Add lib to load paths when application is inherited to be able to load lib...

Add lib to load paths when application is inherited to be able to load lib code during configuration.

railties/lib/rails/application.rb

@@ -67,6 +67,7 @@ def inherited(base)
         raise "You cannot have more than one Rails::Application" if Rails.application
         super
         Rails.application = base.instance
+        Rails.application.add_lib_to_load_paths!
         ActiveSupport.run_load_hooks(:before_configuration, base.instance)
       end
 
@@ -83,11 +84,21 @@ def method_missing(*args, &block)
 
     delegate :middleware, :to => :config
 
+    def add_lib_to_load_paths!
+      path = config.root.join('lib').to_s
+      $LOAD_PATH.unshift(path) if File.exists?(path)
+    end
+
     def require_environment!
       environment = paths.config.environment.to_a.first
       require environment if environment
     end
 
+    def eager_load!
+      railties.all(&:eager_load!)
+      super
+    end
+
     def routes
       @routes ||= ActionDispatch::Routing::RouteSet.new
     end

railties/lib/rails/application/finisher.rb

@@ -38,7 +38,7 @@ module Finisher
       initializer :eager_load! do
         if config.cache_classes && !$rails_rake_task
           ActiveSupport.run_load_hooks(:before_eager_load, self)
-          railties.all(&:eager_load!)
+          eager_load!
         end
       end
 

railties/test/application/initializers/load_path_test.rb

@@ -19,6 +19,23 @@ def setup
       assert $:.include?("#{app_path}/app/models")
     end
 
+    test "initializing an application adds lib path on inheritance hook" do
+      app_file "lib/foo.rb", <<-RUBY
+        module Foo; end
+      RUBY
+
+      add_to_config <<-RUBY
+        require "foo"
+        raise "Expected Foo to be defined" unless defined?(Foo)
+      RUBY
+
+      assert_nothing_raised do
+        require "#{app_path}/config/environment"
+      end
+
+      assert $:.include?("#{app_path}/lib")
+    end
+
     test "initializing an application eager load any path under app" do
       app_file "app/anything/foo.rb", <<-RUBY
         module Foo; end