Send notifications to subscribers when draft status removed

When draft status is removed from a merge request, send notification to
subscribers.

app/mailers/emails/merge_requests.rb

@@ -23,6 +23,14 @@ module Emails
       mail_answer_thread(@merge_request, merge_request_thread_options(updated_by_user_id, recipient_id, reason))
     end
 
+    def change_in_merge_request_draft_status_email(recipient_id, merge_request_id, updated_by_user_id, reason = nil)
+      setup_merge_request_mail(merge_request_id, recipient_id)
+
+      @updated_by_user = User.find(updated_by_user_id)
+
+      mail_answer_thread(@merge_request, merge_request_thread_options(updated_by_user_id, recipient_id, reason))
+    end
+
     # rubocop: disable CodeReuse/ActiveRecord
     def reassigned_merge_request_email(recipient_id, merge_request_id, previous_assignee_ids, updated_by_user_id, reason = nil)
       setup_merge_request_mail(merge_request_id, recipient_id)

app/services/merge_requests/update_service.rb

@@ -154,11 +154,20 @@ module MergeRequests
       elsif old_title_wip && !new_title_wip
         # Unmarked as Draft/WIP
         #
+        notify_draft_status_changed(merge_request)
+
         merge_request_activity_counter
           .track_unmarked_as_draft_action(user: current_user)
       end
     end
 
+    def notify_draft_status_changed(merge_request)
+      notification_service.async.change_in_merge_request_draft_status(
+        merge_request,
+        current_user
+      )
+    end
+
     def handle_milestone_change(merge_request)
       return if skip_milestone_email
 

app/services/notification_service.rb

@@ -189,6 +189,20 @@ class NotificationService
     end
   end
 
+  def change_in_merge_request_draft_status(merge_request, current_user)
+    recipients = NotificationRecipients::BuildService.build_recipients(merge_request, current_user, action: "draft_status_change")
+
+    recipients.each do |recipient|
+      mailer.send(
+        :change_in_merge_request_draft_status_email,
+        recipient.user.id,
+        merge_request.id,
+        current_user.id,
+        recipient.reason
+      ).deliver_later
+    end
+  end
+
   # When a merge request is found to be unmergeable, we should send an email to:
   #
   #  * mr author

changelogs/unreleased/15332-notify-when-merge-request-draft-status-changes.yml

+---
+title: Send notifications to subscribers when merge request draft status removed
+merge_request: 55444
+author:
+type: changed

spec/services/merge_requests/update_service_spec.rb

@@ -656,6 +656,48 @@ RSpec.describe MergeRequests::UpdateService, :mailer do
       end
     end
 
+    context 'when the draft status is changed' do
+      let!(:non_subscriber) { create(:user) }
+      let!(:subscriber) do
+        create(:user) { |u| merge_request.toggle_subscription(u, project) }
+      end
+
+      before do
+        project.add_developer(non_subscriber)
+        project.add_developer(subscriber)
+      end
+
+      context 'removing draft status' do
+        before do
+          merge_request.update_attribute(:title, 'Draft: New Title')
+        end
+
+        it 'sends notifications for subscribers', :sidekiq_might_not_need_inline do
+          opts = { title: 'New title' }
+
+          perform_enqueued_jobs do
+            @merge_request = described_class.new(project, user, opts).execute(merge_request)
+          end
+
+          should_email(subscriber)
+          should_not_email(non_subscriber)
+        end
+      end
+
+      context 'adding draft status' do
+        it 'does not send notifications', :sidekiq_might_not_need_inline do
+          opts = { title: 'Draft: New title' }
+
+          perform_enqueued_jobs do
+            @merge_request = described_class.new(project, user, opts).execute(merge_request)
+          end
+
+          should_not_email(subscriber)
+          should_not_email(non_subscriber)
+        end
+      end
+    end
+
     context 'when the merge request is relabeled' do
       let!(:non_subscriber) { create(:user) }
       let!(:subscriber) { create(:user) { |u| label.toggle_subscription(u, project) } }

spec/services/notification_service_spec.rb

@@ -1868,6 +1868,42 @@ RSpec.describe NotificationService, :mailer do
       end
     end
 
+    describe '#change_in_merge_request_draft_status' do
+      let(:merge_request) { create(:merge_request, author: author, source_project: project) }
+
+      let_it_be(:current_user) { create(:user) }
+
+      it 'sends emails to relevant users only', :aggregate_failures do
+        notification.change_in_merge_request_draft_status(merge_request, current_user)
+
+        merge_request.reviewers.each { |reviewer| should_email(reviewer) }
+        merge_request.assignees.each { |assignee| should_email(assignee) }
+        should_email(merge_request.author)
+        should_email(@u_watcher)
+        should_email(@subscriber)
+        should_email(@watcher_and_subscriber)
+        should_email(@u_guest_watcher)
+        should_not_email(@u_participant_mentioned)
+        should_not_email(@u_guest_custom)
+        should_not_email(@u_custom_global)
+        should_not_email(@unsubscriber)
+        should_not_email(@u_participating)
+        should_not_email(@u_disabled)
+        should_not_email(@u_lazy_participant)
+      end
+
+      it_behaves_like 'participating notifications' do
+        let(:participant) { create(:user, username: 'user-participant') }
+        let(:issuable) { merge_request }
+        let(:notification_trigger) { notification.change_in_merge_request_draft_status(merge_request, @u_disabled) }
+      end
+
+      it_behaves_like 'project emails are disabled' do
+        let(:notification_target)  { merge_request }
+        let(:notification_trigger) { notification.change_in_merge_request_draft_status(merge_request, @u_disabled) }
+      end
+    end
+
     describe '#push_to_merge_request' do
       before do
         update_custom_notification(:push_to_merge_request, @u_guest_custom, resource: project)