Refactored delegation of error message generation

Moved delegation to ActiveModel::Errors#generate_message to
default_error_message and implemented a spec for it.

lib/shoulda/matchers/active_model/allow_value_matcher.rb

@@ -142,15 +142,12 @@ module Shoulda # :nodoc:
         end
 
         def default_attribute_message
-          if @instance.errors.respond_to?(:generate_message)
-            @instance.errors.generate_message(@attribute, @options[:expected_message])
-          else
-            default_error_message(
-              @options[:expected_message],
-              :model_name => model_name,
-              :attribute => @attribute
-            )
-          end
+          default_error_message(
+            @options[:expected_message],
+            :model_name => model_name,
+            :instance => @instance,
+            :attribute => @attribute
+          )
         end
 
         def model_name

lib/shoulda/matchers/active_model/helpers.rb

@@ -11,21 +11,30 @@ module Shoulda # :nodoc:
 
         # Helper method that determines the default error message used by Active
         # Record.  Works for both existing Rails 2.1 and Rails 2.2 with the newly
-        # introduced I18n module used for localization.
+        # introduced I18n module used for localization. Use with Rails 3.0 and
+        # up will delegate to ActiveModel::Errors.generate_error if a model
+        # instance is given.
         #
         #   default_error_message(:blank)
         #   default_error_message(:too_short, :count => 5)
         #   default_error_message(:too_long, :count => 60)
         #   default_error_message(:blank, :model_name => 'user', :attribute => 'name')
+        #   default_error_message(:blank, :instance => #<Model>, :attribute => 'name')
         def default_error_message(key, options = {})
           model_name = options.delete(:model_name)
           attribute = options.delete(:attribute)
-          default_translation = [ :"activerecord.errors.models.#{model_name}.#{key}",
-                                  :"activerecord.errors.messages.#{key}",
-                                  :"errors.attributes.#{attribute}.#{key}",
-                                  :"errors.messages.#{key}" ]
-          I18n.translate(:"activerecord.errors.models.#{model_name}.attributes.#{attribute}.#{key}",
-            { :default => default_translation }.merge(options))
+          instance = options.delete(:instance)
+
+          if instance && instance.errors.respond_to?(:generate_message)
+            instance.errors.generate_message(attribute.to_sym, key, {})
+          else
+            default_translation = [ :"activerecord.errors.models.#{model_name}.#{key}",
+                                    :"activerecord.errors.messages.#{key}",
+                                    :"errors.attributes.#{attribute}.#{key}",
+                                    :"errors.messages.#{key}" ]
+            I18n.translate(:"activerecord.errors.models.#{model_name}.attributes.#{attribute}.#{key}",
+              { :default => default_translation }.merge(options))
+          end
         end
       end
     end

spec/shoulda/matchers/active_model/helpers_spec.rb

@@ -77,6 +77,21 @@ describe Shoulda::Matchers::ActiveModel::Helpers do
         end
       end
     end
+
+    if active_model_3_0?
+      context 'if ActiveModel::Errors.generate_message behavior has changed' do
+        subject { define_model(:divergent_example, :attr => :string) { validates_presence_of :attr }.new }
+
+        let(:message) { 'Oh snap. Behavior has diverged.' }
+
+        before(:each) do
+          store_translations
+          ActiveModel::Errors.any_instance.expects(:generate_message).with(:attr, :blank, {}).at_least_once.returns(message)
+        end
+
+        it { should validate_presence_of(:attr) }
+      end
+    end
   end
 
   def assert_presence_validation_has_correct_message

spec/support/active_model_versions.rb

@@ -1,4 +1,8 @@
 RSpec.configure do |c|
+  def active_model_3_0?
+    ::ActiveModel::VERSION::MAJOR == 3 && ::ActiveModel::VERSION::MINOR >= 0
+  end
+
   def active_model_3_1?
     ::ActiveModel::VERSION::MAJOR == 3 && ::ActiveModel::VERSION::MINOR >= 1
   end