rough script to examine Ruby regexp literals with https://makenowjust-labs.github.io/recheck/

redos-radar.rb

#! /usr/bin/env ruby
# coding: utf-8

# Copyright 2022 Mike Dalessio
#
# Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
# associated documentation files (the "Software"), to deal in the Software without restriction,
# including without limitation the rights to use, copy, modify, merge, publish, distribute,
# sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all copies or
# substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
# NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
# DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT
# OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

require "bundler/inline"

gemfile do
  source "https://rubygems.org/"
  gem "syntax_tree"
end

require "open3"

class Rechecker
  PATH_TO_RECHECK = "/home/flavorjones/Downloads/recheck"

  def check(regexp)
    Open3.capture2(PATH_TO_RECHECK, regexp)
  end
end

class Reporter
  def initialize
    @passes = []
    @fails = []
    @skips = []
  end

  def pass(filename, location, message, regexp)
    @passes << [filename, location, message, regexp]
    putc "."
  end

  def fail(filename, location, message, regexp)
    @fails << [filename, location, message, regexp]
    putc "F"
  end

  def skip(filename, location, message)
    @skips << [filename, location, message]
    putc "S"
  end

  def finish
    total = @passes.length + @fails.length + @skips.length

    puts "\n\n"
    printf "%d tests, %d failures, %d skips\n", total, @fails.length, @skips.length
    puts
    @skips.each { |event| report("Skipped", event) }
    puts
    @fails.each { |event| report("Failed", event) }
  end

  def report(message, event)
    puts
    puts [message, "#{event[0]}:#{event[1].start_line}", event[3]].compact.join(": ")
    puts event[2]
  end
end

require "syntax_tree"

class RegexpVisitor < SyntaxTree::Visitor
  def initialize(filename, reporter)
    @filename = filename
    @reporter = reporter
    @rechecker = Rechecker.new
  end

  def visit_regexp_literal(node)
    if node.child_nodes.length != 1 || !node.child_nodes.first.is_a?(SyntaxTree::TStringContent)
      @reporter.skip(@filename, node.location, node.pretty_inspect)
      return
    end

    # recheck doesn't understand ruby's "\A" and "\z" regexp anchors,
    # so let's use the similar "^" and "$" anchors instead.
    value = node.child_nodes.first.value
    value = "^" + value[2..] if value.start_with?("\\A")
    value = value[..-3] + "$" if value.end_with?("\\z")
    options = node.ending[1..-1]

    regexp = "/#{value}/#{options}" # send the options to rechecker
    result, status = @rechecker.check(regexp)

    if status.success?
      @reporter.pass(@filename, node.location, result, regexp)
    else
      @reporter.fail(@filename, node.location, result, regexp)
    end
  rescue Exception => e
    pp e
  end
end

reporter = Reporter.new
ruby_files = if ARGV[0]
  Dir.glob(ARGV[0].split.map { |d| "#{d}/**/*.rb" })
else
  Dir.glob("lib/**/*.rb")
end
ruby_files.each do |fn|
  visitor = RegexpVisitor.new(fn, reporter)
  visitor.visit(SyntaxTree.parse(SyntaxTree.read(fn)))
end
reporter.finish

If you find this script useful, please let me know. I'm trying to determine whether it would be valuable to ship as a standalone checker, or as a rubocop cop, or in some other form.