Create a deprecation behavior that triggers a notification for deprecation notices, and make the behaviors independent of the environment names.

* In Rails 2.3 apps being upgraded, you will need to add the deprecation
  configuration to each of your environments. Failing to do so will
  result in the same behavior as Rails 2.3, but with an outputted warning
  to provide information on how to set up the setting.
* New Rails 3 applications generate the setting
* The notification style will send deprecation notices using
  ActiveSupport::Notifications. Third-party tools can listen in to
  these notifications to provide a streamlined view of the
  deprecation notices occurring in your app.
* The payload in the notification is the deprecation warning itself
  as well as the callstack from the point that triggered the
  notification.

activesupport/lib/active_support/deprecation/behaviors.rb

@@ -1,28 +1,27 @@
+require "active_support/notifications"
+
 module ActiveSupport
   module Deprecation
     class << self
-      # Behavior is a block that takes a message argument.
-      attr_writer :behavior
-
       # Whether to print a backtrace along with the warning.
       attr_accessor :debug
 
       def behavior
-        @behavior ||= default_behavior
+        @behavior ||= DEFAULT_BEHAVIORS[:stderr]
       end
 
-      def default_behavior
-        Deprecation::DEFAULT_BEHAVIORS[defined?(Rails.env) ? Rails.env.to_s : 'test']
+      def behavior=(behavior)
+        @behavior = DEFAULT_BEHAVIORS[behavior] || behavior
       end
     end
 
-    # Default warning behaviors per Rails.env. Ignored in production.
+    # Default warning behaviors per Rails.env.
     DEFAULT_BEHAVIORS = {
-      'test' => Proc.new { |message, callstack|
+      :stderr => Proc.new { |message, callstack|
          $stderr.puts(message)
          $stderr.puts callstack.join("\n  ") if debug
        },
-      'development' => Proc.new { |message, callstack|
+      :log => Proc.new { |message, callstack|
          logger =
            if defined?(Rails) && Rails.logger
              Rails.logger
@@ -32,6 +31,10 @@ module ActiveSupport
            end
          logger.warn message
          logger.debug callstack.join("\n  ") if debug
+       },
+       :notify => Proc.new { |message, callstack|
+          ActiveSupport::Notifications.instrument("deprecation.rails",
+            :message => message, :callstack => callstack)
        }
     }
   end

activesupport/lib/active_support/railtie.rb

@@ -12,6 +12,34 @@ module ActiveSupport
       require 'active_support/whiny_nil' if app.config.whiny_nils
     end
 
+    initializer "active_support.deprecation_behavior" do |app|
+      if deprecation = app.config.active_support.deprecation
+        ActiveSupport::Deprecation.behavior = deprecation
+      else
+        defaults = {"development" => :log,
+                    "production"  => :notify,
+                    "test"        => :stderr}
+
+        env = Rails.env
+
+        if defaults.key?(env)
+          msg = "You did not specify how you would like Rails to report " \
+                "deprecation notices for your #{env} environment, please " \
+                "set it to :#{defaults[env]} at config/environments/#{env}.rb"
+
+          warn msg
+          ActiveSupport::Deprecation.behavior = defaults[env]
+        else
+          msg = "You did not specify how you would like Rails to report " \
+                "deprecation notices for your #{env} environment, please " \
+                "set it to :log, :notify or :stderr at config/environments/#{env}.rb"
+
+          warn msg
+          ActiveSupport::Deprecation.behavior = :stderr
+        end
+      end
+    end
+
     # Sets the default value for Time.zone
     # If assigned value cannot be matched to a TimeZone, an exception will be raised.
     initializer "active_support.initialize_time_zone" do |app|

railties/lib/rails/generators/rails/app/templates/config/environments/development.rb.tt

@@ -16,4 +16,7 @@
 
   # Don't care if the mailer can't send
   config.action_mailer.raise_delivery_errors = false
+
+  # Print deprecation notices to the Rails logger
+  config.active_support.deprecation = :log
 end

railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt

@@ -43,4 +43,7 @@
   # Enable locale fallbacks for I18n (makes lookups for any locale fall back to
   # the I18n.default_locale when a translation can not be found)
   config.i18n.fallbacks = true
+
+  # Send deprecation notices to registered listeners
+  config.active_support.deprecation = :notification
 end

railties/lib/rails/generators/rails/app/templates/config/environments/test.rb.tt

@@ -29,4 +29,7 @@
   # This is necessary if your schema can't be completely dumped by the schema dumper,
   # like if you have constraints or database-specific column types
   # config.active_record.schema_format = :sql
+
+  # Print deprecation notices to the stderr
+  config.active_support.deprecation = :stderr
 end

railties/test/application/url_generation_test.rb

@@ -16,6 +16,7 @@ module ApplicationTests
       class MyApp < Rails::Application
         config.secret_token = "3b7cd727ee24e8444053437c36cc66c4"
         config.session_store :cookie_store, :key => "_myapp_session"
+        config.active_support.deprecation = :log
       end
 
       MyApp.initialize!

railties/test/isolation/abstract_unit.rb

@@ -100,7 +100,7 @@ module TestHelpers
         end
       end
 
-      add_to_config 'config.secret_token = "3b7cd727ee24e8444053437c36cc66c4"; config.session_store :cookie_store, :key => "_myapp_session"'
+      add_to_config 'config.secret_token = "3b7cd727ee24e8444053437c36cc66c4"; config.session_store :cookie_store, :key => "_myapp_session"; config.active_support.deprecation = :log'
     end
 
     def make_basic_app
@@ -110,6 +110,7 @@ module TestHelpers
       app = Class.new(Rails::Application)
       app.config.secret_token = "3b7cd727ee24e8444053437c36cc66c4"
       app.config.session_store :cookie_store, :key => "_myapp_session"
+      app.config.active_support.deprecation = :log
 
       yield app if block_given?
       app.initialize!