Use :unprocessable_content in generated Devise config for Rack 3.1+, avoid Rack warnings (#5797)

In Rack v3.1.0, the symbol for HTTP status code 422 was changed from `:unprocessable_entity` to `:unprocessable_content`.

As a result, when using rack 3.2 with the following configuration in `config/initializers/devise.rb`, a warning is shown on login failure:

```ruby
# config/initializers/devise.rb
Devise.setup do |config|
  ...
  config.responder.error_status = :unprocessable_entity
```

Warning message:

```sh
/path-to-app/vendor/bundle/ruby/3.4.0/gems/devise-4.9.4/lib/devise/failure_app.rb:80: warning: Status code :unprocessable_entity is deprecated and will be removed in a future version of Rack. Please use :unprocessable_content instead.
```

This warning can be resolved by updating the config as follows:
```diff
# config/initializers/devise.rb
Devise.setup do |config|
  ...
+  config.responder.error_status = :unprocessable_content
-  config.responder.error_status = :unprocessable_entity
```

This fixes the root cause of the warning for new apps by adjusting the generated config during `$ rails generate devise:install` depending on the rack version, so new apps using newer Rack versions generate `error_status = :unprocessable_content` instead of `:unprocessable_entity`.

Existing apps are handled by [latest versions of Rails, which will now transparently convert the code under the hood to avoid the Rack warning](https://github.com/rails/rails/pull/53383), and Devise will use that translation layer when available in the failure app to prevent the warning there as well (since that isn't covered by Rails automatic conversion).

Signed-off-by: Carlos Antonio da Silva <carlosantoniodasilva@gmail.com>

CHANGELOG.md

@@ -27,6 +27,9 @@
 * enhancements
   * Add Rails 8 support.
     - Routes are lazy-loaded by default in test and development environments now so Devise loads them before `Devise.mappings` call. [#5728](https://github.com/heartcombo/devise/pull/5728)
+  * New apps using Rack 3.1+ will be generated using `config.responder.error_status = :unprocessable_content`, since [`:unprocessable_entity` has been deprecated by Rack](https://github.com/rack/rack/pull/2137).
+
+    Latest versions of [Rails transparently convert `:unprocessable_entity` -> `:unprocessable_content`](https://github.com/rails/rails/pull/53383), and Devise will use that in the failure app to avoid Rack deprecation warnings for apps that are configured with `:unprocessable_entity`. They can also simply change their `error_status` to `:unprocessable_content` in latest Rack versions to avoid the warning.
   * Add Ruby 3.4 and 4.0 support.
   * Reenable Mongoid test suite across all Rails 7+ versions, to ensure we continue supporting it. Changes to dirty tracking to support Mongoid 8.0+. [#5568](https://github.com/heartcombo/devise/pull/5568)
   * Password length validator is changed from

README.md

@@ -493,7 +493,8 @@ Devise.setup do |config|
   # apps is `200 OK` and `302 Found` respectively, but new apps are generated with
   # these new defaults that match Hotwire/Turbo behavior.
   # Note: These might become the new default in future versions of Devise.
-  config.responder.error_status = :unprocessable_entity
+  config.responder.error_status = :unprocessable_content # for Rack 3.1 or higher
+  # config.responder.error_status = :unprocessable_entity # for Rack 3.0 or lower
   config.responder.redirect_status = :see_other
 end
 ```

app/controllers/devise/confirmations_controller.rb

@@ -27,7 +27,7 @@ class Devise::ConfirmationsController < DeviseController
       set_flash_message!(:notice, :confirmed)
       respond_with_navigational(resource){ redirect_to after_confirmation_path_for(resource_name, resource) }
     else
-      # TODO: use `error_status` when the default changes to `:unprocessable_entity`.
+      # TODO: use `error_status` when the default changes to `:unprocessable_entity` / `:unprocessable_content`.
       respond_with_navigational(resource.errors, status: :unprocessable_entity){ render :new }
     end
   end

app/controllers/devise/unlocks_controller.rb

@@ -29,7 +29,7 @@ class Devise::UnlocksController < DeviseController
       set_flash_message! :notice, :unlocked
       respond_with_navigational(resource){ redirect_to after_unlock_path_for(resource) }
     else
-      # TODO: use `error_status` when the default changes to `:unprocessable_entity`.
+      # TODO: use `error_status` when the default changes to `:unprocessable_entity` / `:unprocessable_content`.
       respond_with_navigational(resource.errors, status: :unprocessable_entity){ render :new }
     end
   end

lib/devise/failure_app.rb

@@ -77,9 +77,9 @@ module Devise
 
       flash.now[:alert] = i18n_message(:invalid) if is_flashing_format?
       self.response = recall_app(warden_options[:recall]).call(request.env).tap { |response|
-        response[0] = Rack::Utils.status_code(
-          response[0].in?(300..399) ? Devise.responder.redirect_status : Devise.responder.error_status
-        )
+        status = response[0].in?(300..399) ? Devise.responder.redirect_status : Devise.responder.error_status
+        # Avoid warnings translating status to code using Rails if available (e.g. `unprocessable_entity` => `unprocessable_content`)
+        response[0] = ActionDispatch::Response.try(:rack_status_code, status) || Rack::Utils.status_code(status)
       }
     end
 

lib/generators/templates/devise.rb

@@ -305,7 +305,7 @@ Devise.setup do |config|
   # apps is `200 OK` and `302 Found` respectively, but new apps are generated with
   # these new defaults that match Hotwire/Turbo behavior.
   # Note: These might become the new default in future versions of Devise.
-  config.responder.error_status = :unprocessable_entity
+  config.responder.error_status = <%= Rack::Utils::SYMBOL_TO_STATUS_CODE.key(422).inspect %>
   config.responder.redirect_status = :see_other
 
   # ==> Configuration for :registerable

test/generators/devise_generator_test.rb

@@ -37,5 +37,4 @@ class DeviseGeneratorTest < Rails::Generators::TestCase
     FileUtils.mkdir_p(destination)
     FileUtils.cp routes, destination
   end
-
 end

test/generators/install_generator_test.rb

@@ -23,4 +23,12 @@ class InstallGeneratorTest < Rails::Generators::TestCase
     assert_no_file "config/initializers/devise.rb"
     assert_no_file "config/locales/devise.en.yml"
   end
+
+  test "responder error_status based on rack version" do
+    run_generator(["--orm=active_record"])
+
+    error_status = Rack::RELEASE >= "3.1" ? :unprocessable_content : :unprocessable_entity
+
+    assert_file "config/initializers/devise.rb", /config\.responder\.error_status = #{error_status.inspect}/
+  end
 end