Gem::Source#compact_index_cache_dir

# File tmp/rubies/ruby-4.1.0-preview1/lib/rubygems/source.rb, line 466
def compact_index_cache_dir(index_uri)
  if update_cache?
    # Correct for windows paths
    escaped_path = index_uri.path.sub(%r{^/([a-z]):/}i, '/\\1-/')

    File.join Gem.spec_cache_dir, "compact_index",
      "#{index_uri.host}%#{index_uri.port}", *escaped_path.split("/").reject(&:empty?)
  else
    require "tmpdir"
    require "fileutils"
    dir = Dir.mktmpdir "gem_compact_index"
    at_exit { FileUtils.rm_rf dir }
    dir
  end
end