Retrieve full list of sidebars and their widget instance IDs.

Will upgrade sidebar widget list, if needed. Will also save updated list, if
needed.

function wp_get_sidebars_widgets( $deprecated = true ) {
	if ( true !== $deprecated ) {
		_deprecated_argument( __FUNCTION__, '2.8.1' );
	}

	global $_wp_sidebars_widgets, $sidebars_widgets;

	// If loading from front page, consult $_wp_sidebars_widgets rather than options
	// to see if wp_convert_widget_settings() has made manipulations in memory.
	if ( ! is_admin() ) {
		if ( empty( $_wp_sidebars_widgets ) ) {
			$_wp_sidebars_widgets = get_option( 'sidebars_widgets', array() );
		}

		$sidebars_widgets = $_wp_sidebars_widgets;
	} else {
		$sidebars_widgets = get_option( 'sidebars_widgets', array() );
	}

	if ( is_array( $sidebars_widgets ) && isset( $sidebars_widgets['array_version'] ) ) {
		unset( $sidebars_widgets['array_version'] );
	}

	/**
	 * Filters the list of sidebars and their widgets.
	 *
	 * @since 2.7.0
	 *
	 * @param array $sidebars_widgets An associative array of sidebars and their widgets.
	 */
	return apply_filters( 'sidebars_widgets', $sidebars_widgets );
}