class RuboCop::Cop::Rouge::NoBuildingAlternationPatternInRegexp

Checks for the use of ‘.join(’|‘)` or `Regexp.union` inside interpolated regular expressions.

Building alternation patterns by joining arrays or using ‘Regexp.union` inside a regexp harms performance — the regex engine must backtrack through every alternative on each match attempt. It also risks quoting bugs when values contain regex metacharacters.

Prefer a ‘Set` lookup with a simple regex pattern instead.

@example

# bad — joins an array into a huge alternation regex
KEYWORDS = %w[if else while ...]
rule %r/\b(#{KEYWORDS.join('|')})\b/, Keyword

# bad — Regexp.union inside a regex has the same problem
rule %r/#{Regexp.union(keywords)}/

# good — simple regex + Set lookup
KEYWORDS = Set.new(%w[if else while ...])
rule %r/\w+/ do |m|
  if KEYWORDS.include?(m[0])
    token Keyword
  else
    token Name
  end
end

Constants

MSG

Public Instance Methods

on_regexp (node)

Source

# File lib/rubocop/cop/rouge/no_building_alternation_pattern_in_regexp.rb, line 51
def on_regexp(node)
  node.children.each do |child|
    next unless child.begin_type?

    find_offending_calls(child)
  end
end

Private Instance Methods

find_offending_calls (begin_node)

Source

# File lib/rubocop/cop/rouge/no_building_alternation_pattern_in_regexp.rb, line 61
def find_offending_calls(begin_node)
  begin_node.each_descendant(:send) do |send_node|
    next unless join_pipe_call?(send_node) || regexp_union_call?(send_node)

    add_offense(send_node)
  end
end