defining a named_scope which overwrites an existing method is now allowed we just log a warning.

This was motivated by the fact that :open is defined on all classes
as such the named_scope "open" can never be used, without hacking
ActiveRecord with an "undef_method" [#4083 state:resolved]

Signed-off-by: wycats <wycats@gmail.com>

activerecord/lib/active_record/named_scope.rb

@@ -102,7 +102,8 @@ module ActiveRecord
         name = name.to_sym
 
         if !scopes[name] && respond_to?(name, true)
-          raise ArgumentError, "Cannot define scope :#{name} because #{self.name}.#{name} method already exists."
+          logger.warn "Creating scope :#{name}. " \
+                      "Overwriting existing method #{self.name}.#{name}."
         end
 
         scopes[name] = lambda do |parent_scope, *args|

activerecord/test/cases/named_scope_test.rb

@@ -371,8 +371,21 @@ class NamedScopeTest < ActiveRecord::TestCase
   end
 
   def test_named_scopes_with_reserved_names
-    [:where, :with_scope].each do |protected_method|
-      assert_raises(ArgumentError) { Topic.scope protected_method }
+    class << Topic
+      def public_method; end
+      public :public_method
+      
+      def protected_method; end
+      protected :protected_method
+      
+      def private_method; end
+      private :private_method
+    end
+    
+    [:public_method, :protected_method, :private_method].each do |reserved_method|
+      assert Topic.respond_to?(reserved_method, true)
+      ActiveRecord::Base.logger.expects(:warn)
+      Topic.scope(reserved_method)
     end
   end