libxml 2.9.2 ID conflicts

id_unbind_test.pl

#!/usr/perl/bin -w
use strict;
use warnings;

use XML::LibXML;

my $xml_content = <<EOL;
<?xml version="1.0" encoding="UTF-8"?>
  <a xml:id="a">
    <b xml:id="b"></b>
  </a>
EOL

my $dom = XML::LibXML->load_xml(string => $xml_content, no_blanks => 1);

my $a = $dom->documentElement;
my $b = $a->firstChild;

$b->unbindNode();

my $c = $dom->createElement("c");
$c->setAttributeNS('http://www.w3.org/XML/1998/namespace', 'id', "b");
$a->appendChild($c);

print $dom->toString(1),"\n";

This might be worth posting to either the libxml2 or perl-xml lists, or even crosspost (see https://mail.gnome.org/mailman/listinfo/xml or [email protected]).
Might either get suggestions for workarounds, or tickle the patch process!

Do you want to? Or should I? (I'm already subscribed to both; quite low-volume lists)

Feel free to mail it to them, I have my hands full at the moment. I added the appendChild at the end, but the error is raised on the setAttributeNS irrespective of what follows it.

Btw, completely destroying $b removes the warning:

$b->unbindNode();
undef $b;

But this is not so simple in LaTeXML, since we are reusing $b, in a new and different subtree of its original parent.

I also have the eery memory that explicitly calling undef on a node that was just unbound isn't safe and carelessly doing so quickly results in memory leaks.

I don't think the undef should be unsafe, since the DESTROY should only happen if the refcount goes to 0. If there is another reference, it simply won't get destroyed, and the id wont be cleaned up!

I asked on the xml list, and got some good response from Nick Wellnhofer. Basically he made the same suggestions you did! Namely either set to undef, remove the id. Or, also you could put the node into a new document:

XML::LibXML::Document->new->adoptNode($node)

but that would be expensive.

I'm inclined to think that removing the id is the best approach:

$node->removeAttribute('xml:id');

I believe you tested it, and that got rid of the errors? At least the ones from the place where it was used; I'll have to scan through and find all the places that need that treatment. Should just be a few...

Oh, @dginev, so you get a notice! Ha!

For some reason it didn't even send me a notice ... Thanks for that, removeAttribute should do the trick, we just need to hunt down all positions where we unbind nodes (that we don't reuse later).