Rescue unknown checkout errors

app/controllers/checkout_controller.rb

@@ -68,6 +68,10 @@ class CheckoutController < Spree::CheckoutController
         render json: { path: order_path(@order) }, status: :ok
       end
     end
+  rescue StandardError => error
+    Bugsnag.notify(error)
+    flash[:error] = I18n.t("checkout.failed")
+    update_failed
   end
 
   # Clears the cached order. Required for #current_order to return a new order

config/locales/en.yml

@@ -1181,6 +1181,7 @@ en:
     already_ordered:
       cart: "cart"
       message_html: "You have an order for this order cycle already. Check the %{cart} to see the items you ordered before. You can also cancel items as long as the order cycle is open."
+    failed: "The checkout failed. Please let us know so that we can process your order."
   shops:
     hubs:
       show_closed_shops: "Show closed shops"

spec/controllers/checkout_controller_spec.rb

@@ -200,6 +200,14 @@ describe CheckoutController, type: :controller do
       expect(response.body).to eq({ path: spree.order_path(order) }.to_json)
     end
 
+    it "returns an error on unexpected failure" do
+      allow(order).to receive(:update_attributes).and_raise
+
+      spree_post :update, format: :json, order: {}
+      expect(response.status).to eq(400)
+      expect(response.body).to eq({ errors: {}, flash: {error: I18n.t("checkout.failed")} }.to_json)
+    end
+
     describe "stale object handling" do
       it "retries when a stale object error is encountered" do
         allow(ResetOrderService).to receive(:new).with(controller, order) { reset_order_service }