fix user merge to include placeholder submissions

closes FOO-2586
flag = none

Test plan:
• Create an assignment and assign it to the one student with a
  due date (Assignment due date override for individual user)
  excluding the "everyone" default section scope
• Create a second user and merge the first student into the
  newly created user
• Check the submission API for the merged student and assignment
  and notice that the "cached_due_date" displays the assigned due
  date used when creating the assignment
• See Jira for additional notes and attachments
Change-Id: If1ecddc72939fafc373f8aa060ccfd252bd01d8a

Change-Id: Idae972fceb4f28d9b1f9a99fb70f3dba0fc0d9e1
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/282894
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Ben Rinaca <brinaca@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Product-Review: August Thornton <august@instructure.com>

lib/due_date_cacher.rb

@@ -148,7 +148,6 @@ class DueDateCacher
                                    else
                                      Set.new
                                    end
-
     @user_ids = Array(user_ids)
     @update_grades = update_grades
     @original_caller = original_caller

lib/user_merge.rb

@@ -621,6 +621,11 @@ class UserMerge
                             .where.not(unique_id => already_scope.having_submission.select(unique_id))
                             .where.not(id: to_move_ids)
                             .pluck(:id)
+        to_move_ids += scope.without_submission # placeholder submissions
+                            .select(unique_id)
+                            .where.not(unique_id => already_scope.without_submission.select(unique_id))
+                            .where.not(id: to_move_ids)
+                            .pluck(:id)
         to_move = scope.where(id: to_move_ids).to_a
         move_back = already_scope.where(unique_id => to_move.map(&unique_id)).to_a
         merge_data.build_more_data(to_move, data: data) unless to_move.empty?
@@ -644,7 +649,7 @@ class UserMerge
     @data = []
   end
 
-  def swap_submission(model, move_back, table, to_move, to_move_ids, fk)
+  def swap_submission(model, move_back, table, to_move, to_move_ids, fkey)
     return if to_move_ids.empty?
 
     model.transaction do
@@ -653,7 +658,7 @@ class UserMerge
       # to get around this and to allow us to swap we are setting the
       # user_id to the negative user_id and then the user_id, after the
       # conflicting rows have been updated.
-      model.connection.execute("SET CONSTRAINTS #{model.connection.quote_table_name(fk)} DEFERRED")
+      model.connection.execute("SET CONSTRAINTS #{model.connection.quote_table_name(fkey)} DEFERRED")
       model.where(id: move_back).update_all(user_id: -from_user.id)
       model.where(id: to_move_ids).update_all(user_id: target_user.id)
       model.where(id: move_back).update_all(user_id: from_user.id)

spec/lib/user_merge_spec.rb

@@ -19,8 +19,8 @@
 
 describe UserMerge do
   describe "with simple users" do
-    let!(:user1) { user_model }
-    let!(:user2) { user_model }
+    let!(:user1) { user_model(name: "target_user") }
+    let!(:user2) { user_model(name: "from_user") }
     let(:course1) { course_factory(active_all: true) }
     let(:course2) { course_factory(active_all: true) }
 
@@ -161,6 +161,48 @@ describe UserMerge do
       expect(user1.submissions.map(&:id)).to be_include(s3.id)
     end
 
+    it "recalculates cached_due_date on unsubmitted placeholder submissions for the new user" do
+      due_date_timestamp = DateTime.now.iso8601
+      course1.enroll_user(user2, "StudentEnrollment", enrollment_state: "active")
+      assignment = course1.assignments.create!(
+        title: "some assignment",
+        grading_type: "points",
+        submission_types: "online_text_entry",
+        due_at: due_date_timestamp
+      )
+      expect(Submission.where(user_id: user2.id, assignment_id: assignment.id).take.cached_due_date)
+        .to eq due_date_timestamp
+      UserMerge.from(user2).into(user1)
+      run_jobs
+      expect(Submission.where(user_id: user1.id, assignment_id: assignment.id).take.cached_due_date)
+        .to eq due_date_timestamp
+    end
+
+    it "recalculates cached_due_date on submissions for assignments with overrides" do
+      due_date_timestamp = DateTime.now.iso8601
+      course1.enroll_user(user2, "StudentEnrollment", enrollment_state: "active")
+      assignment = course1.assignments.create!(
+        title: "Assignment with student due date override",
+        grading_type: "points",
+        submission_types: "online_text_entry"
+      )
+      override = assignment.assignment_overrides.create!(
+        due_at: due_date_timestamp,
+        due_at_overridden: true,
+        all_day: true,
+        unlock_at_overridden: true,
+        lock_at_overridden: true
+      )
+      override.assignment_override_students.create!(user: user2)
+      assignment.update(due_at: nil, only_visible_to_overrides: true)
+      expect(Submission.where(user_id: user2.id, assignment_id: assignment.id).take.cached_due_date)
+        .to eq due_date_timestamp
+      UserMerge.from(user2).into(user1)
+      run_jobs
+      expect(Submission.where(user_id: user1.id, assignment_id: assignment.id).take.cached_due_date)
+        .to eq due_date_timestamp
+    end
+
     it "does not move or delete submission when both users have submissions" do
       a1 = assignment_model
       s1 = a1.find_or_create_submission(user1)