Rails.application should be set inside before_configuration hook

Fixes #14620

railties/lib/rails/application.rb

@@ -87,7 +87,7 @@ class Application < Engine
     class << self
       def inherited(base)
         super
-        Rails.application ||= base.instance
+        base.instance
       end
 
       # Makes the +new+ method public.
@@ -117,6 +117,8 @@ def initialize(initial_variable_values = {}, &block)
       @railties          = nil
       @message_verifiers = {}
 
+      Rails.application ||= self
+
       add_lib_to_load_path!
       ActiveSupport.run_load_hooks(:before_configuration, self)
 

railties/test/application/multiple_applications_test.rb

@@ -21,6 +21,12 @@ def test_cloning_an_application_makes_a_shallow_copy_of_config
       assert_equal Rails.application.config.secret_key_base, clone.config.secret_key_base, "The base secret key on the config should be the same"
     end
 
+    def test_inheriting_multiple_times_from_application
+      new_application_class = Class.new(Rails::Application)
+
+      assert_not_equal Rails.application.object_id, new_application_class.instance.object_id
+    end
+
     def test_initialization_of_multiple_copies_of_same_application
       application1 = AppTemplate::Application.new
       application2 = AppTemplate::Application.new

railties/test/railties/railtie_test.rb

@@ -72,6 +72,14 @@ class Foo < Rails::Railtie ; config.to_prepare { $to_prepare = true } ; end
       assert $to_prepare
     end
 
+    test "railtie have access to application in before_configuration callbacks" do
+      $after_initialize = false
+      class Foo < Rails::Railtie ; config.before_configuration { $before_configuration = Rails.root.to_path } ; end
+      assert_not $before_configuration
+      require "#{app_path}/config/environment"
+      assert_equal app_path, $before_configuration
+    end
+
     test "railtie can add after_initialize callbacks" do
       $after_initialize = false
       class Foo < Rails::Railtie ; config.after_initialize { $after_initialize = true } ; end