allows custom field_error_proc

lib/formtastic/helpers/form_helper.rb

@@ -58,6 +58,12 @@ module FormHelper
       @@default_form_class = 'formtastic'
       mattr_accessor :default_form_class
 
+      # Allows to set a custom field_error_proc wrapper. By default this wrapper
+      # is disabled since `formtastic` already adds an error class to the LI tag
+      # containing the input. Change this from `config/initializers/formtastic.rb`.
+      @@field_error_proc = proc { |html_tag, instance_tag| html_tag }
+      mattr_accessor :field_error_proc
+
       # Wrapper around Rails' own `form_for` helper to set the `:builder` option to
       # `Formtastic::FormBuilder` and to set some class names on the `<form>` tag such as
       # `formtastic` and the downcased and underscored model name (eg `post`).
@@ -178,17 +184,9 @@ def semantic_fields_for(record_name, record_object = nil, options = {}, &block)
 
       protected
 
-      # Override the default ActiveRecordHelper behaviour of wrapping the input.
-      # This gets taken care of semantically by adding an error class to the LI tag
-      # containing the input.
-      # @private
-      FIELD_ERROR_PROC = proc do |html_tag, instance_tag|
-        html_tag
-      end
-
       def with_custom_field_error_proc(&block)
         default_field_error_proc = ::ActionView::Base.field_error_proc
-        ::ActionView::Base.field_error_proc = FIELD_ERROR_PROC
+        ::ActionView::Base.field_error_proc = @@field_error_proc
         yield
       ensure
         ::ActionView::Base.field_error_proc = default_field_error_proc

spec/helpers/form_helper_spec.rb

@@ -135,6 +135,29 @@
       end
     end
 
+    describe ActionView::Base.field_error_proc do
+      it 'is set to no-op wrapper by default' do
+        semantic_form_for(@new_post, :url => '/hello') do |builder|
+          ::ActionView::Base.field_error_proc.call("html").should == "html"
+        end
+      end
+
+      it 'is set to the configured custom field_error_proc' do
+        field_error_proc = mock()
+        Formtastic::Helpers::FormHelper.field_error_proc = field_error_proc
+        semantic_form_for(@new_post, :url => '/hello') do |builder|
+          ::ActionView::Base.field_error_proc.should == field_error_proc
+        end
+      end
+
+      it 'is restored to its original value after the form is rendered' do
+        lambda do 
+          Formtastic::Helpers::FormHelper.field_error_proc = proc {}
+          semantic_form_for(@new_post, :url => '/hello') { |builder| }
+        end.should_not change(::ActionView::Base, :field_error_proc)
+      end
+    end 
+
     describe "with :builder option" do
       it "yields an instance of the given builder" do
         class MyAwesomeCustomBuilder < Formtastic::FormBuilder