SimpleXMLElement regressions on Psalm 5.15

[edsrzf]

I'm running into a couple regressions related to SimpleXMLElement when trying to upgrade to Psalm 5.15:

• False positive RedundantCondition errors when calling isset on property fetches
• Less specific return type for the asXml method when no arguments are passed

Example code:

<?php

function f(): string|false
{
    $x = new SimpleXMLElement('<a></a>');
    // False positive: RedundantCondition
    if (isset($x->foo)) {
        echo 'hi';
    }
    // Inferred type not specific enough
    return $x->asXml();
}

For some reason I can't reproduce either issue on psalm.dev, but I've created a repository here: https://github.com/edsrzf/psalm-xml-repro

I'm guessing these are both due to #10049.

[edsrzf]

I think the problem is that I didn't have the simplexml extension enabled, by either adding ext-simplexml as a dependency in composer.json or via enableExtensions in psalm.xml. With either of those, the errors go away.

I guess this makes sense but I find it surprising to have to make this change in a minor version update.

[robchett]

I'm not 100% sure, but I think the online tool has all extensions enabled. At the very least it appears to have simplexml. Which is why this can't be reproduced there.

Before a4de6d9 SimpleXMLElement & SimpleXMLIterator were defined as universal_object_crates, even if the extension was not explicitly enabled, and reflection was used for the signatures.

I don't think it's right to reintroduce the definitions without explicit loading of the extension, so would class this as a bugfix instead of a regression.

[edsrzf]

I agree there's probably nothing to fix here. The BC break is mentioned in the linked PR and hopefully anyone running into it will find this issue.

It might be nice to update the 5.15.0 release notes to mention this more clearly though.