Subscriber.attach_to with inherit_all option

activesupport/CHANGELOG.md

@@ -1,3 +1,38 @@
+*   ActiveSupport::Subscriber#attach_to now accepts an inherit_from: argument. When set to true,
+    it allows a subscriber to receive events for methods defined in the subscriber's ancestor class(es)
+
+    ```ruby
+    class ActionControllerSubscriber < ActiveSupport::Subscriber
+      attach_to :action_controller
+
+      def start_processing(event)
+        info "Processing by #{event.payload[:controller]}##{event.payload[:action]} as #{format}"
+      end
+
+      def redirect_to(event)
+        info { "Redirected to #{event.payload[:location]}" }
+      end
+    end
+
+    # We detach ActionControllerSubscriber from the :action_controller namespace so that our CustomActionControllerSubscriber
+    # can provide its own instrumentation for certain events in the namespace
+    ActionControllerSubscriber.detach_from(:action_controller)
+
+    class CustomActionControllerSubscriber < ActionControllerSubscriber
+      attach_to :action_controller, inherit_all: true
+
+      def start_processing(event)
+        info "A custom response to start_processing events"
+      end
+
+      # => CustomActionControllerSubscriber will process events for "start_processing.action_controller" notifications
+      # using its own #start_processing implementation, while retaining ActionControllerSubscriber's instrumentation
+      # for "redirect_to.action_controller" notifications
+    end
+    ```
+
+    *Adrianna Chang*
+
 *   Fix bug to make memcached write_entry expire correctly with unless_exist
 
     *Jye Lee*

activesupport/lib/active_support/log_subscriber.rb

@@ -96,6 +96,11 @@ module ActiveSupport
       def flush_all!
         logger.flush if logger.respond_to?(:flush)
       end
+
+      private
+        def fetch_public_methods(subscriber, inherit_all)
+          subscriber.public_methods(inherit_all) - LogSubscriber.public_instance_methods(true)
+        end
     end
 
     def logger

activesupport/lib/active_support/subscriber.rb

@@ -31,15 +31,16 @@ module ActiveSupport
   class Subscriber
     class << self
       # Attach the subscriber to a namespace.
-      def attach_to(namespace, subscriber = new, notifier = ActiveSupport::Notifications)
+      def attach_to(namespace, subscriber = new, notifier = ActiveSupport::Notifications, inherit_all: false)
         @namespace  = namespace
         @subscriber = subscriber
         @notifier   = notifier
+        @inherit_all = inherit_all
 
         subscribers << subscriber
 
         # Add event subscribers for all existing methods on the class.
-        subscriber.public_methods(false).each do |event|
+        fetch_public_methods(subscriber, inherit_all).each do |event|
           add_event_subscriber(event)
         end
       end
@@ -55,7 +56,7 @@ module ActiveSupport
         subscribers.delete(subscriber)
 
         # Remove event subscribers of all existing methods on the class.
-        subscriber.public_methods(false).each do |event|
+        fetch_public_methods(subscriber, true).each do |event|
           remove_event_subscriber(event)
         end
 
@@ -117,6 +118,10 @@ module ActiveSupport
         def pattern_subscribed?(pattern)
           subscriber.patterns.key?(pattern)
         end
+
+        def fetch_public_methods(subscriber, inherit_all)
+          subscriber.public_methods(inherit_all) - Subscriber.public_instance_methods(true)
+        end
     end
 
     attr_reader :patterns # :nodoc:

activesupport/test/subscriber_test.rb

@@ -4,8 +4,6 @@ require_relative "abstract_unit"
 require "active_support/subscriber"
 
 class TestSubscriber < ActiveSupport::Subscriber
-  attach_to :doodle
-
   cattr_reader :events
 
   def self.clear
@@ -16,23 +14,19 @@ class TestSubscriber < ActiveSupport::Subscriber
     events << event
   end
 
+  def another_open_party(event)
+    events << event
+  end
+
   private
     def private_party(event)
       events << event
     end
 end
 
-class TestSubscriber2 < ActiveSupport::Subscriber
-  attach_to :doodle
-  detach_from :doodle
-
-  cattr_reader :events
-
-  def self.clear
-    @@events = []
-  end
-
-  def open_party(event)
+class PartySubscriber < TestSubscriber
+  def another_open_party(event)
+    event.payload["processing_class"] = self.class
     events << event
   end
 end
@@ -48,31 +42,77 @@ end
 class SubscriberTest < ActiveSupport::TestCase
   def setup
     TestSubscriber.clear
-    TestSubscriber2.clear
   end
 
   def test_attaches_subscribers
+    TestSubscriber.attach_to :doodle
+
     ActiveSupport::Notifications.instrument("open_party.doodle")
 
     assert_equal "open_party.doodle", TestSubscriber.events.first.name
+  ensure
+    TestSubscriber.detach_from :doodle
+  end
+
+  def test_attaches_subscribers_with_inherit_all_option
+    PartySubscriber.attach_to :doodle, inherit_all: true
+
+    ActiveSupport::Notifications.instrument("open_party.doodle")
+
+    assert_equal "open_party.doodle", PartySubscriber.events.first.name
+  ensure
+    PartySubscriber.detach_from :doodle
+  end
+
+  def test_attaches_subscribers_with_inherit_all_option_replaces_original_behaviour
+    PartySubscriber.attach_to :doodle, inherit_all: true
+
+    ActiveSupport::Notifications.instrument("another_open_party.doodle")
+
+    assert_equal 1, PartySubscriber.events.size
+
+    event = PartySubscriber.events.first
+    assert_equal "another_open_party.doodle", event.name
+    assert_equal PartySubscriber, event.payload.fetch("processing_class")
+  ensure
+    PartySubscriber.detach_from :doodle
   end
 
   def test_attaches_only_one_subscriber
+    TestSubscriber.attach_to :doodle
+
     ActiveSupport::Notifications.instrument("open_party.doodle")
 
     assert_equal 1, TestSubscriber.events.size
+  ensure
+    TestSubscriber.detach_from :doodle
   end
 
   def test_does_not_attach_private_methods
+    TestSubscriber.attach_to :doodle
+
     ActiveSupport::Notifications.instrument("private_party.doodle")
 
+    assert_equal [], TestSubscriber.events
+  ensure
+    TestSubscriber.detach_from :doodle
+  end
+
+  def test_detaches_subscribers
+    TestSubscriber.attach_to :doodle
+    TestSubscriber.detach_from :doodle
+
+    ActiveSupport::Notifications.instrument("open_party.doodle")
+
     assert_equal [], TestSubscriber.events
   end
 
-  def test_detaches_subscribers
+  def test_detaches_subscribers_from_inherited_methods
+    PartySubscriber.attach_to :doodle
+    PartySubscriber.detach_from :doodle
+
     ActiveSupport::Notifications.instrument("open_party.doodle")
 
-    assert_equal [], TestSubscriber2.events
-    assert_equal 1, TestSubscriber.events.size
+    assert_equal [], TestSubscriber.events
   end
 end