on_conflict_behavior

# File railties/lib/rails/generators/actions/create_migration.rb, line 42
        def on_conflict_behavior(&block)
          options = base.options.merge(config)
          if identical?
            say_status :identical, :blue, relative_existing_migration
          elsif options[:force]
            say_status :remove, :green, relative_existing_migration
            say_status :create, :green
            unless pretend?
              ::FileUtils.rm_rf(existing_migration)
              block.call
            end
          elsif options[:skip]
            say_status :skip, :yellow
          else
            say_status :conflict, :red
            raise Error, "Another migration is already named #{migration_file_name}: " +
                         "#{existing_migration}. Use --force to replace this migration file."
          end
        end