Run each commit of a repo against current rubocop to check for cop errors

rubocop-fuzz.rb

# frozen_string_literal: true

require "bundler/inline"

extensions = {
  "rubocop-rails" => "2.25.1",
  "rubocop-rspec" => "3.0.4",
  "rubocop-rspec_rails" => "2.30.0",
  "rubocop-minitest" => "0.35.1",
  "rubocop-performance" => "1.21.1",
  "rubocop-capybara" => "2.21.0",
  "rubocop-factory_bot" => "2.26.1",
  "rubocop-rake" => "0.6.0",
  "rubocop-thread_safety" => "0.5.1",
  "rubocop-erb" => "0.5.2",
}

gemfile do
  source "https://rubygems.org"
  gem "rubocop", path: "./rubocop"
  extensions.each { |name, version| gem name, version }
end

require "tempfile"

RubyVM::YJIT.enable

# Supress whatever warnings may occur (wrong department, regexp, etc.)
def Warning.warn(...)
end

# Doesn't work if there is no .rubocop.yml
class RuboCop::TargetRuby::GemspecFile
  def gemspec_filepath
    "#{Dir.pwd}/#{gemspec_filename}"
  end
end

# `rubocop:disable Rspec/PredicateMatcher` raises
class RuboCop::CommentConfig
  def cop_disabled_line_ranges
    {}
  end
end

# source buffer must be valid utf-8
class RuboCop::CachedData
  def deserialize_offenses(offenses)
    []
  end
end

def runner(extensions)
  config_path = RuboCop::ConfigLoader.configuration_file_for("./")
  other_yml = begin
                RuboCop::ConfigLoader.load_yaml_configuration(config_path)
              rescue Psych::SyntaxError
                {}
              end
  other_all_cops = (other_yml.dig("AllCops") || {}).slice("TargetRubyVersion", "TargetRailsVersion")
  other_config = RuboCop::Config.create({ "AllCops" => other_all_cops }, ".rubocop.yml", check: false)

  target_ruby = RuboCop::TargetRuby.new(other_config).version
  target_rails = other_config.target_rails_version

  without = ENV.fetch("WITHOUT", "").split(",").map do |cop|
    <<~YML
      #{cop}:
        Enabled: false
    YML
  end.join("\n")
  config = Tempfile.new
  config << <<~YML
    require: #{extensions.keys.inspect}

    AllCops:
      EnabledByDefault: true
      TargetRubyVersion: #{target_ruby}
      TargetRailsVersion: #{target_rails}
      MaxFilesInCache: 100000

    Style/Copyright:
      Enabled: false
    #{without}
  YML
  config.close

  options = RuboCop::Options.new.parse([
    "--stderr",
    "--format",
    "RuboCop::Formatter::BaseFormatter",
  ]).first
  config_store = RuboCop::ConfigStore.new
  config_store.options_config = config.path
  r = RuboCop::Runner.new(options, config_store)
  def r.run(...)
    super
    raise Interrupt if aborting?
  end
  [r, target_ruby, target_rails]
end

Dir.chdir(ENV.fetch("FOLDER")) do
  start = ENV.fetch("START") do
    `git branch`.split("\n")[1].strip
  end
  system("git checkout #{start}", exception: true)
  remaining_commits = `git rev-list HEAD --count`.to_i

  loop do
    current_commit = `git rev-parse HEAD`.strip
    raise StandardError, "rev-parse failed" if current_commit == ""

    r, target_ruby, target_rails = runner(extensions)
    puts "Commit #{current_commit} (#{remaining_commits}), #{target_ruby}/#{target_rails}"

    r.run(["./"])
    if r.errors.any?
      puts "-" * 20
      pp r.errors
      break
    end

    previous_commit = `git log --pretty=format:"%H" -2`.split("\n").last
    break if previous_commit == current_commit
    remaining_commits -= 1

    system("git checkout #{previous_commit}", exception: true, out: File::NULL, err: File::NULL)
  end
end

puts "DONE!"