`validates_confirmation_of` does not override writer methods.

activemodel/CHANGELOG.md

@@ -1,5 +1,20 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   `validates_confirmation_of` does not override writer methods for
+    the confirmation attribute if no reader is defined.
+
+    Example:
+
+        class Blog
+            def title=(new_title)
+              @title = new_title.downcase
+            end
+
+            # previously this would override the setter above.
+            validates_confirmation_of :title
+        end
+
+    *Yves Senn*
 
 ## Rails 4.0.0.beta1 (February 25, 2013) ##
 

activemodel/lib/active_model/validations/confirmation.rb

@@ -10,9 +10,13 @@ module ActiveModel
       end
 
       def setup(klass)
-        klass.send(:attr_accessor, *attributes.map do |attribute|
+        klass.send(:attr_reader, *attributes.map do |attribute|
           :"#{attribute}_confirmation" unless klass.method_defined?(:"#{attribute}_confirmation")
         end.compact)
+
+        klass.send(:attr_writer, *attributes.map do |attribute|
+          :"#{attribute}_confirmation" unless klass.method_defined?(:"#{attribute}_confirmation=")
+        end.compact)
       end
     end
 

activemodel/test/cases/validations/confirmation_validation_test.rb

@@ -71,4 +71,35 @@ class ConfirmationValidationTest < ActiveModel::TestCase
     I18n.backend = @old_backend
   end
 
+  test "does not override confirmation reader if present" do
+    klass = Class.new do
+      include ActiveModel::Validations
+
+      def title_confirmation
+        "expected title"
+      end
+
+      validates_confirmation_of :title
+    end
+
+    assert_equal "expected title", klass.new.title_confirmation,
+     "confirmation validation should not override the reader"
+  end
+
+  test "does not override confirmation writer if present" do
+    klass = Class.new do
+      include ActiveModel::Validations
+
+      def title_confirmation=(value)
+        @title_confirmation = "expected title"
+      end
+
+      validates_confirmation_of :title
+    end
+
+    model = klass.new
+    model.title_confirmation = "new title"
+    assert_equal "expected title", model.title_confirmation,
+     "confirmation validation should not override the writer"
+  end
 end