Fix #30 by backporting MDL-58395

auth_ldap: User sync now brings problem details and continue
It does not include the error messages, which will appear with
moodle 4.0.
Nevertheless this version should work with moodle 3.11 as well,
but with ugly log messages.

auth.php

@@ -432,6 +432,7 @@ class auth_plugin_ldap_syncplus extends auth_plugin_ldap {
 
             if (!empty($add_users)) {
                 mtrace(get_string('userentriestoadd', 'auth_ldap', count($add_users)));
+                $errors = 0;
 
                 $transaction = $DB->start_delegated_transaction();
                 foreach ($add_users as $user) {
@@ -457,6 +458,14 @@ class auth_plugin_ldap_syncplus extends auth_plugin_ldap {
                     }
 
                     $id = user_create_user($user, false);
+                    try {
+                        $id = user_create_user($user, false);
+                    } catch (Exception $e) {
+                        print_string('invaliduserexception', 'auth_ldap', print_r($user, true) .  $e->getMessage());
+                        $errors++;
+                        continue;
+                    }
+
                     mtrace("\t".get_string('auth_dbinsertuser', 'auth_db', array('name'=>$user->username, 'id'=>$id)));
                     $euser = $DB->get_record('user', array('id' => $id));
 
@@ -470,6 +479,11 @@ class auth_plugin_ldap_syncplus extends auth_plugin_ldap {
                     // Add roles if needed.
                     $this->sync_roles($euser);
                 }
+
+                // Display number of user creation errors, if any.
+                if ($errors) {
+                    print_string('invalidusererrors', 'auth_ldap', $errors);
+                }
                 $transaction->allow_commit();
                 unset($add_users); // free mem
             } else {