Ensure that constantize just rescues NameError that applies to the constant being currently loaded.

activesupport/lib/active_support/inflector/methods.rb

@@ -245,12 +245,15 @@ module ActiveSupport
     #   "blargle".safe_constantize  # => nil
     def safe_constantize(camel_cased_word)
       begin
-        camel_cased_word.constantize
-      rescue NameError
-        nil
+        constantize(camel_cased_word)
+      rescue NameError => e
+        raise unless e.message =~ /uninitialized constant #{const_regexp(camel_cased_word)}$/ ||
+          e.name.to_s == camel_cased_word.to_s
+      rescue ArgumentError => e
+        raise unless e.message =~ /not missing constant #{const_regexp(camel_cased_word)}\!$/
       end
     end
-    
+
     # Turns a number into an ordinal string used to denote the position in an
     # ordered sequence such as 1st, 2nd, 3rd, 4th.
     #
@@ -273,5 +276,18 @@ module ActiveSupport
         end
       end
     end
+
+    private
+
+    # Mount a regular expression that will match part by part of the constant.
+    # For instance, Foo::Bar::Baz will generate Foo(::Bar(::Baz)?)?
+    def const_regexp(camel_cased_word) #:nodoc:
+      parts = camel_cased_word.split("::")
+      last  = parts.pop
+
+      parts.reverse.inject(last) do |acc, part|
+        part.empty? ? acc : "#{part}(::#{acc})?"
+      end
+    end
   end
 end

activesupport/test/constantize_test_cases.rb

@@ -12,8 +12,11 @@ module ConstantizeTestCases
     assert_nothing_raised { assert_equal ConstantizeTestCases, yield("ConstantizeTestCases") }
     assert_nothing_raised { assert_equal ConstantizeTestCases, yield("::ConstantizeTestCases") }
     assert_raise(NameError) { yield("UnknownClass") }
+    assert_raise(NameError) { yield("UnknownClass::Ace") }
+    assert_raise(NameError) { yield("UnknownClass::Ace::Base") }
     assert_raise(NameError) { yield("An invalid string") }
     assert_raise(NameError) { yield("InvalidClass\n") }
+    assert_raise(NameError) { yield("Ace::ConstantizeTestCases") }
     assert_raise(NameError) { yield("Ace::Base::ConstantizeTestCases") }
   end
   
@@ -23,9 +26,12 @@ module ConstantizeTestCases
     assert_nothing_raised { assert_equal ConstantizeTestCases, yield("ConstantizeTestCases") }
     assert_nothing_raised { assert_equal ConstantizeTestCases, yield("::ConstantizeTestCases") }
     assert_nothing_raised { assert_equal nil, yield("UnknownClass") }
+    assert_nothing_raised { assert_equal nil, yield("UnknownClass::Ace") }
+    assert_nothing_raised { assert_equal nil, yield("UnknownClass::Ace::Base") }
     assert_nothing_raised { assert_equal nil, yield("An invalid string") }
     assert_nothing_raised { assert_equal nil, yield("InvalidClass\n") }
     assert_nothing_raised { assert_equal nil, yield("blargle") }
+    assert_nothing_raised { assert_equal nil, yield("Ace::ConstantizeTestCases") }
     assert_nothing_raised { assert_equal nil, yield("Ace::Base::ConstantizeTestCases") }
   end
 end