Show a devise log in or sign up forms in another page

This is an update of an old post of similar name but for a newer version of Devise and with better design decisions. The old post was for Devise 1.0.8, this one covers 4.0.0

I was trying to have a single page with both sign in and sign up forms with Devise 4.0.0 but this applies to whenever you want to show log in or registering individually or together anywhere on your site other than the views and controllers Devise creates for you.

For my task, I created a custom controller for it with a single new action as the create actions would be in the respective already existing Devise controllers. Something like this:

class Users::SessionsOrRegistrationsController < ApplicationController
  def new
  end
end

And then I created a new.html.erb (actually, new.html.haml, but I digress) that contained both log in and sign up one after the other. Something like this:

<h2>Sign up</h2>


<%= form_for(resource, as: resource_name, url: registration_path(resource_name)) do |f| %>
 <%= devise_error_messages! %>


<div class="field">
 <%= f.label :email %>
 <%= f.email_field :email, autofocus: true %>
 </div>



<div class="field">
 <%= f.label :password %>
 <% if @minimum_password_length %>
 <em>(<%= @minimum_password_length %> characters minimum)</em>
 <% end %>
 <%= f.password_field :password, autocomplete: "off" %>
 </div>



<div class="field">
 <%= f.label :password_confirmation %>
 <%= f.password_field :password_confirmation, autocomplete: "off" %>
 </div>



<div class="actions">
 <%= f.submit "Sign up" %>
 </div>

<% end %>

<hr/>


<h2>Log in</h2>


<%= form_for(resource, as: resource_name, url: session_path(resource_name)) do |f| %>

<div class="field">
    <%= f.label :email %>
    <%= f.email_field :email, autofocus: true %>
  </div>



<div class="field">
    <%= f.label :password %>
    <%= f.password_field :password, autocomplete: "off" %>
  </div>


  <% if devise_mapping.rememberable? -%>

<div class="field">
      <%= f.check_box :remember_me %>
      <%= f.label :remember_me %>
    </div>

  <% end -%>


<div class="actions">
    <%= f.submit "Log in" %>
  </div>

<% end %>

I actually ended up creating two _form partials and including them. In either case, when you try to render those views, you’ll get errors about some missing methods. You need to provide those as helper methods so my controller actually looks like this:

class Users::SessionsOrRegistrationsController < ApplicationController
  def new
  end

  private

  def resource_name
    :user
  end
  helper_method :resource_name

  def resource
    @resource ||= User.new
  end
  helper_method :resource

  def devise_mapping
    @devise_mapping ||= Devise.mappings[:user]
  end
  helper_method :devise_mapping

  def resource_class
    User
  end
  helper_method :resource_class
end

And now it works.