get_terms

 *
 * The {@see 'list_terms_exclusions'} filter passes the compiled exclusions along with
 * the $args.
 *
 * The {@see 'get_terms_orderby'} filter passes the `ORDER BY` clause for the query
 * along with the $args array.
 *
 * Prior to 4.5.0, the first parameter of `get_terms()` was a taxonomy or list of taxonomies:
 *
 *     $terms = get_terms( 'post_tag', array(
 *         'hide_empty' => false,
 *     ) );
 *
 * Since 4.5.0, taxonomies should be passed via the 'taxonomy' argument in the `$args` array:
 *
 *     $terms = get_terms( array(
 *         'taxonomy' => 'post_tag',
 *         'hide_empty' => false,
 *     ) );
 *
 * @since 2.3.0
 * @since 4.2.0 Introduced 'name' and 'childless' parameters.
 * @since 4.4.0 Introduced the ability to pass 'term_id' as an alias of 'id' for the `orderby` parameter.
 *              Introduced the 'meta_query' and 'update_term_meta_cache' parameters. Converted to return
 *              a list of WP_Term objects.
 * @since 4.5.0 Changed the function signature so that the `$args` array can be provided as the first parameter.
 *              Introduced 'meta_key' and 'meta_value' parameters. Introduced the ability to order results by metadata.
 * @since 4.8.0 Introduced 'suppress_filter' parameter.
 *
 * @internal The `$deprecated` parameter is parsed for backward compatibility only.
 *
 * @param array|string $args       Optional. Array or string of arguments. See WP_Term_Query::__construct()
 *                                 for information on accepted arguments. Default empty.
 * @param array|string $deprecated Argument array, when using the legacy function parameter format. If present,
 *                                 this parameter will be interpreted as `$args`, and the first function parameter
 *                                 will be parsed as a taxonomy or array of taxonomies.
 * @return WP_Term[]|int|WP_Error Array of WP_Term instances, a count thereof,
 *                                or WP_Error if any of the taxonomies do not exist.
 */
function get_terms( $args = array(), $deprecated = '' ) {
	$term_query = new WP_Term_Query();

	$defaults = array(
		'suppress_filter' => false,
	);

	/*
	 * Legacy argument format ($taxonomy, $args) takes precedence.
	 *
	 * We detect legacy argument format by checking if
	 * (a) a second non-empty parameter is passed, or
	 * (b) the first parameter shares no keys with the default array (ie, it's a list of taxonomies)
	 */
	$_args          = wp_parse_args( $args );
	$key_intersect  = array_intersect_key( $term_query->query_var_defaults, (array) $_args );
	$do_legacy_args = $deprecated || empty( $key_intersect );

	if ( $do_legacy_args ) {
		$taxonomies       = (array) $args;
		$args             = wp_parse_args( $deprecated, $defaults );
		$args['taxonomy'] = $taxonomies;
	} else {
		$args = wp_parse_args( $args, $defaults );
		if ( isset( $args['taxonomy'] ) && null !== $args['taxonomy'] ) {
			$args['taxonomy'] = (array) $args['taxonomy'];