Eager load patches for older solidus versions

Solidus versions < 4.5 `require` some of their application code.
This leads to hard-to-debug problems with Flickwerk patches.
What this does is eager-load all the patches in a `to_prepare`
hook by constantizing them.

lib/solidus_support/engine_extensions.rb

@@ -37,16 +37,16 @@ def activate
       # This allows to add event subscribers to extensions without explicitly subscribing them,
       # similarly to what happens in Solidus core.
       def load_solidus_subscribers_from(path)
-        if SolidusSupport::LegacyEventCompat.using_legacy?
-          path.glob("**/*_subscriber.rb") do |subscriber_path|
-            require_dependency(subscriber_path)
-          end
+        return unless SolidusSupport::LegacyEventCompat.using_legacy?
 
-          if Spree::Event.respond_to?(:activate_all_subscribers)
-            Spree::Event.activate_all_subscribers
-          else
-            Spree::Event.subscribers.each(&:subscribe!)
-          end
+        path.glob("**/*_subscriber.rb") do |subscriber_path|
+          require_dependency(subscriber_path)
+        end
+
+        if Spree::Event.respond_to?(:activate_all_subscribers)
+          Spree::Event.activate_all_subscribers
+        else
+          Spree::Event.subscribers.each(&:subscribe!)
         end
       end
 
@@ -139,6 +139,19 @@ def enable_solidus_engine_support(engine)
             Flickwerk.aliases["Spree.user_class"] = Spree.user_class_name
           end
         end
+
+        initializer "eager_load_#{engine_name}_#{engine}_patches", after: "flickwerk.find_patches" do |app|
+          # Solidus versions < 4.5 `require` some of their application code.
+          # This leads to hard-to-debug problems with Flickwerk patches.
+          # What this does is eager-load all the patches in a `to_prepare`
+          # hook by constantizing them.
+          # You can override this behavior by setting the environment variable `SOLIDUS_LAZY_LOAD_PATCHES`.
+          if Spree.solidus_gem_version < Gem::Version.new("4.5.0.a") && !ENV["SOLIDUS_LAZY_LOAD_PATCHES"]
+            app.reloader.to_prepare do
+              Flickwerk.patches.each_value { _1.each(&:constantize) }
+            end
+          end
+        end
       end
     end
   end