Try to reproduce possible bug in Rails 5.0.1 where attribute value is frozen.

00-README.md

My issue is shown in 01_bug.rb, the value I pass in gets frozen. It looks like this happens in active_model/type/immutable_string.rb, #cast_value.

However as in my attempted reproduce of the bug on a small scale, 02_test.rb, #cast_value is never called.

UPDATE: I found this has been fixed in master branch of Rails: https://github.com/rails/rails/commit/8de7df5b22e853f028e5a71b26d45a0ce7a2c0f4#diff-da764be48e98c7b140730924b50595b0

01_bug.rb

key = 'foo'

TextFieldDefinition.create(key: key)

key.frozen? # => true (not expected

02_test.rb

# gem 'activerecord', '5.0.1'

require 'bundler'
Bundler.require(:default)
require 'active_record'
require 'pry'


ActiveRecord::Base.establish_connection(adapter: 'sqlite3',
                                        database: File.dirname(__FILE__) + "/db.sqlite3")

ActiveRecord::Schema.define do
  self.verbose = false

  create_table :users, :force => true do |t|
    t.string :key
    t.timestamps
  end
end

class User < ActiveRecord::Base; end

KEY = 'foo'

# class String; def freeze; raise if self == KEY; self; end; end

user = User.create(key: KEY)

puts KEY.frozen? # => true

99-pry.md

irb(main):001:0> KEY = 'ff'
=> "ff"
irb(main):002:0> TextFieldDefinition.create(key: KEY)
   (0.2ms)  BEGIN

From: /home/kris/.gem/ruby/2.3.1/gems/activemodel-5.0.1/lib/active_model/type/immutable_string.rb @ line 26 ActiveModel::Type::ImmutableString#cast_value:

    19: def cast_value(value)
    20:   result = case value
    21:            when true then "t"
    22:            when false then "f"
    23:            else value.to_s
    24:            end
    25:   binding.pry
 => 26:   result.freeze
    27: end

[1] pry(#<ActiveRecord::ConnectionAdapters::AbstractMysqlAdapter::MysqlString>)>