lib/rubocop/cop/style/empty_literal.rb


# frozen_string_literal: true

module RuboCop
  module Cop
    module Style
      # This cop checks for the use of a method, the result of which
      # would be a literal, like an empty array, hash, or string.
      #
      # @example
      #   # bad
      #   a = Array.new
      #   h = Hash.new
      #   s = String.new
      #
      #   # good
      #   a = []
      #   h = {}
      #   s = ''
      class EmptyLiteral < Cop
        include FrozenStringLiteral
        include RangeHelp

        ARR_MSG = 'Use array literal `[]` instead of `Array.new`.'
        HASH_MSG = 'Use hash literal `{}` instead of `Hash.new`.'
        STR_MSG = 'Use string literal `%<prefer>s` instead of ' \
                  '`String.new`.'

        def_node_matcher :array_node, '(send (const nil? :Array) :new)'
        def_node_matcher :hash_node, '(send (const nil? :Hash) :new)'
        def_node_matcher :str_node, '(send (const nil? :String) :new)'
        def_node_matcher :array_with_block,
                         '(block (send (const nil? :Array) :new) args _)'
        def_node_matcher :hash_with_block,
                         '(block (send (const nil? :Hash) :new) args _)'

        def on_send(node)
          add_offense(node, message: ARR_MSG)  if offense_array_node?(node)
          add_offense(node, message: HASH_MSG) if offense_hash_node?(node)

          str_node(node) do
            return if frozen_string_literals_enabled?

            add_offense(node,
                        message: format(STR_MSG,
                                        prefer: preferred_string_literal))
          end
        end

        def autocorrect(node)
          lambda do |corrector|
            corrector.replace(replacement_range(node), correction(node))
          end
        end

        private

        def preferred_string_literal
          enforce_double_quotes? ? '""' : "''"
        end

        def enforce_double_quotes?
          string_literals_config['EnforcedStyle'] == 'double_quotes'
        end

        def string_literals_config
          config.for_cop('Style/StringLiterals')
        end

        def first_argument_unparenthesized?(node)
          parent = node.parent
          unless parent && %i[send super zsuper].include?(parent.type)
            return false
          end

          node.object_id == parent.arguments.first.object_id &&
            !parentheses?(node.parent)
        end

        def replacement_range(node)
          if hash_node(node) &&
             first_argument_unparenthesized?(node)
            # `some_method {}` is not same as `some_method Hash.new`
            # because the braces are interpreted as a block. We will have
            # to rewrite the arguments to wrap them in parenthesis.
            args = node.parent.arguments

            range_between(args[0].source_range.begin_pos - 1,
                          args[-1].source_range.end_pos)
          else
            node.source_range
          end
        end

        def offense_array_node?(node)
          array_node(node) && !array_with_block(node.parent)
        end

        def offense_hash_node?(node)
          # If Hash.new takes a block, it can't be changed to {}.
          hash_node(node) && !hash_with_block(node.parent)
        end

        def correction(node)
          if offense_array_node?(node)
            '[]'
          elsif str_node(node)
            preferred_string_literal
          elsif offense_hash_node?(node)
            if first_argument_unparenthesized?(node)
              # `some_method {}` is not same as `some_method Hash.new`
              # because the braces are interpreted as a block. We will have
              # to rewrite the arguments to wrap them in parenthesis.
              args = node.parent.arguments
              "(#{args[1..-1].map(&:source).unshift('{}').join(', ')})"
            else
              '{}'
            end
          end
        end
      end
    end
  end
end