Add failing test for ambiguous names

test/aeso_compiler_tests.erl

@@ -782,6 +782,12 @@ failing_contracts() ->
                    [<<?Pos(1,6)
                       "Only one main contract can be defined.">>
                    ])
+    , ?TYPE_ERROR(using_namespace_ambiguous_name,
+                  [ <<?Pos(2,3)
+                      "Ambiguous name: Xa.f at line 2, column 3\nXb.f at line 5, column 3">>
+                  , <<?Pos(13,23)
+                      "Unbound variable A.f at line 13, column 23">>
+                  ])
     ].
 
 -define(Path(File), "code_errors/" ??File).

test/contracts/using_namespace_ambiguous_name.aes

@@ -0,0 +1,13 @@
+namespace Xa =
+  function f() = 1
+
+namespace Xb =
+  function f() = 2
+
+contract Cntr =
+  using Xa as A
+  using Xb as A
+
+  type state = int
+
+  entrypoint init() = A.f()