Test Trac #6020 again, and #6044

testsuite/tests/polykinds/T6020a.hs

+{-# LANGUAGE DataKinds, FunctionalDependencies, FlexibleInstances,
+              UndecidableInstances, PolyKinds, KindSignatures,
+              ConstraintKinds, FlexibleContexts, GADTs #-}
+
+module T6020a where
+
+class Id (a :: k) (b :: k) | b -> a
+instance a ~ b => Id a b
+
+class Test (x :: a) (y :: a)
+instance (Id x y, Id y z) => Test x z
+
+test :: Test True True => ()
+test = ()
+
+

testsuite/tests/polykinds/T6044.hs

+{-# LANGUAGE PolyKinds, DataKinds, TypeFamilies, KindSignatures #-}
+
+module T6044 where
+
+type family Foo (a :: k) :: Maybe k
+type instance Foo a = Just a

testsuite/tests/polykinds/all.T

@@ -41,3 +41,5 @@ test('T6025', normal, run_command, ['$MAKE -s --no-print-directory T6025'])
 test('T6002', normal, compile, [''])
 test('T6039', normal, compile_fail, [''])
 test('T6021', normal, compile_fail, [''])
+test('T6020a', normal, compile, [''])
+test('T6044', normal, compile, [''])