Fix incorrectly appended square brackets to a multiple select box

If an explicit name has been given and it already ends with "[]"

Before:

    select(:category, [], {}, multiple: true, name: "post[category][]")
    # => <select name="post[category][][]" ...>

After:

    select(:category, [], {}, multiple: true, name: "post[category][]")
    # => <select name="post[category][]" ...>

1 files changed, 8 insertions, 0 deletions

diff --git a/actionpack/test/template/form_options_helper_test.rb b/actionpack/test/template/form_options_helper_test.rb
index 04cdd068c8..29d63d9653 100644
--- a/actionpack/test/template/form_options_helper_test.rb
+++ b/actionpack/test/template/form_options_helper_test.rb
@@ -575,6 +575,14 @@ class FormOptionsHelperTest < ActionView::TestCase
     )
   end
 
+  def test_select_with_multiple_and_with_explicit_name_ending_with_brackets
+    output_buffer =  select(:post, :category, [], {include_hidden: false}, multiple: true, name: 'post[category][]')
+    assert_dom_equal(
+      "<select multiple=\"multiple\" id=\"post_category\" name=\"post[category][]\"></select>",
+      output_buffer
+    )
+  end
+
   def test_select_with_multiple_and_disabled_to_add_disabled_hidden_input
     output_buffer =  select(:post, :category, "", {}, :multiple => true, :disabled => true)
     assert_dom_equal(