Eagerly build the routing helper module after routes are committed

This commit eagerly builds the route helper module after the routes have
been drawn and finalized.  This allows us to cache the helper module but
not have to worry about people accessing the module while route
definition is "in-flight", and automatically deals with cache
invalidation as the module is regenerated anytime someone redraws the
routes.

The restriction this commit introduces is that the url helper module can
only be accessed *after* the routes are done being drawn.

Refs #24554 and #32892

1 files changed, 27 insertions, 10 deletions

diff --git a/actionpack/lib/action_dispatch/testing/assertions/routing.rb b/actionpack/lib/action_dispatch/testing/assertions/routing.rb
index af41521c5c..0e8712f8d9 100644
--- a/actionpack/lib/action_dispatch/testing/assertions/routing.rb
+++ b/actionpack/lib/action_dispatch/testing/assertions/routing.rb
@@ -138,6 +138,20 @@ module ActionDispatch
         assert_generates(path.is_a?(Hash) ? path[:path] : path, generate_options, defaults, extras, message)
       end
 
+      # Provides a hook on `finalize!` so we can mutate a controller after the
+      # route set has been drawn.
+      class WithRouting < ActionDispatch::Routing::RouteSet # :nodoc:
+        def initialize(&block)
+          super()
+          @block = block
+        end
+
+        def finalize!
+          super
+          @block.call self
+        end
+      end
+
       # A helper to make it easier to test different route configurations.
       # This method temporarily replaces @routes with a new RouteSet instance.
       #
@@ -152,16 +166,19 @@ module ActionDispatch
       #   end
       #
       def with_routing
-        old_routes, @routes = @routes, ActionDispatch::Routing::RouteSet.new
-        if defined?(@controller) && @controller
-          old_controller, @controller = @controller, @controller.clone
-          _routes = @routes
-
-          @controller.singleton_class.include(_routes.url_helpers)
-
-          if @controller.respond_to? :view_context_class
-            @controller.view_context_class = Class.new(@controller.view_context_class) do
-              include _routes.url_helpers
+        old_routes = @routes
+        old_controller = nil
+        @routes = WithRouting.new do |_routes|
+          if defined?(@controller) && @controller
+            old_controller, @controller = @controller, @controller.clone
+            _routes = @routes
+
+            @controller.singleton_class.include(_routes.url_helpers)
+
+            if @controller.respond_to? :view_context_class
+              @controller.view_context_class = Class.new(@controller.view_context_class) do
+                include _routes.url_helpers
+              end
             end
           end
         end