Persist student answers on input error

LMS-469

common/lib/capa/capa/responsetypes.py

@@ -1805,7 +1805,10 @@ class FormulaResponse(LoncapaResponse):
     def get_score(self, student_answers):
         given = student_answers[self.answer_id]
         correctness = self.check_formula(
-            self.correct_answer, given, self.samples)
+            self.correct_answer,
+            given,
+            self.samples
+        )
         return CorrectMap(self.answer_id, correctness)
 
     def tupleize_answers(self, answer, var_dict_list):

common/lib/xmodule/xmodule/capa_module.py

@@ -941,6 +941,9 @@ class CapaModule(CapaFields, XModule):
             log.warning("StudentInputError in capa_module:problem_check",
                         exc_info=True)
 
+            # Save the user's state before failing
+            self.set_state_from_lcp()
+
             # If the user is a staff member, include
             # the full exception, including traceback,
             # in the response
@@ -955,6 +958,9 @@ class CapaModule(CapaFields, XModule):
             return {'success': msg}
 
         except Exception as err:
+            # Save the user's state before failing
+            self.set_state_from_lcp()
+
             if self.system.DEBUG:
                 msg = u"Error checking problem: {}".format(err.message)
                 msg += u'\nTraceback:\n{}'.format(traceback.format_exc())