form_for - fix :namespace and :as options clash

:as option should not overwrite :namespace option when
generating html id attribute of the form element. id should be prefixed
by specified namespace even if :as option is present

Add test case showing the issue and code fixing it

1 files changed, 12 insertions, 0 deletions

diff --git a/actionview/test/template/form_helper_test.rb b/actionview/test/template/form_helper_test.rb
index 8cca43d7ca..944884c9dd 100644
--- a/actionview/test/template/form_helper_test.rb
+++ b/actionview/test/template/form_helper_test.rb
@@ -1681,6 +1681,18 @@ class FormHelperTest < ActionView::TestCase
     assert_dom_equal expected, output_buffer
   end
 
+  def test_form_for_with_namespace_and_as_option
+    form_for(@post, namespace: 'namespace', as: 'custom_name') do |f|
+      concat f.text_field(:title)
+    end
+
+    expected = whole_form('/posts/123', 'namespace_edit_custom_name', 'edit_custom_name', method: 'patch') do
+      "<input id='namespace_custom_name_title' name='custom_name[title]' type='text' value='Hello World' />"
+    end
+
+    assert_dom_equal expected, output_buffer
+  end
+
   def test_two_form_for_with_namespace
     form_for(@post, namespace: 'namespace_1') do |f|
       concat f.label(:title)