Add config inheritance test

hancho.py

@@ -695,10 +695,10 @@ def main(self):
 
         # Merge all known command line flags into our global config object.
 
-        global global_config  # pylint: disable=global-statement
-        global_config.start_filename = (
-            start_filename  # pylint: disable=attribute-defined-outside-init
-        )
+        # pylint: disable=global-statement
+        global global_config
+        # pylint: disable=attribute-defined-outside-init
+        global_config.start_filename = start_filename
         global_config |= flags.__dict__
 
         # Unrecognized command line parameters also become global config fields if

tests/config_child.hancho

@@ -0,0 +1,8 @@
+from hancho import *
+import sys
+
+# We should inherit config.foobar from our parent module.
+if config.foobar != "config.foobar":
+  sys.exit(-1)
+
+config.foobar = "this should not change config_parent.config.foobar"

tests/config_parent.hancho

@@ -0,0 +1,10 @@
+from hancho import *
+import sys
+
+config.foobar = "config.foobar"
+
+mod2 = load("config_child.hancho")
+
+# Our child module should not be able to accidentally modify our config
+if config.foobar != "config.foobar":
+  sys.exit(-1)

tests/test.py

@@ -83,6 +83,14 @@ def test_check_output(self):
         """A build rule that doesn't update one of its outputs should fail"""
         self.assertNotEqual(0, run_hancho("check_output"))
 
+    def test_config_inheritance(self):
+        """A module should inherit a config object extended from its parent, but should not be able
+        to modify its parent's config object."""
+        self.assertEqual(0, run_hancho("config_parent"))
+
+        # This should fail because it was expecting inheritance from its parent.
+        self.assertNotEqual(0, run_hancho("config_child"))
+
     def test_recursive_base_is_bad(self):
         """Referring to base.attrib in a template is a bad idea"""
         self.assertNotEqual(0, run_hancho("recursive_base_is_bad"))