get_super_admins() should not return "admin" by default

[thomaswm]

The function get_super_admins(), introduced in [14206], returns an array of users with network admin capabilities. Those are stored in the site_admins network option.

If, for any reason, that network option does not exist, get_super_admins() will return a one-element array containing "admin" instead.

See line 761 in wp-includes/capabilities.php.

return get_site_option( 'site_admins', array('admin') );

This goes back to a time when admin was the default username for the first WordPress user. Since administrators are now discouraged from using admin as a username, get_super_admins() should return an empty array by default:

return get_site_option( 'site_admins', array() );

[thomaswm]

Just realized that grant_super_admin() and revoke_super_admin() are also affected.

Lines 820 and 867 in wp-includes/capabilities.php both read:

$super_admins = get_site_option( 'site_admins', array( 'admin' ) );

[SergeyBiryukov]

Related: #16293, #39174.

[thomaswm]

Patch

Trac ticket: https://core.trac.wordpress.org/ticket/43390

[Soean]

I created a Pull request on GitHub

@Soean, please update your PR since it has conflicts. Let's try to push the ticket forward afterwards.

@lloc I updated the PR and added a @since comment.