Hook on slug generator

Question

I'd like to change the slug that is automatically generated when creating a post.

I'd like to add a meta before, making a thing like [meta]-test-slug-2

I guess there's a hook on when WP automatically creates a slug, and if I could find it, I could inject that meta before the title when creating the slug.

So is there a hook that exists? If so, how can I use it?

Answer 1

I think you should be able to do this using the wp_unique_post_slug filter (which is applied in the function of the same name):

add_filter("wp_unique_post_slug", function($slug, $post_ID, $post_status, $post_type, $post_parent, $original_slug) {
    if($meta = get_post_meta($post_ID, "my-meta", true)) {
        $slug = $meta . '-' . $slug;
    }
    return $slug;
}, 10, 6);

As this is applied at the end of that function and I believe WP expects and relies upon that slug to be unique, you will have to make sure that it is. I believe that it will be generated (and saved) as the post is published, so you'll have to have your meta values ready by then.