Detect missing_constants calls from removed modules and fail accordingly.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4780 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activesupport/CHANGELOG

 *SVN*
 
+* Detect missing_constants calls from removed modules and fail accordingly. [Nicholas Seckar]
+
 * Stop using defined? in Dependencies.qualified_const_defined? since defined? may invoke const_missing. [Nicholas Seckar]
 
 * Dependencies can autoload directories of nested classes. [Jeremy Kemper]

activesupport/lib/active_support/dependencies.rb

@@ -182,6 +182,10 @@ def load_missing_constant(from_mod, const_name)
     # If we have an anonymous module, all we can do is attempt to load from Object.
     from_mod = Object if from_mod.name.empty?
     
+    unless qualified_const_defined?(from_mod.name) && from_mod.name.constantize.object_id == from_mod.object_id
+      raise ArgumentError, "A copy of #{from_mod} has been removed from the module tree but is still active!"
+    end
+    
     raise ArgumentError, "Expected #{from_mod} is not missing constant #{const_name}!" if from_mod.const_defined?(const_name)
     
     qualified_name = qualified_name_for from_mod, const_name

activesupport/test/dependencies_test.rb

@@ -372,4 +372,19 @@ def test_const_missing_within_anonymous_module
     end
   end
   
+  def test_removal_from_tree_should_be_detected
+    with_loading 'dependencies' do
+      root = Dependencies.autoload_paths.first
+      c = ServiceOne
+      Dependencies.clear
+      assert ! defined?(ServiceOne)
+      begin
+        Dependencies.load_missing_constant(c, :FakeMissing)
+        flunk "Expected exception"
+      rescue ArgumentError => e
+        assert_match %r{ServiceOne has been removed from the module tree}i, e.message
+      end
+    end
+  end
+  
 end