Add post type support for adjacent links

[jfarthing84]

I can't tell you how much time I've wasted over the years tracking down bugs caused by Firefox prefetching adjacent post links. Let's face it, most custom post types do not need this feature. I'm proposing adding a post type support, 'adjacent-links', to enable/disable this feature.

[jfarthing84]

Add 'adjacent-links' post type support

[wonderboymusic]

This would be best handled in the theme - conditionally turning off:

add_action( 'wp_head', 'adjacent_posts_rel_link_wp_head', 10, 0 );

[jfarthing84]

The function adjacent_posts_rel_link_wp_head() itself conditionally checks for specific post types. How again is this something that should be handled at a theme level?

[wonderboymusic]

add_action( 'template_redirect', function () {
    $types = [ 'foo, 'bar' ]; 
    if ( ! is_single() || ! in_array( get_query_var( 'post_type'  ), $types ) ) {
         return;
    }

    remove_action( 'wp_head', 'adjacent_posts_rel_link_wp_head', 10, 0 ); 

    // OR

     //  this assumes you already called `add_post_type_support( 'foo', 'adjacent-links' );`
    if ( post_type_supports( get_query_var( 'post_type'  ), 'adjacent-links' ) ) {
        remove_action( 'wp_head', 'adjacent_posts_rel_link_wp_head', 10, 0 ); 
    }

} );

UI elements (<link>s in this case) that appear on the front-end have nothing to do with post_type registration - BUT, you could easily add the value to supports and then check for that support here. So, what you are proposing already exists, it would be up to the theme to implement it anyways. We can't turn off global support for all post types and require people to add new code to turn them on. That could potentially break expected behavior for themes.

Seems like you might just need this anyways:
<meta http-equiv="x-dns-prefetch-control" content="off" />