Bring back support for passing a callable object to the default_scope macro. You can also just use a block.

activerecord/CHANGELOG

@@ -1,5 +1,16 @@
 *Rails 3.1.0 (unreleased)*
 
+* default_scope can take a block, lambda, or any other object which responds to `call` for lazy
+  evaluation:
+
+    default_scope { ... }
+    default_scope lambda { ... }
+    default_scope method(:foo)
+
+  This feature was originally implemented by Tim Morgan, but was then removed in favour of
+  defining a 'default_scope' class method, but has now been added back in by Jon Leighton.
+  The relevant lighthouse ticket is #1812.
+
 * Default scopes are now evaluated at the latest possible moment, to avoid problems where
   scopes would be created which would implicitly contain the default scope, which would then
   be impossible to get rid of via Model.unscoped.

activerecord/lib/active_record/base.rb

@@ -1196,6 +1196,15 @@ MSG
         #   Article.new.published    # => true
         #   Article.create.published # => true
         #
+        # You can also use <tt>default_scope</tt> with a block, in order to have it lazily evaluated:
+        #
+        #   class Article < ActiveRecord::Base
+        #     default_scope { where(:published_at => Time.now - 1.week) }
+        #   end
+        #
+        # (You can also pass any object which responds to <tt>call</tt> to the <tt>default_scope</tt>
+        # macro, and it will be called when building the default scope.)
+        #
         # If you need to do more complex things with a default scope, you can alternatively
         # define it as a class method:
         #
@@ -1233,6 +1242,7 @@ end
             WARN
           end
 
+          scope = Proc.new if block_given?
           self.default_scopes = default_scopes.dup << scope
         end
 
@@ -1245,6 +1255,8 @@ end
             default_scopes.inject(relation) do |default_scope, scope|
               if scope.is_a?(Hash)
                 default_scope.apply_finder_options(scope)
+              elsif !scope.is_a?(Relation) && scope.respond_to?(:call)
+                default_scope.merge(scope.call)
               else
                 default_scope.merge(scope)
               end

activerecord/test/cases/relation_scoping_test.rb

@@ -312,6 +312,18 @@ class DefaultScopingTest < ActiveRecord::TestCase
     assert_equal [developers(:david).becomes(ClassMethodDeveloperCalledDavid)], ClassMethodDeveloperCalledDavid.all
   end
 
+  def test_default_scope_with_lambda
+    assert_equal [developers(:david).becomes(LazyLambdaDeveloperCalledDavid)], LazyLambdaDeveloperCalledDavid.all
+  end
+
+  def test_default_scope_with_block
+    assert_equal [developers(:david).becomes(LazyBlockDeveloperCalledDavid)], LazyBlockDeveloperCalledDavid.all
+  end
+
+  def test_default_scope_with_callable
+    assert_equal [developers(:david).becomes(CallableDeveloperCalledDavid)], CallableDeveloperCalledDavid.all
+  end
+
   def test_default_scope_is_unscoped_on_find
     assert_equal 1, DeveloperCalledDavid.count
     assert_equal 11, DeveloperCalledDavid.unscoped.count

activerecord/test/models/developer.rb

@@ -1,3 +1,5 @@
+require 'ostruct'
+
 module DeveloperProjectsAssociationExtension
   def find_most_recent
     find(:first, :order => "id DESC")
@@ -102,6 +104,21 @@ class DeveloperCalledDavid < ActiveRecord::Base
   default_scope where("name = 'David'")
 end
 
+class LazyLambdaDeveloperCalledDavid < ActiveRecord::Base
+  self.table_name = 'developers'
+  default_scope lambda { where(:name => 'David') }
+end
+
+class LazyBlockDeveloperCalledDavid < ActiveRecord::Base
+  self.table_name = 'developers'
+  default_scope { where(:name => 'David') }
+end
+
+class CallableDeveloperCalledDavid < ActiveRecord::Base
+  self.table_name = 'developers'
+  default_scope OpenStruct.new(:call => where(:name => 'David'))
+end
+
 class ClassMethodDeveloperCalledDavid < ActiveRecord::Base
   self.table_name = 'developers'