fix: certificate generation without Persistent Grades

Fix for an error related to endless recursion

Dev Notes:
The student gets the passing grade
-> CourseGradeFactory sends the `COURSE_GRADE_NOW_PASSED` signal after the grade calculation
-> `listen_for_passing_grade` receives the signal and calls `generate_certificate_task`
-> `generate_certificate_task` calls `_generate_regular_certificate_task`
-> `_generate_regular_certificate_task` trying to get grade by calling the `_get_course_grade`
-> `_get_course_grade` calls `CourseGradeFactory().read()` but I have persistent grades off, so actually that ends with `CourseGradeFactory().update()`
-> `CourseGradeFactory().update()` sends the `COURSE_GRADE_NOW_PASSED`
And so on

lms/djangoapps/certificates/generation_handler.py

@@ -72,7 +72,7 @@ def _generate_regular_certificate_task(user, course_key, generation_mode=None, d
     eligible and a certificate can be generated.
     """
     enrollment_mode = _get_enrollment_mode(user, course_key)
-    course_grade = _get_course_grade(user, course_key)
+    course_grade = _get_course_grade(user, course_key, send_grade_signals=False)
     if _can_generate_regular_certificate(user, course_key, enrollment_mode, course_grade):
         return _generate_certificate_task(user=user, course_key=course_key, enrollment_mode=enrollment_mode,
                                           course_grade=course_grade, generation_mode=generation_mode,
@@ -377,11 +377,11 @@ def _get_grade_value(course_grade):
     return ''
 
 
-def _get_course_grade(user, course_key):
+def _get_course_grade(user, course_key, send_grade_signals=False):
     """
     Get the user's course grade in this course run. Note that this may be None.
     """
-    return CourseGradeFactory().read(user, course_key=course_key)
+    return CourseGradeFactory().read(user, course_key=course_key, send_grade_signals=send_grade_signals)
 
 
 def _get_enrollment_mode(user, course_key):

lms/djangoapps/grades/course_grade_factory.py

@@ -33,6 +33,7 @@ class CourseGradeFactory:
             course_structure=None,
             course_key=None,
             create_if_needed=True,
+            send_grade_signals=True,
     ):
         """
         Returns the CourseGrade for the given user in the course.
@@ -51,7 +52,7 @@ class CourseGradeFactory:
             if assume_zero_if_absent(course_data.course_key):
                 return self._create_zero(user, course_data)
             elif create_if_needed:
-                return self._update(user, course_data)
+                return self._update(user, course_data, send_grade_signals=send_grade_signals)
             else:
                 return None
 
@@ -160,13 +161,16 @@ class CourseGradeFactory:
         )
 
     @staticmethod
-    def _update(user, course_data, force_update_subsections=False):
+    def _update(user, course_data, force_update_subsections=False, send_grade_signals=True):
         """
-        Computes, saves, and returns a CourseGrade object for the
-        given user and course.
-        Sends a COURSE_GRADE_CHANGED signal to listeners and
-        COURSE_GRADE_NOW_PASSED if learner has passed course or
-        COURSE_GRADE_NOW_FAILED if learner is now failing course
+        Computes, saves, and returns a CourseGrade object for the given user and course.
+
+        send_grade_signals defines if signals should be sent. Use it to avoid recursion issues in
+        cases when the signal listener trying to get grades but Persistent Grades are disabled.
+        If True - sends:
+            COURSE_GRADE_CHANGED signal to listeners and
+            COURSE_GRADE_NOW_PASSED if learner has passed course or
+            COURSE_GRADE_NOW_FAILED if learner is now failing course
         """
         should_persist = should_persist_grades(course_data.course_key)
         if should_persist and force_update_subsections:
@@ -193,26 +197,27 @@ class CourseGradeFactory:
                 passed=course_grade.passed,
             )
 
-        COURSE_GRADE_CHANGED.send_robust(
-            sender=None,
-            user=user,
-            course_grade=course_grade,
-            course_key=course_data.course_key,
-            deadline=course_data.course.end,
-        )
-        if course_grade.passed:
-            COURSE_GRADE_NOW_PASSED.send(
-                sender=CourseGradeFactory,
+        if send_grade_signals:
+            COURSE_GRADE_CHANGED.send_robust(
+                sender=None,
                 user=user,
-                course_id=course_data.course_key,
-            )
-        else:
-            COURSE_GRADE_NOW_FAILED.send(
-                sender=CourseGradeFactory,
-                user=user,
-                course_id=course_data.course_key,
-                grade=course_grade,
+                course_grade=course_grade,
+                course_key=course_data.course_key,
+                deadline=course_data.course.end,
             )
+            if course_grade.passed:
+                COURSE_GRADE_NOW_PASSED.send(
+                    sender=CourseGradeFactory,
+                    user=user,
+                    course_id=course_data.course_key,
+                )
+            else:
+                COURSE_GRADE_NOW_FAILED.send(
+                    sender=CourseGradeFactory,
+                    user=user,
+                    course_id=course_data.course_key,
+                    grade=course_grade,
+                )
 
         log.info(
             'Grades: Update, %s, User: %s, %s, persisted: %s',