prevent checkpoints from creating their own discussion topics

closes VICE-4024
flag=discussion_topics

Test Plan:
- specs pass

Change-Id: Id318d6e4dcbc977a1b4a1859bb397cd7088b6e9a
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/335836
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Keith Garner <kgarner@instructure.com>
Reviewed-by: Omar Soto-Fortuño <omar.soto@instructure.com>
Product-Review: Omar Soto-Fortuño <omar.soto@instructure.com>
QA-Review: Chawn Neal <chawn.neal@instructure.com>

app/models/abstract_assignment.rb

@@ -1093,7 +1093,7 @@ class AbstractAssignment < ActiveRecord::Base
   end
 
   def delete_empty_abandoned_children
-    if saved_change_to_submission_types?
+    if governs_submittable? && saved_change_to_submission_types?
       each_submission_type do |submittable, type|
         unless self.submission_types == type.to_s
           submittable&.unlink!(:assignment)
@@ -1120,7 +1120,7 @@ class AbstractAssignment < ActiveRecord::Base
   def update_submittable
     # If we're updating the assignment's muted status as part of posting
     # grades, don't bother doing this
-    return true if deleted? || grade_posting_in_progress
+    return true if !governs_submittable? || deleted? || grade_posting_in_progress
 
     if self.submission_types == "online_quiz" && @saved_by != :quiz
       quiz = Quizzes::Quiz.where(assignment_id: self).first || context.quizzes.build

app/models/assignment.rb

@@ -86,4 +86,8 @@ class Assignment < AbstractAssignment
   def before_soft_delete
     sub_assignments.destroy_all
   end
+
+  def governs_submittable?
+    true
+  end
 end

app/models/discussion_topic.rb

@@ -1836,8 +1836,18 @@ class DiscussionTopic < ActiveRecord::Base
     return false unless assignment.present?
 
     assignment.update!(has_sub_assignments: true)
-    assignment.sub_assignments.create!(context:, sub_assignment_tag: CheckpointLabels::REPLY_TO_TOPIC, points_possible: reply_to_topic_points)
-    assignment.sub_assignments.create!(context:, sub_assignment_tag: CheckpointLabels::REPLY_TO_ENTRY, points_possible: reply_to_entry_points)
+    assignment.sub_assignments.create!(
+      context:,
+      sub_assignment_tag: CheckpointLabels::REPLY_TO_TOPIC,
+      submission_types: "discussion_topic",
+      points_possible: reply_to_topic_points
+    )
+    assignment.sub_assignments.create!(
+      context:,
+      sub_assignment_tag: CheckpointLabels::REPLY_TO_ENTRY,
+      submission_types: "discussion_topic",
+      points_possible: reply_to_entry_points
+    )
     self.reply_to_entry_required_count = reply_to_entry_required_count
 
     save

app/models/sub_assignment.rb

@@ -48,4 +48,8 @@ class SubAssignment < AbstractAssignment
     relevant_changes = tracked_attributes & previous_changes.keys
     relevant_changes.any?
   end
+
+  def governs_submittable?
+    false
+  end
 end

lib/submittable.rb

@@ -19,7 +19,7 @@
 
 module Submittable
   def self.included(klass)
-    klass.belongs_to :assignment, inverse_of: klass.table_name.singularize, class_name: "AbstractAssignment"
+    klass.belongs_to :assignment, inverse_of: klass.table_name.singularize, class_name: "Assignment"
     klass.belongs_to :old_assignment, class_name: "Assignment"
     klass.has_many :assignment_student_visibilities, through: :assignment
 

spec/models/discussion_topic_spec.rb

@@ -3027,6 +3027,12 @@ describe DiscussionTopic do
       expect(@topic).to_not be_valid
     end
 
+    it "does not create a discussion topic per-checkpoint (instead, checkpoints belong to the topic through the parent)" do
+      expect do
+        @topic.create_checkpoints(reply_to_topic_points: 10, reply_to_entry_points: 15, reply_to_entry_required_count: 0)
+      end.not_to change { DiscussionTopic.count }.from(1)
+    end
+
     describe "in place" do
       before do
         @course.root_account.enable_feature!(:discussion_checkpoints)