Typed property DOMDocument::$documentElement must not be accessed before initialization

[TimWolla]

Description

The following code:

<?php

try {
	$xml = new \DOMDocument('1.0', 'UTF-8');
	$xml->loadXML(
		<<<'EOT'
		<?xml version="1.0" encoding="UTF-8"?>
		<dummy>
		</dummy>
		EOT
	);
	var_dump($xml->documentElement);
} catch (Error $e) {
	echo '<pre>'.$e.'</pre>';
}

Resulted in this output:

Error: Typed property DOMDocument::$documentElement must not be accessed before initialization in /var/www/html/xml.php:12
Stack trace:
#0 {main}

But I expected this output instead:

object(DOMElement)#2 (23) { ["schemaTypeInfo"]=> NULL ["tagName"]=> string(5) "dummy" ["firstElementChild"]=> NULL ["lastElementChild"]=> NULL ["childElementCount"]=> int(0) ["previousElementSibling"]=> NULL ["nextElementSibling"]=> NULL ["nodeName"]=> string(5) "dummy" ["nodeValue"]=> string(1) " " ["nodeType"]=> int(1) ["parentNode"]=> string(22) "(object value omitted)" ["childNodes"]=> string(22) "(object value omitted)" ["firstChild"]=> string(22) "(object value omitted)" ["lastChild"]=> string(22) "(object value omitted)" ["previousSibling"]=> NULL ["nextSibling"]=> NULL ["attributes"]=> string(22) "(object value omitted)" ["ownerDocument"]=> string(22) "(object value omitted)" ["namespaceURI"]=> NULL ["prefix"]=> string(0) "" ["localName"]=> string(5) "dummy" ["baseURI"]=> string(14) "/var/www/html/" ["textContent"]=> string(1) " " }

---

Exact reproduction steps on a fresh Ubuntu 22.04 VM:

1. apt install php8.1 php-xml
2. Open the script in the browser: It works fine.
3. sed -i '/Dynamic Extensions/a extension=dom.so' /etc/php/8.1/apache2/php.ini (i.e. adding extension=dom.so to the dynamic extensions section of php.ini).
4. systemctl restart apache2
5. Open the script in the browser: It emits the error.

Note: The cause of the issue is a configuration error on the users end, but the error message is very non-descript and thus hard to debug. This issue is intended to ask for an improvement in error reporting (e.g. emitting an error because the extension is laoded twice or because a necessary dependency is not loaded in the right order).

PHP Version

PHP 8.1.2

Operating System

Ubuntu 22.04

[vmajor]

OK, I have no run into this error as well on my VM with Ubnutu 22.04.

php -v
PHP 8.1.12-1ubuntu4.3 (cli) (built: Aug 17 2023 17:37:48) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.1.12, Copyright (c) Zend Technologies
    with Zend OPcache v8.1.12-1ubuntu4.3, Copyright (c), by Zend Technologies

Code that triggers this error. I am not a php developer, just a user that is stuck with a presumably functioning plugin that fails to function on my brand new VM. This is a short code snippet that is designed to generate the error that crashes the plugin:

<?php

try {
        $xml = new \DOMDocument('1.0', 'UTF-8');
        $xml_string = <<<'EOT'
                <?xml version="1.0" encoding="UTF-8"?>
                <dummy>
                </dummy>
                EOT;
        if ($xml->loadXML($xml_string)) {
          var_dump($xml->documentElement);
        } else {
          echo "Invalid XML string";
        }
} catch (Error $e) {
        echo '<pre>'.$e.'</pre>';
}

?>

Error:

Error: Typed property DOMDocument::$documentElement must not be accessed before initialization in /var/www/*****/test2.php:11
Stack trace:
#0 {main}

DOM section of the php.ini

DOM/XML	enabled
DOM/XML API Version	20031129
libxml Version	2.9.14
HTML Support	enabled
XPath Support	enabled
XPointer Support	enabled
Schema Support	enabled
RelaxNG Support	enabled

I have no option to use a higher version of php because one is not available in the official lunar channel, and I cannot install ondrej/ppa because no repo is available for my version of ubuntu. Attempting to add the ppa fails with a 404.

Help?