allow setting of a demodulized class name when using STI

If your STI class looks like this:

```ruby
class Company < ActiveRecord::Base
  self.store_full_sti_class = false

  class GoodCo < Company
  end

  class BadCo < Company
  end
end
```

The expectation (which is valid) is that the `type` in the database is saved as
`GoodCo` or `BadCo`. However, another expectation should be that setting `type`
to `GoodCo` would correctly instantiate the object as a `Company::GoodCo`. That
second expectation is what this should fix.

2 files changed, 11 insertions, 0 deletions

diff --git a/activerecord/test/cases/inheritance_test.rb b/activerecord/test/cases/inheritance_test.rb
index 278fa63e04..9199066072 100644
--- a/activerecord/test/cases/inheritance_test.rb
+++ b/activerecord/test/cases/inheritance_test.rb
@@ -217,6 +217,14 @@ class InheritanceTest < ActiveRecord::TestCase
     assert_nothing_raised { Client.new(type: 'VerySpecialClient') }
   end
 
+  def test_new_without_storing_full_sti_class
+    without_store_full_sti_class do
+      Company::SpecialCo # force autoloading
+      item = Company.new(type: 'SpecialCo')
+      assert_instance_of Company::SpecialCo, item
+    end
+  end
+
   def test_new_with_autoload_paths
     path = File.expand_path('../../models/autoloadable', __FILE__)
     ActiveSupport::Dependencies.autoload_paths << path
diff --git a/activerecord/test/models/company.rb b/activerecord/test/models/company.rb
index 6961f8fd6f..67936e8e5d 100644
--- a/activerecord/test/models/company.rb
+++ b/activerecord/test/models/company.rb
@@ -26,6 +26,9 @@ class Company < AbstractCompany
   def private_method
     "I am Jack's innermost fears and aspirations"
   end
+
+  class SpecialCo < Company
+  end
 end
 
 module Namespaced