example_rubocop_cop.rb

# lib/rubocop/cop/rails/use_find_each.rb
module RuboCop
  module Cop
    module Rails
      # This cop checks for usage of `all.each`.
      #
      # @example
      #   # bad
      #   Model.all.each do |record|
      #     # do something
      #   end
      #
      #   # good
      #   Model.find_each do |record|
      #     # do something
      #   end
      #
      class UseFindEach < Cop
        MSG = 'Use `find_each` instead of `all.each`.'.freeze

        def_node_matcher :all_each?, '(send (send _ :all) :each)'

        def on_send(node)
          return unless all_each?(node)

          add_offense(node, message: MSG, severity: :warning)
        end

        def autocorrect(node)
          lambda do |corrector|
            range = node.loc.selector.begin_pos...node.loc.expression.end_pos
            corrector.replace(range, 'find_each')
          end
        end
      end
    end
  end
end