Fix getChildren must be compatible with SimpleXMLElement with PHP 8

[luigifab]

Description

This PR fix the following error with PHP 8 (#1602):

Fatal error: Declaration of Mage_Api_Model_Wsdl_Config_Element::getChildren($source)
 must be compatible with SimpleXMLElement::getChildren() in
 [...]/app/code/core/Mage/Api/Model/Wsdl/Config/Element.php on line 179

OpenMage 20.0.10 / PHP 8.0.5

Manual testing scenarios

$proxy = new SoapClient('https://.../api/v2_soap/?wsdl', ['user_agent' => 'Local/Test']);
$sessionId = $proxy->login('...', '...');
$products = $proxy->catalogProductList($sessionId, [], 1);
foreach ($products as $product)
	echo $product->product_id,' ',$product->name,"\n";

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All automated tests passed successfully (all builds are green)

[kiatng]

More info on the error in PHP doc. The mandatory parameter needs to be optional to have signature compatibility.

[Flyingmana]

anyone found the documentation for the SimpleXMLElement::getChildren method?
Is this a new method?

[jfksk]

@Flyingmana
The documentation seems to be missing. According to PHP src iterator functionality was added to SimpleXMLElement in 8.0. The signature according to the stub (changes/added methods):

SimpleXMLElement::getChildren() : ?SimpleXMLElement

[Flyingmana]

thank you. The return type could lead to major issues for us here.
Did someone already test if the return type will also cause a signature error, and if returning an array will cause issues?

[colinmollenhour]

I can see how the this PR would fix the issue but making the parameter optional when it really is required is hard to stomach.. :)

I propose an alternative in #1613 which changes the method name so it doesn't conflict with the parent method. It doesn't use "$this" so I made it static as well.

[Flyingmana]

closed in favor of #1613

Still, thank you a lot