wp_get_object_terms( int|array $object_ids, string|array $taxonomies, array|string $args = array() )

function wp_get_object_terms($object_ids, $taxonomies, $args = array()) {
	if ( empty( $object_ids ) || empty( $taxonomies ) )
		return array();

	if ( !is_array($taxonomies) )
		$taxonomies = array($taxonomies);

	foreach ( $taxonomies as $taxonomy ) {
		if ( ! taxonomy_exists($taxonomy) )
			return new WP_Error( 'invalid_taxonomy', __( 'Invalid taxonomy.' ) );
	}

	if ( !is_array($object_ids) )
		$object_ids = array($object_ids);
	$object_ids = array_map('intval', $object_ids);

	$args = wp_parse_args( $args );

	/**
	 * Filter arguments for retrieving object terms.
	 *
	 * @since WP-4.9.0
	 *
	 * @param array        $args       An array of arguments for retrieving terms for the given object(s).
	 *                                 See {@see wp_get_object_terms()} for details.
	 * @param int|array    $object_ids Object ID or array of IDs.
	 * @param string|array $taxonomies The taxonomies to retrieve terms from.
	 */
	$args = apply_filters( 'wp_get_object_terms_args', $args, $object_ids, $taxonomies );

	/*
	 * When one or more queried taxonomies is registered with an 'args' array,
	 * those params override the `$args` passed to this function.
	 */
	$terms = array();
	if ( count( $taxonomies ) > 1 ) {
		foreach ( $taxonomies as $index => $taxonomy ) {
			$t = get_taxonomy( $taxonomy );
			if ( isset( $t->args ) && is_array( $t->args ) && $args != array_merge( $args, $t->args ) ) {
				unset( $taxonomies[ $index ] );
				$terms = array_merge( $terms, wp_get_object_terms( $object_ids, $taxonomy, array_merge( $args, $t->args ) ) );
			}
		}
	} else {
		$t = get_taxonomy( $taxonomies[0] );
		if ( isset( $t->args ) && is_array( $t->args ) ) {
			$args = array_merge( $args, $t->args );
		}
	}

	$args['taxonomy'] = $taxonomies;
	$args['object_ids'] = $object_ids;

	// Taxonomies registered without an 'args' param are handled here.
	if ( ! empty( $taxonomies ) ) {
		$terms_from_remaining_taxonomies = get_terms( $args );

		// Array keys should be preserved for values of $fields that use term_id for keys.
		if ( ! empty( $args['fields'] ) && 0 === strpos( $args['fields'], 'id=>' ) ) {
			$terms = $terms + $terms_from_remaining_taxonomies;
		} else {
			$terms = array_merge( $terms, $terms_from_remaining_taxonomies );
		}
	}

	/**
	 * Filters the terms for a given object or objects.
	 *
	 * @since WP-4.2.0
	 *
	 * @param array $terms      An array of terms for the given object or objects.
	 * @param array $object_ids Array of object IDs for which `$terms` were retrieved.
	 * @param array $taxonomies Array of taxonomies from which `$terms` were retrieved.
	 * @param array $args       An array of arguments for retrieving terms for the given
	 *                          object(s). See wp_get_object_terms() for details.
	 */
	$terms = apply_filters( 'get_object_terms', $terms, $object_ids, $taxonomies, $args );

	$object_ids = implode( ',', $object_ids );
	$taxonomies = "'" . implode( "', '", array_map( 'esc_sql', $taxonomies ) ) . "'";

	/**
	 * Filters the terms for a given object or objects.
	 *
	 * The `$taxonomies` parameter passed to this filter is formatted as a SQL fragment. The
	 * {@see 'get_object_terms'} filter is recommended as an alternative.
	 *
	 * @since WP-2.8.0
	 *
	 * @param array     $terms      An array of terms for the given object or objects.
	 * @param int|array $object_ids Object ID or array of IDs.
	 * @param string    $taxonomies SQL-formatted (comma-separated and quoted) list of taxonomy names.
	 * @param array     $args       An array of arguments for retrieving terms for the given object(s).
	 *                              See wp_get_object_terms() for details.
	 */
	return apply_filters( 'wp_get_object_terms', $terms, $object_ids, $taxonomies, $args );
}