rename_index

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 590
      def rename_index(table_name, old_name, new_name)
        validate_index_length!(table_name, new_name)

        # this is a naive implementation; some DBs may support this more efficiently (Postgres, for instance)
        old_index_def = indexes(table_name).detect { |i| i.name == old_name }
        return unless old_index_def
        add_index(table_name, old_index_def.columns, name: new_name, unique: old_index_def.unique)
        remove_index(table_name, name: old_name)
      end