Maintain related issues after moving issue

When moving an issue to another project, the related issues are not
retained. We now move all the old issue links to the new issue
without creating system notes

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/13632

ee/app/models/issue_link.rb

@@ -9,6 +9,9 @@ class IssueLink < ApplicationRecord
   validates :source, uniqueness: { scope: :target_id, message: 'is already related' }
   validate :check_self_relation
 
+  scope :for_source_issue, ->(issue) { where(source_id: issue.id) }
+  scope :for_target_issue, ->(issue) { where(target_id: issue.id) }
+
   private
 
   def check_self_relation

ee/app/services/ee/issues/move_service.rb

@@ -8,6 +8,7 @@ module EE
       override :update_old_entity
       def update_old_entity
         rewrite_epic_issue
+        rewrite_related_issues
         super
       end
 
@@ -20,6 +21,14 @@ module EE
         epic_issue.update(issue_id: new_entity.id)
         original_entity.reset
       end
+
+      def rewrite_related_issues
+        source_issue_links = IssueLink.for_source_issue(original_entity)
+        source_issue_links.update_all(source_id: new_entity.id)
+
+        target_issue_links = IssueLink.for_target_issue(original_entity)
+        target_issue_links.update_all(target_id: new_entity.id)
+      end
     end
   end
 end

ee/changelogs/unreleased/sh-move-related-issues.yml

+---
+title: Maintain related issues after moving issue
+merge_request: 15391
+author:
+type: fixed

ee/spec/services/ee/issues/move_service_spec.rb

@@ -28,6 +28,45 @@ describe Issues::MoveService do
     end
   end
 
+  describe '#rewrite_related_issues' do
+    let(:user) { create(:user) }
+    let(:admin) { create(:admin) }
+    let(:authorized_project) { create(:project) }
+    let(:authorized_project2) { create(:project) }
+    let(:unauthorized_project) { create(:project) }
+
+    let(:authorized_issue_b) { create(:issue, project: authorized_project) }
+    let(:authorized_issue_c) { create(:issue, project: authorized_project2) }
+    let(:authorized_issue_d) { create(:issue, project: authorized_project2) }
+    let(:unauthorized_issue) { create(:issue, project: unauthorized_project) }
+
+    let!(:issue_link_a) { create(:issue_link, source: old_issue, target: authorized_issue_b) }
+    let!(:issue_link_b) { create(:issue_link, source: old_issue, target: unauthorized_issue) }
+    let!(:issue_link_c) { create(:issue_link, source: old_issue, target: authorized_issue_c) }
+    let!(:issue_link_d) { create(:issue_link, source: authorized_issue_d, target: old_issue) }
+
+    before do
+      stub_licensed_features(related_issues: true)
+      authorized_project.add_developer(user)
+      authorized_project2.add_developer(user)
+    end
+
+    context 'multiple related issues' do
+      it 'moves all related issues and retains permissions' do
+        new_issue = move_service.execute(old_issue, new_project)
+
+        expect(new_issue.related_issues(admin))
+          .to match_array([authorized_issue_b, authorized_issue_c, authorized_issue_d, unauthorized_issue])
+
+        expect(new_issue.related_issues(user))
+          .to match_array([authorized_issue_b, authorized_issue_c, authorized_issue_d])
+
+        expect(authorized_issue_d.related_issues(user))
+          .to match_array([new_issue])
+      end
+    end
+  end
+
   describe '#rewrite_epic_issue' do
     context 'issue assigned to epic' do
       let!(:epic_issue) { create(:epic_issue, issue: old_issue) }