class Zeitwerk::Loader

def unload
  mutex.synchronize do
    raise SetupRequired unless @setup
    # We are going to keep track of the files that were required by our
    # autoloads to later remove them from $LOADED_FEATURES, thus making them
    # loadable by Kernel#require again.
    #
    # Directories are not stored in $LOADED_FEATURES, keeping track of files
    # is enough.
    unloaded_files = Set.new
    autoloads.each do |abspath, (parent, cname)|
      if parent.autoload?(cname)
        unload_autoload(parent, cname)
      else
        # Could happen if loaded with require_relative. That is unsupported,
        # and the constant path would escape unloadable_cpath? This is just
        # defensive code to clean things up as much as we are able to.
        unload_cref(parent, cname)
        unloaded_files.add(abspath) if ruby?(abspath)
      end
    end
    to_unload.each do |cpath, (abspath, (parent, cname))|
      unless on_unload_callbacks.empty?
        begin
          value = cget(parent, cname)
        rescue ::NameError
          # Perhaps the user deleted the constant by hand, or perhaps an
          # autoload failed to define the expected constant but the user
          # rescued the exception.
        else
          run_on_unload_callbacks(cpath, value, abspath)
        end
      end
      unload_cref(parent, cname)
      unloaded_files.add(abspath) if ruby?(abspath)
    end
    unless unloaded_files.empty?
      # Bootsnap decorates Kernel#require to speed it up using a cache and
      # this optimization does not check if $LOADED_FEATURES has the file.
      #
      # To make it aware of changes, the gem defines singleton methods in
      # $LOADED_FEATURES:
      #
      #   https://github.com/Shopify/bootsnap/blob/master/lib/bootsnap/load_path_cache/core_ext/loaded_features.rb
      #
      # Rails applications may depend on bootsnap, so for unloading to work
      # in that setting it is preferable that we restrict our API choice to
      # one of those methods.
      $LOADED_FEATURES.reject! { |file| unloaded_files.member?(file) }
    end
    autoloads.clear
    autoloaded_dirs.clear
    to_unload.clear
    namespace_dirs.clear
    shadowed_files.clear
    Registry.on_unload(self)
    ExplicitNamespace.__unregister_loader(self)
    @setup        = false
    @eager_loaded = false
  end
end