Checkout shows payment methods which cannot be reused

We need to filter them out, as well as those whose billing country isn't in the list of store's supported billing countries.

Here's a quick patch that accomplishes the filtering on REQUEST_TIME and the store's billing countries. It does not alter the address' country_code options in commerce_payment_gateway_form.

Mostly docs things that can be improved, tests looks good. I think the tag can be removed?

1. +++ b/modules/payment/src/PaymentMethodStorage.php
   @@ -25,13 +79,29 @@ class PaymentMethodStorage extends CommerceContentEntityStorage implements Payme
   +    // @todo Review and refactor for proper entity query condition as billing_profile.entity.address.country_code
   +    // @see https://www.drupal.org/node/2822359
   

   80 cols.

2. +++ b/modules/payment/src/PaymentMethodStorage.php
   @@ -25,13 +79,29 @@ class PaymentMethodStorage extends CommerceContentEntityStorage implements Payme
   +      foreach ($payment_methods as $key => $payment_method) {
   +        $country_code = $payment_method->getBillingProfile()->address->first()->getCountryCode();
   +        if (!in_array($country_code, $store_billing_countries)) {
   +          unset($payment_methods[$key]);
   +        }
   +      }
   

   This probably reads easier as an array_filter($payment_methods, function() { ... }).

   That doesn't really matter though. It's the same result.

3. +++ b/modules/payment/src/PaymentMethodStorageInterface.php
   @@ -18,10 +19,12 @@ interface PaymentMethodStorageInterface extends ContentEntityStorageInterface {
   +   * @param \Drupal\commerce_store\Entity\StoreInterface $store
   +   *   An optional store to filter by, for available billing countries.
   

   I think we can improve the comment here.

   An optional store, when passed the returned payment methods will only be those that are allowed for the the store's billing countries.

   Not sure if that makes sense?

4. +++ b/modules/payment/tests/src/Kernel/PaymentMethodReusableTest.php
   @@ -0,0 +1,172 @@
   +  /**
   +   * Modules to enable.
   +   *
   +   * @var array
   +   */
   +  public static $modules = [
   

   This docblock can be replaced by {@inheritdoc}

5. +++ b/modules/payment/tests/src/Kernel/PaymentMethodReusableTest.php
   @@ -0,0 +1,172 @@
   +    // An order item type that doesn't need a purchasable entity, for simplicity.
   

   80 cols.

6. +++ b/modules/payment/tests/src/Kernel/PaymentMethodReusableTest.php
   @@ -0,0 +1,172 @@
   +
   +
   +
   

   Too many blank lines. 1 should suffice.

7. +++ b/modules/payment/tests/src/Kernel/PaymentMethodReusableTest.php
   @@ -0,0 +1,172 @@
   +  public function testBillingCountryPaymentMethods() {
   

   Needs a docblock.

8. +++ b/modules/payment/tests/src/Kernel/PaymentMethodReusableTest.php
   @@ -0,0 +1,172 @@
   +  }
   +}
   

   Needs a blank link in between.

here is a new patch that add a solution for #2848754: Completing checkout as anonymous user stores payment method.
I included in the patch here as i think it completes the work done here (tests PaymentMethodReusableTest).
Extra: extra check for billing country restrictions added

if ($billing_profile = $payment_method->getBillingProfile()) {

For this patch, i used the PR patch:
https://github.com/drupalcommerce/commerce/pull/605
as the #8 patch throws an error:
PHPUnit_Framework_Exception: PHP Fatal error: Call to a member function getCountryCode() on a non-object in /d8path/modules/contrib/commerce/modules/payment/src/PaymentMethodStorage.php on line 97
Probably, somthing is missing from that patch.
Interdiff available.

We don't want to tag a new beta without this.

The patch in #10 fixed the issue of all anonymous user's payment methods being stored and showing up for other users.

I don't like the passing of $store to loadReusable(), it doesn't make sense from an API standpoint. We should be passing $billing_countries instead.

Making the change.

Um, I thought Expires=0 means "Never expires". But when I use it, the payment method is filtered anyway...?

PS: I've changed PaymentMethodStorage.php like so:

    $query = $this->getQuery();

    $expires = $query->orConditionGroup()
    ->condition('expires', 0)
    ->condition('expires', $this->time->getRequestTime(), '>');

    $query->condition('uid', $account->id())
      ->condition('payment_gateway', $payment_gateway->id())
      ->condition('reusable', TRUE)
      ->condition($expires)
      ->sort('created', 'DESC');

This makes the never-expiring payment methods appear again. Don't know at all whether this naive approach is correct. Put perhaps this quick band-aid fix is useful for anyone.