Merge pull request #8912 from senny/8879_association_empty_method

`CollectionAssociation#empty?` respects newly builded records

activerecord/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
 
+*   Collection associations `#empty?` always respects builded records.
+    Fix #8879.
+
+    Example:
+
+        widget = Widget.new
+        widget.things.build
+        widget.things.empty? # => false
+
+    *Yves Senn*
+
 *   Remove support for parsing YAML parameters from request.
 
     *Aaron Patterson*

activerecord/lib/active_record/associations/collection_association.rb

@@ -273,7 +273,7 @@ def empty?
         if loaded? || options[:counter_sql]
           size.zero?
         else
-          !scope.exists?
+          @target.blank? && !scope.exists?
         end
       end
 

activerecord/test/cases/associations/has_many_associations_test.rb

@@ -625,6 +625,13 @@ def test_collection_size_after_building
     assert_equal 3, company.clients_of_firm.size
   end
 
+  def test_collection_not_empty_after_building
+    company = companies(:first_firm)
+    assert_predicate company.contracts, :empty?
+    company.contracts.build
+    assert_not_predicate company.contracts, :empty?
+  end
+
   def test_collection_size_twice_for_regressions
     post = posts(:thinking)
     assert_equal 0, post.readers.size