class Guard::Watcher

• files (Array) -- the changed files
• guard (Guard::Plugin) -- the Guard plugin which watchers are used

def self.match_files(guard, files)
  return [] if files.empty?
  files.inject([]) do |paths, file|
    guard.watchers.each do |watcher|
      matches = watcher.match(file)
      next(paths) unless matches
      if watcher.action
        result = watcher.call_action(matches)
        if guard.options[:any_return]
          paths << result
        elsif result.respond_to?(:empty?) && !result.empty?
          paths << Array(result)
        else
          next(paths)
        end
      else
        paths << matches[0]
      end
      break if guard.options[:first_match]
    end
    guard.options[:any_return] ? paths : paths.flatten.map(&:to_s)
  end
end