regex_anchors.rb

# encoding: utf-8

module Rubocop
  module Cop
    module Style
      # This cop checks for ^/$ usage in regexps and reports violations
      class RegexAnchors < Cop

        def on_regexp(node)
          string_parts = node.children.select { |child| child.type == :str }
          total_string = string_parts.map { |s| s.loc.expression.source }.join

          if start_anchor?(total_string)
            add_offence(node, :expression, "Use \\A rather than ^ for checking start of string")
          end

          if end_anchor?(total_string)
            add_offence(node, :expression, "Use \\z rather than $ for checking termination of string")
          end
        end

        private

        def start_anchor?(string)
          return false unless string["^"]

          string.scan(/.?\^/).each do |m|
            return true unless m["[^"] || m["\\^"]
          end

          false
        end

        def end_anchor?(string)
          return false unless string["$"]

          string.scan(/.?\$/).each do |m|
            return true unless m["\\$"]
          end

          false
        end

      end
    end
  end
end