Validate order items modified on the cart form

Blind patch to at least scaffold out what the code should kind of look like.

1. --- a/modules/cart/src/Plugin/views/field/EditQuantity.php
   +++ b/modules/cart/src/Plugin/views/field/EditQuantity.php
   
   @@ -169,6 +180,54 @@ class EditQuantity extends FieldPluginBase {
   +  public function viewsFormValidate(array &$form, FormStateInterface $form_state) {
   

   😂 had to find this, man.. Views.

       // Call the validation method on every field handler that has it.
       foreach ($view->field as $field) {
         if (method_exists($field, 'viewsFormValidate')) {
           $field->viewsFormValidate($form, $form_state);
         }
       }
   

2. +++ b/modules/cart/src/Plugin/views/field/EditQuantity.php
   @@ -169,6 +180,54 @@ class EditQuantity extends FieldPluginBase {
   +      if (!is_numeric($quantity) || $quantity < 0) {
   ...
   +      if ($order_item->getQuantity() == $quantity || $quantity <= 0) {
   +        // The quantity hasn't changed.
   +        continue;
   

   Above we check $quantity < 0 and here we check if it is also equal to 0. The could still mean the quantity changed. Should we change

   if (!is_numeric($quantity) || $quantity < 0) {
   

   to

   if (!is_numeric($quantity) || $quantity =< 0) {
   

   and update the inline comments? This handles invalid values or purposely set to 0 quantities?

3. +++ b/modules/cart/src/Plugin/views/field/EditQuantity.php
   @@ -169,6 +180,54 @@ class EditQuantity extends FieldPluginBase {
   +        ->filterByFieldAccess($this->currentUser)
   

   I don't think we need to filter by field access if we are then filtering by the two specified fields

4. +++ b/modules/cart/src/Plugin/views/field/EditQuantity.php
   @@ -169,6 +180,54 @@ class EditQuantity extends FieldPluginBase {
   +      $order_item->setValidationRequired(FALSE);
   

   Is this required? This isn't a content entity form, so I don't think this affects anything.

   And, upon further digging.. it looks like this flag is mostly used when importing entities via Migrate, not even the content entity form.

5. +++ b/modules/cart/src/Plugin/views/field/EditQuantity.php
   @@ -169,6 +180,54 @@ class EditQuantity extends FieldPluginBase {
   +      // Restore the quantity so the logic in viewsFormSubmit() proceeds with
   +      // the quantity update.
   +      $order_item->setQuantity($original_quantity);
   

   Actually, we could remove this and just update viewsFormSubmit to trust the set quantity value. We've validated it already, so the form submit no longer needs to.

Ah okay. Thanks @jsacksick for clarifying Views form handling 🙂.

Moving to RTBC as my sign off, if you'd like the honors of commit.