Resolve #2852463 "Configurable plugin trait 10.1"

Closes #2852463

core/lib/Drupal/Component/Plugin/ConfigurableTrait.php

+<?php
+
+namespace Drupal\Component\Plugin;
+
+use Drupal\Component\Utility\NestedArray;
+
+/**
+ * Implements \Drupal\Component\Plugin\ConfigurableInterface.
+ *
+ * In order for configurable plugins to maintain their configuration, the
+ * default configuration must be merged into any explicitly defined
+ * configuration. This trait provides the appropriate getters and setters to
+ * handle this logic, removing the need for excess boilerplate.
+ *
+ * @ingroup Plugin
+ */
+trait ConfigurableTrait {
+
+  /**
+   * Configuration information passed into the plugin.
+   *
+   * @var array
+   */
+  protected $configuration;
+
+  /**
+   * Gets this plugin's configuration.
+   *
+   * @return array
+   *   An array of this plugin's configuration.
+   *
+   * @see \Drupal\Component\Plugin\ConfigurableInterface::getConfiguration()
+   */
+  public function getConfiguration() {
+    return $this->configuration;
+  }
+
+  /**
+   * Sets the configuration for this plugin instance.
+   *
+   * @param array $configuration
+   *   An associative array containing the plugin's configuration. Provided
+   *   value is merged with default configuration.
+   *
+   * @return $this
+   *
+   * @see \Drupal\Component\Plugin\ConfigurableInterface::setConfiguration()
+   */
+  public function setConfiguration(array $configuration) {
+    $this->configuration = NestedArray::mergeDeepArray([$this->defaultConfiguration(), $configuration], TRUE);
+    return $this;
+  }
+
+  /**
+   * Gets default configuration for this plugin.
+   *
+   * @return array
+   *   An associative array with the default configuration.
+   *
+   * @see \Drupal\Component\Plugin\ConfigurableInterface::defaultConfiguration()
+   */
+  public function defaultConfiguration() {
+    return [];
+  }
+
+}