e4e1b62 broke `to_param` handling:

- There was an issue inside controller tests where order params were not respected, the reason
  was because we were calling `Hash#to_query` which sorts the results lexicographically.
  1e4e1b62 fixed that issue by not using `to_query` but instead a utility function provided by rack.
- However with the fix came another issue where it's now no longer possible to do this

  ```
   post :foo, params: { user: User.first }

   # Prior to the patch the controller will receive { "user" => "1" }
   # Whereas now you get { "user": "#<User: ...>" }
  ```

  The fix in this PR is to modify `Hash#to_query` to sort only when it
  doesn't contain an array structure that looks something like "bar[]"

  Ref https://github.com/rails/rails/pull/33341#issuecomment-404039396

1 files changed, 15 insertions, 2 deletions

diff --git a/actionpack/test/controller/test_case_test.rb b/actionpack/test/controller/test_case_test.rb
index 663832e9bb..2d0b6cd602 100644
--- a/actionpack/test/controller/test_case_test.rb
+++ b/actionpack/test/controller/test_case_test.rb
@@ -220,7 +220,7 @@ XML
     params = Hash[:page, { name: "page name" }, "some key", 123]
     post :render_raw_post, params: params.dup
 
-    assert_equal Rack::Utils.build_nested_query(params), @response.body
+    assert_equal params.to_query, @response.body
   end
 
   def test_params_round_trip
@@ -231,12 +231,25 @@ XML
     assert_equal params.merge(controller_info), JSON.parse(@response.body)
   end
 
+  def test_handle_to_params
+    klass = Class.new do
+      def to_param
+        "bar"
+      end
+    end
+
+    post :test_params, params: { foo: klass.new }
+
+    assert_equal JSON.parse(@response.body)["foo"], "bar"
+  end
+
+
   def test_body_stream
     params = Hash[:page, { name: "page name" }, "some key", 123]
 
     post :render_body, params: params.dup
 
-    assert_equal Rack::Utils.build_nested_query(params), @response.body
+    assert_equal params.to_query, @response.body
   end
 
   def test_document_body_and_params_with_post