wfw:commentRss Not pulling url

@jwertin, where did you change that code? Is that in a core file somewhere? Can we come up with a fix to put in functions.php?

I don’t understand how/where RSS feeds are generated in WP. Have had this problem for years. Is this a genuine WP bug?

In my case, this function in feedwordpress.php seems to be the source of the problem:

/**
 * syndication_comments_feed_link: Escape XML special characters in comments
 * feed links
 *
 * @param string $link
 * @return string
 *
 * @uses is_syndicated()
 * @uses FeedWordPress::munge_permalinks()
 */
function syndication_comments_feed_link ($link) {
	global $feedwordpress_the_original_permalink, $id;

	if (is_syndicated() and FeedWordPress::munge_permalinks()) :
		// If the source post provided a comment feed URL using
		// wfw:commentRss or atom:link/@rel="replies" we can make use of
		// that value here.
		$source = get_syndication_feed_object();
		$replacement = NULL;

		if ($source->setting('munge comments feed links', 'munge_comments_feed_links', 'no') != 'no') :
			$commentFeeds = get_post_custom_values('wfw:commentRSS');
			if (
				is_array($commentFeeds)
				and (count($commentFeeds) > 0)
				and (strlen($commentFeeds[0]) > 0)
			) :
				$replacement = $commentFeeds[0];

				// This is a foreign link; WordPress can't vouch for its not
				// having any entities that need to be &-escaped. So we'll do it
				// here.
				$replacement = esc_html($replacement);
			endif;
		endif;

		if (is_null($replacement)) :
			// Q: How can we get the proper feed format, since the
			// format is, stupidly, not passed to the filter?
			// A: Kludge kludge kludge kludge!
			$fancy_permalinks = ('' != get_option('permalink_structure'));
			if ($fancy_permalinks) :
				preg_match('|/feed(/([^/]+))?/?$|', $link, $ref);

				$format = (isset($ref[2]) ? $ref[2] : '');
				if (strlen($format) == 0) : $format = get_default_feed(); endif;

				$replacement = trailingslashit($feedwordpress_the_original_permalink) . 'feed';
				if ($format != get_default_feed()) :
					$replacement .= '/'.$format;
				endif;
				$replacement = user_trailingslashit($replacement, 'single_feed');
			else :
				// No fancy permalinks = no problem
				// WordPress doesn't call get_permalink() to
				// generate the comment feed URL, so the
				// comments feed link is never munged by FWP.
			endif;
		endif;

		if (!is_null($replacement)) : $link = $replacement; endif;
	endif;
	return $link;
} /* function syndication_comments_feed_link() */

This function is hacking around some WordPress issue – ‘Q: How can we get the proper feed format, since the format is, stupidly, not passed to the filter?’

A PHP Fatal error is caused by the line if ($source->setting('munge comments feed links ... -> Call to a member function setting() on a non-object