Make it possible to install WP multisite directly

[Denis-de-Bernardy]

On a completely new site, functions in wp-includes/ms-*.php kick in very early on when multisite-related defines are around.

Visiting / in such a setup yields a cryptic establishing a connection error message which is far too similar to an actual problem.

Visiting /wp-admin is only slightly more informative, with WP assuming that the database's sites or blogs table is corrupt, with links to the codex on how to debug the problem.

Visiting /wp-admin/install.php seems to be working OK, with a whole bunch of E_NOTICE errors occurring when WP_DEBUG is defined.

Instead of the above, could we make it so that when the defines are around, WP will instead a) understand that an install is in order and redirect you to wp-admin/install.php and b) proceed with installing a network right then and there?

[nacin]

It's painful to do, but it's currently possible: ​https://github.com/jquery/jquery-wp-content/blob/master/sunrise.php#L9:L26. I wouldn't recommend that to anyone, though. Would be nice if we made this better in the future.

[scribu]

For the record, WP-CLI has the ​wp core multisite-install command, which installs multisite from scratch.

It relies on various ugly hacks, such as:

1. ​faking the `$current_site` and `$current_blog` globals
2. ​duplicating code from `populate_network()`

[chriscct7]

Closing as maybelater. Complete lack of interest on the feature on the ticket over the last 2 years. Feel free to reopen when more interest re-emerges (particularly if there's a patch)