Return super in ActionController::Parameters.const_missing

The current implementation of ActionController::Parameters.const_missing
returns `ActionController::Parameters.always_permitted_parameters` even
if its `super` returns a constant without raising error. This prevents its
subclass in a autoloading module/class from taking advantage of
autoloading constants.

    class SomeParameters < ActionController::Parameters
      def do_something
        DefinedSomewhere.do_something
      end
    end

In the code above, `DefinedSomewhere` is to be autoloaded with
`Module.const_missing` but `ActionController::Parameters.const_missing`
returns `always_permitted_parameters` instead of the autoloaded
constant.

This pull request fixes the issue respecting `const_missing`'s `super`.

1 files changed, 8 insertions, 1 deletions

diff --git a/actionpack/test/controller/parameters/always_permitted_parameters_test.rb b/actionpack/test/controller/parameters/always_permitted_parameters_test.rb
index 059f310d49..59be08db54 100644
--- a/actionpack/test/controller/parameters/always_permitted_parameters_test.rb
+++ b/actionpack/test/controller/parameters/always_permitted_parameters_test.rb
@@ -1,5 +1,6 @@
 require 'abstract_unit'
 require 'action_controller/metal/strong_parameters'
+require 'minitest/mock'
 
 class AlwaysPermittedParametersTest < ActiveSupport::TestCase
   def setup
@@ -14,7 +15,13 @@ class AlwaysPermittedParametersTest < ActiveSupport::TestCase
 
   test "shows deprecations warning on NEVER_UNPERMITTED_PARAMS" do
     assert_deprecated do
-       ActionController::Parameters::NEVER_UNPERMITTED_PARAMS
+      ActionController::Parameters::NEVER_UNPERMITTED_PARAMS
+    end
+  end
+
+  test "returns super on missing constant other than NEVER_UNPERMITTED_PARAMS" do
+    ActionController::Parameters.superclass.stub :const_missing, "super" do
+      assert_equal "super", ActionController::Parameters::NON_EXISTING_CONSTANT
     end
   end