Remove variant from cart when it becomes out of stock

app/models/spree/order_populator_decorator.rb

@@ -60,6 +60,8 @@ Spree::OrderPopulator.class_eval do
 
       if quantity_to_add > 0
         @order.add_variant(variant, quantity_to_add, max_quantity_to_add, currency)
+      else
+        @order.remove_variant variant
       end
     end
   end

spec/models/spree/order_populator_spec.rb

@@ -177,6 +177,19 @@ module Spree
 
         op.attempt_cart_add(333, quantity.to_s, quantity.to_s)
       end
+
+      it "removes variants which have become out of stock" do
+        op.should_receive(:quantities_to_add).with(variant, 123, 123).
+          and_return([0, 0])
+
+        op.stub(:check_order_cycle_provided_for) { true }
+        op.stub(:check_variant_available_under_distribution) { true }
+
+        order.should_receive(:remove_variant).with(variant)
+        order.should_receive(:add_variant).never
+
+        op.attempt_cart_add(333, quantity.to_s, quantity.to_s)
+      end
     end
 
     describe "quantities_to_add" do