Source

File: wp-includes/taxonomy.php

function get_ancestors( $object_id = 0, $object_type = '', $resource_type = '' ) {
	$object_id = (int) $object_id;

	$ancestors = array();

	if ( empty( $object_id ) ) {

		/** This filter is documented in wp-includes/taxonomy.php */
		return apply_filters( 'get_ancestors', $ancestors, $object_id, $object_type, $resource_type );
	}

	if ( ! $resource_type ) {
		if ( is_taxonomy_hierarchical( $object_type ) ) {
			$resource_type = 'taxonomy';
		} elseif ( post_type_exists( $object_type ) ) {
			$resource_type = 'post_type';
		}
	}

	if ( 'taxonomy' === $resource_type ) {
		$term = get_term( $object_id, $object_type );
		while ( ! is_wp_error( $term ) && ! empty( $term->parent ) && ! in_array( $term->parent, $ancestors, true ) ) {
			$ancestors[] = (int) $term->parent;
			$term        = get_term( $term->parent, $object_type );
		}
	} elseif ( 'post_type' === $resource_type ) {
		$ancestors = get_post_ancestors( $object_id );
	}

	/**
	 * Filters a given object's ancestors.
	 *
	 * @since 3.1.0
	 * @since 4.1.1 Introduced the `$resource_type` parameter.
	 *
	 * @param int[]  $ancestors     An array of IDs of object ancestors.
	 * @param int    $object_id     Object ID.
	 * @param string $object_type   Type of object.
	 * @param string $resource_type Type of resource $object_type is.
	 */
	return apply_filters( 'get_ancestors', $ancestors, $object_id, $object_type, $resource_type );
}