Course Blocks API: Fix handling of incorrectly-cased course keys (#25911)

Commit 7f59688f attempted to solve this using
`CourseOverview.course_exists`, but that check is case-
insensitive. This commit instead does a small refactor
to `lms.djangoapps.courseware.get_course` so that we can
handle a failed course lookup without broadly catching
a `ValueError`.

lms/djangoapps/bulk_email/tests/test_err_handling.py

@@ -21,6 +21,7 @@ from six.moves import range
 
 from lms.djangoapps.bulk_email.models import SEND_TO_MYSELF, BulkEmailFlag, CourseEmail
 from lms.djangoapps.bulk_email.tasks import perform_delegate_email_batches, send_course_email
+from lms.djangoapps.courseware.exceptions import CourseRunNotFound
 from lms.djangoapps.instructor_task.exceptions import DuplicateTaskException
 from lms.djangoapps.instructor_task.models import InstructorTask
 from lms.djangoapps.instructor_task.subtasks import (
@@ -200,8 +201,7 @@ class TestEmailErrors(ModuleStoreTestCase):
         email.save()
         entry = InstructorTask.create(course_id, "task_type", "task_key", "task_input", self.instructor)
         task_input = {"email_id": email.id}
-        # (?i) is a regex for ignore case
-        with self.assertRaisesRegex(ValueError, r"(?i)course not found"):
+        with self.assertRaises(CourseRunNotFound):
             perform_delegate_email_batches(entry.id, course_id, task_input, "action_name")
 
     def test_nonexistent_to_option(self):

lms/djangoapps/course_api/blocks/permissions.py

@@ -7,6 +7,7 @@ from opaque_keys.edx.keys import CourseKey
 from lms.djangoapps.courseware.access import has_access
 from lms.djangoapps.courseware.access_response import AccessResponse
 from lms.djangoapps.courseware.access_utils import ACCESS_DENIED, ACCESS_GRANTED, check_public_access
+from lms.djangoapps.courseware.exceptions import CourseRunNotFound
 from lms.djangoapps.courseware.courses import get_course
 from openedx.core.djangoapps.content.course_overviews.models import CourseOverview
 from common.djangoapps.student.models import CourseEnrollment
@@ -47,7 +48,8 @@ def is_course_public(course_key: CourseKey) -> AccessResponse:
     """
     This checks if a course is publicly accessible or not.
     """
-    if not CourseOverview.course_exists(course_key):
+    try:
+        course = get_course(course_key, depth=0)
+    except CourseRunNotFound:
         return ACCESS_DENIED
-    course = get_course(course_key, depth=0)
     return check_public_access(course, [COURSE_VISIBILITY_PUBLIC])

lms/djangoapps/courseware/courses.py

@@ -41,6 +41,7 @@ from lms.djangoapps.courseware.date_summary import (
     VerificationDeadlineDate,
     VerifiedUpgradeDeadlineDate
 )
+from lms.djangoapps.courseware.exceptions import CourseRunNotFound
 from lms.djangoapps.courseware.masquerade import check_content_start_date_for_masquerade_user
 from lms.djangoapps.courseware.model_data import FieldDataCache
 from lms.djangoapps.courseware.module_render import get_module
@@ -80,7 +81,7 @@ def get_course(course_id, depth=0):
     """
     Given a course id, return the corresponding course descriptor.
 
-    If the course does not exist, raises a ValueError.  This is appropriate
+    If the course does not exist, raises a CourseRunNotFound. This is appropriate
     for internal use.
 
     depth: The number of levels of children for the modulestore to cache.
@@ -88,7 +89,7 @@ def get_course(course_id, depth=0):
     """
     course = modulestore().get_course(course_id, depth=depth)
     if course is None:
-        raise ValueError(u"Course not found: {0}".format(course_id))
+        raise CourseRunNotFound(course_key=course_id)
     return course
 
 

lms/djangoapps/courseware/exceptions.py

@@ -25,3 +25,19 @@ class CourseAccessRedirect(Redirect):
     def __init__(self, url, access_error=None):
         super(CourseAccessRedirect, self).__init__(url)
         self.access_error = access_error
+
+
+class CourseRunNotFound(ValueError):
+    """
+    Indicate that a supplied course run key does not map to a course run in the system.
+    """
+
+    def __init__(self, course_key):
+        """
+        Initialize CourseRunNotFound exception.
+
+        Arguments:
+            course_key (CourseKey|str):
+                course run key or stringified version thereof.
+        """
+        super().__init__(f"Course run not found: {course_key}")