Make pretty permalinks work for attachments

Hey all,

I have for the first time needed to create an attachment template, but permalinks for this template are not working as I would expect.

I have my permalinks set to the ‘Post name’ structure (/%postname%/), and while that works fine for things like the author template, it doesn’t work for attachments.

For example, this is what I get for a author permalink –
– https://www.mysite.com/author/aname/

This is what I expect to get for the attachment permalink –
– https://www.mysite.com/attachment/media-slug/

What I actually get for an attachment permalink –
– https://www.mysite.com/?attachment_id=111

I have tried to manually add some rules (followed by re-saving the permalink structure to unsure the generate_rewrite_rules action was called) –

add_action('generate_rewrite_rules', 'djg_attachment_rewrite_rule');
function djg_attachment_rewrite_rule($wp_rewrite){
  $new_rules = array();
  $new_rules['attachment/(\d*)$'] = 'index.php?attachment_id=$matches[1]';
  $wp_rewrite->rules = $new_rules + $wp_rewrite->rules;
}

However, I can’t get attachment permalinks. Does anybody know how to do this, and why WP doesn’t do it out of the box?

Thanks