function wp_resource_hints() {
  $hints = array(
    'dns-prefetch' => wp_dependencies_unique_hosts(),
    'preconnect'   => array(),
    'prefetch'     => array(),
    'prerender'    => array(),
  );

  /*
	 * Add DNS prefetch for the Emoji CDN.
	 * The path is removed in the foreach loop below.
	 */
  
/** This filter is documented in wp-includes/formatting.php */
  $hints['dns-prefetch'][] = apply_filters( 'emoji_svg_url', 'https://s.w.org/images/core/emoji/12.0.0-1/svg/' );

  foreach ( $hints as $relation_type => $urls ) {
    $unique_urls = array();

    
/**
 * Filters domains and URLs for resource hints of relation type.
 *
 * @since 4.6.0
 *
 * @param array  $urls          URLs to print for resource hints.
 * @param string $relation_type The relation type the URLs are printed for, e.g. 'preconnect' or 'prerender'.
 */
    $urls = apply_filters( 'wp_resource_hints', $urls, $relation_type );

    foreach ( $urls as $key => $url ) {
      $atts = array();

      if ( is_array( $url ) ) {
        if ( isset( $url['href'] ) ) {
          $atts = $url;
          $url  = $url['href'];
        } else {
          continue;
        }
      }

      $url = esc_url( $url, array( 'http', 'https' ) );

      if ( ! $url ) {
        continue;
      }

      if ( isset( $unique_urls[ $url ] ) ) {
        continue;
      }

      if ( in_array( $relation_type, array( 'preconnect', 'dns-prefetch' ) ) ) {
        $parsed = wp_parse_url( $url );

        if ( empty( $parsed['host'] ) ) {
          continue;
        }

        if ( 'preconnect' === $relation_type && ! empty( $parsed['scheme'] ) ) {
          $url = $parsed['scheme'] . '://' . $parsed['host'];
        } else {
          // Use protocol-relative URLs for dns-prefetch or if scheme is missing.
          $url = '//' . $parsed['host'];
        }
      }

      $atts['rel']  = $relation_type;
      $atts['href'] = $url;

      $unique_urls[ $url ] = $atts;
    }

    foreach ( $unique_urls as $atts ) {
      $html = '';

      foreach ( $atts as $attr => $value ) {
        if ( ! is_scalar( $value ) ||
          ( ! in_array( $attr, array( 'as', 'crossorigin', 'href', 'pr', 'rel', 'type' ), true ) && ! is_numeric( $attr ) ) ) {

          continue;
        }

        $value = ( 'href' === $attr ) ? esc_url( $value ) : esc_attr( $value );

        if ( ! is_string( $attr ) ) {
          $html .= " $value";
        } else {
          $html .= " $attr='$value'";
        }
      }

      $html = trim( $html );

      echo "<link $html />\n";
    }
  }
}