Thought of a rails feature and about to submit it. I can haz feedback?

rails_feature.diff

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 3b905b1..2bc0653 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,28 @@
+*   Exceptions classes responding to `#to_proc` can be passed to `rescue_from` in
+    controllers without an handler. Exceptions can be extended to reply by themselves
+    to errors.
+
+        class JediError < StandardError
+          def to_proc
+            Proc.new do |e|
+              redirect_to :root, notice: "Error: #{e.message}"
+            end
+          end
+        end
+
+        class DroidsController < ApplicationController
+          rescue_from MyError
+
+          def index
+            raise JediError.new("These are not the droids you're looking for.")
+          end
+        end
+
+    I know of no exceptions classes that respond to `#to_proc` so breaking existing APIs
+    shouldn't be a concern.
+
+    *Arnaud Rouyer*
+
 *   Add Integer#positive? and Integer#negative? query methods in the vein of Fixnum#zero?
     This makes it nicer to do things like bunch_of_numbers.select(&:positive?).
 
diff --git a/activesupport/lib/active_support/rescuable.rb b/activesupport/lib/active_support/rescuable.rb
index fcf5553..739cbda 100644
--- a/activesupport/lib/active_support/rescuable.rb
+++ b/activesupport/lib/active_support/rescuable.rb
@@ -55,7 +55,11 @@ module ActiveSupport
           if block_given?
             options[:with] = block
           else
-            raise ArgumentError, "Need a handler. Supply an options hash that has a :with key as the last argument."
+            unless klasses.select do |klass|
+              klass.is_a?(Module) && klass.method_defined?(:to_proc)
+            end.length == klasses.length
+              raise ArgumentError, "Need a handler. Supply an options hash that has a :with key as the last argument."
+            end
           end
         end
 
@@ -104,6 +108,7 @@ module ActiveSupport
         klass === exception if klass
       end
 
+      rescuer = exception.to_proc if rescuer.is_a?(NilClass) && exception.respond_to?(:to_proc)
       case rescuer
       when Symbol
         method(rescuer)
diff --git a/activesupport/test/rescuable_test.rb b/activesupport/test/rescuable_test.rb
index bd43ad0..2ef2001 100644
--- a/activesupport/test/rescuable_test.rb
+++ b/activesupport/test/rescuable_test.rb
@@ -18,6 +18,14 @@ module WeirdError
   end
 end
 
+class AsgardError < StandardError
+  def to_proc
+    Proc.new do |e|
+      @result = e.message
+    end
+  end
+end
+
 class Stargate
   attr_accessor :result
 
@@ -39,6 +47,8 @@ class Stargate
     @result = 'weird'
   end
 
+  rescue_from AsgardError
+
   def dispatch(method)
     send(method)
   rescue Exception => e
@@ -67,6 +77,10 @@ class Stargate
     end
   end
 
+  def call_asgard
+    raise AsgardError.new("asgard?")
+  end
+
   def sos
     @result = 'killed'
   end
@@ -116,14 +130,19 @@ class RescuableTest < ActiveSupport::TestCase
     assert_equal 'weird', @stargate.result
   end
 
+  def test_rescue_from_with_self_replying_exception
+    @stargate.dispatch :call_asgard
+    assert_equal 'asgard?', @stargate.result
+  end
+
   def test_rescues_defined_later_are_added_at_end_of_the_rescue_handlers_array
-    expected = ["WraithAttack", "WraithAttack", "NuclearExplosion", "MadRonon", "WeirdError"]
+    expected = ["WraithAttack", "WraithAttack", "NuclearExplosion", "MadRonon", "WeirdError", "AsgardError"]
     result = @stargate.send(:rescue_handlers).collect(&:first)
     assert_equal expected, result
   end
 
   def test_children_should_inherit_rescue_definitions_from_parents_and_child_rescue_should_be_appended
-    expected = ["WraithAttack", "WraithAttack", "NuclearExplosion", "MadRonon", "WeirdError", "CoolError"]
+    expected = ["WraithAttack", "WraithAttack", "NuclearExplosion", "MadRonon", "WeirdError", "AsgardError", "CoolError"]
     result = @cool_stargate.send(:rescue_handlers).collect(&:first)
     assert_equal expected, result
   end