Preserve original method visibility when deprecating a method

activesupport/lib/active_support/deprecation/method_wrappers.rb

@@ -60,6 +60,13 @@ def deprecate_methods(target_module, *method_names)
               deprecator.deprecation_warning(method_name, options[method_name])
               super(*args, &block)
             end
+
+            case
+            when target_module.protected_method_defined?(method_name)
+              protected method_name
+            when target_module.private_method_defined?(method_name)
+              private method_name
+            end
           end
         end
 

activesupport/test/deprecation/method_wrappers_test.rb

@@ -8,6 +8,16 @@ def setup
     @klass = Class.new do
       def new_method; "abc" end
       alias_method :old_method, :new_method
+
+      protected
+
+        def new_protected_method; "abc" end
+        alias_method :old_protected_method, :new_protected_method
+
+      private
+
+        def new_private_method; "abc" end
+        alias_method :old_private_method, :new_private_method
     end
   end
 
@@ -33,4 +43,16 @@ def test_deprecate_methods_warning_when_deprecated_with_custom_deprecator
 
     assert_deprecated(warning, deprecator) { assert_equal "abc", @klass.new.old_method }
   end
+
+  def test_deprecate_methods_protected_method
+    ActiveSupport::Deprecation.deprecate_methods(@klass, old_protected_method: :new_protected_method)
+
+    assert(@klass.protected_method_defined?(:old_protected_method))
+  end
+
+  def test_deprecate_methods_private_method
+    ActiveSupport::Deprecation.deprecate_methods(@klass, old_private_method: :new_private_method)
+
+    assert(@klass.private_method_defined?(:old_private_method))
+  end
 end