lib/rubocop/cop/lint/useless_numeric_operation.rb


# frozen_string_literal: true

module RuboCop
  module Cop
    module Lint
      # Certain numeric operations have no impact, being:
      # Adding or subtracting 0, multiplying or dividing by 1 or raising to the power of 1.
      # These are probably leftover from debugging, or are mistakes.
      #
      # @example
      #
      #   # bad
      #   x + 0
      #   x - 0
      #   x * 1
      #   x / 1
      #   x ** 1
      #
      #   # good
      #   x
      #
      #   # bad
      #   x += 0
      #   x -= 0
      #   x *= 1
      #   x /= 1
      #   x **= 1
      #
      #   # good
      #   x = x
      #
      class UselessNumericOperation < Base
        extend AutoCorrector
        MSG = 'Do not apply inconsequential numeric operations to variables.'
        RESTRICT_ON_SEND = %i[+ - * / **].freeze

        # @!method useless_operation?(node)
        def_node_matcher :useless_operation?, '(call (call nil? $_) $_ (int $_))'

        # @!method useless_abbreviated_assignment?(node)
        def_node_matcher :useless_abbreviated_assignment?, '(op-asgn (lvasgn $_) $_ (int $_))'

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

          variable, operation, number = useless_operation?(node)
          return unless useless?(operation, number)

          add_offense(node) do |corrector|
            corrector.replace(node, variable)
          end
        end
        alias on_csend on_send

        def on_op_asgn(node)
          return unless useless_abbreviated_assignment?(node)

          variable, operation, number = useless_abbreviated_assignment?(node)
          return unless useless?(operation, number)

          add_offense(node) do |corrector|
            corrector.replace(node, "#{variable} = #{variable}")
          end
        end

        private

        def useless?(operation, number)
          if number.zero?
            true if %i[+ -].include?(operation)
          elsif number == 1
            true if %i[* / **].include?(operation)
          end
        end
      end
    end
  end
end