How can I determine what php files are being called by a given WP page?

Question

I'd like to debug some WordPress functionality, but to do so I need to know where to find the php file that is executing on a given page. How can I set up something that will tell me what php files (or functions, objects) are being called to generate a given page? I'm using a ridiculous amount of plugins, and I have a complicated theme structure, so it's not really practical to insert debug messages into every single php file I have, like the answer to this question suggests.

Answer 1

There's a native PHP function get_included_files() for that.

Simply attach it to an action on the hook from where you want to know it. The first one is muplugins_loaded and the last accessible on is shutdown.

add_action( 'muplugins_loaded', function()
{
    $files = get_included_files();
    foreach ( $files as $f )
        echo $f.'<br>';

    // or...
    var_dump( $files );
}

Answer 2

I am not sure there is a generic answer to this question but my advice would be to:

1. Enable debugging
2. Learn to drive grep
3. Run debug_backtrace() for a more detailed history of what has occurred up to some point in a page load or function call-- var_dump(debug_backtrace());