wp_update_term

	if ( ! term_exists( $slug ) || get_option( 'db_version' ) >= 30133 && ! get_term_by( 'slug', $slug, $term->taxonomy ) ) {
		$needs_suffix = false;
	}

	/*
	 * If the taxonomy supports hierarchy and the term has a parent, make the slug unique
	 * by incorporating parent slugs.
	 */
	$parent_suffix = '';
	if ( $needs_suffix && is_taxonomy_hierarchical( $term->taxonomy ) && ! empty( $term->parent ) ) {
		$the_parent = $term->parent;
		while ( ! empty( $the_parent ) ) {
			$parent_term = get_term( $the_parent, $term->taxonomy );
			if ( is_wp_error( $parent_term ) || empty( $parent_term ) ) {
				break;
			}
			$parent_suffix .= '-' . $parent_term->slug;
			if ( ! term_exists( $slug . $parent_suffix ) ) {
				break;
			}

			if ( empty( $parent_term->parent ) ) {
				break;
			}
			$the_parent = $parent_term->parent;
		}
	}

	// If we didn't get a unique slug, try appending a number to make it unique.

	/**
	 * Filters whether the proposed unique term slug is bad.
	 *
	 * @since 4.3.0
	 *
	 * @param bool   $needs_suffix Whether the slug needs to be made unique with a suffix.
	 * @param string $slug         The slug.
	 * @param object $term         Term object.
	 */
	if ( apply_filters( 'wp_unique_term_slug_is_bad_slug', $needs_suffix, $slug, $term ) ) {
		if ( $parent_suffix ) {
			$slug .= $parent_suffix;
		}

		if ( ! empty( $term->term_id ) ) {
			$query = $wpdb->prepare( "SELECT slug FROM $wpdb->terms WHERE slug = %s AND term_id != %d", $slug, $term->term_id );
		} else {
			$query = $wpdb->prepare( "SELECT slug FROM $wpdb->terms WHERE slug = %s", $slug );
		}

		if ( $wpdb->get_var( $query ) ) { // phpcs:ignore WordPress.DB.PreparedSQL.NotPrepared
			$num = 2;
			do {
				$alt_slug = $slug . "-$num";
				$num++;
				$slug_check = $wpdb->get_var( $wpdb->prepare( "SELECT slug FROM $wpdb->terms WHERE slug = %s", $alt_slug ) );
			} while ( $slug_check );
			$slug = $alt_slug;
		}
	}

	/**
	 * Filters the unique term slug.
	 *
	 * @since 4.3.0
	 *
	 * @param string $slug          Unique term slug.
	 * @param object $term          Term object.
	 * @param string $original_slug Slug originally passed to the function for testing.
	 */
	return apply_filters( 'wp_unique_term_slug', $slug, $term, $original_slug );
}

/**
 * Update term based on arguments provided.
 *
 * The `$args` will indiscriminately override all values with the same field name.
 * Care must be taken to not override important information need to update or
 * update will fail (or perhaps create a new term, neither would be acceptable).
 *
 * Defaults will set 'alias_of', 'description', 'parent', and 'slug' if not
 * defined in `$args` already.
 *
 * 'alias_of' will create a term group, if it doesn't already exist, and
 * update it for the `$term`.
 *
 * If the 'slug' argument in `$args` is missing, then the 'name' will be used.
 * If you set 'slug' and it isn't unique, then a WP_Error is returned.
 * If you don't pass any slug, then a unique one will be created.
 *
 * @since 2.3.0
 *
 * @global wpdb $wpdb WordPress database abstraction object.
 *
 * @param int          $term_id  The ID of the term.
 * @param string       $taxonomy The taxonomy of the term.
 * @param array|string $args {
 *     Optional. Array or string of arguments for updating a term.
 *
 *     @type string $alias_of    Slug of the term to make this term an alias of.
 *                               Default empty string. Accepts a term slug.
 *     @type string $description The term description. Default empty string.
 *     @type int    $parent      The id of the parent term. Default 0.
 *     @type string $slug        The term slug to use. Default empty string.
 * }
 * @return array|WP_Error An array containing the `term_id` and `term_taxonomy_id`,
 *                        WP_Error otherwise.
 */
function wp_update_term( $term_id, $taxonomy, $args = array() ) {
	global $wpdb;

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

	$term_id = (int) $term_id;

	// First, get all of the original args.
	$term = get_term( $term_id, $taxonomy );

	if ( is_wp_error( $term ) ) {
		return $term;
	}

	if ( ! $term ) {
		return new WP_Error( 'invalid_term', __( 'Empty Term.' ) );
	}

	$term = (array) $term->data;

	// Escape data pulled from DB.
	$term = wp_slash( $term );

	// Merge old and new args with new args overwriting old ones.
	$args = array_merge( $term, $args );

	$defaults    = array(
		'alias_of'    => '',
		'description' => '',
		'parent'      => 0,
		'slug'        => '',
	);
	$args        = wp_parse_args( $args, $defaults );
	$args        = sanitize_term( $args, $taxonomy, 'db' );
	$parsed_args = $args;

	// expected_slashed ($name)
	$name        = wp_unslash( $args['name'] );
	$description = wp_unslash( $args['description'] );

	$parsed_args['name']        = $name;
	$parsed_args['description'] = $description;

	if ( '' === trim( $name ) ) {
		return new WP_Error( 'empty_term_name', __( 'A name is required for this term.' ) );
	}

	if ( $parsed_args['parent'] > 0 && ! term_exists( (int) $parsed_args['parent'] ) ) {
		return new WP_Error( 'missing_parent', __( 'Parent term does not exist.' ) );
	}

	$empty_slug = false;
	if ( empty( $args['slug'] ) ) {
		$empty_slug = true;
		$slug       = sanitize_title( $name );
	} else {
		$slug = $args['slug'];
	}

	$parsed_args['slug'] = $slug;

	$term_group = isset( $parsed_args['term_group'] ) ? $parsed_args['term_group'] : 0;
	if ( $args['alias_of'] ) {
		$alias = get_term_by( 'slug', $args['alias_of'], $taxonomy );
		if ( ! empty( $alias->term_group ) ) {
			// The alias we want is already in a group, so let's use that one.
			$term_group = $alias->term_group;
		} elseif ( ! empty( $alias->term_id ) ) {
			/*
			 * The alias is not in a group, so we create a new one
			 * and add the alias to it.
			 */
			$term_group = $wpdb->get_var( "SELECT MAX(term_group) FROM $wpdb->terms" ) + 1;

			wp_update_term(
				$alias->term_id,
				$taxonomy,
				array(
					'term_group' => $term_group,
				)
			);
		}

		$parsed_args['term_group'] = $term_group;
	}

	/**
	 * Filters the term parent.
	 *
	 * Hook to this filter to see if it will cause a hierarchy loop.
	 *
	 * @since 3.1.0
	 *
	 * @param int    $parent      ID of the parent term.
	 * @param int    $term_id     Term ID.
	 * @param string $taxonomy    Taxonomy slug.
	 * @param array  $parsed_args An array of potentially altered update arguments for the given term.
	 * @param array  $args        An array of update arguments for the given term.
	 */
	$parent = (int) apply_filters( 'wp_update_term_parent', $args['parent'], $term_id, $taxonomy, $parsed_args, $args );

	// Check for duplicate slug.
	$duplicate = get_term_by( 'slug', $slug, $taxonomy );
	if ( $duplicate && $duplicate->term_id !== $term_id ) {
		// If an empty slug was passed or the parent changed, reset the slug to something unique.
		// Otherwise, bail.
		if ( $empty_slug || ( $parent !== (int) $term['parent'] ) ) {
			$slug = wp_unique_term_slug( $slug, (object) $args );
		} else {
			/* translators: %s: Taxonomy term slug. */
			return new WP_Error( 'duplicate_term_slug', sprintf( __( 'The slug “%s” is already in use by another term.' ), $slug ) );
		}
	}

	$tt_id = (int) $wpdb->get_var( $wpdb->prepare( "SELECT tt.term_taxonomy_id FROM $wpdb->term_taxonomy AS tt INNER JOIN $wpdb->terms AS t ON tt.term_id = t.term_id WHERE tt.taxonomy = %s AND t.term_id = %d", $taxonomy, $term_id ) );

	// Check whether this is a shared term that needs splitting.
	$_term_id = _split_shared_term( $term_id, $tt_id );
	if ( ! is_wp_error( $_term_id ) ) {
		$term_id = $_term_id;
	}

	/**
	 * Fires immediately before the given terms are edited.
	 *
	 * @since 2.9.0
	 *
	 * @param int    $term_id  Term ID.
	 * @param string $taxonomy Taxonomy slug.
	 */
	do_action( 'edit_terms', $term_id, $taxonomy );

	$data = compact( 'name', 'slug', 'term_group' );