Fix polymorphic_url and polymorphic_path:

- Fix rails#54890
- ### Problem

  Calling `polyphormic_url` in a integration test or anywhere else
  when routes may not be loaded yet will result in either crashing
  or returning a wrong url.

  ### Details

  When the routes are not yet loaded, any `resolve` routes are not
  taken in consideration when calling `polymorphic_url`.

  ```ruby
  # config/routes.rb
  resolve("Post") { "https://example.org" }

  # test.rb
  polymorphic_url(@post) # Crash: `post_url` is not defined.
  ```

  ### Solution

  Load the routes when `polymorphic_mappings` ultimately gets called
  by `polymorphic_url`
  https://github.com/rails/rails/blob/42a71a03a0adb465dc49b4e21dec8e0ea29e8e35/actionpack/lib/action_dispatch/routing/polymorphic_routes.rb#L179

  ### Side note

  It's worth to note that `polymorphic_url` was overriden to
  load the routes, but it only worked if one attempted to call it on
  the singleton route's url_helpers:

  ```ruby
    class MyTest << ActionDispatch::IntegrationTest
      test "example" do
        # Works correctly on main
        Rails.application.routes.url_helpers.polymorphic_url(@post)

        # Does not work without this patch
        polymorphic_url(@post)
      end
    end
  ```

  I removed the previous implementation because it was at the wrong
  level.

Author: Edouard-chin

railties/lib/rails/engine/lazy_route_set.rb

@@ -34,16 +34,6 @@ def optimize_routes_generation?
           Rails.application&.reload_routes_unless_loaded
           super
         end
-
-        def polymorphic_url(record_or_hash_or_array, options = {})
-          Rails.application&.reload_routes_unless_loaded
-          super
-        end
-
-        def polymorphic_path(record_or_hash_or_array, options = {})
-          Rails.application&.reload_routes_unless_loaded
-          super
-        end
       end
 
       def initialize(config = DEFAULT_CONFIG)
@@ -68,6 +58,11 @@ def call(req)
         super
       end
 
+      def polymorphic_mappings
+        Rails.application&.reload_routes_unless_loaded
+        super
+      end
+
       def draw(&block)
         Rails.application&.reload_routes_unless_loaded
         super

railties/test/engine/lazy_route_set_test.rb

@@ -52,6 +52,26 @@ class UsersController < ActionController::Base
         assert_equal(200, response.first)
       end
 
+      test "app lazily loads routes when polymorphic_url is called" do
+        app_file "test/integration/my_test.rb", <<~RUBY
+          require "test_helper"
+
+          class MyTest < ActionDispatch::IntegrationTest
+            test "polymorphic_url works" do
+              puts polymorphic_url(Comment.new)
+            end
+          end
+        RUBY
+
+        app_file "app/models/comment.rb", <<~RUBY
+          class Comment
+          end
+        RUBY
+
+        output = rails("test", "test/integration/my_test.rb")
+        assert_match("https://example.org", output)
+      end
+
       test "engine lazily loads routes when making a request" do
         require "#{app_path}/config/environment"
 
@@ -137,6 +157,7 @@ class User < ActiveRecord::Base
 
               resources :products
               resources :users, module: "rails/engine/lazy_route_set_test"
+              resolve("Comment") { "https://example.org" }
 
               mount Plugin::Engine, at: "/plugin"
             end