Retry once when saving submissions

If two submissions are saved in rapid successon,
the simply_versioned gem can throw a unique constraint
error when it tries to create new records.

simply_versioned creates a new version of a record, which
is numbered as simply (previous_version_number + 1). The
version numbers must be unique. So, if two get started at
the same time -- or almost the same time -- they can
have the same number.

The unique_constraint_retry method will retry whatever
is in its block one time if there is a unique constraint
error. Retrying one time should be enough for us to avoid
this simply_versioned error that we're getting; in our
logs, we rarely get more than one in a row. The stack
traces show that it's happening in the broadcast_group_submission
method.

fixes INTEROP-8494

flag = none

test plan:
- specs pass

Change-Id: I0fa67c9c766e98f27a29c83a45576b5900164ed9
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/345096
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Ryan Hawkins <ryan.hawkins@instructure.com>
QA-Review: Tucker Mcknight <tmcknight@instructure.com>
Product-Review: Tucker Mcknight <tmcknight@instructure.com>

app/models/submission.rb

@@ -2460,9 +2460,11 @@ def students
   end
 
   def broadcast_group_submission
-    @group_broadcast_submission = true
-    save!
-    @group_broadcast_submission = false
+    Submission.unique_constraint_retry do
+      @group_broadcast_submission = true
+      save!
+      @group_broadcast_submission = false
+    end
   end
 
   # in a module so they can be included in other Submission-like objects. the

spec/models/submission_spec.rb

@@ -1792,6 +1792,34 @@
         ActiveRecord::Associations.preload([version].map(&:model), :originality_reports)
       end.not_to raise_error
     end
+
+    it "retries if there is a conflict with an existing version number" do
+      submission_spec_model
+      version = Version.find_by(versionable: @submission)
+
+      allow(@submission.versions).to receive(:create).and_call_original
+      called_times = 0
+      expect(@submission.versions).to receive(:create) { |attributes|
+        called_times += 1
+        # This is a hacky way of mimicing a bug where two responses, received very quickly,
+        # would create a RecordNotUnique error when the tried to increment the version
+        # number at the same time.
+        v = Version.create(
+          **attributes,
+          versionable_id: version.versionable_id,
+          versionable_type: version.versionable_type
+        )
+        v.update_attribute(:number, version.number) if called_times == 1
+        v
+      }.twice
+
+      submission_versions = @submission.versions.count
+      @submission.with_versioning(explicit: true) do
+        @submission.broadcast_group_submission
+      end
+
+      expect(@submission.versions.count).to eq(submission_versions + 1)
+    end
   end
 
   it "ensures the media object exists" do