Added hacking check for jsonutils

jsonutils provides some additional features in comparison to pure json
or simplejson modules. For example, on Python 2.6, it automatically
switches to simplejson that provides significant performance boost.

So let's enforce usage of the module in replacement to stdlib json.

Change-Id: I86ed6cd3316dd4da5e1b10b36a3ddba3739316d3

nova/hacking/checks.py

@@ -286,6 +286,23 @@ def check_explicit_underscore_import(logical_line, filename):
         yield(0, "N323: Found use of _() without explicit import of _ !")
 
 
+def use_jsonutils(logical_line, filename):
+    # the code below that path is not meant to be executed from neutron
+    # tree where jsonutils module is present, so don't enforce its usage
+    # for this subdirectory
+    if "plugins/xenserver" in filename:
+        return
+
+    msg = "N323: jsonutils.%(fun)s must be used instead of json.%(fun)s"
+
+    if "json." in logical_line:
+        json_funcs = ['dumps', 'dump', 'loads', 'load']
+        for f in json_funcs:
+            pos = logical_line.find('json.%s' % f)
+            if pos != -1:
+                return (pos, msg % {'fun': f})
+
+
 def factory(register):
     register(import_no_db_in_virt)
     register(no_db_session_in_public_api)
@@ -303,3 +320,4 @@ def factory(register):
     register(validate_log_translations)
     register(no_mutable_default_args)
     register(check_explicit_underscore_import)
+    register(use_jsonutils)

nova/tests/test_hacking.py

@@ -217,3 +217,24 @@ class HackingTestCase(test.NoDBTestCase):
         self.assertEqual(len(list(checks.check_explicit_underscore_import(
             "msg = _('My message')",
             "cinder/tests/other_files3.py"))), 0)
+
+    def test_use_jsonutils(self):
+        def __get_msg(fun):
+            msg = ("N323: jsonutils.%(fun)s must be used instead of "
+                   "json.%(fun)s" % {'fun': fun})
+            return (0, msg)
+
+        for method in ('dump', 'dumps', 'load', 'loads'):
+            self.assertEqual(
+                __get_msg(method),
+                checks.use_jsonutils("json.%s" % method,
+                                     "./nova/virt/xenapi/driver.py"))
+            self.assertIsNone(
+                checks.use_jsonutils("json.%s" % method,
+                                     "./plugins/xenserver/script.py"))
+            self.assertIsNone(
+                checks.use_jsonutils("jsonx.%s" % method,
+                                     "./nova/virt/xenapi/driver.py"))
+        self.assertIsNone(
+            checks.use_jsonutils("json.dumb",
+                                 "./nova/virt/xenapi/driver.py"))