class RuboCop::Cop::Rails::UniqueValidationWithoutIndex

def with_index?(klass, table, names)
  # Compatibility for Rails 4.2.
  add_indicies = schema.add_indicies_by(table_name: table_name(klass))
  (table.indices + add_indicies).any? do |index|
    index.unique &&
      (index.columns.to_set == names ||
       include_column_names_in_expression_index?(index, names))
  end
end