Allow passing record being validated to error message generator

- Pass object to I18n helper so that when calling message proc, it will
  pass that object as argument to the proc and we can generate custom
  error messages based on current record being validated.
- Based on https://github.com/rails/rails/issues/856.

[Łukasz Bandzarewicz, Prathamesh Sonpatki]

3 files changed, 15 insertions, 1 deletions

diff --git a/activemodel/CHANGELOG.md b/activemodel/CHANGELOG.md
index fb7ab5cb40..7be8b2e522 100644
--- a/activemodel/CHANGELOG.md
+++ b/activemodel/CHANGELOG.md
@@ -1,3 +1,8 @@
+*   Allow passing record being validated to the message proc to generate
+    customized error messages for that object using I18n helper.
+
+    *Prathamesh Sonpatki*
+
 ## Rails 5.0.0.beta3 (February 24, 2016) ##
 
 *   No changes.
diff --git a/activemodel/lib/active_model/errors.rb b/activemodel/lib/active_model/errors.rb
index 836201535f..d925960b41 100644
--- a/activemodel/lib/active_model/errors.rb
+++ b/activemodel/lib/active_model/errors.rb
@@ -486,7 +486,8 @@ module ActiveModel
         default: defaults,
         model: @base.model_name.human,
         attribute: @base.class.human_attribute_name(attribute),
-        value: value
+        value: value,
+        object: @base
       }.merge!(options)
 
       I18n.translate(key, options)
diff --git a/activemodel/test/cases/validations_test.rb b/activemodel/test/cases/validations_test.rb
index f0317ad219..18b8d9e4af 100644
--- a/activemodel/test/cases/validations_test.rb
+++ b/activemodel/test/cases/validations_test.rb
@@ -444,4 +444,12 @@ class ValidationsTest < ActiveModel::TestCase
     assert topic.invalid?
     assert duped.valid?
   end
+
+  def test_validation_with_message_as_proc_that_takes_a_record_as_a_parameter
+    Topic.validates_presence_of(:title, message: proc { |record| "You have failed me for the last time, #{record.author_name}." })
+
+    t = Topic.new(author_name: 'Admiral')
+    assert t.invalid?
+    assert_equal ["You have failed me for the last time, Admiral."], t.errors[:title]
+  end
 end