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?

[nielsdos]

@vmajor you are somehow loading the DOM extension twice, causing it to get confused.
Either the DOM extension is embedded in the php binary, and you don't need to load it in the php.ini again. In that case remove the extension line for DOM in php.ini.
Or you are loading it twice in the php.ini and you have to remove the duplicate line.

I have no experience with ppa.
But in any case, you can always install a newer PHM version by compiling from the git repo yourself.

[vmajor]

Oh... thank you for the extremely fast, and correct reply. I had only one instance of DOM in php.ini, but I commented it out and now the test script works. Next, testing the presumably functional plugin.

Thank you so much.