collection_radio_buttons doesn't work in Rails 5

[kyamaguchi]

When I use collection_radio_buttons on the form and submit it, I get an error and a blank page on the browser.
(Rails version: commit 1f8cc53 , Date: Sun Nov 8 17:40:46 2015 -0800)

The issue #18303 might be related.

In app/views/posts/_form.html.erb, I have

  <div class="field">
    <%= f.label :choice %><br>
    <%= f.collection_radio_buttons :choice, {choice1: 'Choice 1', choice2: 'Choice 2'}.map{|k,v| OpenStruct.new(value: v, label: k) }, :value, :label %>
  </div>

HTML

  <div class="field">
    <label for="post_choice">Choice</label><br>
    <input type="radio" value="Choice 1" name="post[choice]" id="post_choice_choice_1" /><label for="post_choice_choice_1">choice1</label><input type="radio" value="Choice 2" name="post[choice]" id="post_choice_choice_2" /><label for="post_choice_choice_2">choice2</label><input type="hidden" name="post[choice][]" value="" />
  </div>

When I submit the form, I see the following error in log.

Started POST "/posts" for ::1 at 2015-11-09 15:01:12 +0900

ActionController::BadRequest (Invalid request parameters: expected Array (got String) for param `choice'):
  /gems/rack-c393176b0edf/lib/rack/query_parser.rb:93:in `normalize_params'
  /gems/rack-c393176b0edf/lib/rack/query_parser.rb:107:in `normalize_params'
  /gems/rack-c393176b0edf/lib/rack/query_parser.rb:67:in `block in parse_nested_query'
  /gems/rack-c393176b0edf/lib/rack/query_parser.rb:64:in `each'
  /gems/rack-c393176b0edf/lib/rack/query_parser.rb:64:in `parse_nested_query'
  /gems/rack-c393176b0edf/lib/rack/request.rb:458:in `parse_query'
  /gems/rack-c393176b0edf/lib/rack/request.rb:360:in `POST'
  /gems/rails-1f8cc53689ea/actionpack/lib/action_dispatch/http/request.rb:355:in `block (2 levels) in POST'
  /gems/rails-1f8cc53689ea/actionpack/lib/action_dispatch/http/parameters.rb:54:in `block in parse_formatted_parameters'
  /gems/rails-1f8cc53689ea/actionpack/lib/action_dispatch/http/parameters.rb:54:in `fetch'
  /gems/rails-1f8cc53689ea/actionpack/lib/action_dispatch/http/parameters.rb:54:in `parse_formatted_parameters'
  /gems/rails-1f8cc53689ea/actionpack/lib/action_dispatch/http/request.rb:354:in `block in POST'
  /gems/rack-c393176b0edf/lib/rack/request.rb:74:in `fetch'
  /gems/rack-c393176b0edf/lib/rack/request.rb:74:in `fetch_header'
  /gems/rails-1f8cc53689ea/actionpack/lib/action_dispatch/http/request.rb:353:in `POST'
  /gems/rails-1f8cc53689ea/actionpack/lib/action_dispatch/http/parameters.rb:26:in `parameters'
  /gems/rails-1f8cc53689ea/actionpack/lib/action_dispatch/http/filter_parameters.rb:35:in `filtered_parameters'
  /gems/rails-1f8cc53689ea/actionpack/lib/action_controller/metal/instrumentation.rb:21:in `process_action'
  /gems/rails-1f8cc53689ea/actionpack/lib/action_controller/metal/params_wrapper.rb:248:in `process_action'
  /gems/rails-1f8cc53689ea/activerecord/lib/active_record/railties/controller_runtime.rb:18:in `process_action'

In Gemfile, I have

gem 'rails', '5.0.0.alpha', github: 'rails/rails'
gem 'arel', github: 'rails/arel'
gem 'rack', '2.0.0.alpha', github: 'rack/rack'

In Gemfile.lock, I have

GIT
  remote: git://github.com/rack/rack.git
  revision: c393176b0edf3e5d06cabbb6eb9d9c7a07b2afa7
  specs:
    rack (2.0.0.alpha)
      json

GIT
  remote: git://github.com/rails/arel.git
  revision: 3c429c5d86e9e2201c2a35d934ca6a8911c18e69
  specs:
    arel (7.0.0.alpha)

GIT
  remote: git://github.com/rails/rails.git
  revision: 1f8cc53689ead6befbbb6d8d7436596270738ff3

---

I can work around with include_hidden: false option and it is OK in most cases.

  <div class="field">
    <%= f.label :choice %><br>
    <%= f.collection_radio_buttons :choice, {choice1: 'Choice 1', choice2: 'Choice 2'}.map{|k,v| OpenStruct.new(value: v, label: k) }, :value, :label, include_hidden: false %>
  </div>

And It is also OK with rails 4.2.4 and rack 1.6.4.

[rafaelfranca]

Can you please provide a sample application that reproduces the error?

[kyamaguchi]

Here is a sample app https://github.com/kyamaguchi/rails5_collection_radio_buttons .

You can start testing with visiting /posts and creating records.
I used ruby 2.2.2.

---

Snippet in the first comment was wrong.
.map{|k,v| OpenStruct.new(value: v, label: k) } should be .map{|k,v| OpenStruct.new(value: k, label: v) } .

[nathanpena]

I downloaded the sample app and was able to replicate the exact error log.

[al2o3cr]

This looks like a case of dehydration (too much DRY). In particular, this line makes the correct field for collection checkboxes (with the [], since many checkboxes can be checked simultaneously) but not for collection radio buttons (which are defined by only one being selectable at a time).

Would it make sense to delegate the task of naming the hidden field to CheckBoxBuilder and RadioButtonBuilder? It doesn't seem ideal, but neither does passing the value in to render_collection_for directly.

[prathamesh-sonpatki]

I think the hidden field should come before the actual fields. I tried to fix it here #22804