Fix bug #81468: Inconsistent default namespace inheritance

[NathanFreeman]

https://bugs.php.net/bug.php?id=81468

[cmb69]

I think the problem with Travis CI is that it tries to test against "master", although the target branch is PHP-8.0.

[NathanFreeman]

I choose wrong target branch to merge at the begining.
I close wrong pr and make a new one.
But Travis CI didn't run again.

[NathanFreeman]

cc @beberlei

[beberlei]

Sorry i wont have time to review this PR. Many tests are good, so cautiosly optimisic about this

[cmb69]

Thank you for the PR! It seems to me this approach is going in the right direction, but is not yet complete. Besides my comment below, DOMNode::insertBefore() has the same issue, and maybe other methods, too.

[cmb69]

I'm not sure whether this shouldn't be:

Suggested change

	if (!child->ns && nodep->nsDef) {
	if (!child->ns && nodep->ns) {

That would solve:

$dom = new \DOMDocument();
$dom
  ->appendChild($dom->createElementNS('some:namespace', 'foo'))
  ->appendChild($dom->createElement('bar'))
  ->appendChild($dom->createElement('baz'));
echo ($xml = $dom->saveXML());

$xpath = new \DOMXPath($dom);
$xpath->registerNamespace('n', 'some:namespace');
echo count($xpath->query('/n:foo/bar')) . " should be 0\n";
echo count($xpath->query('/n:foo/n:bar')) . " should be 1\n";
echo count($xpath->query('/n:foo/n:bar/baz')) . " should be 0\n";
echo count($xpath->query('/n:foo/n:bar/n:baz')) . " should be 1\n\n";

[NathanFreeman]

nodep->ns is not a nullptr but point to a invalid address if nodep is the root node.

[nielsdos]

This is already fixed in a better way in the new DOM classes. The old classes retain the old behaviour.
The fix in this PR is also wrong btw: adding an element should not inherit the namespace of the parent, namespaces can't change after the element's creation according to spec.