Dynamic properties of SimpleXMLElement should be inferred as being SimpleXMLElement

[stof]

https://psalm.dev/r/100575e0f4

This reports mixed errors saying it cannot infer the type of expressions. But dynamic properties of SimpleXMLElement are always SimpleXMLElement themselves.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/100575e0f4

<?php

$string = <<<XML
<a>
 <foo name="one" game="lonely">1</foo>
</a>
XML;

$xml = new SimpleXMLElement($string);
foreach($xml->foo[0]->attributes() as $a => $b) {
    echo $a,'="',$b,"\"\n";
}

Psalm output (using commit 8fe1f15):

INFO: MixedArrayAccess - 10:9 - Cannot access array value on mixed variable $xml->foo

INFO: MixedMethodCall - 10:23 - Cannot determine the type of $xml->foo[0] when calling method attributes

INFO: MixedAssignment - 10:39 - Unable to determine the type that $a is being assigned to

INFO: MixedAssignment - 10:45 - Unable to determine the type that $b is being assigned to

INFO: MixedArgument - 11:10 - Argument 1 of echo cannot be mixed, expecting string

INFO: MixedArgument - 11:18 - Argument 3 of echo cannot be mixed, expecting string

[stof]

Based on the discussion in phpstan/phpstan#9575, it should be inferred as SimpleXMLElement|null