Upgrade path for shipping rate tax data

CHANGELOG.md

@@ -20,12 +20,15 @@
     The shipping rate taxer class can be exchanged for a custom estimator class
     using the new Spree::Appconfiguration.shipping_rate_taxer_class preference.
 
-    Shipping rates for completed orders before this change will, unfortunately, not be shown
-    with their taxes from Solidus 1.3 onwards. If you do change the shipping rate on an
-    old order, its taxes will be calculated correctly, though.
-
     https://github.com/solidusio/solidus/pull/904
 
+    In order to convert your historical shipping rate taxation data, please run  
+    `rake solidus:upgrade:one_point_three` - this will create persisted taxation notes
+    for historical shipping rates. Be aware though that these taxation notes are
+    estimations and should not be used for accounting purposes.
+
+    https://github.com/solidusio/solidus/pull/1068
+
 *   Deprecate setting a line item's currency by hand
 
     Previously, a line item's currency could be set directly, and differently from the line item's

core/lib/tasks/migrations/migrate_shipping_rate_taxes.rake

@@ -0,0 +1,17 @@
+namespace :solidus do
+  namespace :migrations do
+    namespace :migrate_shipping_rate_taxes do
+      task up: :environment do
+        puts "Adding persisted tax notes to historic shipping rates"
+        Spree::ShippingRate.where.not(tax_rate_id: nil).find_each do |shipping_rate|
+          tax_rate = Spree::TaxRate.unscoped.find(shipping_rate.tax_rate_id)
+          shipping_rate.taxes.find_or_create_by!(
+            tax_rate: tax_rate,
+            amount: tax_rate.compute_amount(shipping_rate)
+          )
+        end
+        Spree::ShippingRate.where.not(tax_rate_id: nil).update_all(tax_rate: nil)
+      end
+    end
+  end
+end

core/lib/tasks/upgrade.rake

@@ -2,7 +2,8 @@ namespace :solidus do
   namespace :upgrade do
     desc "Upgrade Solidus to version 1.3"
     task one_point_three: [
-        'solidus:migrations:assure_store_on_orders:up'
+        'solidus:migrations:assure_store_on_orders:up',
+        'solidus:migrations:migrate_shipping_rate_taxes:up'
       ] do
       puts "Your Solidus install is ready for Solidus 1.3."
     end