Raise NameError instead of ArgumentError in ActiveSupport::Dependencies

ActiveSupport::Dependencies now raises NameError if it finds an existing
constant in load_missing_constant. This better reflects the nature of
the error which is usually caused by calling constantize on a nested constant.

Closes #1423

3 files changed, 4 insertions, 2 deletions

diff --git a/activesupport/CHANGELOG b/activesupport/CHANGELOG
index bf48306684..6b7044aeae 100644
--- a/activesupport/CHANGELOG
+++ b/activesupport/CHANGELOG
@@ -7,6 +7,8 @@
 
 *Rails 3.1.0 (unreleased)*
 
+* ActiveSupport::Dependencies now raises NameError if it finds an existing constant in load_missing_constant. This better reflects the nature of the error which is usually caused by calling constantize on a nested constant. [Andrew White]
+
 * Deprecated ActiveSupport::SecureRandom in favour of SecureRandom from the standard library [Jon Leighton]
 
 * New reporting method Kernel#quietly. [fxn]
diff --git a/activesupport/lib/active_support/dependencies.rb b/activesupport/lib/active_support/dependencies.rb
index cae68c3c95..26c5c157cb 100644
--- a/activesupport/lib/active_support/dependencies.rb
+++ b/activesupport/lib/active_support/dependencies.rb
@@ -473,7 +473,7 @@ module ActiveSupport #:nodoc:
         raise ArgumentError, "A copy of #{from_mod} has been removed from the module tree but is still active!"
       end
 
-      raise ArgumentError, "#{from_mod} is not missing constant #{const_name}!" if local_const_defined?(from_mod, const_name)
+      raise NameError, "#{from_mod} is not missing constant #{const_name}!" if local_const_defined?(from_mod, const_name)
 
       qualified_name = qualified_name_for from_mod, const_name
       path_suffix = qualified_name.underscore
diff --git a/activesupport/test/dependencies_test.rb b/activesupport/test/dependencies_test.rb
index 2ddbce5150..b4edf0f51d 100644
--- a/activesupport/test/dependencies_test.rb
+++ b/activesupport/test/dependencies_test.rb
@@ -441,7 +441,7 @@ class DependenciesTest < Test::Unit::TestCase
     with_autoloading_fixtures do
       require_dependency '././counting_loader'
       assert_equal 1, $counting_loaded_times
-      assert_raise(ArgumentError) { ActiveSupport::Dependencies.load_missing_constant Object, :CountingLoader }
+      assert_raise(NameError) { ActiveSupport::Dependencies.load_missing_constant Object, :CountingLoader }
       assert_equal 1, $counting_loaded_times
     end
   end