let demodulize do less work, and add tests

This is also faster on 1.9.

2 files changed, 5 insertions, 1 deletions

diff --git a/activesupport/lib/active_support/inflector/methods.rb b/activesupport/lib/active_support/inflector/methods.rb
index 934529d496..454637191e 100644
--- a/activesupport/lib/active_support/inflector/methods.rb
+++ b/activesupport/lib/active_support/inflector/methods.rb
@@ -166,7 +166,9 @@ module ActiveSupport
     #   "ActiveRecord::CoreExtensions::String::Inflections".demodulize # => "Inflections"
     #   "Inflections".demodulize                                       # => "Inflections"
     def demodulize(class_name_in_module)
-      class_name_in_module.to_s.gsub(/^.*::/, '')
+      # If you remove the module part of an empty string, you get an empty string.
+      # That's why the regexp uses the * quantifier.
+      class_name_in_module.to_s[/[^:]*\z/]
     end
 
     # Creates a foreign key name from a class name.
diff --git a/activesupport/test/inflector_test.rb b/activesupport/test/inflector_test.rb
index 5c956e0075..7d15b3c7e5 100644
--- a/activesupport/test/inflector_test.rb
+++ b/activesupport/test/inflector_test.rb
@@ -194,6 +194,8 @@ class InflectorTest < Test::Unit::TestCase
 
   def test_demodulize
     assert_equal "Account", ActiveSupport::Inflector.demodulize("MyApplication::Billing::Account")
+    assert_equal "Account", ActiveSupport::Inflector.demodulize("Account")
+    assert_equal "", ActiveSupport::Inflector.demodulize("")
   end
 
   def test_foreign_key