Enable feed autodiscovery for custom post type archives

[mdgl]

When creating a new custom post type with register_post_type() it is possible to enable the automatic creation of archives and the corresponding feeds.

Unfortunately, such feeds (if enabled) are not advertised through the "feed autodiscovery" mechanism. That is, if you view a custom post type archive page, there is no <link> added to point to the corresponding feed. This does happen, for example with other archive pages such as those for search, author, date, category and tag.

To me, it looks like there is some missing code in feed_links_extra() [file: general_template.php] that would check is_post_type_archive() and output the appropriate link using get_post_type_archive_feed_link() and post_type_archive_title().

[mdgl]

Suggested patch, although we could argue about the content of the title itself (eg. should it include "Post Type") and I'm not completely sure whether the use of get_post_type() here is correct.

[nacin]

Looks good to me. "Post Type Feed" should probably become just "Feed". Then it'd be "Books Feed" or whatever.

[wonderboymusic]

Refresh patch added

[nacin]

In [21984]:

Auto feeds for post type archives. props mgdl, wonderboymusic. fixes #21648.

[mdgl]

Sorry, but I noticed a couple of issues with this in further testing:

1) As I suspected, the use of get_post_type() fails with empty post type archives (because the global $post is not set). In this case, we output an invalid link (because of issue 2 below). To find the post type, we need to go via the queried object instead (all a bit messy!).

2) The two uses of isset() later in function feed_links_extra() don't work as expected because functions such as get_post_type_archive_feed_link() can return false rather than null. I think these two calls should be replaced with !empty().

[nacin]

Moving to bug, now.

[mdgl]

Yeah, this code is designed to be run during wp_head so should not rely on there being anything meaningful in the $post global (a common failing, however). A possible fix is to replace the following line in the patch:

   $href = get_post_type_archive_feed_link( get_post_type() );

with:

   $post_type_obj = get_queried_object();
   $href = get_post_type_archive_feed_link( $post_type_obj->name );

This is slightly fragile, but a similar approach is taken elsewhere in the codebase and I don't really want to open up the can of worms which is the nature and type of the queried object in the context of complex queries :-)

You could argue it would be nicer for the two "get post type archive [feed] link" functions to default to the current post type automatically, but that would require changes in link-template.php also.

Replacing the two subsequent calls to isset() with !empty() is not strictly necessary but would add further bulletproofing.

[MikeHansenMe]

update based on comment 8

[wonderboymusic]

Refreshed to use queried object

[nacin]

In 22483:

Consult the queried object for the post type. props mdgl, MikeHansenMe, wonderboymusic. fixes #21648.