Add comments functionality to taxonomy.php

I was looking to do something similar. I haven’t solved it yet, but I did do some digging into the comments table. It appears that each comment is bound to an object in the wp_posts table. So I can see how comments can be added to any post inside a loop (whether its on a single page of not), but I can’t see how comments can be added when outside the loop — unless a specific post_id is supplied to bind them to.

Theoretically it would be possible to create a hidden post type which mirrored the taxonomy terms. Any comments on a dynamic term page would then be bound to the equivalent instance of the hidden post type. It’s not something I’ve tried yet; I’m still hoping for an easier solution to present itself.

I think I may have something. Following my idea above and keesiemeijer’s point about the comments_template needing a $post object. The methodology is

1. Create a new hidden custom post-type to which the comments are bound.
2. Provide for basic post instance creation.
3. By default the comments for will loop back to the post-types default url and not the referring page. Therefore we need to provide filters for get_comments_link.
4. A wp_rewrite rule addition is needed to deal with paged comments
5. Minimal wrapper to comments_template

The key is creating some sort of deterministic link between a single term and a single post. The following is a proof of concept.

define( 'CAW_TYPE', 'caw_stubb' );

//ACTIONS
add_action( 'init', 'caw_init', 100);

//FILTERS
add_filter( 'get_comment_link', 'caw_comment_link', 1, 3 );

//INIT Function -- setup post type and wp_rewrite riles
function caw_init() {

	$singular = 'Comments Stub';
	$plural = 'Comments Stubs';

	$args = array(
		'label' => $plural,
		'labels' => array( 'name' => $plural, 'singular_name' => $singular, 'add_new' => 'Add '.$singular, 'add_new_item' => 'Add New '.$singular, 'edit_item' => 'Edit '.$singular, 'new_item' => 'New '.$singular, 'view_item' => 'View '.$singular, 'search_items' => 'Search '.$plural, 'not_found' => 'No '.$singular.' found', 'not_found_in_trash' => 'No '.$singular.' found in Trash', 'parent_item_colon' =>  $singular.': ' ),
		'description' => 'Hidden post type used to bind any comment to',
		'public' => false,
		'capability_type' => 'post',
		'supports' => array( 'title', 'trackbacks', 'custom-fields', 'comments' ),
		'query_var' => false
		);

	register_post_type( CAW_TYPE, $args );

	caw_add_rewrite_rules($rules);
}

//ADD wp_rewrite rules for all public taxonomies
function caw_add_rewrite_rules($rules) {
	$taxes = get_taxonomies( array(), 'objects');
	foreach ( $taxes as $tax ) {
		if ( $tax->public ) {
			add_rewrite_rule(
				$tax->rewrite['slug'].'/([^/]+)/comment-page-([0-9]{1,})/?$',
				'index.php?'.$tax->query_var.'=$matches[1]&cpage=$matches[2]',
				'top');
		}
	}
	flush_rewrite_rules();
}

//FILTER get_comments_link to redirect from the hidden post types uri to the uri
//uri of the dynamically generated term page.
function caw_comment_link($link,$comment,$var) {
	global $post;

	if ( get_post_type() == CAW_TYPE ) {
		$meta = get_post_custom();
		$postlink = get_permalink($comment_post_ID);
		$termlink = get_term_link( intval($meta['caw_term_id'][0]), $meta['caw_taxonomy'][0] );
		$link = str_replace( $postlink, $termlink, $link );
	}
	return $link;
}

//RETURN the hidden post associated with a specific term object. Optionally
//create that post if it does not already exist
function caw_getstubb_term($term, $create=true) {
	$oldposts = get_posts( array( 'name' => $term->taxonomy.'-'.$term->term_id, 'post_type' => CAW_TYPE ));
	if ( count($oldposts) == 1 ) {
		return $oldposts[0];
	} elseif ( $create) {
		$newpostid = caw_addstubb_term($term);
		if ( !is_wp_error($newpost) ) {
			return get_post($newpost);
		} else {
			return false;
		}
	} else {
		return false;
	}
}

//CREATE hiiden post associated with a specific term object. Record the parent term using
//the post custom fields
function caw_addstubb_term($term) {

	$newpost = wp_insert_post(
		array(
			'post_title' => $term->name,
			'post_name' => $term->taxonomy.'-'.$term->term_id,
			'post_status' => 'publish',
			'post_type' => CAW_TYPE
			)
		);

	add_post_meta($newpost->ID, 'caw_taxonomy', $term->taxonomy, true);
	add_post_meta($newpost->ID, 'caw_term_id', $term->term_id, true);

	return $newpost;
}

//DISPLAY COMMENTS function. Retrieves hidden post & runs comments_template.
// $file and $seperate are passed directly to comments_template.
function caw_comments_template($term, $file='', $seperate=true, $create=true) {
	global $post, $withcomments;
	if ( isset($post) ) $oldpost = $post;
	$post = caw_getstubb_term($term, $create);
	$withcomments = "1";
	comments_template( $file, $seperate);
	if ( isset($oldpost) ) $post = $oldpost;
}

This is still very generic as it adds the possibility of comments on all public taxonomies. Ideally the creation of the hidden posts would be hooked into the creation/deletion of the original terms. However, I had to do this for a site redesign where those terms were already in
existence.