Make errors during course loading not break the site, but just hide that course instead

common/lib/xmodule/xmodule/modulestore/xml.py

@@ -13,6 +13,7 @@ from importlib import import_module
 from lxml import etree
 from path import path
 
+from xmodule.error_module import ErrorDescriptor
 from xmodule.errortracker import make_error_tracker, exc_info_to_str
 from xmodule.course_module import CourseDescriptor
 from xmodule.mako_module import MakoDescriptorSystem
@@ -167,8 +168,6 @@ class ImportSystem(XMLParsingSystem, MakoDescriptorSystem):
                 # Didn't load properly.  Fall back on loading as an error
                 # descriptor.  This should never error due to formatting.
 
-                # Put import here to avoid circular import errors
-                from xmodule.error_module import ErrorDescriptor
 
                 msg = "Error loading from xml. " + str(err)[:200]
                 log.warning(msg)
@@ -311,7 +310,7 @@ class XMLModuleStore(ModuleStoreBase):
             log.exception(msg)
             errorlog.tracker(msg)
 
-        if course_descriptor is not None:
+        if course_descriptor is not None and not isinstance(course_descriptor, ErrorDescriptor):
             self.courses[course_dir] = course_descriptor
             self._location_errors[course_descriptor.location] = errorlog
             self.parent_trackers[course_descriptor.id].make_known(course_descriptor.location)
@@ -423,6 +422,10 @@ class XMLModuleStore(ModuleStoreBase):
 
             course_descriptor = system.process_xml(etree.tostring(course_data, encoding='unicode'))
 
+            # If we fail to load the course, then skip the rest of the loading steps
+            if isinstance(course_descriptor, ErrorDescriptor):
+                return course_descriptor
+
             # NOTE: The descriptors end up loading somewhat bottom up, which
             # breaks metadata inheritance via get_children().  Instead
             # (actually, in addition to, for now), we do a final inheritance pass