dependencies.rb

require 'set'
require 'thread'
require 'thread_safe'
require 'pathname'
require 'active_support/core_ext/module/aliasing'
require 'active_support/core_ext/module/attribute_accessors'
require 'active_support/core_ext/module/introspection'
require 'active_support/core_ext/module/anonymous'
require 'active_support/core_ext/module/qualified_const'
require 'active_support/core_ext/object/blank'
require 'active_support/core_ext/load_error'
require 'active_support/core_ext/name_error'
require 'active_support/core_ext/string/starts_ends_with'
require 'active_support/inflector'

module ActiveSupport #:nodoc:
  module Dependencies #:nodoc:
    extend self

    # Should we turn on Ruby warnings on the first load of dependent files?
    mattr_accessor :warnings_on_first_load
    self.warnings_on_first_load = false

    # All files ever loaded.
    mattr_accessor :history
    self.history = Set.new

    # All files currently loaded.
    mattr_accessor :loaded
    self.loaded = Set.new

    # Should we load files or require them?
    mattr_accessor :mechanism
    self.mechanism = ENV['NO_RELOAD'] ? :require : :load

    # The set of directories from which we may automatically load files. Files
    # under these directories will be reloaded on each request in development mode,
    # unless the directory also appears in autoload_once_paths.
    mattr_accessor :autoload_paths
    self.autoload_paths = []

    # The set of directories from which automatically loaded constants are loaded
    # only once. All directories in this set must also be present in +autoload_paths+.
    mattr_accessor :autoload_once_paths
    self.autoload_once_paths = []

    # An array of qualified constant names that have been loaded. Adding a name
    # to this array will cause it to be unloaded the next time Dependencies are
    # cleared.
    mattr_accessor :autoloaded_constants
    self.autoloaded_constants = []

    # An array of constant names that need to be unloaded on every request. Used
    # to allow arbitrary constants to be marked for unloading.
    mattr_accessor :explicitly_unloadable_constants
    self.explicitly_unloadable_constants = []

    # The logger is used for generating information on the action run-time
    # (including benchmarking) if available. Can be set to nil for no logging.
    # Compatible with both Ruby's own Logger and Log4r loggers.
    mattr_accessor :logger

    # Set to +true+ to enable logging of const_missing and file loads.
    mattr_accessor :log_activity
    self.log_activity = false

    # The WatchStack keeps a stack of the modules being watched as files are
    # loaded. If a file in the process of being loaded (parent.rb) triggers the
    # load of another file (child.rb) the stack will ensure that child.rb
    # handles the new constants.
    #
    # If child.rb is being autoloaded, its constants will be added to
    # autoloaded_constants. If it was being `require`d, they will be discarded.
    #
    # This is handled by walking back up the watch stack and adding the constants
    # found by child.rb to the list of original constants in parent.rb.
    class WatchStack
      include Enumerable

      # @watching is a stack of lists of constants being watched. For instance,
      # if parent.rb is autoloaded, the stack will look like [[Object]]. If
      # parent.rb then requires namespace/child.rb, the stack will look like
      # [[Object], [Namespace]].

      def initialize
        @watching = []
        @stack = Hash.new { |h,k| h[k] = [] }
      end

      def each(&block)
        @stack.each(&block)
      end

      def watching?
        !@watching.empty?
      end

      # Returns a list of new constants found since the last call to
      # <tt>watch_namespaces</tt>.
      def new_constants
        constants = []

        # Grab the list of namespaces that we're looking for new constants under
        @watching.last.each do |namespace|
          # Retrieve the constants that were present under the namespace when watch_namespaces
          # was originally called
          original_constants = @stack[namespace].last

          mod = Inflector.constantize(namespace) if Dependencies.qualified_const_defined?(namespace)
          next unless mod.is_a?(Module)

          # Get a list of the constants that were added
          new_constants = mod.local_constants - original_constants

          # self[namespace] returns an Array of the constants that are being evaluated
          # for that namespace. For instance, if parent.rb requires child.rb, the first
          # element of self[Object] will be an Array of the constants that were present
          # before parent.rb was required. The second element will be an Array of the
          # constants that were present before child.rb was required.
          @stack[namespace].each do |namespace_constants|
            namespace_constants.concat(new_constants)
          end

          # Normalize the list of new constants, and add them to the list we will return
          new_constants.each do |suffix|
            constants << ([namespace, suffix] - ["Object"]).join("::")
          end
        end
        constants
      ensure
        # A call to new_constants is always called after a call to watch_namespaces
        pop_modules(@watching.pop)
      end

      # Add a set of modules to the watch stack, remembering the initial
      # constants.
      def watch_namespaces(namespaces)
        @watching << namespaces.map do |namespace|
          module_name = Dependencies.to_constant_name(namespace)
          original_constants = Dependencies.qualified_const_defined?(module_name) ?
            Inflector.constantize(module_name).local_constants : []

          @stack[module_name] << original_constants
          module_name
        end
      end

      private
      def pop_modules(modules)
        modules.each { |mod| @stack[mod].pop }
      end
    end

    # An internal stack used to record which constants are loaded by any block.
    mattr_accessor :constant_watch_stack
    self.constant_watch_stack = WatchStack.new

    # Module includes this module.
    module ModuleConstMissing #:nodoc:
      def self.append_features(base)
        base.class_eval do
          # Emulate #exclude via an ivar
          return if defined?(@_const_missing) && @_const_missing
          @_const_missing = instance_method(:const_missing)
          remove_method(:const_missing)
        end
        super
      end

      def self.exclude_from(base)
        base.class_eval do
          define_method :const_missing, @_const_missing
          @_const_missing = nil
        end
      end

      def const_missing(const_name)
        # The interpreter does not pass nesting information, and in the
        # case of anonymous modules we cannot even make the trade-off of
        # assuming their name reflects the nesting. Resort to Object as
        # the only meaningful guess we can make.
        from_mod = anonymous? ? ::Object : self
        Dependencies.load_missing_constant(from_mod, const_name)
      end

      def unloadable(const_desc = self)
        super(const_desc)
      end
    end

    # Object includes this module.
    module Loadable #:nodoc:
      def self.exclude_from(base)
        base.class_eval { define_method(:load, Kernel.instance_method(:load)) }
      end

      def require_or_load(file_name)
        Dependencies.require_or_load(file_name)
      end

      def require_dependency(file_name, message = "No such file to load -- %s")
        unless file_name.is_a?(String)
          raise ArgumentError, "the file name must be a String -- you passed #{file_name.inspect}"
        end

        Dependencies.depend_on(file_name, message)
      end

      def load_dependency(file)
        if Dependencies.load? && ActiveSupport::Dependencies.constant_watch_stack.watching?
          Dependencies.new_constants_in(Object) { yield }
        else
          yield
        end
      rescue Exception => exception  # errors from loading file
        exception.blame_file! file
        raise
      end

      def load(file, wrap = false)
        result = false
        load_dependency(file) { result = super }
        result
      end

      def require(file)
        result = false
        load_dependency(file) { result = super }
        result
      end

      # Mark the given constant as unloadable. Unloadable constants are removed
      # each time dependencies are cleared.
      #
      # Note that marking a constant for unloading need only be done once. Setup
      # or init scripts may list each unloadable constant that may need unloading;
      # each constant will be removed for every subsequent clear, as opposed to
      # for the first clear.
      #
      # The provided constant descriptor may be a (non-anonymous) module or class,
      # or a qualified constant name as a string or symbol.
      #
      # Returns +true+ if the constant was not previously marked for unloading,
      # +false+ otherwise.
      def unloadable(const_desc)
        Dependencies.mark_for_unload const_desc
      end
    end

    # Exception file-blaming.
    module Blamable #:nodoc:
      def blame_file!(file)
        (@blamed_files ||= []).unshift file
      end

      def blamed_files
        @blamed_files ||= []
      end

      def describe_blame
        return nil if blamed_files.empty?
        "This error occurred while loading the following files:\n   #{blamed_files.join "\n   "}"
      end

      def copy_blame!(exc)
        @blamed_files = exc.blamed_files.clone
        self
      end
    end

    def hook!
      Object.class_eval { include Loadable }
      Module.class_eval { include ModuleConstMissing }
      Exception.class_eval { include Blamable }
    end

    def unhook!
      ModuleConstMissing.exclude_from(Module)
      Loadable.exclude_from(Object)
    end

    def load?
      mechanism == :load
    end

    def depend_on(file_name, message = "No such file to load -- %s.rb")
      path = search_for_file(file_name)
      require_or_load(path || file_name)
    rescue LoadError => load_error
      if file_name = load_error.message[/ -- (.*?)(\.rb)?$/, 1]
        load_error.message.replace(message % file_name)
        load_error.copy_blame!(load_error)
      end
      raise
    end

    def clear
      log_call
      loaded.clear
      remove_unloadable_constants!
    end

    def require_or_load(file_name, const_path = nil)
      log_call file_name, const_path
      file_name = $` if file_name =~ /\.rb\z/
      expanded = File.expand_path(file_name)
      return if loaded.include?(expanded)

      # Record that we've seen this file *before* loading it to avoid an
      # infinite loop with mutual dependencies.
      loaded << expanded

      begin
        if load?
          log "loading #{file_name}"

          # Enable warnings if this file has not been loaded before and
          # warnings_on_first_load is set.
          load_args = ["#{file_name}.rb"]
          load_args << const_path unless const_path.nil?

          if !warnings_on_first_load or history.include?(expanded)
            result = load_file(*load_args)
          else
            enable_warnings { result = load_file(*load_args) }
          end
        else
          log "requiring #{file_name}"
          result = require file_name
        end
      rescue Exception
        loaded.delete expanded
        raise
      end

      # Record history *after* loading so first load gets warnings.
      history << expanded
      result
    end

    # Is the provided constant path defined?
    def qualified_const_defined?(path)
      Object.qualified_const_defined?(path.sub(/^::/, ''), false)
    end

    # Given +path+, a filesystem path to a ruby file, return an array of
    # constant paths which would cause Dependencies to attempt to load this
    # file.
    def loadable_constants_for_path(path, bases = autoload_paths)
      path = $` if path =~ /\.rb\z/
      expanded_path = File.expand_path(path)
      paths = []

      bases.each do |root|
        expanded_root = File.expand_path(root)
        next unless %r{\A#{Regexp.escape(expanded_root)}(/|\\)} =~ expanded_path

        nesting = expanded_path[(expanded_root.size)..-1]
        nesting = nesting[1..-1] if nesting && nesting[0] == ?/
        next if nesting.blank?

        paths << nesting.camelize
      end

      paths.uniq!
      paths
    end

    # Search for a file in autoload_paths matching the provided suffix.
    def search_for_file(path_suffix)
      path_suffix = path_suffix.sub(/(\.rb)?$/, ".rb")

      autoload_paths.each do |root|
        path = File.join(root, path_suffix)
        return path if File.file? path
      end
      nil # Gee, I sure wish we had first_match ;-)
    end

    # Does the provided path_suffix correspond to an autoloadable module?
    # Instead of returning a boolean, the autoload base for this module is
    # returned.
    def autoloadable_module?(path_suffix)
      autoload_paths.each do |load_path|
        return load_path if File.directory? File.join(load_path, path_suffix)
      end
      nil
    end

    def load_once_path?(path)
      # to_s works around a ruby1.9 issue where #starts_with?(Pathname) will always return false
      autoload_once_paths.any? { |base| path.starts_with? base.to_s }
    end

    # Attempt to autoload the provided module name by searching for a directory
    # matching the expected path suffix. If found, the module is created and
    # assigned to +into+'s constants with the name +const_name+. Provided that
    # the directory was loaded from a reloadable base path, it is added to the
    # set of constants that are to be unloaded.
    def autoload_module!(into, const_name, qualified_name, path_suffix)
      return nil unless base_path = autoloadable_module?(path_suffix)
      mod = Module.new
      into.const_set const_name, mod
      autoloaded_constants << qualified_name unless autoload_once_paths.include?(base_path)
      mod
    end

    # Load the file at the provided path. +const_paths+ is a set of qualified
    # constant names. When loading the file, Dependencies will watch for the
    # addition of these constants. Each that is defined will be marked as
    # autoloaded, and will be removed when Dependencies.clear is next called.
    #
    # If the second parameter is left off, then Dependencies will construct a
    # set of names that the file at +path+ may define. See
    # +loadable_constants_for_path+ for more details.
    def load_file(path, const_paths = loadable_constants_for_path(path))
      log_call path, const_paths
      const_paths = [const_paths].compact unless const_paths.is_a? Array
      parent_paths = const_paths.collect { |const_path| const_path[/.*(?=::)/] || :Object }

      result = nil
      newly_defined_paths = new_constants_in(*parent_paths) do
        result = Kernel.load path
      end

      autoloaded_constants.concat newly_defined_paths unless load_once_path?(path)
      autoloaded_constants.uniq!
      log "loading #{path} defined #{newly_defined_paths * ', '}" unless newly_defined_paths.empty?
      result
    end

    # Returns the constant path for the provided parent and constant name.
    def qualified_name_for(mod, name)
      mod_name = to_constant_name mod
      mod_name == "Object" ? name.to_s : "#{mod_name}::#{name}"
    end

    # Load the constant named +const_name+ which is missing from +from_mod+. If
    # it is not possible to load the constant into from_mod, try its parent
    # module using +const_missing+.
    def load_missing_constant(from_mod, const_name)
      log_call from_mod, const_name

      unless qualified_const_defined?(from_mod.name) && Inflector.constantize(from_mod.name).equal?(from_mod)
        raise ArgumentError, "A copy of #{from_mod} has been removed from the module tree but is still active!"
      end

      raise NameError, "#{from_mod} is not missing constant #{const_name}!" if from_mod.const_defined?(const_name, false)

      qualified_name = qualified_name_for from_mod, const_name
      path_suffix = qualified_name.underscore

      file_path = search_for_file(path_suffix)

      if file_path
        expanded = File.expand_path(file_path)
        expanded.sub!(/\.rb\z/, '')

        if loaded.include?(expanded)
          raise "Circular dependency detected while autoloading constant #{qualified_name}"
        else
          require_or_load(expanded)
          raise LoadError, "Unable to autoload constant #{qualified_name}, expected #{file_path} to define it" unless from_mod.const_defined?(const_name, false)
          return from_mod.const_get(const_name)
        end
      elsif mod = autoload_module!(from_mod, const_name, qualified_name, path_suffix)
        return mod
      elsif (parent = from_mod.parent) && parent != from_mod &&
            ! from_mod.parents.any? { |p| p.const_defined?(const_name, false) }
        # If our parents do not have a constant named +const_name+ then we are free
        # to attempt to load upwards. If they do have such a constant, then this
        # const_missing must be due to from_mod::const_name, which should not
        # return constants from from_mod's parents.
        begin
          # Since Ruby does not pass the nesting at the point the unknown
          # constant triggered the callback we cannot fully emulate constant
          # name lookup and need to make a trade-off: we are going to assume
          # that the nesting in the body of Foo::Bar is [Foo::Bar, Foo] even
          # though it might not be. Counterexamples are
          #
          #   class Foo::Bar
          #     Module.nesting # => [Foo::Bar]
          #   end
          #
          # or
          #
          #   module M::N
          #     module S::T
          #       Module.nesting # => [S::T, M::N]
          #     end
          #   end
          #
          # for example.
          return parent.const_missing(const_name)
        rescue NameError => e
          raise unless e.missing_name? qualified_name_for(parent, const_name)
        end
      end

      raise NameError,
            "uninitialized constant #{qualified_name}",
            caller.reject { |l| l.starts_with? __FILE__ }
    end

    # Remove the constants that have been autoloaded, and those that have been
    # marked for unloading. Before each constant is removed a callback is sent
    # to its class/module if it implements +before_remove_const+.
    #
    # The callback implementation should be restricted to cleaning up caches, etc.
    # as the environment will be in an inconsistent state, e.g. other constants
    # may have already been unloaded and not accessible.
    def remove_unloadable_constants!
      autoloaded_constants.each { |const| remove_constant const }
      autoloaded_constants.clear
      Reference.clear!
      explicitly_unloadable_constants.each { |const| remove_constant const }
    end

    class ClassCache
      def initialize
        @store = ThreadSafe::Cache.new
      end

      def empty?
        @store.empty?
      end

      def key?(key)
        @store.key?(key)
      end

      def get(key)
        key = key.name if key.respond_to?(:name)
        @store[key] ||= Inflector.constantize(key)
      end
      alias :[] :get

      def safe_get(key)
        key = key.name if key.respond_to?(:name)
        @store[key] ||= Inflector.safe_constantize(key)
      end

      def store(klass)
        return self unless klass.respond_to?(:name)
        raise(ArgumentError, 'anonymous classes cannot be cached') if klass.name.empty?
        @store[klass.name] = klass
        self
      end

      def clear!
        @store.clear
      end
    end

    Reference = ClassCache.new

    # Store a reference to a class +klass+.
    def reference(klass)
      Reference.store klass
    end

    # Get the reference for class named +name+.
    # Raises an exception if referenced class does not exist.
    def constantize(name)
      Reference.get(name)
    end

    # Get the reference for class named +name+ if one exists.
    # Otherwise returns +nil+.
    def safe_constantize(name)
      Reference.safe_get(name)
    end

    # Determine if the given constant has been automatically loaded.
    def autoloaded?(desc)
      return false if desc.is_a?(Module) && desc.anonymous?
      name = to_constant_name desc
      return false unless qualified_const_defined? name
      return autoloaded_constants.include?(name)
    end

    # Will the provided constant descriptor be unloaded?
    def will_unload?(const_desc)
      autoloaded?(const_desc) ||
        explicitly_unloadable_constants.include?(to_constant_name(const_desc))
    end

    # Mark the provided constant name for unloading. This constant will be
    # unloaded on each request, not just the next one.
    def mark_for_unload(const_desc)
      name = to_constant_name const_desc
      if explicitly_unloadable_constants.include? name
        false
      else
        explicitly_unloadable_constants << name
        true
      end
    end

    # Run the provided block and detect the new constants that were loaded during
    # its execution. Constants may only be regarded as 'new' once -- so if the
    # block calls +new_constants_in+ again, then the constants defined within the
    # inner call will not be reported in this one.
    #
    # If the provided block does not run to completion, and instead raises an
    # exception, any new constants are regarded as being only partially defined
    # and will be removed immediately.
    def new_constants_in(*descs)
      log_call(*descs)

      constant_watch_stack.watch_namespaces(descs)
      aborting = true

      begin
        yield # Now yield to the code that is to define new constants.
        aborting = false
      ensure
        new_constants = constant_watch_stack.new_constants

        log "New constants: #{new_constants * ', '}"
        return new_constants unless aborting

        log "Error during loading, removing partially loaded constants "
        new_constants.each { |c| remove_constant(c) }.clear
      end

      []
    end

    # Convert the provided const desc to a qualified constant name (as a string).
    # A module, class, symbol, or string may be provided.
    def to_constant_name(desc) #:nodoc:
      case desc
        when String then desc.sub(/^::/, '')
        when Symbol then desc.to_s
        when Module
          desc.name.presence ||
            raise(ArgumentError, "Anonymous modules have no name to be referenced by")
        else raise TypeError, "Not a valid constant descriptor: #{desc.inspect}"
      end
    end

    def remove_constant(const) #:nodoc:
      # Normalize ::Foo, ::Object::Foo, Object::Foo, Object::Object::Foo, etc. as Foo.
      normalized = const.to_s.sub(/\A::/, '')
      normalized.sub!(/\A(Object::)+/, '')

      constants = normalized.split('::')
      to_remove = constants.pop

      if constants.empty?
        parent = Object
      else
        # This method is robust to non-reachable constants.
        #
        # Non-reachable constants may be passed if some of the parents were
        # autoloaded and already removed. It is easier to do a sanity check
        # here than require the caller to be clever. We check the parent
        # rather than the very const argument because we do not want to
        # trigger Kernel#autoloads, see the comment below.
        parent_name = constants.join('::')
        return unless qualified_const_defined?(parent_name)
        parent = constantize(parent_name)
      end

      log "removing constant #{const}"

      # In an autoloaded user.rb like this
      #
      #   autoload :Foo, 'foo'
      #
      #   class User < ActiveRecord::Base
      #   end
      #
      # we correctly register "Foo" as being autoloaded. But if the app does
      # not use the "Foo" constant we need to be careful not to trigger
      # loading "foo.rb" ourselves. While #const_defined? and #const_get? do
      # require the file, #autoload? and #remove_const don't.
      #
      # We are going to remove the constant nonetheless ---which exists as
      # far as Ruby is concerned--- because if the user removes the macro
      # call from a class or module that were not autoloaded, as in the
      # example above with Object, accessing to that constant must err.
      unless parent.autoload?(to_remove)
        begin
          constantized = parent.const_get(to_remove, false)
        rescue NameError
          log "the constant #{const} is not reachable anymore, skipping"
          return
        else
          constantized.before_remove_const if constantized.respond_to?(:before_remove_const)
        end
      end

      begin
        parent.instance_eval { remove_const to_remove }
      rescue NameError
        log "the constant #{const} is not reachable anymore, skipping"
      end
    end

    protected
      def log_call(*args)
        if log_activity?
          arg_str = args.collect { |arg| arg.inspect } * ', '
          /in `([a-z_\?\!]+)'/ =~ caller(1).first
          selector = $1 || '<unknown>'
          log "called #{selector}(#{arg_str})"
        end
      end

      def log(msg)
        logger.debug "Dependencies: #{msg}" if log_activity?
      end

      def log_activity?
        logger && log_activity
      end
  end
end

ActiveSupport::Dependencies.hook!