From b2672c739b9fe3a5b37249d899bdec9c3b9726cf Mon Sep 17 00:00:00 2001
From: Kasper Timm Hansen <kaspth@gmail.com>
Date: Sun, 18 Dec 2016 20:17:52 +0100
Subject: fields: support attributes not on model.

Ensure the support works like form_with.
---
 actionview/lib/action_view/helpers/form_helper.rb  |  2 ++
 .../test/template/form_helper/form_with_test.rb    | 35 ++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/actionview/lib/action_view/helpers/form_helper.rb b/actionview/lib/action_view/helpers/form_helper.rb
index ac4b4196cd..a66a56d441 100644
--- a/actionview/lib/action_view/helpers/form_helper.rb
+++ b/actionview/lib/action_view/helpers/form_helper.rb
@@ -1037,6 +1037,7 @@ module ActionView
       # to work with an object as a base, like
       # FormOptionHelper#collection_select and DateHelper#datetime_select.
       def fields(scope = nil, model: nil, **options, &block)
+        options[:allow_method_names_outside_object] = true
         options[:skip_default_ids] = true
 
         if model
@@ -1945,6 +1946,7 @@ module ActionView
 
       # See the docs for the <tt>ActionView::FormHelper.fields</tt> helper method.
       def fields(scope = nil, model: nil, **options, &block)
+        options[:allow_method_names_outside_object] = true
         options[:skip_default_ids] = true
 
         convert_to_legacy_options(options)
diff --git a/actionview/test/template/form_helper/form_with_test.rb b/actionview/test/template/form_helper/form_with_test.rb
index 96b797992f..dd0883e071 100644
--- a/actionview/test/template/form_helper/form_with_test.rb
+++ b/actionview/test/template/form_helper/form_with_test.rb
@@ -935,6 +935,41 @@ class FormWithActsLikeFormForTest < FormWithTest
     end
   end
 
+  def test_fields_with_attributes_not_on_model
+    form_with(model: @post) do |f|
+      concat f.fields(:comment) { |c|
+        concat c.text_field :dont_exist_on_model
+      }
+    end
+
+    expected = whole_form("/posts/123", method: :patch) do
+      '<input type="text" name="post[comment][dont_exist_on_model]">'
+    end
+
+    assert_dom_equal expected, output_buffer
+  end
+
+  def test_fields_with_attributes_not_on_model_deep_nested
+    @comment.save
+    form_with(scope: :posts) do |f|
+      f.fields("post[]", model: @post) do |f2|
+        f2.text_field(:id)
+        @post.comments.each do |comment|
+          concat f2.fields("comment[]", model: comment) { |c|
+            concat c.text_field(:dont_exist_on_model)
+          }
+        end
+      end
+    end
+
+    expected = whole_form do
+      '<input name="posts[post][0][comment][1][dont_exist_on_model]" type="text">'
+    end
+
+    assert_dom_equal expected, output_buffer
+  end
+
+
   def test_nested_fields
     @comment.body = "Hello World"
     form_with(model: @post) do |f|
-- 
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