Ensure config.after_initializer is executed before building the middleware stack.

railties/lib/rails/application/finisher.rb

@@ -27,17 +27,19 @@ module Rails
         end
       end
 
-      initializer :build_middleware_stack do
-        app
-      end
-
       # Fires the user-supplied after_initialize block (config.after_initialize)
+      # Should run before the middleware stack is built, because building the
+      # middleware already fires to_prepare callbacks in test and production.
       initializer :after_initialize do
         config.after_initialize_blocks.each do |block|
           block.call(self)
         end
       end
 
+      initializer :build_middleware_stack do
+        app
+      end
+
       # Disable dependency loading during request cycle
       initializer :disable_dependency_loading do
         if config.cache_classes && !config.dependency_loading

railties/lib/rails/engine.rb

@@ -15,6 +15,7 @@ module Rails
       def inherited(base)
         unless abstract_railtie?(base)
           base.called_from = begin
+            # Remove the line number from backtraces making sure we don't leave anything behind
             call_stack = caller.map { |p| p.split(':')[0..-2].join(':') }
             File.dirname(call_stack.detect { |p| p !~ %r[railties[\w\-]*/lib/rails|rack[\w\-]*/lib/rack] })
           end

railties/test/application/initializers/initializers_test.rb

@@ -51,5 +51,19 @@ module ApplicationTests
       assert $activerecord_configurations
       assert $activerecord_configurations['development']
     end
+
+    test "after_initialize happens before to_prepare (i.e. before the middleware stack is built) on production" do
+      $order = []
+      add_to_config <<-RUBY
+        config.after_initialize { $order << :after_initialize }
+        config.to_prepare { $order << :to_prepare }
+      RUBY
+
+      require "#{app_path}/config/application"
+      Rails.env.replace "production"
+      require "#{app_path}/config/environment"
+      assert [:after_initialize, :to_prepare], $order
+    end
+
   end
 end