Fixed canonical tags when Wordpress is installed in a sub-folder

Fixed bug where plugin would generate invalid canonical urls.

If you set up a Wordpress site at "example.com/blog" then both site_url() and home_url() will be "http://example.com/blog". The previous code assumed that home_url() would instead return "http://example.com". Therefore the previous code when converting href="/blog/page1" would convert it into "http://example.com/blog/blog/page1" for the canonical tag. This is obviously incorrect.

Sometimes other logic is triggered hiding this bug. To replicate install Wordpress to a subfolder so that home_url() and site_url() give a domain name with a path at the end (such as "example.com/blog"). Then view a blog archive or tag page. (Other pages are also affected but not all pages are).

This bug was introduced in 1.5.4 when all canonical urls were converted to be absolute.

I would be very happy if you could merge this small change quickly as it is likely very bad for SEO that many pages on my websites now have a incorrect canonical url set.

Thank you.

Do not hesitate to contact me if you have any questions or queries.

Kind regards,
Shanee Vanstone.