fix duedatecacher crashing when dealing with bc dates

closes EVAL-2499
flag=none

Test Plan:
- Smoke test creating assignments with various due dates and ensure
  the generated submissions have the correct cached_due_date on them.

Change-Id: I9a7792d1f49b0cef13334cbf94870f7518fc59ce
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/297120
Tested-by: Service Cloud Jenkins <[email protected]>
Product-Review: Keith Garner <[email protected]>
QA-Review: Kai Bjorkman <[email protected]>
Reviewed-by: Kai Bjorkman <[email protected]>
Reviewed-by: Paulo Chaves <[email protected]>

lib/due_date_cacher.rb

@@ -210,7 +210,7 @@ def recompute
 
         student_due_dates.each_key do |student_id|
           submission_info = student_due_dates[student_id]
-          due_date = submission_info[:due_at] ? "'#{submission_info[:due_at].iso8601}'::timestamptz" : "NULL"
+          due_date = submission_info[:due_at] ? "'#{ActiveRecord::Base.connection.quoted_date(submission_info[:due_at].change(usec: 0))}'::timestamptz" : "NULL"
           grading_period_id = submission_info[:grading_period_id] || "NULL"
 
           anonymous_id = Anonymity.generate_id(existing_ids: existing_anonymous_ids)

spec/lib/due_date_cacher_spec.rb

@@ -680,6 +680,14 @@
           }.from(0).to(1)
         end
 
+        it "doesn't blow up when handling BC dates" do
+          bc_date = 5000.years.ago
+          @assignment.update_columns(due_at: bc_date)
+          expect { cacher.recompute }.to change {
+            Submission.find_by(assignment: @assignment, user: @student)&.cached_due_date
+          }.from(nil).to(bc_date.change(usec: 0))
+        end
+
         it "deletes submissions for enrollments that are deleted" do
           @course.student_enrollments.update_all(workflow_state: "deleted")