Remove weird object creation in SimpleXML

[nikic]

Currently SXE optimizes for maximum WTF per minute:

$xml = new SimpleXMLElement('<root><elem>Text</elem></root>');
var_dump(isset($xml->doesNotExist)); // bool(false)
var_dump($xml->doesNotExist); // object(SimpleXMLElement)
var_dump($xml->doesNotExist->alsoDoesntExist); // null

There was a partial fix in https://bugs.php.net/bug.php?id=72957 to at least treat this correctly in BP_VAR_IS mode.

I think we should make use of the chance in PHP 8, and stop returning a dummy object if the node does not exist:

$xml = new SimpleXMLElement('<root><elem>Text</elem></root>');
var_dump(isset($xml->doesNotExist)); // bool(false)
var_dump($xml->doesNotExist); // null
var_dump($xml->doesNotExist->alsoDoesntExist); // null + warning

However, I'm not entirely clear on whether this is a small or a large BC break. Any thoughts?

[nikic]

Based on discussion in chat (with @cmb69 @beberlei maybe? It's been a while) I think the consensus was that SimpleXML has a lot of weird behavior that people rely on in even weirder ways, and it's probably not worth trying to change anything about it... Going to close this one.

[cmb69]

Unfortunately, I have to agree. Before doing actual improvements to SimpleXML, the desired behavior would need to be specified exactly. Any volunteers?