feat: make it possible to globally disable forum v2 with setting

We introduce a setting that allows us to bypass any course waffle flag
check. The advantage of such a setting is that we don't need to find the
course ID: in some cases, we might not have access to the course ID, and
we need to look for it... in forum v2.

See discussion here: openedx/forum#137

openedx/core/djangoapps/discussions/config/waffle.py

@@ -2,6 +2,7 @@
 This module contains various configuration settings via
 waffle switches for the discussions app.
 """
+from django.conf import settings
 
 from openedx.core.djangoapps.waffle_utils import CourseWaffleFlag
 
@@ -57,6 +58,17 @@
 
 def is_forum_v2_enabled(course_id):
     """
-    Returns a boolean if forum V2 is enabled on the course
+    Returns whether forum V2 is enabled on the course. This is a 2-step check:
+
+    1. Check value of settings.DISABLE_FORUM_V2: if it exists and is true, this setting overrides any course flag.
+    2. Else, check the value of the corresponding course waffle flag.
     """
+    if is_forum_v2_disabled_globally():
+        return False
     return ENABLE_FORUM_V2.is_enabled(course_id)
+
+def is_forum_v2_disabled_globally() -> bool:
+    """
+    Return True if DISABLE_FORUM_V2 is defined and true-ish.
+    """
+    return getattr(settings, "DISABLE_FORUM_V2", False)

openedx/core/djangoapps/django_comment_common/comment_client/models.py

@@ -2,10 +2,11 @@
 
 
 import logging
+import typing as t
 
 from .utils import CommentClientRequestError, extract, perform_request, get_course_key
 from forum import api as forum_api
-from openedx.core.djangoapps.discussions.config.waffle import is_forum_v2_enabled
+from openedx.core.djangoapps.discussions.config.waffle import is_forum_v2_enabled, is_forum_v2_disabled_globally
 
 log = logging.getLogger(__name__)
 
@@ -72,13 +73,14 @@ def retrieve(self, *args, **kwargs):
 
     def _retrieve(self, *args, **kwargs):
         course_id = self.attributes.get("course_id") or kwargs.get("course_id")
-        if not course_id:
-            course_id = forum_api.get_course_id_by_comment(self.id)
-        course_key = get_course_key(course_id)
+        if course_id:
+            use_forumv2 = is_forum_v2_enabled(course_id)
+        else:
+            use_forumv2, course_id = is_forum_v2_enabled_for_comment(self.id)
         response = None
-        if is_forum_v2_enabled(course_key):
+        if use_forumv2:
             if self.type == "comment":
-                response = forum_api.get_parent_comment(comment_id=self.attributes["id"], course_id=str(course_key))
+                response = forum_api.get_parent_comment(comment_id=self.attributes["id"], course_id=course_id)
             if response is None:
                 raise CommentClientRequestError("Forum v2 API call is missing")
         else:
@@ -369,3 +371,21 @@ def handle_create_thread(self, course_id):
             context=request_data.get("context", None),
         )
         return response
+
+def is_forum_v2_enabled_for_comment(comment_id: str) -> tuple[bool, t.Optional[str]]:
+    """
+    Figure out whether we use forum v2 for a given comment.
+
+    See is_forum_v2_enabled_for_thread.
+
+    Return:
+
+        enabled (bool)
+        course_id (str or None)
+    """
+    if is_forum_v2_disabled_globally():
+        return False, None
+
+    course_id = forum_api.get_course_id_by_comment(comment_id)
+    course_key = get_course_key(course_id)
+    return is_forum_v2_enabled(course_key), course_id

openedx/core/djangoapps/django_comment_common/comment_client/thread.py

@@ -2,12 +2,13 @@
 
 
 import logging
+import typing as t
 
 from eventtracking import tracker
 
 from . import models, settings, utils
 from forum import api as forum_api
-from openedx.core.djangoapps.discussions.config.waffle import is_forum_v2_enabled
+from openedx.core.djangoapps.discussions.config.waffle import is_forum_v2_enabled, is_forum_v2_disabled_globally
 
 log = logging.getLogger(__name__)
 
@@ -171,17 +172,14 @@ def _retrieve(self, *args, **kwargs):
             'merge_question_type_responses': kwargs.get('merge_question_type_responses', False)
         }
         request_params = utils.strip_none(request_params)
-        course_id = kwargs.get("course_id")
-        if not course_id:
-            course_id = forum_api.get_course_id_by_thread(self.id)
-        course_key = utils.get_course_key(course_id)
-        if is_forum_v2_enabled(course_key):
+        use_forumv2, course_id = is_forum_v2_enabled_for_thread(self.id)
+        if use_forumv2:
             if user_id := request_params.get('user_id'):
                 request_params['user_id'] = str(user_id)
             response = forum_api.get_thread(
                 thread_id=self.id,
                 params=request_params,
-                course_id=str(course_key)
+                course_id=course_id,
             )
         else:
             response = utils.perform_request(
@@ -296,3 +294,28 @@ def _url_for_pin_thread(thread_id):
 
 def _url_for_un_pin_thread(thread_id):
     return f"{settings.PREFIX}/threads/{thread_id}/unpin"
+
+
+def is_forum_v2_enabled_for_thread(thread_id: str) -> tuple[bool, t.Optional[str]]:
+    """
+    Figure out whether we use forum v2 for a given thread.
+
+    This is a complex affair... First, we check the value of the DISABLE_FORUM_V2
+    setting, which overrides everything. If this setting does not exist, then we need to
+    find the course ID that corresponds to the thread ID. Then, we return the value of
+    the course waffle flag for this course ID.
+
+    Note that to fetch the course ID associated to a thread ID, we need to connect both
+    to mongodb and mysql. As a consequence, when forum v2 needs adequate connection
+    strings for both backends.
+
+    Return:
+
+        enabled (bool)
+        course_id (str or None)
+    """
+    if is_forum_v2_disabled_globally():
+        return True, None
+    course_id = forum_api.get_course_id_by_thread(thread_id)
+    course_key = utils.get_course_key(course_id)
+    return is_forum_v2_enabled(course_key), course_id