Add a DummyApp sprockets 4 configuration manifest

This is needed from Sprockets, since v4. It contains
all dependencies that needs to be compiled.

Co-Authored-By: Elia Schito <[email protected]>

Gemfile

@@ -12,11 +12,6 @@ else
 end
 # rubocop:enable Bundler/DuplicatedGem
 
-# Temporarily locking sprockets to v3.x
-# see https://github.com/solidusio/solidus/issues/3374
-# and https://github.com/rails/sprockets-rails/issues/369
-gem 'sprockets', '~> 3'
-
 gem 'pry'
 gem 'launchy', require: false
 

core/lib/spree/testing_support/dummy_app.rb

@@ -34,8 +34,11 @@ module ApplicationHelper
 module DummyApp
   def self.setup(gem_root:, lib_name:, auto_migrate: true)
     ENV["LIB_NAME"] = lib_name
-    DummyApp::Application.config.root = File.join(gem_root, 'spec', 'dummy')
+    root = Pathname(gem_root).join('spec/dummy')
+    root.join("app/assets/config").mkpath
+    root.join("app/assets/config/manifest.js").write("// Intentionally empty\n")
 
+    DummyApp::Application.config.root = root
     DummyApp::Application.initialize! unless DummyApp::Application.initialized?
 
     if auto_migrate

core/lib/spree/testing_support/dummy_app/assets/config/manifest.js

@@ -0,0 +1,3 @@
+// This manifest is left empty because we are already
+// injecting Solidus manifests to be compiled in the
+// precompile array manually.