Undefined variable warnings in WP Class

[dd32]

It's possible to hit these two PHP Warnings in the WP class:

E_WARNING: Undefined variable $query in wp-includes/class-wp.php:270
E_WARNING: Undefined variable $matches in wp-includes/class-wp.php:273

​https://github.com/WordPress/wordpress-develop/blob/9b21204565430c1b22f29b5e57043adf8a71cfa5/src/wp-includes/class-wp.php#L268-L284

If you trace that around a bit, you'll think how on earth can this be triggered. Well, I'll tell you - Calling this late in a request (Such as within a rest-api endpoint)

        // Ugly, but this works..
        $_SERVER['REQUEST_URI'] = $url;
        wp( $_REQUEST );

In short: The WP::parse_request() method expects it'll be called exactly once, and doesn't pre-initialize the class properties / etc in the method.

The attached PR will pre-initialize them, but adding an additional isset() would be possible too, as would Closed: wontfix, _doing_it_wrong( 'dd32 is doing unsupported things.' ); I'm mostly filing this for future searching of these specific warnings.

Trac ticket: https://core.trac.wordpress.org/ticket/63998#ticket