Resolve #3440293 : Source plugins for entity reference fields

Closes #3440293

src/Plugin/Derivative/EntityReferencedDerivableContextDeriver.php

+<?php
+
+namespace Drupal\ui_patterns\Plugin\Derivative;
+
+use Drupal\Component\Plugin\PluginBase;
+use Drupal\Core\Plugin\Context\ContextDefinition;
+use Drupal\Core\Plugin\Context\EntityContextDefinition;
+
+/**
+ * Provides derivable context for every field from referenced entities.
+ */
+class EntityReferencedDerivableContextDeriver extends EntityFieldSourceDeriverBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getDerivativeDefinitionsForEntityBundleField(string $entity_type_id, string $bundle, string $field_name, array $base_plugin_derivative): void {
+    $entity_reference_data = $this->getReferenceableEntityData($entity_type_id, $bundle, $field_name);
+    if (empty($entity_reference_data)) {
+      return;
+    }
+    $target_entity_type_id = $entity_reference_data["entity_type_id"];
+    $target_bundles = $entity_reference_data["bundles"];
+    if (count($target_bundles) > 1) {
+      $target_bundles[] = "";
+    }
+    unset($base_plugin_derivative["context_definitions"]["field_name"]);
+    if (!isset($base_plugin_derivative['tags']) || !is_array($base_plugin_derivative['tags'])) {
+      $base_plugin_derivative['tags'] = [];
+    }
+    $base_plugin_derivative['tags'][] = "entity_referenced";
+    $base_plugin_derivative['tags'] = array_filter($base_plugin_derivative['tags'], function ($tag) {
+      return $tag !== "field";
+    });
+    $this->generateDefinitionsForReferencedEntityTypes($entity_type_id, $bundle, $field_name, $base_plugin_derivative, $target_entity_type_id, $target_bundles);
+  }
+
+  /**
+   * Get referenceable entity data for a field.
+   *
+   * @param string $entity_type_id
+   *   The entity type id.
+   * @param string $bundle
+   *   The bundle.
+   * @param string $field_name
+   *   The field name.
+   *
+   * @return array|null
+   *   The entity reference data or NULL.
+   */
+  private function getReferenceableEntityData(string $entity_type_id, string $bundle, string $field_name): ?array {
+    $entity_reference_data = $this->entityFieldsMetadata[$entity_type_id]["bundles"][$bundle]["fields"][$field_name]["entity_reference"];
+    if (!is_array($entity_reference_data) || (count($entity_reference_data) === 0) ||
+      !isset($entity_reference_data["fieldable"]) || !$entity_reference_data["fieldable"] ||
+      !isset($entity_reference_data["bundles"]) || (count($entity_reference_data["bundles"]) === 0)) {
+      return NULL;
+    }
+    return $entity_reference_data;
+  }
+
+  /**
+   * Get entity bundle labels.
+   *
+   * @param string $entity_type_id
+   *   The entity type id.
+   * @param array $bundles
+   *   The bundles.
+   *
+   * @return array
+   *   The entity bundle labels.
+   */
+  private function getEntityBundleLabels(string $entity_type_id, array $bundles): array {
+    $target_bundle_to_label = [];
+    foreach ($bundles as $target_bundle) {
+      $target_entity_type_fields_data = $this->entityFieldsMetadata[$entity_type_id];
+      $target_bundle_data = [];
+      if (isset($target_entity_type_fields_data["bundles"]) && is_array($target_entity_type_fields_data["bundles"])) {
+        $target_bundle_data = $target_entity_type_fields_data["bundles"][$target_bundle] ?? [];
+      }
+      $target_bundle_to_label[$target_bundle] = $target_bundle_data["label"] ?? $this->entityFieldsMetadata[$entity_type_id]["label"];
+    }
+    return $target_bundle_to_label;
+  }
+
+  /**
+   * Generate definitions for referenced entity types.
+   *
+   * @param string $entity_type_id
+   *   The entity type id.
+   * @param string $bundle
+   *   The bundle.
+   * @param string $field_name
+   *   The field name.
+   * @param array $base_plugin_derivative
+   *   The base plugin derivative.
+   * @param string $target_entity_type_id
+   *   The target entity type id.
+   * @param array $target_bundles
+   *   The target bundles.
+   */
+  private function generateDefinitionsForReferencedEntityTypes(string $entity_type_id, string $bundle, string $field_name, array $base_plugin_derivative, string $target_entity_type_id, array $target_bundles): void {
+    $target_bundle_to_label = $this->getEntityBundleLabels($target_entity_type_id, $target_bundles);
+    $base_label = $base_plugin_derivative["label"];
+    $target_entity_label = $this->entityFieldsMetadata[$target_entity_type_id]["label"] ?? "";
+    $no_bundle_context = (new ContextDefinition('string'))
+      ->setRequired()
+      ->setLabel("Bundle")
+      ->addConstraint('AllowedValues', [""]);
+    $entity_context = EntityContextDefinition::fromEntityTypeId($entity_type_id)
+      ->setRequired()
+      ->setLabel((string) ($this->entityFieldsMetadata[$entity_type_id]["label"] ?? ""));
+    foreach ($target_bundle_to_label as $target_bundle => $entity_bundle_label) {
+      $id = implode(PluginBase::DERIVATIVE_SEPARATOR, [
+        $entity_type_id,
+        $bundle,
+        $field_name,
+        $target_entity_type_id,
+        $target_bundle,
+      ]);
+      $bundle_label = ($target_bundle !== "" && (count($target_bundle_to_label) > 1)) ? $entity_bundle_label : sprintf("%s (%s)", $entity_bundle_label, $target_entity_label);
+      $this->derivatives[$id] = array_merge($base_plugin_derivative, [
+        "id" => $id,
+        "label" => t("@bundle referenced by @field", [
+          "@field" => $base_label,
+          "@bundle" => ($target_bundle == "") ? $target_entity_label : $bundle_label,
+        ]),
+      ]);
+      // Check plugin exists for host entity type without bundle.
+      $id_no_bundle = implode(PluginBase::DERIVATIVE_SEPARATOR, [
+        $entity_type_id,
+        "",
+        $field_name,
+        $target_entity_type_id,
+        $target_bundle,
+      ]);
+      if (!isset($this->derivatives[$id_no_bundle])) {
+        $field_storage_metadata = $this->entityFieldsMetadata[$entity_type_id]["field_storages"][$field_name];
+        $this->derivatives[$id_no_bundle] = array_merge($this->derivatives[$id], [
+          "id" => $id_no_bundle,
+          "label" => t("@target referenced by @field", [
+            "@field" => $field_storage_metadata["label"] ?? $field_name,
+            "@target" => $target_entity_label,
+          ]),
+        ]);
+        $this->derivatives[$id_no_bundle]["context_definitions"]["bundle"] = $no_bundle_context;
+        $this->derivatives[$id_no_bundle]["context_definitions"]["entity"] = $entity_context;
+      }
+    }
+  }
+
+}