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

2 files changed, 51 insertions, 3 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
diff --git a/activerecord/test/cases/attribute_methods_test.rb b/activerecord/test/cases/attribute_methods_test.rb
index 9c66ed354e..6c581a432f 100644
--- a/activerecord/test/cases/attribute_methods_test.rb
+++ b/activerecord/test/cases/attribute_methods_test.rb
@@ -767,8 +767,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
   # that by defining a 'foo' method in the generated methods module for B.
   # (That module will be inserted between the two, e.g. [B, <GeneratedAttributes>, A].)
   def test_inherited_custom_accessors
-    klass = Class.new(ActiveRecord::Base) do
-      self.table_name = "topics"
+    klass = new_topic_like_ar_class do
       self.abstract_class = true
       def title; "omg"; end
       def title=(val); self.author_name = val; end
@@ -783,8 +782,40 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal "lol", topic.author_name
   end
 
+  def test_on_the_fly_super_invokable_generated_attribute_methods_via_method_missing
+    klass = new_topic_like_ar_class do
+      def title
+        super + '!'
+      end
+    end
+
+    real_topic = topics(:first)
+    assert_equal real_topic.title + '!', klass.find(real_topic.id).title
+  end
+
+  def test_on_the_fly_super_invokable_generated_predicate_attribute_methods_via_method_missing
+    klass = new_topic_like_ar_class do
+      def title?
+        !super
+      end
+    end
+
+    real_topic = topics(:first)
+    assert_equal !real_topic.title?, klass.find(real_topic.id).title?
+  end
+
   private
 
+  def new_topic_like_ar_class(&block)
+    klass = Class.new(ActiveRecord::Base) do
+      self.table_name = 'topics'
+      class_eval(&block)
+    end
+
+    assert_empty klass.generated_attribute_methods.instance_methods(false)
+    klass
+  end
+
   def cached_columns
     Topic.columns.map(&:name) - Topic.serialized_attributes.keys
   end