Remove the upgrade task and point to additional steps from the update…

… generator

Having both an `upgrade` task and an `update` generator is confusing. On
top of that, it's better to have actionable items, which can be
undesirable in some situations, the most explicit as possible. For this
reason, we leave in place the `update` generator, which is just a safe
path to update preferences, and remove the `upgrade` task. Instead, we
add a generic message into the `update` generator pointing to the
detailed instructions in the Changelog.

In particular, at this point, the `update` task was calling to a single
task introduced in solidusio#3987. We still keep the task reachable by end-users,
but we rename it slightly to be more friendly.

core/lib/generators/solidus/update/update_generator.rb

@@ -57,6 +57,22 @@ def create_new_defaults_initializer
                File.join(options[:initializer_directory], "#{options[:initializer_basename]}.rb")
     end
 
+    def print_message
+      say <<~MSG
+
+        ***********************************************************************
+
+        Other tasks may be needed to update to the new Solidus version. Please,
+        check https://github.com/solidusio/solidus/blob/v#{options[:to]}/CHANGELOG.md
+        for details.
+
+        Thanks for using Solidus!
+
+        ***********************************************************************
+
+      MSG
+    end
+
     private
 
     def core_changes_template(from, to)

core/lib/tasks/solidus/delete_prices_with_nil_amount.rake

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+namespace :solidus do
+  desc "Delete Spree::Price records which amount field is NULL"
+  task delete_prices_with_nil_amount: :environment do
+    Spree::Price.where(amount: nil).delete_all
+  end
+end

core/spec/lib/tasks/migrations/delete_prices_with_nil_amount_spec.rb → core/spec/lib/tasks/solidus/delete_prices_with_nil_amount_spec.rb

@@ -2,14 +2,14 @@
 
 require 'rails_helper'
 
-path = Spree::Core::Engine.root.join('lib/tasks/migrations/delete_prices_with_nil_amount.rake')
+path = Spree::Core::Engine.root.join('lib/tasks/solidus/delete_prices_with_nil_amount.rake')
 
-RSpec.describe 'solidus:migrations:delete_prices_with_nil_amount' do
-  describe 'up' do
+RSpec.describe 'solidus' do
+  describe 'delete_prices_with_nil_amount' do
     include_context(
       'rake',
       task_path: path,
-      task_name: 'solidus:migrations:delete_prices_with_nil_amount:up'
+      task_name: 'solidus:delete_prices_with_nil_amount'
     )
 
     it 'removes all prices which amount column is NULL' do