class Zeitwerk::Loader

Attributes

default_logger[RW]

: call(String) -> void | debug(String) -> void | nil

autoloaded_dirs[R]
We keep track of autoloaded directories to remove them from the registry
at the end of eager loading.

Files are removed as they are autoloaded, but directories need to wait due
to concurrency (see why in Zeitwerk::Loader::Callbacks#on_dir_autoloaded).

: Array

autoloads[R]
Maps absolute paths for which an autoload has been set ---and not
executed--- to their corresponding Zeitwerk::Cref object.

  "/Users/fxn/blog/app/models/user.rb"          => #<Zeitwerk::Cref:... @mod=Object, @cname=:User, ...>,
  "/Users/fxn/blog/app/models/hotel/pricing.rb" => #<Zeitwerk::Cref:... @mod=Hotel, @cname=:Pricing, ...>,
  ...

: Hash[String, Zeitwerk::Cref]

dirs_autoload_monitor[R]

: Monitor

inceptions[R]
When the path passed to Module#autoload is in the stack of features being
loaded at the moment, Ruby passes. For example, Module#autoload? returns
`nil` even if the autoload has not been attempted. See

    https://bugs.ruby-lang.org/issues/21035

We call these "inceptions".

A common case is the entry point of gems managed by Zeitwerk. Their main
file is normally required and, while doing so, the loader sets an autoload
on the gem namespace. That autoload hits this edge case.

There is some logic that needs to know if an autoload for a given constant
already exists. We check Module#autoload? first, and fallback to the
inceptions just in case.

This map keeps track of pairs (cref, autoload_path) found by the loader.
The object Zeitwerk::Registry.inceptions, on the other hand, acts as a
global registry for them.

: Zeitwerk::Cref::Map

mutex[R]

: Mutex

namespace_dirs[R]
Maps namespace crefs to the directories that conform the namespace.

When these crefs get defined we know their children are spread over those
directories. We'll visit them to set up the corresponding autoloads.

: Zeitwerk::Cref::Map

shadowed_files[R]
A shadowed file is a file managed by this loader that is ignored when
setting autoloads because its matching constant is already taken.

This private set is populated lazily, as we descend. For example, if the
loader has only scanned the top-level, `shadowed_files` does not have the
shadowed files that may exist deep in the project tree.

: Set

to_unload[R]
If reloading is enabled, this collection maps autoload paths to their
autoloaded crefs.

On unload, the autoload paths are passed to callbacks, files deleted from
$LOADED_FEATURES, and the crefs are deleted.

: Hash[String, Zeitwerk::Cref]

Public Class Methods

all_dirs() click to toggle source
Returns an array with the absolute paths of the root directories of all
registered loaders. This is a read-only collection.

: () -> Array

# File lib/zeitwerk/loader.rb, line 467
def all_dirs
  dirs = []
  Registry.loaders.each do |loader|
    dirs.concat(loader.dirs)
  end
  dirs.freeze
end
eager_load_all() click to toggle source
Broadcasts `eager_load` to all loaders. Those that have not been setup
are skipped.

: () -> void

# File lib/zeitwerk/loader.rb, line 439
def eager_load_all
  Registry.loaders.each do |loader|
    begin
      loader.eager_load
    rescue SetupRequired
      # This is fine, we eager load what can be eager loaded.
    end
  end
end
eager_load_namespace(mod) click to toggle source
Broadcasts `eager_load_namespace` to all loaders. Those that have not
been setup are skipped.

: (Module) -> void

# File lib/zeitwerk/loader.rb, line 453
def eager_load_namespace(mod)
  Registry.loaders.each do |loader|
    begin
      loader.eager_load_namespace(mod)
    rescue SetupRequired
      # This is fine, we eager load what can be eager loaded.
    end
  end
end
for_gem(warn_on_extra_files: true) click to toggle source
This is a shortcut for

  require "zeitwerk"

  loader = Zeitwerk::Loader.new
  loader.tag = File.basename(__FILE__, ".rb")
  loader.inflector = Zeitwerk::GemInflector.new(__FILE__)
  loader.push_dir(__dir__)

except that this method returns the same object in subsequent calls from
the same file, in the unlikely case the gem wants to be able to reload.

This method returns a subclass of Zeitwerk::Loader, but the exact type
is private, client code can only rely on the interface.

: (?warn_on_extra_files: boolish) -> Zeitwerk::GemLoader

# File lib/zeitwerk/loader.rb, line 401
def for_gem(warn_on_extra_files: true)
  called_from = caller_locations(1, 1).first.path
  Registry.loader_for_gem(called_from, namespace: Object, warn_on_extra_files: warn_on_extra_files)
end
for_gem_extension(namespace) click to toggle source
This is a shortcut for

  require "zeitwerk"

  loader = Zeitwerk::Loader.new
  loader.tag = namespace.name + "-" + File.basename(__FILE__, ".rb")
  loader.inflector = Zeitwerk::GemInflector.new(__FILE__)
  loader.push_dir(__dir__, namespace: namespace)

except that this method returns the same object in subsequent calls from
the same file, in the unlikely case the gem wants to be able to reload.

This method returns a subclass of Zeitwerk::Loader, but the exact type
is private, client code can only rely on the interface.

: (Module) -> Zeitwerk::GemLoader

# File lib/zeitwerk/loader.rb, line 422
def for_gem_extension(namespace)
  unless namespace.is_a?(Module) # Note that Class < Module.
    raise Zeitwerk::Error, "#{namespace.inspect} is not a class or module object, should be"
  end

  unless real_mod_name(namespace)
    raise Zeitwerk::Error, "extending anonymous namespaces is unsupported"
  end

  called_from = caller_locations(1, 1).first.path
  Registry.loader_for_gem(called_from, namespace: namespace, warn_on_extra_files: false)
end
new() click to toggle source
Calls superclass method Zeitwerk::Loader::Config::new
# File lib/zeitwerk/loader.rb, line 105
def initialize
  super

  @autoloads       = {}
  @inceptions      = Zeitwerk::Cref::Map.new
  @autoloaded_dirs = []
  @to_unload       = {}
  @namespace_dirs  = Zeitwerk::Cref::Map.new
  @shadowed_files  = Set.new
  @setup           = false
  @eager_loaded    = false
  @fs              = FileSystem.new(self)

  @mutex = Mutex.new
  @dirs_autoload_monitor = Monitor.new

  Registry.loaders.register(self)
end

Public Instance Methods

all_expected_cpaths() click to toggle source
Returns a hash that maps the absolute paths of the managed files and
directories to their respective expected constant paths.

: () -> Hash[String, String]

# File lib/zeitwerk/loader.rb, line 246
def all_expected_cpaths
  result = {}

  actual_roots.each do |root_dir, root_namespace|
    queue = [[root_dir, real_mod_name(root_namespace)]]

    while (dir, cpath = queue.shift)
      result[dir] = cpath

      prefix = cpath == "Object" ? "" : cpath + "::"

      @fs.ls(dir) do |basename, abspath, ftype|
        if ftype == :file
          basename.delete_suffix!(".rb")
          result[abspath] = "#{prefix}#{cname_for(basename, abspath)}"
        else
          if collapse?(abspath)
            queue << [abspath, cpath]
          else
            queue << [abspath, "#{prefix}#{cname_for(basename, abspath)}"]
          end
        end
      end
    end
  end

  result
end
cpath_expected_at(path) click to toggle source

: (String | Pathname) -> String?

# File lib/zeitwerk/loader.rb, line 276
def cpath_expected_at(path)
  abspath = File.expand_path(path)

  raise Zeitwerk::Error.new("#{abspath} does not exist") unless File.exist?(abspath)

  ftype = @fs.supported_ftype?(abspath)
  return unless ftype

  return if ignored_path?(abspath)

  paths = []

  if :file == ftype
    basename = File.basename(abspath, ".rb")
    return if @fs.hidden?(basename)

    paths << [basename, abspath]
    walk_up_from = File.dirname(abspath)
  else
    walk_up_from = abspath
  end

  root_namespace = nil

  @fs.walk_up(walk_up_from) do |dir|
    break if root_namespace = roots[dir]
    return if ignored_path?(dir)

    basename = File.basename(dir)
    return if @fs.hidden?(basename)

    paths << [basename, dir] unless collapse?(dir)
  end

  return unless root_namespace

  if paths.empty?
    real_mod_name(root_namespace)
  else
    cnames = paths.reverse_each.map { cname_for(_1, _2) }

    if root_namespace == Object
      cnames.join("::")
    else
      "#{real_mod_name(root_namespace)}::#{cnames.join("::")}"
    end
  end
end
log() { || ... } click to toggle source
# File lib/zeitwerk/loader.rb, line 368
         def log
  return unless logger

  message = yield
  method_name = logger.respond_to?(:debug) ? :debug : :call
  logger.send(method_name, "Zeitwerk@#{tag}: #{message}")
end
reload() click to toggle source
Unloads all loaded code, and calls setup again so that the loader is able
to pick any changes in the file system.

This method is not thread-safe, please see how this can be achieved by
client code in the README of the project.

: () -> void ! Zeitwerk::Error

# File lib/zeitwerk/loader.rb, line 232
def reload
  raise ReloadingDisabledError unless reloading_enabled?
  raise SetupRequired unless @setup

  unload
  recompute_ignored_paths
  recompute_collapse_dirs
  setup
end
setup() click to toggle source
Sets autoloads in the root namespaces.

: () -> void

# File lib/zeitwerk/loader.rb, line 127
def setup
  mutex.synchronize do
    break if @setup

    actual_roots.each do |root_dir, root_namespace|
      define_autoloads_for_dir(root_dir, root_namespace)
    end

    on_setup_callbacks.each(&:call)

    @setup = true
  end
end
shadowed_file?(file) click to toggle source
# File lib/zeitwerk/loader.rb, line 363
         def shadowed_file?(file)
  shadowed_files.member?(file)
end
unload() click to toggle source
Removes loaded constants and configured autoloads.

The objects the constants stored are no longer reachable through them. In
addition, since said objects are normally not referenced from anywhere
else, they are eligible for garbage collection, which would effectively
unload them.

This method is public but undocumented. Main interface is `reload`, which
means `unload` + `setup`. This one is available to be used together with
`unregister`, which is undocumented too.

: () -> void

# File lib/zeitwerk/loader.rb, line 153
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, cref|
      if cref.autoload?
        unload_autoload(cref)
      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(cref)
        unloaded_files.add(abspath) if @fs.rb_extension?(abspath)
      end
    end

    to_unload.each do |abspath, cref|
      unless on_unload_callbacks.empty?
        begin
          value = cref.get
        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(cref, value, abspath)
        end
      end

      unload_cref(cref)
      unloaded_files.add(abspath) if @fs.rb_extension?(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/rails/bootsnap/blob/main/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

    unregister_inceptions
    unregister_explicit_namespaces

    Registry.autoloads.unregister_loader(self)

    @setup        = false
    @eager_loaded = false
  end
end
unloadable_cpath?(cpath) click to toggle source
Says if the given constant path would be unloaded on reload. This
predicate returns `false` if reloading is disabled.

This is an undocumented method that I wrote to help transition from the
classic autoloader in Rails. Its usage was removed from Rails in 7.0.

: (String) -> bool

# File lib/zeitwerk/loader.rb, line 332
def unloadable_cpath?(cpath)
  unloadable_cpaths.include?(cpath)
end
unloadable_cpaths() click to toggle source
Returns an array with the constant paths that would be unloaded on reload.
This predicate returns an empty array if reloading is disabled.

This is an undocumented method that I wrote to help transition from the
classic autoloader in Rails. Its usage was removed from Rails in 7.0.

: () -> Array

# File lib/zeitwerk/loader.rb, line 343
def unloadable_cpaths
  to_unload.values.map(&:path)
end
unregister() click to toggle source
This is a dangerous method.

@experimental

: () -> void

# File lib/zeitwerk/loader.rb, line 351
def unregister
  unregister_inceptions
  unregister_explicit_namespaces
  Registry.loaders.unregister(self)
  Registry.autoloads.unregister_loader(self)
  Registry.unregister_loader(self)
end

Private Instance Methods

autoload_file(cref, file) click to toggle source

: (Zeitwerk::Cref, String) -> void

# File lib/zeitwerk/loader.rb, line 524
        def autoload_file(cref, file)
  if autoload_path = cref.autoload? || Registry.inceptions.registered?(cref)
    # First autoload for a Ruby file wins, just ignore subsequent ones.
    if @fs.rb_extension?(autoload_path)
      shadowed_files << file
      log { "file #{file} is ignored because #{autoload_path} has precedence" }
    else
      promote_namespace_from_implicit_to_explicit(dir: autoload_path, file: file, cref: cref)
    end
  elsif cref.defined?
    shadowed_files << file
    log { "file #{file} is ignored because #{cref} is already defined" }
  else
    define_autoload(cref, file)
  end
end
autoload_path_set_by_me_for?(cref) click to toggle source

: (Zeitwerk::Cref) -> String?

# File lib/zeitwerk/loader.rb, line 576
        def autoload_path_set_by_me_for?(cref)
  if autoload_path = cref.autoload?
    autoload_path if autoloads.key?(autoload_path)
  else
    inceptions[cref]
  end
end
autoload_subdir(cref, subdir) click to toggle source

: (Zeitwerk::Cref, String) -> void

# File lib/zeitwerk/loader.rb, line 495
        def autoload_subdir(cref, subdir)
  if autoload_path = autoload_path_set_by_me_for?(cref)
    if @fs.rb_extension?(autoload_path)
      # Scanning visited a Ruby file first, and now a directory for the same
      # constant has been found. This means we are dealing with an explicit
      # namespace whose definition was seen first.
      #
      # Registering is idempotent, and we have to keep the autoload pointing
      # to the file. This may run again if more directories are found later
      # on, no big deal.
      register_explicit_namespace(cref)
    end
    # If the existing autoload points to a file, it has to be preserved, if
    # not, it is fine as it is. In either case, we do not need to override.
    # Just remember the subdirectory conforms this namespace.
    namespace_dirs.get_or_set(cref) { [] } << subdir
  elsif !cref.defined?
    # First time we find this namespace, set an autoload for it.
    namespace_dirs.get_or_set(cref) { [] } << subdir
    define_autoload(cref, subdir)
  else
    # For whatever reason the constant that corresponds to this namespace has
    # already been defined, we have to recurse.
    log { "the namespace #{cref} already exists, descending into #{subdir}" }
    define_autoloads_for_dir(subdir, cref.get)
  end
end
define_autoload(cref, abspath) click to toggle source

: (Zeitwerk::Cref, String) -> void

# File lib/zeitwerk/loader.rb, line 558
        def define_autoload(cref, abspath)
  cref.autoload(abspath)

  if logger
    if @fs.rb_extension?(abspath)
      log { "autoload set for #{cref}, to be loaded from #{abspath}" }
    else
      log { "autoload set for #{cref}, to be autovivified from #{abspath}" }
    end
  end

  autoloads[abspath] = cref
  Registry.autoloads.register(abspath, self)

  register_inception(cref, abspath) unless cref.autoload?
end
define_autoloads_for_dir(dir, parent) click to toggle source

: (String, Module) -> void

# File lib/zeitwerk/loader.rb, line 477
        def define_autoloads_for_dir(dir, parent)
  @fs.ls(dir) do |basename, abspath, ftype|
    if ftype == :file
      basename.delete_suffix!(".rb")
      cref = Cref.new(parent, cname_for(basename, abspath))
      autoload_file(cref, abspath)
    else
      if collapse?(abspath)
        define_autoloads_for_dir(abspath, parent)
      else
        cref = Cref.new(parent, cname_for(basename, abspath))
        autoload_subdir(cref, abspath)
      end
    end
  end
end
promote_namespace_from_implicit_to_explicit(dir:, file:, cref:) click to toggle source
`dir` is the directory that would have autovivified a namespace. `file` is
the file where we've found the namespace is explicitly defined.

: (dir: String, file: String, cref: Zeitwerk::Cref) -> void

# File lib/zeitwerk/loader.rb, line 545
        def promote_namespace_from_implicit_to_explicit(dir:, file:, cref:)
  autoloads.delete(dir)
  Registry.autoloads.unregister(dir)

  log { "earlier autoload for #{cref} discarded, it is actually an explicit namespace defined in #{file}" }

  # Order matters: When Module#const_added is triggered by the autoload, we
  # don't want the namespace to be registered yet.
  define_autoload(cref, file)
  register_explicit_namespace(cref)
end
raise_if_conflicting_root_dir(root_dir) click to toggle source

: (String) -> void

# File lib/zeitwerk/loader.rb, line 609
        def raise_if_conflicting_root_dir(root_dir)
  if loader = Registry.conflicting_root_dir?(self, root_dir)
    require "pp" # Needed to have pretty_inspect available.
    raise Error,
      "loader\n\n#{pretty_inspect}\n\nwants to manage directory #{root_dir}," \
      " which is already managed by\n\n#{loader.pretty_inspect}\n"
  end
end
register_explicit_namespace(cref) click to toggle source

: (Zeitwerk::Cref) -> void

# File lib/zeitwerk/loader.rb, line 585
        def register_explicit_namespace(cref)
  Registry.explicit_namespaces.register(cref, self)
end
register_inception(cref, abspath) click to toggle source

: (Zeitwerk::Cref, String) -> void

# File lib/zeitwerk/loader.rb, line 595
        def register_inception(cref, abspath)
  inceptions[cref] = abspath
  Registry.inceptions.register(cref, abspath)
end
run_on_unload_callbacks(cref, value, abspath) click to toggle source

: (String, top, String) -> void

# File lib/zeitwerk/loader.rb, line 619
        def run_on_unload_callbacks(cref, value, abspath)
  # Order matters. If present, run the most specific one.
  on_unload_callbacks[cref.path]&.each { |c| c.call(value, abspath) }
  on_unload_callbacks[:ANY]&.each { |c| c.call(cref.path, value, abspath) }
end
unload_autoload(cref) click to toggle source

: (Zeitwerk::Cref) -> void

# File lib/zeitwerk/loader.rb, line 626
        def unload_autoload(cref)
  cref.remove
  log { "autoload for #{cref} removed" }
end
unload_cref(cref) click to toggle source

: (Zeitwerk::Cref) -> void

# File lib/zeitwerk/loader.rb, line 632
        def unload_cref(cref)
  # Let's optimistically remove_const. The way we use it, this is going to
  # succeed always if all is good.
  cref.remove
rescue ::NameError
  # There are a few edge scenarios in which this may happen. If the constant
  # is gone, that is OK, anyway.
else
  log { "#{cref} unloaded" }
end
unregister_explicit_namespaces() click to toggle source

: () -> void

# File lib/zeitwerk/loader.rb, line 590
        def unregister_explicit_namespaces
  Registry.explicit_namespaces.unregister_loader(self)
end
unregister_inceptions() click to toggle source

: () -> void

# File lib/zeitwerk/loader.rb, line 601
        def unregister_inceptions
  inceptions.each_key do |cref|
    Registry.inceptions.unregister(cref)
  end
  inceptions.clear
end