Symfony version(s) affected

6.3

Description

When using XmlEncoder::decode on a node that does not have children and the node has a namespace defined then the namespace is not in the array even if it is needed for attributes on that node.
This results in an invalid xml when encoding it again to XML.

In the following example on how to reproduce there is a namespaced attribute xsi:noNamespaceSchemaLocation but after reading the xml and writing it again this is now invalid xml and throws a warning when trying to read it:
PHP Warning: XMLReader::read(): test.xml:2: namespace error : Namespace prefix xsi for noNamespaceSchemaLocation on property is not defined

How to reproduce

$encoder = new XmlEncoder();

$data = $encoder->decode(
    <<<'XML'
<?xml version="1.0" encoding="UTF-8"?>
<property xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="http://domain.com/path/to/schema.xsd" modification_timestamp="2009-11-10T10:52:16.0Z"></property>
XML,
    'array'
);

var_export($data);
// array (
//  '@xsi:noNamespaceSchemaLocation' => 'http://domain.com/path/to/schema.xsd',
//  '@modification_timestamp' => '2009-11-10T10:52:16.0Z',
//  '#' => '',
//)

echo $encode->encode($data, 'xml');
// <response xsi:noNamespaceSchemaLocation="http://domain.com/path/to/schema.xsd" modification_timestamp="2009-11-10T10:52:16.0Z"></response>

Possible Solution

The method XmlEncoder::parseXmlAttributes could check if an attribute has a namespace and at least fetch this namespace from the $node like it is done in XmlEncoder::decode in case the root node has child nodes:

foreach ($xpath->query('namespace::*', $dom->documentElement) as $nsNode) {
    $data['@'.$nsNode->nodeName] = $nsNode->nodeValue;
}

Additional Context

No response