Add ransacker for product variants option values

Introduce a ransacker `variants_option_values` on Spree::Product.
This ransacker enables dynamic filtering combined with ransack on
product variants option values.
For now, this attribute is geared towards usage in the admin interface.

https://activerecord-hackery.github.io/ransack/going-further/ransackers/

core/app/models/spree/product.rb

@@ -131,8 +131,16 @@ def find_or_build_master
 
     alias :options :product_option_types
 
+    ransacker :variants_option_values, formatter: proc { |v|
+      joins(variants_including_master: :option_values)
+      .where(spree_option_values: { id: v })
+      .pluck(:id)
+    } do |parent|
+      parent.table[:id]
+    end
+
     self.allowed_ransackable_associations = %w[stores variants_including_master master variants]
-    self.allowed_ransackable_attributes = %w[name slug]
+    self.allowed_ransackable_attributes = %w[name slug variants_option_values]
     self.allowed_ransackable_scopes = %i[available with_discarded with_all_variant_sku_cont with_kept_variant_sku_cont]
 
     # @return [Boolean] true if there are any variants

core/spec/models/spree/product_spec.rb

@@ -641,6 +641,58 @@ class Extension < Spree::Base
     end
   end
 
+  context "ransacker :variants_option_values" do
+    it "filters products based on option values of their variants" do
+      product_1 = create(:product)
+      option_value_1 = create(:option_value)
+      create(:variant, product: product_1, option_values: [option_value_1])
+
+      result = Spree::Product.ransack(variants_option_values_in: [option_value_1.id]).result
+      expect(result).to contain_exactly(product_1)
+    end
+
+    it "returns multiple products for the same option value" do
+      product_1 = create(:product)
+      product_2 = create(:product)
+      option_value_1 = create(:option_value)
+      create(:variant, product: product_1, option_values: [option_value_1])
+      create(:variant, product: product_2, option_values: [option_value_1])
+
+      result = Spree::Product.ransack(variants_option_values_in: [option_value_1.id]).result
+      expect(result).to contain_exactly(product_1, product_2)
+    end
+
+    it "returns no products if there is no match" do
+      non_existing_option_value_id = 99999
+      result = Spree::Product.ransack(variants_option_values_in: [non_existing_option_value_id]).result
+      expect(result).to be_empty
+    end
+
+    it "returns products that match any of the provided option value IDs" do
+      product_1 = create(:product)
+      product_2 = create(:product)
+      option_value_1 = create(:option_value)
+      option_value_2 = create(:option_value)
+      create(:variant, product: product_1, option_values: [option_value_1])
+      create(:variant, product: product_2, option_values: [option_value_2])
+
+      result = Spree::Product.ransack(variants_option_values_in: [option_value_1.id, option_value_2.id]).result
+      expect(result).to contain_exactly(product_1, product_2)
+    end
+
+    it "doesn't return products that have other option values not in the query" do
+      product_1 = create(:product)
+      product_2 = create(:product)
+      option_value_1 = create(:option_value)
+      option_value_2 = create(:option_value)
+      create(:variant, product: product_1, option_values: [option_value_1])
+      create(:variant, product: product_2, option_values: [option_value_2])
+
+      result = Spree::Product.ransack(variants_option_values_in: [option_value_1.id]).result
+      expect(result).not_to include(product_2)
+    end
+  end
+
   describe "ransack scopes" do
     context "available scope" do
       subject { described_class.ransack(available: true).result }