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Contents
# frozen_string_literal: true
module RuboCop
module Cop
module Performance
# This cop identifies unnecessary use of a regex where
# `String#start_with?` would suffice.
#
# @example
# # bad
# 'abc'.match?(/\Aab/)
# 'abc' =~ /\Aab/
# 'abc'.match(/\Aab/)
#
# # good
# 'abc'.start_with?('ab')
class StartWith < Cop
MSG = 'Use `String#start_with?` instead of a regex match anchored to ' \
'the beginning of the string.'.freeze
SINGLE_QUOTE = "'".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 :=~} $_)}
PATTERN
def literal_at_start?(regex_str)
# is this regexp 'literal' in the sense of only matching literal
# chars, rather than using metachars like `.` and `*` and so on?
# also, is it anchored at the start of the string?
# (tricky: \s, \d, and so on are metacharacters, but other characters
# escaped with a slash are just literals. LITERAL_REGEX takes all
# that into account.)
regex_str =~ /\A\\A(?:#{LITERAL_REGEX})+\z/
end
def on_send(node)
return unless redundant_regex?(node)
add_offense(node)
end
def autocorrect(node)
redundant_regex?(node) do |receiver, regex_str|
receiver, regex_str = regex_str, receiver if receiver.is_a?(String)
regex_str = regex_str[2..-1] # drop \A anchor
regex_str = interpret_string_escapes(regex_str)
lambda do |corrector|
new_source = receiver.source + '.start_with?(' +
to_string_literal(regex_str) + ')'
corrector.replace(node.source_range, new_source)
end
end
end
end
end
end
end
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