Issue #2823380 by LOBsTerr, heddn: SoapClient not found

composer.json

@@ -17,7 +17,9 @@
     "source": "https://cgit.drupalcode.org/migrate_plus"
   },
   "minimum-stability": "dev",
-  "require": {},
+  "require": {
+    "ext-soap": "*"
+  },
   "suggest": {
     "sainsburys/guzzle-oauth2-plugin": "3.0 required for the OAuth2 authentication plugin"
   }

src/Plugin/migrate_plus/data_parser/Soap.php

@@ -3,6 +3,7 @@
 namespace Drupal\migrate_plus\Plugin\migrate_plus\data_parser;
 
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\migrate\Exception\RequirementsException;
 use Drupal\migrate\MigrateException;
 use Drupal\migrate_plus\DataParserPluginBase;
 
@@ -46,8 +47,14 @@ class Soap extends DataParserPluginBase implements ContainerFactoryPluginInterfa
 
   /**
    * {@inheritdoc}
+   *
+   * @throws \Drupal\migrate\Exception\RequirementsException
+   *   If PHP SOAP extension is not installed.
    */
   public function __construct(array $configuration, $plugin_id, $plugin_definition) {
+    if (!class_exists('\SoapClient')) {
+      throw new RequirementsException('The PHP SOAP extension is not installed');
+    }
     parent::__construct($configuration, $plugin_id, $plugin_definition);
     $this->function = $configuration['function'];
     $this->parameters = $configuration['parameters'];
@@ -63,7 +70,7 @@ class Soap extends DataParserPluginBase implements ContainerFactoryPluginInterfa
    *   If we can't resolve the SOAP function or its response property.
    */
   protected function openSourceUrl($url) {
-    // Will throw SoapFault if there's
+    // Will throw SoapFault if there's an error in a SOAP call.
     $client = new \SoapClient($url);
     // Determine the response property name.
     $function_found = FALSE;