Reinstate Object.subclasses_of and Class#descendents for plugin compat.

This reverts commits 7d312e54bad9c39634c137caec07dfc8df471650, 5f981ff0294ba45aa44ad15aa063970b29aeec44, f85f5dfc8ffefff174b695c6363211d342f77a57, 245bfafe335ff883f7a096eab95ac22fe2848679, and ec7c642f5fe60afc857aa64f1a9b4c2be56f9d70

3 files changed, 70 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/core_ext/class.rb b/activesupport/lib/active_support/core_ext/class.rb
index 62df7d8b82..f2ca9c7cc9 100644
--- a/activesupport/lib/active_support/core_ext/class.rb
+++ b/activesupport/lib/active_support/core_ext/class.rb
@@ -1,3 +1,4 @@
 require 'active_support/core_ext/class/attribute_accessors'
 require 'active_support/core_ext/class/inheritable_attributes'
 require 'active_support/core_ext/class/delegating_attributes'
+require 'active_support/core_ext/class/subclasses'
diff --git a/activesupport/lib/active_support/core_ext/class/subclasses.rb b/activesupport/lib/active_support/core_ext/class/subclasses.rb
new file mode 100644
index 0000000000..c166ce8079
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/class/subclasses.rb
@@ -0,0 +1,58 @@
+require 'active_support/core_ext/object/blank'
+
+class Class #:nodoc:
+  # Returns an array with the names of the subclasses of +self+ as strings.
+  #
+  #   Integer.subclasses # => ["Bignum", "Fixnum"]
+  def subclasses
+    Class.subclasses_of(self).map { |o| o.to_s }
+  end
+
+  def reachable? #:nodoc:
+    eval("defined?(::#{self}) && ::#{self}.equal?(self)")
+  end
+
+  # Rubinius
+  if defined?(Class.__subclasses__)
+    def descendents
+      subclasses = []
+      __subclasses__.each {|k| subclasses << k; subclasses.concat k.descendents }
+      subclasses
+    end
+  else
+    # MRI
+    begin
+      ObjectSpace.each_object(Class.new) {}
+
+      def descendents
+        subclasses = []
+        ObjectSpace.each_object(class << self; self; end) do |k|
+          subclasses << k unless k == self
+        end
+        subclasses
+      end
+    # JRuby
+    rescue StandardError
+      def descendents
+        subclasses = []
+        ObjectSpace.each_object(Class) do |k|
+          subclasses << k if k < self
+        end
+        subclasses.uniq!
+        subclasses
+      end
+    end
+  end
+
+  # Exclude this class unless it's a subclass of our supers and is defined.
+  # We check defined? in case we find a removed class that has yet to be
+  # garbage collected. This also fails for anonymous classes -- please
+  # submit a patch if you have a workaround.
+  def self.subclasses_of(*superclasses) #:nodoc:
+    subclasses = []
+    superclasses.each do |klass|
+      subclasses.concat klass.descendents.select {|k| k.name.blank? || k.reachable?}
+    end
+    subclasses
+  end
+end
diff --git a/activesupport/lib/active_support/core_ext/object/extending.rb b/activesupport/lib/active_support/core_ext/object/extending.rb
new file mode 100644
index 0000000000..c4c37b6a2a
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/object/extending.rb
@@ -0,0 +1,11 @@
+require 'active_support/core_ext/class/subclasses'
+
+class Object
+  # Exclude this class unless it's a subclass of our supers and is defined.
+  # We check defined? in case we find a removed class that has yet to be
+  # garbage collected. This also fails for anonymous classes -- please
+  # submit a patch if you have a workaround.
+  def subclasses_of(*superclasses) #:nodoc:
+    Class.subclasses_of(*superclasses)
+  end
+end