Make one, some or all list widgets (advanced and regular) show events in publication order (most recent first)

list-widget-order-by-publication.php

class EventsListWidget_NewlyAddedEvents {
	protected $constraints = array(
		'sidebar_id'   => null,
		'widget_id'    => null,
		'widget_title' => null
	);

	public function __construct( array $constraints = array() ) {
		$this->constraints = array_merge( $this->constraints, $constraints );
		add_filter( 'widget_display_callback', array( $this, 'setup' ), 10, 3 );
	}

	public function setup( $instance, $widget, $args ) {
		// We're interested only in the (advanced or regular) events list widgets
		$targets = array( 'tribe-events-adv-list-widget', 'tribe-events-list-widget' );
		if ( ! in_array( $widget->id_base, $targets ) ) return $instance;

		// Check for constraints
		if ( ! $this->constraints_met( $instance, $args ) ) return $instance;

		// Modify behaviour
		add_filter( 'tribe_events_list_widget_query_args', array( $this, 'order_by_latest' ) );
		return $instance;
	}

	protected function constraints_met( $instance, $args ) {
		$fail = false;

		// Should only run within a specific sidebar?
		if ( ! is_null( $this->constraints['sidebar_id'] ) && $this->constraints['sidebar_id'] !== $args['id'] )
			$fail = true;

		// Should only run in relation to a specific instance of the widget?
		if ( ! is_null( $this->constraints['widget_id'] ) && $this->constraints['widget_id'] !== $args['widget_id'] )
			$fail = true;

		// Should only run when the widget title is set to something specific?
		if ( ! is_null( $this->constraints['widget_title'] ) && $this->constraints['widget_title'] !== $instance['title'] )
			$fail = true;

		return ! $fail;
	}

	public function order_by_latest( $args ) {
		// Don't interfere in other queries
		remove_filter( 'tribe_events_list_widget_query_args', array( $this, 'order_by_latest' ) );

		// Tweak the actual orderby clause
		add_filter( 'posts_orderby', array( $this, 'override_orderby' ), 100 );
		return $args;
	}

	public function override_orderby( $orderby_sql ) {
		global $wpdb;

		// Don't interfere in other queries
		remove_filter( 'posts_orderby', array( $this, 'override_orderby' ), 100 );

		return "$wpdb->posts.post_date DESC, $orderby_sql";
	}
}

/**
 * By itself, the following line will impact *all* list widgets. However it may
 * be desirable to impact just one. To achieve this, it is possible to specify
 * one or more constraints.
 *
 * Valid constraints include:
 *
 *     sidebar_id   (the ID of the sidebar - list widgets in other sidebars will not be affected)
 *     widget_id    (the specific widget ID itself)
 *     widget_title (if you don't know how to determine the widget/sidebar ID, you can specify the title)
 *
 * Example:
 *
 *     new EventsListWidget_NewlyAddedEvents( array(
 *         'sidebar_id' => 'sidebar-1'
 *     ) );
 *
 * Or:
 *
 *     new EventsListWidget_NewlyAddedEvents( array(
 *         'widget_title' => 'Newly Added Events!'
 *     ) );
 */
new EventsListWidget_NewlyAddedEvents();