Problematic attribute names (open, format) to decorated rails objects (with draper gem) send to Kernel

[klyonrad]

I first reported this in the draper project but received no feedback, so I thought I'd share this here as well - for the rare case that someone else trips into this.

I ran into this very surprising issue back then. I added the attribute open to a model and then to the edit form of that model in a rails project that has draper and ransack installed.

---

Upon opening that edit form I saw an ArgumentError and the stack trace indicates that somehow the method open from open-uri got called.

The stack trace also included a monkey patch from the ransack gem so it was a bit of bad luck that I ran into this issue. They replaced the public_send call with send which is why this bug does not appear in a normal rails installation with draper.

So I played detective for way too long 🕵️. Then I saw it! We also use the decorates_assigned method in the culprit controller and the object that gets passed to the form is actually a Decorator object and not really the model.

So I am creating the bug report here as well so that maybe it can be evaluated if the monkey patch for the form helper method is still necessary.

Appendix

Problematic Draper behaviour

class SomeObject
  def open
    'false'
  end  
end
class SomeObjectDecorator
  delegate_all
end
SomeObject.new.send('open')
=> "false"
SomeObjectDecorator.new(SomeObject.new).send('open')
ArgumentError: wrong number of arguments (given 0, expected 1+)
from .../ruby-2.6.6/lib/ruby/2.6.0/open-uri.rb:29:in `open'

rails integration test

Personally, I tested this with draper 3.x and 4.x.

# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  # Activate the gem you are reporting the issue against.
  gem "rails", '~> 5.2'
  # Activate the gem you are reporting the issue against.
  gem "sqlite3"

  gem 'hamlit'
  gem 'discard' # loading/requiring ransack fails without this. No idea why.
  gem 'draper'
  gem 'ransack'
end

require "active_record"
require "rack/test"
require "action_controller/railtie"

class TestApp < Rails::Application
  config.root = __dir__
  # config.hosts << "example.org"
  config.session_store :cookie_store, key: "cookie_store_key"
  secrets.secret_key_base = "secret_key_base"

  config.logger = Logger.new($stdout)
  Rails.logger  = config.logger

  routes.draw do
    resources :comments
  end
end

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :comments, force: true do |t|
    t.string :open, default: 'false'
    t.string :author_name
  end
end

class Comment < ActiveRecord::Base
  include Draper::Decoratable
end

class CommentDecorator < Draper::Decorator
  delegate_all
end

class CommentsController < ActionController::Base
  include Rails.application.routes.url_helpers
  include Draper::DecoratesAssigned # grrr not working
  # decorates_assigned :comment

  def index
    render plain: "Home"
  end

  def edit
    @comment = Comment.find(params[:id]).decorate

    template = <<ERB
<%= form_for(@comment) do |f| %>
  <%= f.text_field :open %>
<% end %>
ERB
    render inline: template, layout: false
  end
end

require "minitest/autorun"

class BugTest < Minitest::Test
  include Rack::Test::Methods

  def test_smoke
    get "/comments"
    assert last_response.ok?
  end

  def test_returns_success
    comment = Comment.create!(open: 'true')
    get "/comments/#{comment.id}/edit"
    assert last_response.ok?
  end

  private

  def app
    Rails.application
  end
end

Stacktrace

test leads to

F, [2020-08-18T17:39:40.429260 #14860] FATAL -- : ActionView::Template::Error (wrong number of arguments (given 0, expected 1..3)):
F, [2020-08-18T17:39:40.429340 #14860] FATAL -- :     1: <%= form_for(@comment) do |f| %>
    2:   <%= f.text_field :open %>
    3: <% end %>
F, [2020-08-18T17:39:40.429357 #14860] FATAL -- :   
F, [2020-08-18T17:39:40.429388 #14860] FATAL -- : ransack (2.3.2) lib/ransack/helpers/form_builder.rb:14:in `initialize'
ransack (2.3.2) lib/ransack/helpers/form_builder.rb:14:in `open'
ransack (2.3.2) lib/ransack/helpers/form_builder.rb:14:in `value'
actionview (5.2.4.3) lib/action_view/helpers/tags/base.rb:53:in `value_before_type_cast'
actionview (5.2.4.3) lib/action_view/helpers/tags/text_field.rb:15:in `block in render'
actionview (5.2.4.3) lib/action_view/helpers/tags/text_field.rb:15:in `fetch'
actionview (5.2.4.3) lib/action_view/helpers/tags/text_field.rb:15:in `render'
actionview (5.2.4.3) lib/action_view/helpers/form_helper.rb:1136:in `text_field'
actionview (5.2.4.3) lib/action_view/helpers/form_helper.rb:1680:in `text_field'