/wp-includes/user.php get_blogs_of_user( ) bad multisite check

[scottconnerly]

Should not use defined( 'MULTISITE' )
should use is_multisite() instead

[SergeyBiryukov]

Related: [18928]

[nacin]

is_multisite() is a broad function that returns true in one of two cases:

• If the site was a MU-era multisite, by detecting the SUNRISE or VHOST constants (or the VHOST successor, SUBDOMAIN_INSTALL).
• If the site was a 3.0-era multisite, by detecting the MULTISITE constant.

There is a distinct difference between MU and 3.0. In MU, the first site's tables were the table prefix (so we'll say wp_) plus the site ID (so wp_1_). The next site was wp_2_, etc.

In 3.0, the first site's tables keep the original table prefix. So, the first site is wp_, the second is wp_2_, etc.

We use a check against the raw MULTISITE constant whenever we need to tell the difference between wp_ and wp_1_. This happens at the database layer and in a few other places.

In this case, get_blogs_of_user() is looking to see if there is a usermeta row in the form of wp_capabilities. This is something that would only apply in a 3.0-era site, as a MU-era site would have wp_1_capabilities as the usermeta row for capabilities for the first site. Thus, the check.