make devise work with turbo streams

devise.rb

# need to update devise config with these settings
config.parent_controller = 'Users::DeviseController'

devise_controller.rb

class Users::DeviseController < ApplicationController
  self.responder = TurboDeviseResponder
  respond_to :turbo_stream, :html
end

package.json

 "dependencies": {
    "@hotwired/turbo": "https://github.com/hotwired/turbo/archive/dev-builds/latest.tar.gz",
  }

turbo_devise_responder.rb

class TurboDeviseResponder < ActionController::Responder
  def initialize(controller, resources, options = nil)
    super

    options[:formats] = :html
  end

  def to_turbo_stream
    return to_html if get?

    unless has_errors?
      return redirect_to navigation_location
    end

    display_errors
  end

  protected

  def display_errors
    controller.render(rendering_options.merge(status: :unprocessable_entity))
  end

  def rendering_options
    super.merge! formats: :html
  end

  def has_errors?
    return true if controller.flash.alert.present?
    super
  end
end

The only problem on login resource.valid? fills resource.errors array, so each error message gets displayed. By default devise doesn't show errors on login, it just shows a flash message.

I don't even have the failure app and I seem to be pretty close. What does that portion provide for us?

I don't even have the failure app and I seem to be pretty close. What does that portion provide for us?

I run into some issues where it adds .turbo_stream to the url 🤷‍♂️ but since this PR hotwired/turbo#39 got merged, all we need to do now is to return 422 if there are any errors. I updated the example, seems to work good for me.