Source

File: wp-includes/widgets.php

function wp_set_sidebars_widgets( $sidebars_widgets ) {
	global $_wp_sidebars_widgets;

	// Clear cached value used in wp_get_sidebars_widgets().
	$_wp_sidebars_widgets = null;

	if ( ! isset( $sidebars_widgets['array_version'] ) ) {
		$sidebars_widgets['array_version'] = 3;
	}

	update_option( 'sidebars_widgets', $sidebars_widgets );
}