[Bug 844933] Only accept troubleshooting dicts.

There is apparently some questions in SUMO that have this data as a list
that contained the string 'modifedPreferenes', which caused errors.
Being specific about the type will prevent this kind of error.

apps/questions/tests/test_templates.py

@@ -637,6 +637,16 @@ def test_empty_troubleshooting_info(self):
         response = get(self.client, 'questions.answers', args=[q.id])
         eq_(200, response.status_code)
 
+    def test_weird_list_troubleshooting_info(self):
+        """Test the corner case in which 'modifiedPReferences' is in a
+        list in troubleshooting data. This is weird, but caused a bug."""
+        q = question(save=True)
+        q.add_metadata(troubleshooting='["modifiedPreferences"]')
+
+        # This case should not raise an error.
+        response = get(self.client, 'questions.answers', args=[q.id])
+        eq_(200, response.status_code)
+
 
 class TaggedQuestionsTestCase(TaggingTestCaseBase):
     """Questions/answers template tests that require tagged questions."""

apps/questions/views.py

@@ -215,17 +215,23 @@ def answers(request, template, question_id, form=None, watch_form=None,
     # Try to parse troubleshooting data as JSON.
     try:
         parsed = json.loads(question.metadata['troubleshooting'])
+        if not isinstance(parsed, dict):
+            # If something not a dict comes out of JSON, it is probably
+            # a list, and should not be treated like parsed data.
+            raise TypeError
         # Remove all the printing preferences. These probably aren't relavent,
         # and are really noisy.
         if 'modifiedPreferences' in parsed:
             parsed['modifiedPreferences'] = dict(
                 (k, v) for k, v in parsed['modifiedPreferences'].items()
                 if not k.startswith('print'))
         question.metadata['troubleshooting_parsed'] = parsed
-    except (ValueError, KeyError):
+    except (ValueError, KeyError, TypeError):
         # If the field was not filled in, KeyError will be raised.
         # If the field was filled manually and is not valid JSON,
-        # ValueError will be raised. The template will display the raw
+        # ValueError will be raised. If the field was filled in with
+        # JSON data that is a list and not a dict, it will raise
+        # TypeError. In any case, the template will display the raw
         # data.
         question.metadata['troubleshooting_parsed'] = None