wp_get_shortlink

/**
 * Returns a shortlink for a post, page, attachment, or site.
 *
 * This function exists to provide a shortlink tag that all themes and plugins can target.
 * A plugin must hook in to provide the actual shortlinks. Default shortlink support is
 * limited to providing ?p= style links for posts. Plugins can short-circuit this function
 * via the {@see 'pre_get_shortlink'} filter or filter the output via the {@see 'get_shortlink'}
 * filter.
 *
 * @since 3.0.0
 *
 * @param int    $id          Optional. A post or site ID. Default is 0, which means the current post or site.
 * @param string $context     Optional. Whether the ID is a 'site' id, 'post' id, or 'media' id. If 'post',
 *                            the post_type of the post is consulted. If 'query', the current query is consulted
 *                            to determine the ID and context. Default 'post'.
 * @param bool   $allow_slugs Optional. Whether to allow post slugs in the shortlink. It is up to the plugin how
 *                            and whether to honor this. Default true.
 * @return string A shortlink or an empty string if no shortlink exists for the requested resource or if shortlinks
 *                are not enabled.
 */
function wp_get_shortlink( $id = 0, $context = 'post', $allow_slugs = true ) {
	/**
	 * Filters whether to preempt generating a shortlink for the given post.
	 *
	 * Returning a truthy value from the filter will effectively short-circuit
	 * the shortlink generation process, returning that value instead.
	 *
	 * @since 3.0.0
	 *
	 * @param false|string $return      Short-circuit return value. Either false or a URL string.
	 * @param int          $id          Post ID, or 0 for the current post.
	 * @param string       $context     The context for the link. One of 'post' or 'query',
	 * @param bool         $allow_slugs Whether to allow post slugs in the shortlink.
	 */
	$shortlink = apply_filters( 'pre_get_shortlink', false, $id, $context, $allow_slugs );

	if ( false !== $shortlink ) {
		return $shortlink;
	}

	$post_id = 0;
	if ( 'query' === $context && is_singular() ) {
		$post_id = get_queried_object_id();
		$post    = get_post( $post_id );
	} elseif ( 'post' === $context ) {
		$post = get_post( $id );
		if ( ! empty( $post->ID ) ) {
			$post_id = $post->ID;
		}
	}

	$shortlink = '';

	// Return `?p=` link for all public post types.
	if ( ! empty( $post_id ) ) {