fix(imap_client): avoid array-to-string warning in getNamespaces

lib/Horde/Imap/Client/Base.php

@@ -1,3 +1,3 @@
 <?php
 
 /**
@@ -712,7 +712,8 @@
      *                           additional namespaces to add to the
      *                           namespace list that are not broadcast by
      *                           the server. The namespaces must be UTF-8
-     *                           strings.
+     *                           strings. Non-scalar entries (e.g. nested
+     *                           arrays) are ignored.
      * @param array $opts        Additional options:
      *   - ob_return: (boolean) If true, returns a
      *                Horde_Imap_Client_Namespace_List object instead of an
@@ -741,7 +742,19 @@
         array $additional = [],
         array $opts = []
     ) {
-        $additional = array_map('strval', $additional);
+        /* Only scalar/Stringable values are valid namespace names. Nested
+         * arrays (e.g. from a misconfigured IMP backends.php 'namespace'
+         * entry) must not be passed to strval() — that triggers
+         * "Array to string conversion" on PHP 8+. */
+        $normalized = [];
+        foreach ($additional as $val) {
+            if (is_array($val) ||
+                (is_object($val) && !($val instanceof Stringable))) {
+                continue;
+            }
+            $normalized[] = strval($val);
+        }
+        $additional = $normalized;
         $sig = hash(
             'md5',
             json_encode($additional) . intval(empty($opts['ob_return']))
@@ -756,7 +769,7 @@
 
             /* Skip namespaces if we have already auto-detected them. Also,
              * hidden namespaces cannot be empty. */
-            $to_process = array_diff(array_filter($additional, 'strlen'), array_map('strlen', iterator_to_array($ns)));
+            $to_process = array_diff(array_filter($additional, 'strlen'), array_map('strval', iterator_to_array($ns)));
             if (!empty($to_process)) {
                 foreach ($this->listMailboxes($to_process, Horde_Imap_Client::MBOX_ALL, ['delimiter' => true]) as $key => $val) {
                     $ob = new Horde_Imap_Client_Data_Namespace();

test/Unit/Base/GetNamespacesTest.php

@@ -0,0 +1,165 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * Copyright 2026 The Horde Project (http://www.horde.org/)
+ *
+ * See the enclosed file LICENSE for license information (LGPL). If you
+ * did not receive this file, see http://www.horde.org/licenses/lgpl21.
+ *
+ * @author     Torben Dannhauer <torben@dannhauer.de>
+ * @category   Horde
+ * @copyright  2026 The Horde Project
+ * @license    http://www.horde.org/licenses/lgpl21 LGPL 2.1
+ * @package    Imap_Client
+ */
+
+namespace Horde\Imap\Client\Test\Unit\Base;
+
+use Horde\Imap\Client\Test\Stub\Base;
+use Horde_Imap_Client_Data_Namespace;
+use Horde_Imap_Client_Mailbox;
+use Horde_Imap_Client_Namespace_List;
+use PHPUnit\Framework\Attributes\CoversNothing;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Tests for Horde_Imap_Client_Base#getNamespaces().
+ *
+ * @author     Torben Dannhauer <torben@dannhauer.de>
+ * @copyright  2026 The Horde Project
+ * @license    http://www.horde.org/licenses/lgpl21 LGPL 2.1
+ */
+#[CoversNothing]
+class GetNamespacesTest extends TestCase
+{
+    /**
+     * Nested-array additional namespaces must not trigger
+     * "Array to string conversion" (horde/imp#94).
+     */
+    public function testAdditionalNestedArraysDoNotWarn(): void
+    {
+        $ob = new class ([
+            'username' => 'user',
+            'password' => 'pass',
+        ]) extends Base {
+            protected function _getNamespaces()
+            {
+                $ns = new Horde_Imap_Client_Data_Namespace();
+                $ns->delimiter = '/';
+                $ns->name = '';
+                $ns->type = Horde_Imap_Client_Data_Namespace::NS_PERSONAL;
+
+                return new Horde_Imap_Client_Namespace_List([$ns]);
+            }
+        };
+
+        $result = $ob->getNamespaces(
+            [
+                '#shared/',
+                '#broken' => ['delimiter' => '/'],
+                ['nested'],
+            ],
+            ['ob_return' => true]
+        );
+
+        $this->assertInstanceOf(Horde_Imap_Client_Namespace_List::class, $result);
+        $this->assertCount(1, $result);
+    }
+
+    /**
+     * Already-advertised namespaces in $additional must be skipped
+     * (array_map must use strval, not strlen, on the namespace list).
+     */
+    public function testSkipsAlreadyDetectedAdditionalNamespaces(): void
+    {
+        $listed = [];
+
+        $ob = new class ([
+            'username' => 'user',
+            'password' => 'pass',
+        ], $listed) extends Base {
+            /** @var array */
+            private $listedRef;
+
+            public function __construct(array $params, array &$listed)
+            {
+                parent::__construct($params);
+                $this->listedRef = &$listed;
+            }
+
+            protected function _getNamespaces()
+            {
+                $ns = new Horde_Imap_Client_Data_Namespace();
+                $ns->delimiter = '/';
+                $ns->name = '#shared/';
+                $ns->type = Horde_Imap_Client_Data_Namespace::NS_SHARED;
+
+                return new Horde_Imap_Client_Namespace_List([$ns]);
+            }
+
+            protected function _listMailboxes($pattern, $mode, $options)
+            {
+                $this->listedRef[] = $pattern;
+
+                return [];
+            }
+        };
+
+        $ob->getNamespaces(['#shared/', '#public/'], ['ob_return' => true]);
+
+        $this->assertCount(1, $listed);
+        $this->assertSame(
+            ['#public/'],
+            array_map('strval', $listed[0])
+        );
+    }
+
+    public function testStringableAdditionalNamespacesAreAccepted(): void
+    {
+        $listed = [];
+
+        $ob = new class ([
+            'username' => 'user',
+            'password' => 'pass',
+        ], $listed) extends Base {
+            /** @var array */
+            private $listedRef;
+
+            public function __construct(array $params, array &$listed)
+            {
+                parent::__construct($params);
+                $this->listedRef = &$listed;
+            }
+
+            protected function _getNamespaces()
+            {
+                $ns = new Horde_Imap_Client_Data_Namespace();
+                $ns->delimiter = '/';
+                $ns->name = '';
+                $ns->type = Horde_Imap_Client_Data_Namespace::NS_PERSONAL;
+
+                return new Horde_Imap_Client_Namespace_List([$ns]);
+            }
+
+            protected function _listMailboxes($pattern, $mode, $options)
+            {
+                $this->listedRef[] = $pattern;
+
+                return [];
+            }
+        };
+
+        $ob->getNamespaces(
+            [Horde_Imap_Client_Mailbox::get('#shared/')],
+            ['ob_return' => true]
+        );
+
+        $this->assertCount(1, $listed);
+        $this->assertSame(
+            ['#shared/'],
+            array_map('strval', $listed[0])
+        );
+    }
+}