Adding an Arbitrary Link to the Admin Menu?

Hi @Tom,

If I understand your question correctly you don’t so much need to know how to add a link to the menu (it seems you already know that) but instead need to learn how to get your link to redirect correctly, right?

Redirecting to an External URL from an Admin Menu Item

If so what you need to do is to not use the menu item function but instead “hook” WordPress early enough such that it hasn’t output anything except possibly HTTP headers. The earliest hook when calling /wp-admin/themes.php appears to be after_setup_theme and it appears to work well.

Use a “Menu Slug” So You Can Test for it in a Hook

But to get it to work we first need to modify your call to add_theme_page in the admin_menu hook / your create_theme_style_page() function. We dropped the fifth parameter (the function to call to implement the admin option) because we don’t need it, and changed the fourth parameter (the “menu slug”) to be themes.php?goto=build-styleguide-page.

Although we could have chosen almost literally anything for the fourth parameter, given we are going to redirect I routed to the same page (themes.php) as other appearance options for consistency. I also just arbitrarily came up with the name goto because WordPress doesn’t use it and it seems to make sense for this.

add_action('admin_menu', 'create_theme_style_page');
function create_theme_style_page() {
  add_theme_page(
    'Theme Styleguide',
    'Theme Styleguide',
    'administrator',
    'themes.php?goto=build-styleguide-page'
  );
}

BTW, we got rid of your build_styleguide_page() function because we don’t need it for this solution.

Redirect in the Earliest Hook for themes.php: after_setup_theme

As our last bit of code we implement our after_setup_theme hook in our redirect_from_admin_menu() function. We have it test to see if the current page is themes.php and to ensure a URL parameter of goto was passed on the URL. Then it tests the value of goto using a switch/case statement to see if it has a value of 'build-styleguide-page'; if so it redirects to your stated hypothetical e.g. Google otherwise we just redirect back to the admin dashboard:

add_action('after_setup_theme', 'redirect_from_admin_menu');
function redirect_from_admin_menu($value) {
  global $pagenow;
  if ($pagenow=='themes.php' && !empty($_GET['goto'])) {
    switch ($_GET['goto']) {
      case 'build-styleguide-page':
        wp_redirect("http://www.google.com");
        break;
      default:
        wp_safe_redirect('/wp-admin/');
        break;
    }
    exit;
  }
}

Notes:

1. I chose to use the switch/case statement in the after_setup_theme hook / redirect_from_admin_menu() function so that it would be easier to add additional goto redirects if you need to; just add more case statements.

2. the wp_redirect() and wp_safe_redirect() functions don’t actually terminate; you need to explicit issue an exit statement to get WordPress to stop and not override your redirect.

Hope this helps!