Provide a custom field formatter

Patchfile uploaded for field formatter. This formatter shows customised price i.e. it shows striked default price and next to it shows new price. I tried to show 'reason for the customised price' as required in the issue summary but I think for 'reason for the customised price' we will need a new field in price rule entity. @krystalcode What do you suggest?

1. +++ b/src/Plugin/Field/FieldFormatter/PriceRuleFormatter.php
   @@ -0,0 +1,55 @@
   +      $purchasable_entity = $items->getEntity();
   

   I think it should be $item->getEntity()

2. +++ b/src/Plugin/Field/FieldFormatter/PriceRuleFormatter.php
   @@ -0,0 +1,55 @@
   +      $number = $resolved_price->getNumber();
   

   Can we mention the data type here.

3. +++ b/src/Plugin/Field/FieldFormatter/PriceRuleFormatter.php
   @@ -0,0 +1,55 @@
   +      $currency = $this->currencyStorage->load($resolved_price->getCurrencyCode());
   

   Can we mention the data type here as well.

4. +++ b/src/Plugin/Field/FieldFormatter/PriceRuleFormatter.php
   @@ -0,0 +1,55 @@
   +        '#markup' => '<del>' . $default_price . '</del>&nbsp;' . $new_price,
   

   It is recommended to use #plain_text here, or Xss::filterAdmin()

@subhojit777 I referred this code from the price module`s PriceCalculatedFormatter. These things are there as it is. But if you still think that this patch needs your mentioned changes then I will do it.

I think it should be $item->getEntity()

I am quite sure about this one. Rest of them are code improvements, and writing more secure code.

+++ b/src/Plugin/Field/FieldFormatter/PriceRuleFormatter.php
@@ -0,0 +1,55 @@
+  public function viewElements(FieldItemListInterface $items, $langcode) {
+    $context = new Context($this->currentUser, $this->currentStore->getStore());
+    $elements = [];
+    /** @var \Drupal\commerce_price\Plugin\Field\FieldType\PriceItem $item */
+    foreach ($items as $delta => $item) {
+      /** @var \Drupal\commerce\PurchasableEntityInterface $purchasable_entity */
+      $purchasable_entity = $items->getEntity();

See its $items provided in viewElements() method as argument. Therefore, I will need to change that argument to $item is I make change suggested by you. Its same as in PriceCalculatedFormatter.

I am talking about the $item in the loop foreach ($items as $delta => $item)

As per discussion with @subhojit777 over the chat -

+      /** @var \Drupal\commerce\PurchasableEntityInterface $purchasable_entity */
+      $purchasable_entity = $items->getEntity();
+      $resolved_price = $this->chainPriceResolver->resolve($purchasable_entity, 1, $context);
+      $number = $resolved_price->getNumber();
+      $currency = $this->currencyStorage->load($resolved_price->getCurrencyCode());
+      $default_price = $this->numberFormatter->formatCurrency($item->number, $currency);
+      $new_price = $this->numberFormatter->formatCurrency($number, $currency);

This hunk of code should be outside of the loop.

New patch contains above changes. Please review.

+++ b/src/Plugin/Field/FieldFormatter/PriceRuleFormatter.php
@@ -0,0 +1,55 @@
+        '#cache' => [
+          'tags' => $purchasable_entity->getCacheTags(),
+          'contexts' => Cache::mergeContexts($purchasable_entity->getCacheContexts(), [
+            'languages:' . LanguageInterface::TYPE_INTERFACE,
+            'country',
+          ]),
+        ],

Since cache tag only dependes on $purchasable_entity, therefore it can be created as an array variable outside the loop. We can then just use the variable in #cache

Patch updated with changes mentioned in #12. Please review.

Patch looks good to me.

This looks interesting. Can it be used yet?

Old thread, so probably not valid anymore. But just thought I'd mention the patch in #13 does not work for me. Failed with

Error: Call to a member function load() on null in Drupal\commerce_price_rule\Plugin\Field\FieldFormatter\PriceRuleFormatter->viewElements() (line 35 of modules/contrib/commerce_price_rule/src/Plugin/Field/FieldFormatter/PriceRuleFormatter.php).

This against the 1.0@alpha version. I did a quick check and the PriceCalculatedFormatter class that this patch extends does not have a field called currencyStorage, so that's probably why the null pointer exception. Seems the base repository has moved on since this patch was created...

#16 should be fixed. Also, the last patch did not check if there was a new price or not so it was possible for the formatter to show $10 $10. This new patch will use the parent formatter (“Calculated”) when there isn’t a cheaper price.