Wikimedia Bugzilla is closed!

Define a simple parser tag extension <junk> that returns "abcde":

<?php
$wgHooks['ParserFirstCallInit'][] = 'efJunk';
function efJunk(&$parser) {
  $parser->setHook('junk', 'efJunkCallback');
  return true;
}
function efJunkCallback($input, $args, $parser, $frame) {
  return 'abcde';
}

When displayed in the wiki, it seems to work fine:

{{#tag:junk}}
==> abcde

But when the value is passed to other parser functions, it breaks:

{{#len:{{#tag:junk}}}}
==> 1

{{#ifeq:{{#tag:junk}}|abcde|yes|no}}
==> no

Since the value display correctly, I hypothesize that {{#tag:junk}} is returning a 1-character, null-terminated string in front of "abcde".