Capa response now displays full stack trace on student input error

if the user is a staff member.
Otherwise, it displays just the exception message.

common/lib/capa/capa/responsetypes.py

@@ -17,6 +17,7 @@ import logging
 import numbers
 import numpy
 import os
+import sys
 import random
 import re
 import requests
@@ -1233,9 +1234,9 @@ def sympy_check2():
         log.debug(msg, exc_info=True)
         log.debug(traceback.format_exc())
 
-        # Notify student
-        raise StudentInputError(
-            "Error: Problem could not be evaluated with your input")
+        # Notify student with a student input error
+        _, _, traceback_obj = sys.exc_info()
+        raise StudentInputError, StudentInputError(err.message), traceback_obj
 
 #-----------------------------------------------------------------------------
 

common/lib/xmodule/xmodule/capa_module.py

@@ -725,9 +725,23 @@ class CapaModule(CapaFields, XModule):
         try:
             correct_map = self.lcp.grade_answers(answers)
             self.set_state_from_lcp()
+
         except StudentInputError as inst:
             log.exception("StudentInputError in capa_module:problem_check")
-            return {'success': inst.message}
+
+            # If the user is a staff member, include
+            # the full exception, including traceback,
+            # in the response 
+            if self.system.user_is_staff:
+                msg = traceback.format_exc()
+
+            # Otherwise, display just the error message,
+            # without a stack trace
+            else:
+                msg = inst.message
+
+            return {'success': msg }
+
         except Exception, err:
             if self.system.DEBUG:
                 msg = "Error checking problem: " + str(err)

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

@@ -505,6 +505,9 @@ class CapaModuleTest(unittest.TestCase):
     def test_check_problem_student_input_error(self):
         module = CapaFactory.create(attempts=1)
 
+        # Ensure that the user is NOT staff
+        module.system.user_is_staff = False
+
         # Simulate a student input exception
         with patch('capa.capa_problem.LoncapaProblem.grade_answers') as mock_grade:
             mock_grade.side_effect = capa.responsetypes.StudentInputError('test error')
@@ -515,10 +518,32 @@ class CapaModuleTest(unittest.TestCase):
             # Expect an AJAX alert message in 'success'
             self.assertTrue('test error' in result['success'])
 
+            # We do NOT include traceback information for
+            # a non-staff user
+            self.assertFalse('Traceback' in result['success'])
+
         # Expect that the number of attempts is NOT incremented
         self.assertEqual(module.attempts, 1)
 
+    def test_check_problem_student_input_error_with_staff_user(self):
+        module = CapaFactory.create(attempts=1)
+
+        # Ensure that the user IS staff
+        module.system.user_is_staff = True
+
+        # Simulate a student input exception
+        with patch('capa.capa_problem.LoncapaProblem.grade_answers') as mock_grade:
+            mock_grade.side_effect = capa.responsetypes.StudentInputError('test error')
+
+            get_request_dict = { CapaFactory.input_key(): '3.14'}
+            result = module.check_problem(get_request_dict)
+
+            # Expect an AJAX alert message in 'success'
+            self.assertTrue('test error' in result['success'])
 
+            # We DO include traceback information for staff users
+            self.assertTrue('Traceback' in result['success'])
+        
     def test_reset_problem(self):
         module = CapaFactory.create(done=True)
         module.new_lcp = Mock(wraps=module.new_lcp)