don't cache invalid subsets when preloading hmt associations.

Backport #9252.

Conflicts:

	activerecord/CHANGELOG.md
	activerecord/test/cases/associations/eager_test.rb

The preloader code on 3-2-stable is not based on relations but on option hashes.
I had to modify the original patch and comparing the option hashes could be more
fuzzy than comparing the relations. All the tests passed though.

1 files changed, 6 insertions, 0 deletions

diff --git a/activerecord/test/cases/associations/eager_test.rb b/activerecord/test/cases/associations/eager_test.rb
index 20c6b691fc..5d07ffa241 100644
--- a/activerecord/test/cases/associations/eager_test.rb
+++ b/activerecord/test/cases/associations/eager_test.rb
@@ -1112,4 +1112,10 @@ class EagerAssociationTest < ActiveRecord::TestCase
       Post.includes(:comments).order(nil).where(:comments => {:body => "Thank you for the welcome"}).first
     end
   end
+
+  test "preloading does not cache has many association subset when preloaded with a through association" do
+    author = Author.includes(:comments_with_order_and_conditions, :posts).first
+    assert_no_queries { assert_equal 2, author.comments_with_order_and_conditions.size }
+    assert_no_queries { assert_equal 5, author.posts.size, "should not cache a subset of the association" }
+  end
 end