Merge pull request #28270 from mmangino/dont_ignore_seralization_options

Don't accidentally lose includes in serialization

activemodel/CHANGELOG.md

 ## Rails 6.0.0.alpha (Unreleased) ##
 
+*   Do not lose all multiple `:includes` with options in serialization.
+
+    *Mike Mangino*
+
 *   Rails 6 requires Ruby 2.4.1 or newer.
 
     *Jeremy Daer*

activemodel/lib/active_model/serialization.rb

@@ -179,7 +179,7 @@ def serializable_add_includes(options = {}) #:nodoc:
         return unless includes = options[:include]
 
         unless includes.is_a?(Hash)
-          includes = Hash[Array(includes).map { |n| n.is_a?(Hash) ? n.to_a.first : [n, {}] }]
+          includes = Hash[Array(includes).flat_map { |n| n.is_a?(Hash) ? n.to_a : [[n, {}]] }]
         end
 
         includes.each do |association, opts|

activemodel/test/cases/serialization_test.rb

@@ -174,4 +174,11 @@ def test_multiple_includes_with_options
                            { "name" => "Sue", "email" => "sue@example.com", "gender" => "female" }] }
     assert_equal expected, @user.serializable_hash(include: [{ address: { only: "street" } }, :friends])
   end
+
+  def test_all_includes_with_options
+    expected = { "email" => "david@example.com", "gender" => "male", "name" => "David",
+                "address" => { "street" => "123 Lane" },
+                "friends" => [{ "name" => "Joe" }, { "name" => "Sue" }] }
+    assert_equal expected, @user.serializable_hash(include: [address: { only: "street" }, friends: { only: "name" }])
+  end
 end