Test Trac #10503

testsuite/tests/polykinds/T10503.hs

+{-# LANGUAGE RankNTypes, PolyKinds, DataKinds, TypeFamilies #-}
+module GHCBug where
+
+data Proxy p = Proxy
+
+data KProxy (a :: *) = KProxy
+
+h :: forall r . (Proxy ('KProxy :: KProxy k) ~ Proxy ('KProxy :: KProxy *) => r) -> r
+h = undefined

testsuite/tests/polykinds/T10503.stderr

+
+T10503.hs:8:6: error:
+    Couldn't match kind ‘k’ with ‘*’
+    ‘k’ is a rigid type variable bound by
+        the type signature for:
+        h :: ((Proxy 'KProxy ~ Proxy 'KProxy) => r) -> r
+        at T10503.hs:8:6
+    Expected type: Proxy 'KProxy
+      Actual type: Proxy 'KProxy
+    In the ambiguity check for the type signature for ‘h’:
+      h :: forall (k :: BOX) r.
+           ((Proxy 'KProxy ~ Proxy 'KProxy) => r) -> r
+    To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
+    In the type signature for ‘h’:
+      h :: forall r.
+           (Proxy (KProxy :: KProxy k) ~ Proxy (KProxy :: KProxy *) => r) -> r

testsuite/tests/polykinds/all.T

@@ -117,3 +117,4 @@ test('T7908', normal, compile, [''])
 test('T10041', normal, compile, [''])
 test('T10451', normal, compile_fail, [''])
 test('T10516', normal, compile_fail, [''])
+test('T10503', normal, compile_fail, [''])