When creating my webmentions author directory I originally wanted to avoid any reliance on the #indieweb Semantic Linkbacks plugin, as not everyone will be using it, and I wanted to keep things fairly self-contained.
It also meant that if you are not using webmentions you could just remove that argument from the initial query and just use the template for any comments.
Unfortunately, WordPress doesn't provide proper support for comment types as it does post types.
So, when a webmention reply is received (as opposed to likes or RSVPs etc.)
WordPress the plugin converts it to a normal comment, removing its 'comment_type' value. This means it doesn't get caught if filtering for only webmentions. (Thanks to Michael for the full lowdown.)
In order to catch these replies I am forced to add a check against the
'semantic_linkbacks_type' for each comment to see if it is actually a reply.
$wmreply = get_comment_meta( $comment->comment_ID, 'semantic_linkbacks_type', true ); then check if $wmreply == 'reply'
The original query included
'type' => 'webmention' but this, obviously, had to be removed so that the linkbacks check could be performed against all comments.
Combining the two type checks gives the desired result but, for my purposes, there is a caveat.
I wanted the directory to list those engaging via directly from their own sites but the above also lists replies send from Micro.blog as the service supports webmentions. I have, therefore, added it to the list of exceptions not to return authors for - I had already excluded my own domains and blank urls.
The current (sanitised) version of the directory page template is available on GitHub.
After making these changes I realised there should actually be an easier way, or a more streamlined one at least.
What if when a comment is received we immediately perform the linkbacks type check and, if true, rewrite the comment_type value back to the comments table in the database?
But that's a project for another time.