1 files changed, 49 insertions, 0 deletions
diff --git a/rubocop/cop/migration/add_reference.rb b/rubocop/cop/migration/add_reference.rb
new file mode 100644
index 00000000000..4b67270c97a
--- /dev/null
+++ b/rubocop/cop/migration/add_reference.rb
@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+require_relative '../../migration_helpers'
+
+module RuboCop
+  module Cop
+    module Migration
+      # Cop that checks if a foreign key constraint is added and require a index for it
+      class AddReference < RuboCop::Cop::Cop
+        include MigrationHelpers
+
+        MSG = '`add_reference` requires `index: true`'
+
+        def on_send(node)
+          return unless in_migration?(node)
+
+          name = node.children[1]
+
+          return unless name == :add_reference
+
+          opts = node.children.last
+
+          add_offense(node, location: :selector) unless opts && opts.type == :hash
+
+          index_present = false
+
+          opts.each_node(:pair) do |pair|
+            index_present ||= index_enabled?(pair)
+          end
+
+          add_offense(node, location: :selector) unless index_present
+        end
+
+        private
+
+        def index_enabled?(pair)
+          hash_key_type(pair) == :sym && hash_key_name(pair) == :index && pair.children[1].true_type?
+        end
+
+        def hash_key_type(pair)
+          pair.children[0].type
+        end
+
+        def hash_key_name(pair)
+          pair.children[0].children[0]
+        end
+      end
+    end
+  end
+end