[API][Extract to PR?] Enforce creating option values with an option type

Add a NOT NULL validation at the database level on top
of removing the existing deprecation warning.

Ref solidusio#4385.

core/app/models/spree/option_value.rb

@@ -2,9 +2,7 @@
 
 module Spree
   class OptionValue < Spree::Base
-    # TODO: Remove optional on Solidus v4.0. Don't forget adding a migration to
-    # enforce at the database layer
-    belongs_to :option_type, class_name: 'Spree::OptionType', inverse_of: :option_values, optional: true
+    belongs_to :option_type, class_name: 'Spree::OptionType', inverse_of: :option_values
     acts_as_list scope: :option_type
 
     has_many :option_values_variants, dependent: :destroy
@@ -15,15 +13,8 @@ class OptionValue < Spree::Base
 
     after_save :touch, if: :saved_changes?
     after_touch :touch_all_variants
-    after_save do
-      Spree::Deprecation.warn <<~MSG if option_type.nil?
-        Having an option_value with no associated option_type will be deprecated
-        on Solidus v4.0
-      MSG
-    end
 
-    # TODO: Remove allow_nil once option_type is required on Solidus v4.0
-    delegate :name, :presentation, to: :option_type, prefix: :option_type, allow_nil: true
+    delegate :name, :presentation, to: :option_type, prefix: :option_type
 
     self.allowed_ransackable_attributes = %w[name presentation]
 

core/db/migrate/20230321161854_change_column_null_option_values_option_type_id.rb

@@ -0,0 +1,5 @@
+class ChangeColumnNullOptionValuesOptionTypeId < ActiveRecord::Migration[5.2]
+  def change
+    change_column_null(:spree_option_values, :option_type_id, false)
+  end
+end

core/spec/models/spree/option_value_spec.rb

@@ -50,9 +50,9 @@
     end
   end
 
-  it 'deprecates creating an option_value with no associated option_type' do
-    expect(Spree::Deprecation).to receive(:warn).with(/deprecated/)
-
-    create(:option_value, option_type: nil)
+  it 'raises when creating an option_value with no associated option_type' do
+    expect {
+      create(:option_value, option_type: nil)
+    }.to raise_error(ActiveRecord::RecordInvalid)
   end
 end