Fix AR#method_missing re-dispatching into overwritten attribute methods.

This was happening when a `super` call in an overwritten attribute method
was triggering a method_missing fallback, because attribute methods
haven't been generated yet.

  class Topic < ActiveRecord::Base
    def title
      # `super` would re-invoke this method if define_attribute_methods
      # hasn't been called yet resulting in double '!' appending
      super + '!'
    end
  end

1 files changed, 18 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/attribute_methods.rb b/activerecord/lib/active_record/attribute_methods.rb
index bf270c1829..f90c11dcf7 100644
--- a/activerecord/lib/active_record/attribute_methods.rb
+++ b/activerecord/lib/active_record/attribute_methods.rb
@@ -128,6 +128,16 @@ module ActiveRecord
         end
       end
 
+      def find_generated_attribute_method(method_name) # :nodoc:
+        klass = self
+        until klass == Base
+          gen_methods = klass.generated_attribute_methods
+          return gen_methods.instance_method(method_name) if method_defined_within?(method_name, gen_methods, Object)
+          klass = klass.superclass
+        end
+        nil
+      end
+
       # Returns +true+ if +attribute+ is an attribute method and table exists,
       # +false+ otherwise.
       #
@@ -163,7 +173,14 @@ module ActiveRecord
     def method_missing(method, *args, &block) # :nodoc:
       if self.class.define_attribute_methods
         if respond_to_without_attributes?(method)
-          send(method, *args, &block)
+          # make sure to invoke the correct attribute method, as we might have gotten here via a `super`
+          # call in a overwritten attribute method
+          if attribute_method = self.class.find_generated_attribute_method(method)
+            # this is probably horribly slow, but should only happen at most once for a given AR class
+            attribute_method.bind(self).call(*args, &block)
+          else
+            send(method, *args, &block)
+          end
         else
           super
         end