Union/intersection tag query URLs broken

[wahgnube]

I noticed some time ago that links querying multiple tags, e.g. site.org/tag/foo,bar/ and site.org/tag/foo+bar/ , stopped working on my site which runs WordPress trunk. Both these queries rewrite to site.org/tag/foo/

After systematically stepping backward through svn changesets, I believe that the changeset that was causing this problem is the following:

​http://core.trac.wordpress.org/changeset/13170/trunk

[scribu]

If you turn off pretty permalinks, do you get the correct posts?

[scribu]

What I mean is, does ?tag=foo,bar display posts with tags foo OR bar?

[scribu]

Also see [13480].

[wahgnube]

Replying to scribu:

If you turn off pretty permalinks, do you get the correct posts?

This is the first thing I tried, and no, it does not work without pretty permalinks either.

[wahgnube]

I have temporarily fixed it with the following modification on line 135 of wp-includes/canonical.php:

} elseif ( is_category() + } elseif ( is_category()

is_tag()	is_tax() ) { Terms (Tags/categories)
is_tax() ) { Terms (Tags/categories)

I don't know what the implications of this change are, other than it prevents a bunch of calls to remove_query_arg()s.

[automattor]

(In [13623]) Correct logic inversion in Canonical Taxonomy Term links. Fixes #12547