Allow railties to use lazy routes

Previously, railtie initializers couldn't access app.routes without
missing the route_set_class setting and using a regular route set. Now,
the route set class config is set early enough that railties don't
interfere with lazy routes.

Author: gmcgibbon

railties/lib/rails/engine.rb

@@ -590,7 +590,7 @@ def load_seed
       config.eager_load_paths.freeze
     end
 
-    initializer :make_routes_lazy, before: :set_routes_reloader_hook do |app|
+    initializer :make_routes_lazy, before: :bootstrap_hook do |app|
       config.route_set_class = LazyRouteSet if Rails.env.local?
     end
 

railties/test/engine/lazy_route_set_test.rb

@@ -8,7 +8,6 @@ class LazyRouteSetTest < ActiveSupport::TestCase
       include ActiveSupport::Testing::Isolation
 
       setup :build_app
-
       teardown :teardown_app
 
       test "app lazily loads routes when invoking url helpers" do
@@ -83,6 +82,21 @@ class LazyRouteSetTest < ActiveSupport::TestCase
         assert_not_operator(:plugin_posts_path, :in?, engine_url_helpers.methods)
       end
 
+      test "railties can access lazy routes" do
+        app_file("config/application.rb", <<~RUBY, "a+")
+
+          class MyRailtie < ::Rails::Railtie
+            initializer :some_railtie_init do |app|
+              app.routes
+            end
+          end
+        RUBY
+
+        require "#{app_path}/config/environment"
+
+        assert_operator(Rails.application.routes, :is_a?, Engine::LazyRouteSet)
+      end
+
       private
         def build_app
           super
@@ -118,6 +132,7 @@ class Engine < ::Rails::Engine
                 end
               end
             RUBY
+
             plugin.write "config/routes.rb", <<~RUBY
               Plugin::Engine.routes.draw do
                 root to: proc { [200, {}, []] }