Make sure named_scope names are not used as method names already

activerecord/lib/active_record/named_scope.rb

@@ -99,6 +99,11 @@ module ActiveRecord
       #   assert_equal expected_options, Shirt.colored('red').proxy_options
       def named_scope(name, options = {}, &block)
         name = name.to_sym
+
+        if !scopes[name] && respond_to?(name, true)
+          raise ArgumentError, "Cannot define named_scope :#{name} because #{self.name}.#{name} method already exists."
+        end
+
         scopes[name] = lambda do |parent_scope, *args|
           Scope.new(parent_scope, case options
             when Hash

activerecord/test/cases/named_scope_test.rb

@@ -150,13 +150,13 @@ class NamedScopeTest < ActiveRecord::TestCase
   end
 
   def test_named_scopes_honor_current_scopes_from_when_defined
-    assert !Post.ranked_by_comments.limit(5).empty?
-    assert !authors(:david).posts.ranked_by_comments.limit(5).empty?
-    assert_not_equal Post.ranked_by_comments.limit(5), authors(:david).posts.ranked_by_comments.limit(5)
+    assert !Post.ranked_by_comments.limit_by(5).empty?
+    assert !authors(:david).posts.ranked_by_comments.limit_by(5).empty?
+    assert_not_equal Post.ranked_by_comments.limit_by(5), authors(:david).posts.ranked_by_comments.limit_by(5)
     assert_not_equal Post.top(5), authors(:david).posts.top(5)
     # Oracle sometimes sorts differently if WHERE condition is changed
-    assert_equal authors(:david).posts.ranked_by_comments.limit(5).sort_by(&:id), authors(:david).posts.top(5).sort_by(&:id)
-    assert_equal Post.ranked_by_comments.limit(5), Post.top(5)
+    assert_equal authors(:david).posts.ranked_by_comments.limit_by(5).sort_by(&:id), authors(:david).posts.top(5).sort_by(&:id)
+    assert_equal Post.ranked_by_comments.limit_by(5), Post.top(5)
   end
 
   def test_active_records_have_scope_named__all__
@@ -374,6 +374,12 @@ class NamedScopeTest < ActiveRecord::TestCase
       Comment.for_first_post.for_first_author.all
     end
   end
+
+  def test_named_scopes_with_reserved_names
+    [:where, :with_scope].each do |protected_method|
+      assert_raises(ArgumentError) { Topic.named_scope protected_method }
+    end
+  end
 end
 
 class DynamicScopeMatchTest < ActiveRecord::TestCase

activerecord/test/models/post.rb

@@ -1,7 +1,7 @@
 class Post < ActiveRecord::Base
   named_scope :containing_the_letter_a, :conditions => "body LIKE '%a%'"
   named_scope :ranked_by_comments, :order => "comments_count DESC"
-  named_scope :limit, lambda {|limit| {:limit => limit} }
+  named_scope :limit_by, lambda {|limit| {:limit => limit} }
   named_scope :with_authors_at_address, lambda { |address| {
       :conditions => [ 'authors.author_address_id = ?', address.id ],
       :joins => 'JOIN authors ON authors.id = posts.author_id'
@@ -73,7 +73,7 @@ class Post < ActiveRecord::Base
   has_many :impatient_people, :through => :skimmers, :source => :person
 
   def self.top(limit)
-    ranked_by_comments.limit(limit)
+    ranked_by_comments.limit_by(limit)
   end
 
   def self.reset_log