Fix inconsistent results of params.deep_transform_keys (#50361)

* Fix inconsistent results of params.deep_transform_keys

* fix: specs

* fix: implements own deep_transform methods to ActionController::Parameters

Co-authored-by: Rafael Mendonça França <rafael@rubyonrails.org>

actionpack/lib/action_controller/metal/strong_parameters.rb

@@ -796,7 +796,7 @@ module ActionController
     # and from all nested hashes and arrays. The values are unchanged.
     def deep_transform_keys(&block)
       new_instance_with_inherited_permitted_status(
-        @parameters.deep_transform_keys(&block)
+        _deep_transform_keys_in_object(@parameters, &block).to_unsafe_h
       )
     end
 
@@ -804,7 +804,7 @@ module ActionController
     # This includes the keys from the root hash and from all nested hashes and
     # arrays. The values are unchanged.
     def deep_transform_keys!(&block)
-      @parameters.deep_transform_keys!(&block)
+      @parameters = _deep_transform_keys_in_object(@parameters, &block).to_unsafe_h
       self
     end
 
@@ -1042,6 +1042,46 @@ module ActionController
         end
       end
 
+      def _deep_transform_keys_in_object(object, &block)
+        case object
+        when Hash
+          object.each_with_object(self.class.new) do |(key, value), result|
+            result[yield(key)] = _deep_transform_keys_in_object(value, &block)
+          end
+        when Parameters
+          if object.permitted?
+            object.to_h.deep_transform_keys(&block)
+          else
+            object.to_unsafe_h.deep_transform_keys(&block)
+          end
+        when Array
+          object.map { |e| _deep_transform_keys_in_object(e, &block) }
+        else
+          object
+        end
+      end
+
+      def _deep_transform_keys_in_object!(object, &block)
+        case object
+        when Hash
+          object.keys.each do |key|
+            value = object.delete(key)
+            object[yield(key)] = _deep_transform_keys_in_object!(value, &block)
+          end
+          object
+        when Parameters
+          if object.permitted?
+            object.to_h.deep_transform_keys!(&block)
+          else
+            object.to_unsafe_h.deep_transform_keys!(&block)
+          end
+        when Array
+          object.map! { |e| _deep_transform_keys_in_object!(e, &block) }
+        else
+          object
+        end
+      end
+
       def specify_numeric_keys?(filter)
         if filter.respond_to?(:keys)
           filter.keys.any? { |key| /\A-?\d+\z/.match?(key) }

actionpack/test/controller/parameters/mutators_test.rb

@@ -124,6 +124,25 @@ class ParametersMutatorsTest < ActiveSupport::TestCase
     assert_predicate @params.deep_transform_keys! { |k| k }, :permitted?
   end
 
+  test "deep_transform_keys! transforms nested keys" do
+    @params.permit!
+    @params.deep_transform_keys!(&:upcase)
+
+    expected_hash = { "PERSON" => { "AGE" => "32", "NAME" => { "FIRST" => "David", "LAST" => "Heinemeier Hansson" }, "ADDRESSES" => [{ "CITY" => "Chicago", "STATE" => "Illinois" }] } }
+    assert_equal @params.to_hash, expected_hash
+  end
+
+  test "deep_transform_keys transforms nested keys" do
+    original_hash = @params.to_unsafe_h
+    @params.permit!
+    new_params = @params.deep_transform_keys(&:upcase)
+
+    assert_equal @params.to_hash, original_hash
+
+    expected_hash = { "PERSON" => { "AGE" => "32", "NAME" => { "FIRST" => "David", "LAST" => "Heinemeier Hansson" }, "ADDRESSES" => [{ "CITY" => "Chicago", "STATE" => "Illinois" }] } }
+    assert_equal new_params.to_hash, expected_hash
+  end
+
   test "deep_transform_keys! retains unpermitted status" do
     assert_not_predicate @params.deep_transform_keys! { |k| k }, :permitted?
   end