mojo: Allow circular dependencies between structs

mojo/python/tests/bindings_structs_unittest.py

Index: mojo/python/tests/bindings_structs_unittest.py
diff --git a/mojo/python/tests/bindings_structs_unittest.py b/mojo/python/tests/bindings_structs_unittest.py
index f7746acd763158c1365942697bc46d8e59c04862..f03ca2637dae642a3fbfa730e43fd0cea59aa32c 100644
--- a/mojo/python/tests/bindings_structs_unittest.py
+++ b/mojo/python/tests/bindings_structs_unittest.py
@@ -10,6 +10,7 @@ import mojo.system
 
 # Generated files
 # pylint: disable=F0401
+import regression_tests_mojom
 import sample_import_mojom
 import sample_import2_mojom
 import sample_service_mojom
@@ -179,3 +180,10 @@ class StructBindingsTest(unittest.TestCase):
     self.assertEquals(foo_instance.a, False)
     self.assertEquals(foo_instance.bar, bar_instance)
 
+  def testCyclicDefinition(self):
+    a = regression_tests_mojom.A()
+    b = regression_tests_mojom.B()
+    self.assertIsNone(a.b)
+    self.assertIsNone(b.a)
+    a.b = b
+    self.assertIs(a.b, b)