Including 'wp-load.php' after another include() generates an error

Question

I know all the downsides of trying to include wp-load.php, but bear with me :)

I'm trying to create my own admin-ajax-like functionality, in a way that I can control whether or not I load the default WordPress environment, whether I load it with the SHORTINIT constant defined as true, and with granular control over each module of my plug-in, as required by the specific function being access via AJAX. The only way I can think of doing that is doing AJAX via a custom file, other than admin-ajax.php, and then including wp-load.php when desired.

I've actually used it successfully for months. I've named the file bootstrap.php, and it sits inside my plugin's 'includes' directory. Requiring wp-load.php from within bootstrap.php will load WP just fine.

Today I decided I needed more control, so I attempted to delay the request for wp-load.php for when I've loaded the files containing the AJAX functions. Those files are called within bootstrap.php with include(), but requiring wp-load.php within those files will generate the following error:

Notice: Undefined variable: wpdb in .../wp-includes/ms-settings.php on line 126
Fatal error: Call to a member function set_prefix() on a non-object in .../wp-includes/ms-settings.php on line 126 

The problem occurs within the loading of WP, so obviously the require() call points to the correct location of the wp-load.php file. Calling it from the file of the URL request works fine, but calling it after an include() breaks the entire thing... any ideas why?

Thanks in advance!

Answer 1

A different way of fixing it:

function load_wp(){
    global $wpdb;
    include_once('wp-load.php');
}

Answer 2

Well, it turns out it was a problem of variable scope. I discovered that $wpdb was loading fine, but was inaccessible outside of the function that generated it, so it kind of led me to the solution: the includes() I mention in the question are done inside a function, with local (not global) scope. I'm sure, then, that it would have been a problem for all WP global variables, but $wpdb was the first one to generate a fatal error.

I didn't mention I was loading wp-load.php from a function because I didn't really know it was important. So remember, kids: don't include wp-load.php, but if you do, don't do it from inside a function.