rubocop/cop/performance/readlines_each.rb


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# frozen_string_literal: true

module RuboCop
  module Cop
    module Performance
      class ReadlinesEach < RuboCop::Cop::Base
        extend RuboCop::Cop::AutoCorrector

        MESSAGE = 'Avoid `IO.readlines.each`, since it reads contents into memory in full. ' \
          'Use `IO.each_line` or `IO.each` instead.'

        def_node_matcher :full_file_read_via_class?, <<~PATTERN
          (send
            (send (const nil? {:IO :File}) :readlines _) :each)
        PATTERN

        def_node_matcher :full_file_read_via_instance?, <<~PATTERN
          (... (... :readlines) :each)
        PATTERN

        def on_send(node)
          return unless full_file_read_via_class?(node) || full_file_read_via_instance?(node)

          add_offense(node.loc.selector, message: MESSAGE) do |corrector|
            corrector.replace(node.loc.expression, node.source.gsub('readlines.each', 'each_line'))
          end
        end
      end
    end
  end
end