Workaround Rails inheritance bug in Spree::Gateway

Due to a bug in ActiveRecord we need to load the tagging code in Gateway which
should have inherited it from its parent PaymentMethod.
We have to call it before loading the PaymentMethod decorator because the
tagging code won't load twice within the inheritance chain.

https://github.com/openfoodfoundation/openfoodnetwork/issues/3121

config/initializers/spree.rb

@@ -8,6 +8,16 @@
 
 require 'spree/product_filters'
 
+# Due to a bug in ActiveRecord we need to load the tagging code in Gateway which
+# should have inherited it from its parent PaymentMethod.
+# We have to call it before loading the PaymentMethod decorator because the
+# tagging code won't load twice within the inheritance chain.
+# https://github.com/openfoodfoundation/openfoodnetwork/issues/3121
+Spree::Gateway.class_eval do
+  acts_as_taggable
+  attr_accessible :tag_list
+end
+
 require "#{Rails.root}/app/models/spree/payment_method_decorator"
 require "#{Rails.root}/app/models/spree/gateway_decorator"
 

spec/models/spree/gateway_tagging_spec.rb

@@ -0,0 +1,27 @@
+require "spec_helper"
+
+# An inheritance bug made these specs fail.
+# See config/initializers/spree.rb
+shared_examples "taggable" do |parameter|
+  it "uses the given parameter" do
+    expect(subject.tag_list).to eq []
+  end
+end
+
+module Spree
+  describe PaymentMethod do
+    it_behaves_like "taggable"
+  end
+
+  describe Gateway do
+    it_behaves_like "taggable"
+  end
+
+  describe Gateway::PayPalExpress do
+    it_behaves_like "taggable"
+  end
+
+  describe Gateway::StripeConnect do
+    it_behaves_like "taggable"
+  end
+end