8 :: RuntimeRep -> Type
+data family Dix8 r
+newtype instance Dix8 _ = Dix8 Int
+
+dix8 :: Dix8 FloatRep -> Int
+dix8 (Dix8 x) = x
+
+
+-- named wildcards
+type Dix9 :: RuntimeRep -> Type
+data family Dix9 r
+newtype instance Dix9 _r = Dix9 Int
+
+dix8 :: Dix9 FloatRep -> Int
+dix8 (Dix9 x) = x