Ensure Spree::Country.available and Zone#country_list consistently return AR relations

core/app/models/spree/country.rb

@@ -17,9 +17,11 @@ def self.default
     def self.available(restrict_to_zone: Spree::Config[:checkout_zone])
       checkout_zone = Zone.find_by(name: restrict_to_zone)
 
-      return checkout_zone.country_list if checkout_zone.try(:kind) == 'country'
-
-      all
+      if checkout_zone.try(:kind) == 'country'
+        checkout_zone.country_list
+      else
+        all
+      end
     end
 
     def <=>(other)

core/app/models/spree/zone.rb

@@ -86,11 +86,11 @@ def include?(address)
 
     # convenience method for returning the countries contained within a zone
     def country_list
-      @countries ||= case kind
-                     when 'country' then zoneables
-                     when 'state' then zoneables.collect(&:country)
-                     else []
-                     end.flatten.compact.uniq
+      case kind
+      when 'country' then countries
+      when 'state' then Spree::Country.where(id: states.select(:id))
+      else Spree::Country.none
+      end
     end
 
     def <=>(other)

core/spec/models/spree/country_spec.rb

@@ -43,24 +43,28 @@
 
         context 'with no arguments' do
           it 'returns "Checkout Zone" countries' do
+            expect(described_class.available).to be_an(ActiveRecord::Relation)
             expect(described_class.available).to contain_exactly(united_states, canada)
           end
         end
 
         context 'setting nil as restricting zone' do
           it 'returns all countries' do
+            expect(described_class.available(restrict_to_zone: nil)).to be_an(ActiveRecord::Relation)
             expect(described_class.available(restrict_to_zone: nil)).to contain_exactly(united_states, canada, italy)
           end
         end
 
         context 'setting "Custom Zone" as restricting zone' do
           it 'returns "Custom Zone" countries' do
+            expect(described_class.available(restrict_to_zone: 'Custom Zone')).to be_an(ActiveRecord::Relation)
             expect(described_class.available(restrict_to_zone: 'Custom Zone')).to contain_exactly(united_states, italy)
           end
         end
 
         context 'setting "Checkout Zone" as restricting zone' do
           it 'returns "Checkout Zone" countries' do
+            expect(described_class.available(restrict_to_zone: 'Checkout Zone')).to be_an(ActiveRecord::Relation)
             expect(described_class.available(restrict_to_zone: 'Checkout Zone')).to contain_exactly(united_states, canada)
           end
         end

core/spec/models/spree/zone_spec.rb

@@ -57,6 +57,7 @@
       before { country_zone.members.create(zoneable: country) }
 
       it 'should return a list of countries' do
+        expect(country_zone.country_list).to be_a(ActiveRecord::Relation)
         expect(country_zone.country_list).to eq([country])
       end
     end
@@ -67,9 +68,19 @@
       before { state_zone.members.create(zoneable: state) }
 
       it 'should return a list of countries' do
+        expect(state_zone.country_list).to be_a(ActiveRecord::Relation)
         expect(state_zone.country_list).to eq([state.country])
       end
     end
+
+    context "when zone doesn't consist of either countries nor states" do
+      let(:zone) { create(:zone, name: 'Zone') }
+
+      it 'should return an empty list' do
+        expect(zone.country_list).to be_a(ActiveRecord::Relation)
+        expect(zone.country_list).to be_empty
+      end
+    end
   end
 
   context "#include?" do