Prevent updating WordPress users data

[MAILPOET-6168]

doc/api_methods/UpdateSubscriber.md

@@ -9,6 +9,8 @@ The argument `$subscriber` is similar to [Add Subscriber](AddSubscriber.md) meth
 
 It returns the updated subscriber. See [Get Subscriber](GetSubscriber.md) for a subscriber data structure.
 
+If the subscriber is a WordPress user, the method does not allow updating `email`, `first_name` and `last_name`. It needs to be updated in the `wp_users` and MailPoet will synchronise the new values.
+
 ## Arguments
 
 | Argument             | Type          | Description                               |

mailpoet/lib/API/MP/v1/Subscribers.php

@@ -177,6 +177,12 @@ class Subscribers {
     // filter out all incoming data that we don't want to change, like status ...
     $defaultFields = array_intersect_key($defaultFields, array_flip(['email', 'first_name', 'last_name', 'subscribed_ip']));
 
+    if ($subscriber->getWpUserId() !== null) {
+      unset($defaultFields['email']);
+      unset($defaultFields['first_name']);
+      unset($defaultFields['last_name']);
+    };
+
     if (empty($defaultFields['subscribed_ip'])) {
       $defaultFields['subscribed_ip'] = Helpers::getIP();
     }
@@ -201,7 +207,7 @@ class Subscribers {
         APIException::FAILED_TO_SAVE_SUBSCRIBER
       );
     }
-    
+
     return $this->subscribersResponseBuilder->build($subscriberEntity);
   }
 

mailpoet/tests/integration/API/MP/SubscribersTest.php

@@ -810,10 +810,24 @@ class SubscribersTest extends \MailPoetTest {
     $this->assertEquals('new value', $result['cf_' . $customField->getId()]);
   }
 
+  public function testUpdateSubscriberWordPressUser() {
+    $subscriber = $this->subscriberFactory->create();
+    $subscriber->setWpUserId(4);
+    $this->entityManager->flush();
+
+    $result = $this->getApi()->updateSubscriber($subscriber->getId(), [
+      'email' => 'newemail@example.com',
+      'first_name' => 'New Name',
+    ]);
+
+    $this->assertEquals($subscriber->getEmail(), $result['email']);
+    $this->assertEquals($subscriber->getFirstName(), $result['first_name']);
+  }
+
   public function testUpdateSubscriberFailsForNonExisting() {
     $this->expectException(APIException::class);
     $this->expectExceptionMessage('This subscriber does not exist.');
-    
+
     $this->getApi()->updateSubscriber('non existing', [
       'email' => 'newemail@example.com',
       'first_name' => 'New Name',