Display warning for issues moved from service desk

Backend part for displaying a warning when issues gets moved
from service desk.

app/helpers/issues_helper.rb

@@ -177,6 +177,10 @@ module IssuesHelper
     end
   end
 
+  def show_moved_service_desk_issue_warning?(issue)
+    false
+  end
+
   # Required for Banzai::Filter::IssueReferenceFilter
   module_function :url_for_issue
   module_function :url_for_internal_issue

app/models/issue.rb

@@ -29,10 +29,12 @@ class Issue < ApplicationRecord
   SORTING_PREFERENCE_FIELD = :issues_sort
 
   belongs_to :project
-  belongs_to :moved_to, class_name: 'Issue'
   belongs_to :duplicated_to, class_name: 'Issue'
   belongs_to :closed_by, class_name: 'User'
 
+  belongs_to :moved_to, class_name: 'Issue'
+  has_one :moved_from, class_name: 'Issue', foreign_key: :moved_to_id
+
   has_internal_id :iid, scope: :project, track_if: -> { !importing? }, init: ->(s) { s&.project&.issues&.maximum(:iid) }
 
   has_many :events, as: :target, dependent: :delete_all # rubocop:disable Cop/ActiveRecordDependent

ee/app/helpers/ee/issues_helper.rb

@@ -39,5 +39,13 @@ module EE
         super
       end
     end
+
+    override :show_moved_service_desk_issue_warning?
+    def show_moved_service_desk_issue_warning?(issue)
+      return false unless issue.moved_from
+      return false unless issue.from_service_desk?
+
+      issue.moved_from.project.service_desk_enabled? && !issue.project.service_desk_enabled?
+    end
   end
 end

ee/spec/helpers/ee/issues_helper_spec.rb

@@ -2,7 +2,7 @@
 
 require "spec_helper"
 
-describe IssuesHelper do
+describe EE::IssuesHelper do
   let(:project) { create(:project) }
   let(:issue) { create :issue, project: project }
 
@@ -42,4 +42,26 @@ describe IssuesHelper do
       end
     end
   end
+
+  describe '#show_moved_service_desk_issue_warning?' do
+    let(:project1) { create(:project, service_desk_enabled: true) }
+    let(:project2) { create(:project, service_desk_enabled: true) }
+    let!(:old_issue) { create(:issue, author: User.support_bot, project: project1) }
+    let!(:new_issue) { create(:issue, author: User.support_bot, project: project2) }
+
+    before do
+      allow(::EE::Gitlab::ServiceDesk).to receive(:enabled?).and_return(true)
+      old_issue.update(moved_to: new_issue)
+    end
+
+    it 'is true when moved issue project has service desk disabled' do
+      project2.update!(service_desk_enabled: false)
+
+      expect(helper.show_moved_service_desk_issue_warning?(new_issue)).to be(true)
+    end
+
+    it 'is false when moved issue project has service desk enabled' do
+      expect(helper.show_moved_service_desk_issue_warning?(new_issue)).to be(false)
+    end
+  end
 end

spec/lib/gitlab/import_export/all_models.yml

@@ -18,6 +18,7 @@ issues:
 - todos
 - user_agent_detail
 - moved_to
+- moved_from
 - duplicated_to
 - promoted_to_epic
 - events

spec/models/issue_spec.rb

@@ -9,6 +9,7 @@ describe Issue do
     it { is_expected.to belong_to(:milestone) }
     it { is_expected.to belong_to(:project) }
     it { is_expected.to belong_to(:moved_to).class_name('Issue') }
+    it { is_expected.to have_one(:moved_from).class_name('Issue') }
     it { is_expected.to belong_to(:duplicated_to).class_name('Issue') }
     it { is_expected.to belong_to(:closed_by).class_name('User') }
     it { is_expected.to have_many(:assignees) }