3 files changed, 92 insertions, 0 deletions
diff --git a/app/services/issue_links/create_service.rb b/app/services/issue_links/create_service.rb
new file mode 100644
index 00000000000..63762b1af79
--- /dev/null
+++ b/app/services/issue_links/create_service.rb
@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+module IssueLinks
+  class CreateService < IssuableLinks::CreateService
+    # rubocop: disable CodeReuse/ActiveRecord
+    def relate_issuables(referenced_issue)
+      link = IssueLink.find_or_initialize_by(source: issuable, target: referenced_issue)
+
+      set_link_type(link)
+
+      if link.changed? && link.save
+        create_notes(referenced_issue)
+      end
+
+      link
+    end
+    # rubocop: enable CodeReuse/ActiveRecord
+
+    def linkable_issuables(issues)
+      @linkable_issuables ||= begin
+        issues.select { |issue| can?(current_user, :admin_issue_link, issue) }
+      end
+    end
+
+    def create_notes(referenced_issue)
+      SystemNoteService.relate_issue(issuable, referenced_issue, current_user)
+      SystemNoteService.relate_issue(referenced_issue, issuable, current_user)
+    end
+
+    def previous_related_issuables
+      @related_issues ||= issuable.related_issues(current_user).to_a
+    end
+
+    private
+
+    def set_link_type(_link)
+      # EE only
+    end
+
+    def track_event
+      track_incident_action(current_user, issuable, :incident_relate)
+    end
+  end
+end
+
+IssueLinks::CreateService.prepend_if_ee('EE::IssueLinks::CreateService')
diff --git a/app/services/issue_links/destroy_service.rb b/app/services/issue_links/destroy_service.rb
new file mode 100644
index 00000000000..25a45fc697b
--- /dev/null
+++ b/app/services/issue_links/destroy_service.rb
@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+module IssueLinks
+  class DestroyService < IssuableLinks::DestroyService
+    private
+
+    def source
+      @source ||= link.source
+    end
+
+    def target
+      @target ||= link.target
+    end
+
+    def permission_to_remove_relation?
+      can?(current_user, :admin_issue_link, source) && can?(current_user, :admin_issue_link, target)
+    end
+
+    def create_notes
+      SystemNoteService.unrelate_issue(source, target, current_user)
+      SystemNoteService.unrelate_issue(target, source, current_user)
+    end
+
+    def track_event
+      track_incident_action(current_user, target, :incident_unrelate)
+    end
+  end
+end
diff --git a/app/services/issue_links/list_service.rb b/app/services/issue_links/list_service.rb
new file mode 100644
index 00000000000..5ac731d3fbc
--- /dev/null
+++ b/app/services/issue_links/list_service.rb
@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+module IssueLinks
+  class ListService < IssuableLinks::ListService
+    extend ::Gitlab::Utils::Override
+
+    private
+
+    def child_issuables
+      issuable.related_issues(current_user, preload: preload_for_collection)
+    end
+
+    override :serializer
+    def serializer
+      LinkedProjectIssueSerializer
+    end
+  end
+end