Deprecated functionality: preg_match(): Passing null to parameter #4 ($flags) of type int is deprecated

[addison74]

[Test Environment]

• Windows 11 + WSL
• Docker 4.34.2
• DDEV (Apache 2.4.61, PHP 8.3.10, MariaDB 10.11.8) with MAGE_IS_DEVELOPER_MODE=1
• Magento Sample Data

Go the Backend > System > Configuration > Advanced > Developer > Translate Inline. Set "Enablde for Admin" to Yes and save. Here is the error message you will see in the browser page

Deprecated functionality: preg_match(): Passing null to parameter #4 ($flags) of type int is deprecated  in /var/www/html/app/code/core/Mage/Core/Model/Translate/Inline.php on line 521

#0 [internal function]: mageCoreErrorHandler()
#1 /var/www/html/app/code/core/Mage/Core/Model/Translate/Inline.php(521): preg_match()
#2 /var/www/html/app/code/core/Mage/Core/Model/Translate/Inline.php(463): Mage_Core_Model_Translate_Inline->findEndOfTag()
#3 /var/www/html/app/code/core/Mage/Core/Model/Translate/Inline.php(404): Mage_Core_Model_Translate_Inline->_translateTags()
#4 /var/www/html/app/code/core/Mage/Core/Model/Translate/Inline.php(223): Mage_Core_Model_Translate_Inline->_specialTags()
#5 /var/www/html/app/code/core/Mage/Core/Controller/Varien/Action.php(389): Mage_Core_Model_Translate_Inline->processResponseBody()
#6 /var/www/html/app/code/core/Mage/Adminhtml/controllers/DashboardController.php(37): Mage_Core_Controller_Varien_Action->renderLayout()
#7 /var/www/html/app/code/core/Mage/Core/Controller/Varien/Action.php(419): Mage_Adminhtml_DashboardController->indexAction()
#8 /var/www/html/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(255): Mage_Core_Controller_Varien_Action->dispatch()
#9 /var/www/html/app/code/core/Mage/Core/Controller/Varien/Front.php(180): Mage_Core_Controller_Varien_Router_Standard->match()
#10 /var/www/html/app/code/core/Mage/Core/Model/App.php(358): Mage_Core_Controller_Varien_Front->dispatch()
#11 /var/www/html/app/Mage.php(748): Mage_Core_Model_App->run()
#12 /var/www/html/index.php(56): Mage::run()
#13 {main}

From now on you cannot access the Backend. You have to change in the database > table core_config_data > "dev/translate_inline/active_admin" from 1 to 0 in the "path" column.

if (preg_match('#<\\\\?\/' . $tagName . '\s*?>#i', $body, $tagMatch, null, $end))

This issue can be reproduced starting with PHP version 8.1. It is strange how it was not discovered by the GitHub tests.