Add "only" match policy to product rule

app/models/solidus_friendly_promotions/rules/product.rb

@@ -17,7 +17,7 @@ def preload_relations
         [:products]
       end
 
-      MATCH_POLICIES = %w[any all none].freeze
+      MATCH_POLICIES = %w[any all none only].freeze
 
       validates :preferred_match_policy, inclusion: {in: MATCH_POLICIES}
 
@@ -50,6 +50,11 @@ def eligible?(order, _options = {})
             eligibility_errors.add(:base, eligibility_error_message(:has_excluded_product),
               error_code: :has_excluded_product)
           end
+        when "only"
+          unless order_products(order).all? { |product| eligible_products.include?(product) }
+            eligibility_errors.add(:base, eligibility_error_message(:has_excluded_product),
+              error_code: :has_excluded_product)
+          end
         else
           raise "unexpected match policy: #{preferred_match_policy.inspect}"
         end

config/locales/en.yml

@@ -45,10 +45,11 @@ en:
         promotions: This is used to determine the promotional discount to be applied to an order, an item, or shipping charges.
     product_rule:
       choose_products: Choose products
-      label: Order must contain %{select} of these products
-      match_all: all
-      match_any: at least one
-      match_none: none
+      label: Order must contain %{select} these products
+      match_all: all of
+      match_any: at least one of
+      match_none: none of
+      match_only: only
       product_source:
         group: From product group
         manual: Manually choose

spec/models/solidus_friendly_promotions/rules/product_spec.rb

@@ -113,6 +113,43 @@
       end
     end
 
+    context "with 'only' match policy" do
+      let(:rule_options) { super().merge(preferred_match_policy: "only") }
+
+      it "is not eligible if none of the order's products are in eligible products" do
+        allow(rule).to receive_messages(order_products: [product_one])
+        allow(rule).to receive_messages(eligible_products: [product_two, product_three])
+        expect(rule).not_to be_eligible(order)
+      end
+
+      it "is eligible if all of the order's products are in eligible products" do
+        allow(rule).to receive_messages(order_products: [product_one])
+        allow(rule).to receive_messages(eligible_products: [product_one])
+        expect(rule).to be_eligible(order)
+      end
+
+      context "when any of the order's products are in eligible products" do
+        before do
+          allow(rule).to receive_messages(order_products: [product_one, product_two])
+          allow(rule).to receive_messages(eligible_products: [product_two, product_three])
+        end
+
+        it { expect(rule).not_to be_eligible(order) }
+
+        it "sets an error message" do
+          rule.eligible?(order)
+          expect(rule.eligibility_errors.full_messages.first)
+            .to eq "Your cart contains a product that prevents this coupon code from being applied."
+        end
+
+        it "sets an error code" do
+          rule.eligible?(order)
+          expect(rule.eligibility_errors.details[:base].first[:error_code])
+            .to eq :has_excluded_product
+        end
+      end
+    end
+
     context "with an invalid match policy" do
       let(:rule) do
         described_class.create!(