Fix association with extension issues

This fixes the following issues.

* `association_scope` doesn't include `default_scope`. Should use `scope` instead.
* We can't use `method_missing` for customizing existing method.
* We can't use `relation_delegate_class` for sharing extensions. Should extend per association.

2 files changed, 11 insertions, 1 deletions

diff --git a/activerecord/test/models/comment.rb b/activerecord/test/models/comment.rb
index 76b484e616..8cba788598 100644
--- a/activerecord/test/models/comment.rb
+++ b/activerecord/test/models/comment.rb
@@ -19,6 +19,16 @@ class Comment < ActiveRecord::Base
   has_many :children, class_name: "Comment", foreign_key: :parent_id
   belongs_to :parent, class_name: "Comment", counter_cache: :children_count
 
+  class ::OopsError < RuntimeError; end
+
+  module OopsExtension
+    def destroy_all(*)
+      raise OopsError
+    end
+  end
+
+  default_scope { extending OopsExtension }
+
   # Should not be called if extending modules that having the method exists on an association.
   def self.greeting
     raise
diff --git a/activerecord/test/models/post.rb b/activerecord/test/models/post.rb
index a2028b3eb9..4c913b3b72 100644
--- a/activerecord/test/models/post.rb
+++ b/activerecord/test/models/post.rb
@@ -13,7 +13,7 @@ class Post < ActiveRecord::Base
 
   module NamedExtension2
     def greeting
-      "hello"
+      "hullo"
     end
   end