WordPress at a glance
function is not described

wp_unique_post_slug() WP 2.8.0

Computes a unique slug for the post, when given the desired slug and some post details.

Return

String. Unique slug for the post, based on $post_name (with a -1, -2, etc. suffix)

Usage

wp_unique_post_slug( $slug, $post_ID, $post_status, $post_type, $post_parent );
$slug(string) (required)
The desired slug (post_name).
$post_ID(int) (required)
Post ID.
$post_status(string) (required)
No uniqueness checks are made if the post is still draft or pending.
$post_type(string) (required)
Post type.
$post_parent(int) (required)
Post parent ID.

Notes

  • Global. wpdb. $wpdb WordPress database abstraction object.
  • Global. WP_Rewrite. $wp_rewrite WordPress rewrite component.

Changelog

Since 2.8.0 Introduced.

Code of wp_unique_post_slug() WP 5.5.3

<?php
function wp_unique_post_slug( $slug, $post_ID, $post_status, $post_type, $post_parent ) {
	if ( in_array( $post_status, array( 'draft', 'pending', 'auto-draft' ), true )
		|| ( 'inherit' === $post_status && 'revision' === $post_type ) || 'user_request' === $post_type
	) {
		return $slug;
	}

	/**
	 * Filters the post slug before it is generated to be unique.
	 *
	 * Returning a non-null value will short-circuit the
	 * unique slug generation, returning the passed value instead.
	 *
	 * @since 5.1.0
	 *
	 * @param string|null $override_slug Short-circuit return value.
	 * @param string      $slug          The desired slug (post_name).
	 * @param int         $post_ID       Post ID.
	 * @param string      $post_status   The post status.
	 * @param string      $post_type     Post type.
	 * @param int         $post_parent   Post parent ID.
	 */
	$override_slug = apply_filters( 'pre_wp_unique_post_slug', null, $slug, $post_ID, $post_status, $post_type, $post_parent );
	if ( null !== $override_slug ) {
		return $override_slug;
	}

	global $wpdb, $wp_rewrite;

	$original_slug = $slug;

	$feeds = $wp_rewrite->feeds;
	if ( ! is_array( $feeds ) ) {
		$feeds = array();
	}

	if ( 'attachment' === $post_type ) {
		// Attachment slugs must be unique across all types.
		$check_sql       = "SELECT post_name FROM $wpdb->posts WHERE post_name = %s AND ID != %d LIMIT 1";
		$post_name_check = $wpdb->get_var( $wpdb->prepare( $check_sql, $slug, $post_ID ) );

		/**
		 * Filters whether the post slug would make a bad attachment slug.
		 *
		 * @since 3.1.0
		 *
		 * @param bool   $bad_slug Whether the slug would be bad as an attachment slug.
		 * @param string $slug     The post slug.
		 */
		$is_bad_attachment_slug = apply_filters( 'wp_unique_post_slug_is_bad_attachment_slug', false, $slug );

		if ( $post_name_check
			|| in_array( $slug, $feeds, true ) || 'embed' === $slug
			|| $is_bad_attachment_slug
		) {
			$suffix = 2;
			do {
				$alt_post_name   = _truncate_post_slug( $slug, 200 - ( strlen( $suffix ) + 1 ) ) . "-$suffix";
				$post_name_check = $wpdb->get_var( $wpdb->prepare( $check_sql, $alt_post_name, $post_ID ) );
				$suffix++;
			} while ( $post_name_check );
			$slug = $alt_post_name;
		}
	} elseif ( is_post_type_hierarchical( $post_type ) ) {
		if ( 'nav_menu_item' === $post_type ) {
			return $slug;
		}

		/*
		 * Page slugs must be unique within their own trees. Pages are in a separate
		 * namespace than posts so page slugs are allowed to overlap post slugs.
		 */
		$check_sql       = "SELECT post_name FROM $wpdb->posts WHERE post_name = %s AND post_type IN ( %s, 'attachment' ) AND ID != %d AND post_parent = %d LIMIT 1";
		$post_name_check = $wpdb->get_var( $wpdb->prepare( $check_sql, $slug, $post_type, $post_ID, $post_parent ) );

		/**
		 * Filters whether the post slug would make a bad hierarchical post slug.
		 *
		 * @since 3.1.0
		 *
		 * @param bool   $bad_slug    Whether the post slug would be bad in a hierarchical post context.
		 * @param string $slug        The post slug.
		 * @param string $post_type   Post type.
		 * @param int    $post_parent Post parent ID.
		 */
		$is_bad_hierarchical_slug = apply_filters( 'wp_unique_post_slug_is_bad_hierarchical_slug', false, $slug, $post_type, $post_parent );

		if ( $post_name_check
			|| in_array( $slug, $feeds, true ) || 'embed' === $slug
			|| preg_match( "@^($wp_rewrite->pagination_base)?\d+$@", $slug )
			|| $is_bad_hierarchical_slug
		) {
			$suffix = 2;
			do {
				$alt_post_name   = _truncate_post_slug( $slug, 200 - ( strlen( $suffix ) + 1 ) ) . "-$suffix";
				$post_name_check = $wpdb->get_var( $wpdb->prepare( $check_sql, $alt_post_name, $post_type, $post_ID, $post_parent ) );
				$suffix++;
			} while ( $post_name_check );
			$slug = $alt_post_name;
		}
	} else {
		// Post slugs must be unique across all posts.
		$check_sql       = "SELECT post_name FROM $wpdb->posts WHERE post_name = %s AND post_type = %s AND ID != %d LIMIT 1";
		$post_name_check = $wpdb->get_var( $wpdb->prepare( $check_sql, $slug, $post_type, $post_ID ) );

		$post = get_post( $post_ID );

		// Prevent new post slugs that could result in URLs that conflict with date archives.
		$conflicts_with_date_archive = false;
		if ( 'post' === $post_type && ( ! $post || $post->post_name !== $slug ) && preg_match( '/^[0-9]+$/', $slug ) ) {
			$slug_num = intval( $slug );

			if ( $slug_num ) {
				$permastructs   = array_values( array_filter( explode( '/', get_option( 'permalink_structure' ) ) ) );
				$postname_index = array_search( '%postname%', $permastructs, true );

				/*
				* Potential date clashes are as follows:
				*
				* - Any integer in the first permastruct position could be a year.
				* - An integer between 1 and 12 that follows 'year' conflicts with 'monthnum'.
				* - An integer between 1 and 31 that follows 'monthnum' conflicts with 'day'.
				*/
				if ( 0 === $postname_index ||
					( $postname_index && '%year%' === $permastructs[ $postname_index - 1 ] && 13 > $slug_num ) ||
					( $postname_index && '%monthnum%' === $permastructs[ $postname_index - 1 ] && 32 > $slug_num )
				) {
					$conflicts_with_date_archive = true;
				}
			}
		}

		/**
		 * Filters whether the post slug would be bad as a flat slug.
		 *
		 * @since 3.1.0
		 *
		 * @param bool   $bad_slug  Whether the post slug would be bad as a flat slug.
		 * @param string $slug      The post slug.
		 * @param string $post_type Post type.
		 */
		$is_bad_flat_slug = apply_filters( 'wp_unique_post_slug_is_bad_flat_slug', false, $slug, $post_type );

		if ( $post_name_check
			|| in_array( $slug, $feeds, true ) || 'embed' === $slug
			|| $conflicts_with_date_archive
			|| $is_bad_flat_slug
		) {
			$suffix = 2;
			do {
				$alt_post_name   = _truncate_post_slug( $slug, 200 - ( strlen( $suffix ) + 1 ) ) . "-$suffix";
				$post_name_check = $wpdb->get_var( $wpdb->prepare( $check_sql, $alt_post_name, $post_type, $post_ID ) );
				$suffix++;
			} while ( $post_name_check );
			$slug = $alt_post_name;
		}
	}

	/**
	 * Filters the unique post slug.
	 *
	 * @since 3.3.0
	 *
	 * @param string $slug          The post slug.
	 * @param int    $post_ID       Post ID.
	 * @param string $post_status   The post status.
	 * @param string $post_type     Post type.
	 * @param int    $post_parent   Post parent ID
	 * @param string $original_slug The original post slug.
	 */
	return apply_filters( 'wp_unique_post_slug', $slug, $post_ID, $post_status, $post_type, $post_parent, $original_slug );
}