Silence XML parse error in capa_module

TNL-5057 This un-actionable error is polluting the stream of devops pages, and
should be quieted. A longer term fix will be made in TNL-5245.

common/lib/xmodule/xmodule/capa_module.py

@@ -220,9 +220,13 @@ class CapaDescriptor(CapaFields, RawDescriptor):
     @property
     def problem_types(self):
         """ Low-level problem type introspection for content libraries filtering by problem type """
-        tree = etree.XML(self.data)
+        try:
+            tree = etree.XML(self.data)
+        except etree.XMLSyntaxError:
+            log.error('Error parsing problem types from xml for capa module {}'.format(self.display_name))
+            return None  # short-term fix to prevent errors (TNL-5057). Will be more properly addressed in TNL-4525.
         registered_tags = responsetypes.registry.registered_tags()
-        return set([node.tag for node in tree.iter() if node.tag in registered_tags])
+        return {node.tag for node in tree.iter() if node.tag in registered_tags}
 
     def index_dictionary(self):
         """
@@ -263,9 +267,10 @@ class CapaDescriptor(CapaFields, RawDescriptor):
         Returns whether the given view has support for the given functionality.
         """
         if functionality == "multi_device":
-            return all(
+            types = self.problem_types  # Avoid calculating this property twice
+            return types is not None and all(
                 responsetypes.registry.get_class_for_tag(tag).multi_device_support
-                for tag in self.problem_types
+                for tag in types
             )
         return False
 

common/lib/xmodule/xmodule/tests/test_capa_module.py

@@ -13,6 +13,7 @@ import textwrap
 import unittest
 import ddt
 
+from lxml import etree
 from mock import Mock, patch, DEFAULT
 import webob
 from webob.multidict import MultiDict
@@ -2517,6 +2518,21 @@ class CapaDescriptorTest(unittest.TestCase):
             }
         )
 
+    def test_invalid_xml_handling(self):
+        """
+        Tests to confirm that invalid XML does not throw a wake-up-ops level error.
+        See TNL-5057 for quick fix, TNL-5245 for full resolution.
+        """
+        sample_invalid_xml = textwrap.dedent("""
+            <problem>
+            </proble-oh no my finger broke and I can't close the problem tag properly...
+        """)
+        descriptor = self._create_descriptor(sample_invalid_xml, name="Invalid XML")
+        try:
+            descriptor.has_support(None, "multi_device")
+        except etree.XMLSyntaxError:
+            self.fail("Exception raised during XML parsing, this method should be resilient to such errors")
+
 
 class ComplexEncoderTest(unittest.TestCase):
     def test_default(self):