Make Devise.mappings work with lazy loaded routes.

[nashby]

Starting from Rails 8.0, routes are lazy-loaded by default in test and development environments. However, Devise's mappings are built during the routes loading phase. To ensure it works correctly, we need to load the routes first before accessing @@mappings.

Closes #5705 #5695

[kjellberg]

When can we expect a release with this? Thanks

[jrochkind]

Main branch is labelled devise version 5.0.0-beta. I'm not sure the release plan/schedule, or what changes/backwards compat might be included in forthcoming devise 5.

But would it be possible to backport this to a devise 4.x branch and do a 4.x release with it? I too believe I am blocked from a Rails 8 upgrade on this.

[jrochkind]

Converting this PR to this patch in a config/initializers/devise_rails8_patch.rb file seems to let me get going with Rails 8 and devise 4.9.4.

  require 'devise'
  Devise # make sure it's already loaded

  module Devise
    def self.mappings
      # Starting from Rails 8.0, routes are lazy-loaded by default in test and development environments.
      # However, Devise's mappings are built during the routes loading phase.
      # To ensure it works correctly, we need to load the routes first before accessing @@mappings.
      Rails.application.try(:reload_routes_unless_loaded)
      @@mappings
    end
  end