Issue #3316144: Field cardinality is not preserved on inheritance

field_inheritance.module

@@ -16,6 +16,9 @@ use Drupal\Core\Ajax\AjaxResponse;
 use Drupal\Core\Ajax\OpenModalDialogCommand;
 use Drupal\Core\Url;
 use Drupal\Component\Serialization\Json;
+use Drupal\Core\Field\FieldDefinitionInterface;
+use Drupal\Core\Field\FieldStorageDefinitionInterface;
+use Drupal\field_inheritance\Entity\FieldInheritanceInterface;
 
 /**
  * Implements hook_help().
@@ -45,6 +48,7 @@ function field_inheritance_entity_bundle_field_info_alter(&$fields, EntityTypeIn
     $inherited_fields = \Drupal::entityTypeManager()->getStorage('field_inheritance')->loadMultiple($inherited_field_ids);
     if (!empty($inherited_fields)) {
       $x = 0;
+      /** @var \Drupal\field_inheritance\Entity\FieldInheritanceInterface $field */
       foreach ($inherited_fields as $field) {
         // We are only interested in adding computed fields to the destination
         // entity type.
@@ -75,24 +79,13 @@ function field_inheritance_entity_bundle_field_info_alter(&$fields, EntityTypeIn
           $settings['destination field'] = $field->destinationField();
         }
 
-        // Grab the configuration of the source field.
-        $source_field = FieldConfig::loadByName($field->sourceEntityType(), $field->sourceEntityBundle(), $field->sourceField());
-        if (!empty($source_field)) {
-          $settings = array_merge($settings, $source_field->getSettings());
-          $type = $source_field->getType();
-        }
-        else {
-          // This may be a basefield.
-          $basefields = \Drupal::service('entity_field.manager')->getBaseFieldDefinitions($field->sourceEntityType());
-          if (!empty($basefields[$field->sourceField()])) {
-            $source_field = $basefields[$field->sourceField()];
-            $settings = array_merge($settings, $source_field->getSettings());
-            $type = $source_field->getType();
-          }
-          else {
-            continue;
-          }
+        $source_field = _field_inheritance_get_field_definition('source', $field);
+        if (!$source_field) {
+          continue;
         }
+        $cardinality = _field_inheritance_determine_cardinality($field);
+        $settings = array_merge($settings, $source_field->getSettings());
+        $type = $source_field->getType();
 
         // Set the factory class used to inherit the data from the source.
         $class = '\Drupal\field_inheritance\FieldInheritanceFactory';
@@ -109,6 +102,7 @@ function field_inheritance_entity_bundle_field_info_alter(&$fields, EntityTypeIn
           ->setLabel(t('@label', ['@label' => $field->label()]))
           ->setName($field->idWithoutTypeAndBundle())
           ->setDescription(t('The inherited field: @field', ['@field' => $field->label()]))
+          ->setCardinality($cardinality)
           ->setComputed(TRUE)
           ->setClass($class)
           ->setSettings($settings)
@@ -129,6 +123,84 @@ function field_inheritance_entity_bundle_field_info_alter(&$fields, EntityTypeIn
   }
 }
 
+/**
+ * Get the field definition for the source or destination field.
+ *
+ * @param string $type
+ *   The 'source' or 'destination' field.
+ * @param Drupal\field_inheritance\Entity\FieldInheritanceInterface $inherited_field
+ *   The inherited field configuration.
+ */
+function _field_inheritance_get_field_definition(string $type, FieldInheritanceInterface $inherited_field): ?FieldDefinitionInterface {
+  switch ($type) {
+    case 'destination':
+      if (!$inherited_field->destinationField()) {
+        return NULL;
+      }
+      $field = FieldConfig::loadByName($inherited_field->destinationEntityType(), $inherited_field->destinationEntityBundle(), $inherited_field->destinationField());
+      if (!empty($field)) {
+        return $field;
+      }
+      $basefields = \Drupal::service('entity_field.manager')->getBaseFieldDefinitions($inherited_field->destinationEntityType());
+      return $basefields[$inherited_field->destinationField()] ?? NULL;
+
+    case 'source':
+    default:
+      if (!$inherited_field->sourceField()) {
+        return NULL;
+      }
+      $field = FieldConfig::loadByName($inherited_field->sourceEntityType(), $inherited_field->sourceEntityBundle(), $inherited_field->sourceField());
+      if (!empty($field)) {
+        return $field;
+      }
+      $basefields = \Drupal::service('entity_field.manager')->getBaseFieldDefinitions($inherited_field->sourceEntityType());
+      return $basefields[$inherited_field->sourceField()] ?? NULL;
+  }
+}
+
+
+/**
+ * Determine what the cardinality of the inherited field should be.
+ *
+ * @param Drupal\field_inheritance\Entity\FieldInheritanceInterface $field
+ *   The inherited field configuration.
+ */
+function _field_inheritance_determine_cardinality(FieldInheritanceInterface $field): int {
+  $source_cardinality = $destination_cardinality = 1;
+  $source_field = _field_inheritance_get_field_definition('source', $field);
+  if ($source_field) {
+    $source_cardinality = $source_field->getFieldStorageDefinition()->getCardinality();
+  }
+
+  if ($field->destinationField()) {
+    $destination_field = _field_inheritance_get_field_definition('destination', $field);
+    if ($destination_field) {
+      $destination_cardinality = $destination_field->getFieldStorageDefinition()->getCardinality();
+    }
+  }
+
+  switch ($field->type()) {
+    case 'prepend':
+    case 'append':
+      if (in_array(FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED, [$source_cardinality, $destination_cardinality])) {
+        return FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED;
+      }
+      return $source_cardinality + $destination_cardinality;
+      break;
+
+    case 'fallback':
+      if (in_array(FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED, [$source_cardinality, $destination_cardinality])) {
+        return FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED;
+      }
+      return max($source_cardinality, $destination_cardinality);
+
+    case 'inherit':
+    default:
+      return $source_cardinality;
+  }
+  return 1;
+}
+
 /**
  * Implements hook_form_alter().
  */