Don't let destructive loc change

leak out to callers.
Also, use the return from update_item rather than assume
it was just side effecting.
LMS-11361

cms/djangoapps/contentstore/views/item.py

@@ -314,7 +314,7 @@ def _update_with_callback(xblock, user, old_metadata=None, old_content=None):
         xblock.editor_saved(user, old_metadata, old_content)
 
     # Update after the callback so any changes made in the callback will get persisted.
-    modulestore().update_item(xblock, user.id)
+    return modulestore().update_item(xblock, user.id)
 
 
 def _save_xblock(user, xblock, data=None, children_strings=None, metadata=None, nullout=None,
@@ -356,7 +356,7 @@ def _save_xblock(user, xblock, data=None, children_strings=None, metadata=None,
                 if old_parent_location:
                     old_parent = store.get_item(old_parent_location)
                     old_parent.children.remove(new_child)
-                    _update_with_callback(old_parent, user)
+                    old_parent = _update_with_callback(old_parent, user)
                 else:
                     # the Studio UI currently doesn't present orphaned children, so assume this is an error
                     return JsonResponse({"error": "Invalid data, possibly caused by concurrent authors."}, 400)
@@ -411,7 +411,7 @@ def _save_xblock(user, xblock, data=None, children_strings=None, metadata=None,
                         field.write_to(xblock, value)
 
         # update the xblock and call any xblock callbacks
-        _update_with_callback(xblock, user, old_metadata, old_content)
+        xblock = _update_with_callback(xblock, user, old_metadata, old_content)
 
         # for static tabs, their containing course also records their display name
         if xblock.location.category == 'static_tab':
@@ -550,7 +550,7 @@ def _duplicate_item(parent_usage_key, duplicate_source_usage_key, user, display_
             dest_module.children.append(dupe)
         store.update_item(dest_module, user.id)
 
-    if not 'detached' in source_item.runtime.load_block_type(category)._class_tags:
+    if 'detached' not in source_item.runtime.load_block_type(category)._class_tags:
         parent = store.get_item(parent_usage_key)
         # If source was already a child of the parent, add duplicate immediately afterward.
         # Otherwise, add child to end.

cms/djangoapps/contentstore/views/tests/test_item.py

@@ -117,7 +117,6 @@ class GetItemTest(ItemTest):
         with check_mongo_calls(problem_queries):
             self.client.get(reverse_usage_url('xblock_handler', self.populated_usage_keys['problem'][-1]))
 
-
     def test_get_vertical(self):
         # Add a vertical
         resp = self.create_xblock(category='vertical')
@@ -197,7 +196,6 @@ class GetItemTest(ItemTest):
         self.assertIn('Announcement', html)
         self.assertIn('Zooming', html)
 
-
     def test_split_test_edited(self):
         """
         Test that rename of a group changes display name of child vertical.

common/lib/xmodule/xmodule/modulestore/split_mongo/split_draft.py

@@ -89,7 +89,8 @@ class DraftVersioningModuleStore(ModuleStoreDraftAndPublished, SplitMongoModuleS
             self.publish(location.version_agnostic(), user_id, blacklist=EXCLUDE_ALL, **kwargs)
 
     def update_item(self, descriptor, user_id, allow_not_found=False, force=False, **kwargs):
-        descriptor.location = self._map_revision_to_branch(descriptor.location)
+        old_descriptor_locn = descriptor.location
+        descriptor.location = self._map_revision_to_branch(old_descriptor_locn)
         with self.bulk_operations(descriptor.location.course_key):
             item = super(DraftVersioningModuleStore, self).update_item(
                 descriptor,
@@ -99,6 +100,7 @@ class DraftVersioningModuleStore(ModuleStoreDraftAndPublished, SplitMongoModuleS
                 **kwargs
             )
             self._auto_publish_no_children(item.location, item.location.category, user_id, **kwargs)
+            descriptor.location = old_descriptor_locn
             return item
 
     def create_item(