Make staff view work w/ pure xblocks (that only have a descriptor system)

common/djangoapps/xmodule_modifiers.py

@@ -173,9 +173,9 @@ def add_staff_debug_info(user, block, view, frag, context):  # pylint: disable=u
         histogram = None
         render_histogram = False
 
-    if settings.FEATURES.get('ENABLE_LMS_MIGRATION'):
+    if settings.FEATURES.get('ENABLE_LMS_MIGRATION') and hasattr(block.runtime, 'filestore'):
         [filepath, filename] = getattr(block, 'xml_attributes', {}).get('filename', ['', None])
-        osfs = block.system.filestore
+        osfs = block.runtime.filestore
         if filename is not None and osfs.exists(filename):
             # if original, unmangled filename exists then use it (github
             # doesn't like symlinks)

common/lib/xmodule/xmodule/x_module.py

@@ -141,6 +141,10 @@ class XModuleMixin(XBlockMixin):
         default=None
     )
 
+    @property
+    def system(self):
+        return self.runtime
+
     @property
     def course_id(self):
         return self.runtime.course_id
@@ -400,7 +404,6 @@ class XModule(XModuleMixin, HTMLSnippet, XBlock):  # pylint: disable=abstract-me
         self.descriptor = descriptor
         super(XModule, self).__init__(*args, **kwargs)
         self._loaded_children = None
-        self.system = self.runtime
         self.runtime.xmodule_instance = self
 
     def __unicode__(self):
@@ -634,7 +637,6 @@ class XModuleDescriptor(XModuleMixin, HTMLSnippet, ResourceTemplates, XBlock):
         XModuleDescriptor.__init__ takes the same arguments as xblock.core:XBlock.__init__
         """
         super(XModuleDescriptor, self).__init__(*args, **kwargs)
-        self.system = self.runtime
         # update_version is the version which last updated this xblock v prev being the penultimate updater
         # leaving off original_version since it complicates creation w/o any obv value yet and is computable
         # by following previous until None