A regression in deprecate_methods was introduced in a982a42d:

- Refactoring alias_chain to Module#prepend broke the possibility to deprecate class methods since the module
  generated was prepended to the target's instance.

  A suggestion to fix this was  to use `AS#redefine_method` which would solve the
  problem but with the cost of redefining directly the method.
  Decided to go with the same alias_chain implementation as before instead.

- Fixes #33253

activesupport/lib/active_support/deprecation/method_wrappers.rb

@@ -54,23 +54,26 @@ def deprecate_methods(target_module, *method_names)
         deprecator = options.delete(:deprecator) || self
         method_names += options.keys
 
-        mod = Module.new do
-          method_names.each do |method_name|
-            define_method(method_name) do |*args, &block|
-              deprecator.deprecation_warning(method_name, options[method_name])
-              super(*args, &block)
-            end
+        method_names.each do |method_name|
+          aliased_method, punctuation = method_name.to_s.sub(/([?!=])$/, ""), $1
+          with_method = "#{aliased_method}_with_deprecation#{punctuation}"
+          without_method = "#{aliased_method}_without_deprecation#{punctuation}"
 
-            case
-            when target_module.protected_method_defined?(method_name)
-              protected method_name
-            when target_module.private_method_defined?(method_name)
-              private method_name
-            end
+          target_module.send(:define_method, with_method) do |*args, &block|
+            deprecator.deprecation_warning(method_name, options[method_name])
+            send(without_method, *args, &block)
           end
-        end
 
-        target_module.prepend(mod)
+          target_module.send(:alias_method, without_method, method_name)
+          target_module.send(:alias_method, method_name, with_method)
+
+          case
+          when target_module.protected_method_defined?(without_method)
+            target_module.send(:protected, method_name)
+          when target_module.private_method_defined?(without_method)
+            target_module.send(:private, method_name)
+          end
+        end
       end
     end
   end

activesupport/test/deprecation/method_wrappers_test.rb

@@ -55,4 +55,39 @@ def test_deprecate_methods_private_method
 
     assert(@klass.private_method_defined?(:old_private_method))
   end
+
+  def test_deprecate_class_method
+    mod = Module.new do
+      extend self
+
+      def old_method
+        "abc"
+      end
+    end
+    ActiveSupport::Deprecation.deprecate_methods(mod, old_method: :new_method)
+
+    warning = /old_method is deprecated and will be removed from Rails \d.\d \(use new_method instead\)/
+    assert_deprecated(warning) { assert_equal "abc", mod.old_method }
+  end
+
+  def test_deprecate_method_when_class_extends_module
+    mod = Module.new do
+      def old_method
+        "abc"
+      end
+    end
+    @klass.extend mod
+    ActiveSupport::Deprecation.deprecate_methods(mod, old_method: :new_method)
+
+    warning = /old_method is deprecated and will be removed from Rails \d.\d \(use new_method instead\)/
+    assert_deprecated(warning) { assert_equal "abc", @klass.old_method }
+  end
+
+  def test_method_with_without_deprecation_is_exposed
+    ActiveSupport::Deprecation.deprecate_methods(@klass, old_method: :new_method)
+
+    warning = /old_method is deprecated and will be removed from Rails \d.\d \(use new_method instead\)/
+    assert_deprecated(warning) { assert_equal "abc", @klass.new.old_method_with_deprecation }
+    assert_equal "abc", @klass.new.old_method_without_deprecation
+  end
 end