# frozen_string_literal: true module RuboCop module Cop module Performance # Identifies unnecessary use of a regex where `String#start_with?` would suffice. # # This cop has `SafeMultiline` configuration option that `true` by default because # `^start` is unsafe as it will behave incompatible with `start_with?` # for receiver is multiline string. # # @safety # This will change to a new method call which isn't guaranteed to be on the # object. Switching these methods has to be done with knowledge of the types # of the variables which rubocop doesn't have. # # @example # # bad # 'abc'.match?(/\Aab/) # /\Aab/.match?('abc') # 'abc' =~ /\Aab/ # /\Aab/ =~ 'abc' # 'abc'.match(/\Aab/) # /\Aab/.match('abc') # # # good # 'abc'.start_with?('ab') # # @example SafeMultiline: true (default) # # # good # 'abc'.match?(/^ab/) # /^ab/.match?('abc') # 'abc' =~ /^ab/ # /^ab/ =~ 'abc' # 'abc'.match(/^ab/) # /^ab/.match('abc') # # @example SafeMultiline: false # # # bad # 'abc'.match?(/^ab/) # /^ab/.match?('abc') # 'abc' =~ /^ab/ # /^ab/ =~ 'abc' # 'abc'.match(/^ab/) # /^ab/.match('abc') # class StartWith < Base include RegexpMetacharacter extend AutoCorrector MSG = 'Use `String#start_with?` instead of a regex match anchored to the beginning of the string.' RESTRICT_ON_SEND = %i[match =~ match?].freeze def_node_matcher :redundant_regex?, <<~PATTERN {(send $!nil? {:match :=~ :match?} (regexp (str $#literal_at_start?) (regopt))) (send (regexp (str $#literal_at_start?) (regopt)) {:match :match?} $_) (match-with-lvasgn (regexp (str $#literal_at_start?) (regopt)) $_)} PATTERN def on_send(node) return unless (receiver, regex_str = redundant_regex?(node)) add_offense(node) do |corrector| receiver, regex_str = regex_str, receiver if receiver.is_a?(String) regex_str = drop_start_metacharacter(regex_str) regex_str = interpret_string_escapes(regex_str) new_source = "#{receiver.source}.start_with?(#{to_string_literal(regex_str)})" corrector.replace(node, new_source) end end alias on_match_with_lvasgn on_send end end end end