class Bootsnap::LoadPathCache::Path

def latest_mtime(path, dirs)

/a/b/c, pass ('/a/b', ['c'])
list of relative paths to directories under +path+. e.g. for /a/b and
last time a directory was modified in this subtree. +dirs+ should be a 
def latest_mtime(path, dirs)
  max = -1
  ["", *dirs].each do |dir|
    curr = begin
      File.mtime("#{path}/#{dir}").to_i
    rescue Errno::ENOENT
      -1
    end
    max = curr if curr > max
  end
  max
end