PROD-448: Gracefully handle exceptions from user-supplied code in

advanced problems so that they do not become uneditable.

common/lib/xmodule/xmodule/capa_base.py

@@ -387,8 +387,11 @@ class CapaMixin(ScorableXBlockMixin, CapaFields):
         """
         For now, just return weighted earned / weighted possible
         """
-        raw_earned = self.score.raw_earned
-        raw_possible = self.score.raw_possible
+        if self.score:
+            raw_earned = self.score.raw_earned
+            raw_possible = self.score.raw_possible
+        else:
+            raw_earned = raw_possible = 0
 
         if raw_possible > 0:
             if self.weight is not None:
@@ -439,6 +442,18 @@ class CapaMixin(ScorableXBlockMixin, CapaFields):
             'graded': self.graded,
         })
 
+    def handle_fatal_lcp_error(self, error):
+        if error:
+            return(
+                HTML(u'<p>Error formatting HTML for problem:</p><p><pre style="color:red">{msg}</pre></p>').format(
+                    msg=text_type(error))
+            )
+        else:
+            return HTML(
+                u'<p>Could not format HTML for problem. '
+                u'Contact course staff in the discussion forum for assistance.</p>'
+            )
+
     def submit_button_name(self):
         """
         Determine the name for the "submit" button.
@@ -549,8 +564,8 @@ class CapaMixin(ScorableXBlockMixin, CapaFields):
         # TODO (vshnayder): another switch on DEBUG.
         if self.runtime.DEBUG:
             msg = HTML(
-                u'[courseware.capa.capa_module] <font size="+1" color="red">'
-                u'Failed to generate HTML for problem {url}</font>'
+                u'[courseware.capa.capa_module] '
+                u'Failed to generate HTML for problem {url}'
             ).format(
                 url=text_type(self.location)
             )
@@ -564,6 +579,7 @@ class CapaMixin(ScorableXBlockMixin, CapaFields):
 
             # Presumably, student submission has corrupted LoncapaProblem HTML.
             #   First, pull down all student answers
+
             student_answers = self.lcp.student_answers
             answer_ids = list(student_answers.keys())
 

common/lib/xmodule/xmodule/capa_module.py

@@ -103,13 +103,18 @@ class ProblemBlock(
         if 'lcp' in self.__dict__:
             del self.__dict__['lcp']
 
-    def student_view(self, _context):
+    def student_view(self, _context, show_detailed_errors=False):
         """
         Return the student view.
         """
         # self.score is initialized in self.lcp but in this method is accessed before self.lcp so just call it first.
-        self.lcp
-        fragment = Fragment(self.get_html())
+        try:
+            self.lcp
+        except Exception as err:
+            html = self.handle_fatal_lcp_error(err if show_detailed_errors else None)
+        else:
+            html = self.get_html()
+        fragment = Fragment(html)
         add_webpack_to_fragment(fragment, 'ProblemBlockPreview')
         shim_xmodule_js(fragment, 'Problem')
         return fragment
@@ -118,7 +123,7 @@ class ProblemBlock(
         """
         Renders the Studio preview view.
         """
-        return self.student_view(context)
+        return self.student_view(context, show_detailed_errors=True)
 
     def studio_view(self, _context):
         """