Fix the comparison between unit and empty tuple

src/aeso_ast_infer_types.erl

@@ -921,6 +921,10 @@ compare_types({app_t, _, Type1, ArgsTypes1}, {app_t, _, Type2, ArgsTypes2}) ->
     compare_types(Type1, Type2) andalso compare_types(ArgsTypes1, ArgsTypes2);
 compare_types({tuple_t, _, Types1}, {tuple_t, _, Types2}) ->
     compare_types(Types1, Types2);
+compare_types({tuple_t, _, []}, {id, _, "unit"}) ->
+    true;
+compare_types({id, _, "unit"}, {tuple_t, _, []}) ->
+    true;
 compare_types(T1 = {Id, _, Type}, {Id, _, Type}) when ?is_type_id(T1) ->
     true;
 compare_types({if_t, _, {id, _, Id}, Ta1, Tb1}, {if_t, _, {id, _, Id}, Ta2, Tb2}) ->

test/contracts/contract_interface_polymorphism.aes

@@ -1,9 +1,9 @@
 contract interface II =
-    entrypoint f : () => int
+    entrypoint f : () => unit
 
 contract interface I : II =
-    entrypoint g : () => int
+    entrypoint g : () => unit
 
 contract C : I =
-    entrypoint f() = 1
-    entrypoint g() = 2
+    entrypoint f() = ()
+    entrypoint g() = ()