Prefix: restore variable for the sake of error logging

lib/active_resource/base.rb

@@ -818,12 +818,14 @@ def prefix=(value = "/")
         # Clear prefix parameters in case they have been cached
         @prefix_parameters = nil
 
+        code, line = <<-RUBY_EVAL, __LINE__ + 1
+          def prefix_source() "#{value}" end
+          def prefix(options={}) "#{prefix_call}" end
+        RUBY_EVAL
+
         silence_warnings do
           # Redefine the new methods.
-          instance_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
-            def prefix_source() "#{value}" end
-            def prefix(options={}) "#{prefix_call}" end
-          RUBY_EVAL
+          instance_eval code, __FILE__, line
         end
       rescue Exception => e
         logger.error "Couldn't set prefix: #{e}\n  #{code}" if logger

test/cases/base_test.rb

@@ -43,6 +43,17 @@ def test_site_accessor_accepts_uri_or_string_argument
     assert_equal site, Person.site
   end
 
+  def test_prefix_error_message
+    previous_prefix = Person.prefix
+    previous_logger, Person.logger = Person.logger, ActiveSupport::Logger.new(output = StringIO.new)
+
+    error = assert_raises(NoMethodError) { Person.prefix = nil }
+    assert_equal "Couldn't set prefix: #{error}", output.string.strip
+  ensure
+    Person.prefix = previous_prefix
+    Person.logger = previous_logger
+  end
+
   def test_should_use_site_prefix_and_credentials
     assert_equal "http://foo:[email protected]", Forum.site.to_s
     assert_equal "http://foo:[email protected]/forums/:forum_id", Topic.site.to_s