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>
