When get_feed_permastruct() return false, get_feed_link() return incorrect non feed url

[hauvong]

When $this->permalink_structure is empty & $this->feed_structure is not set, the function get_feed_permastruct() would return boolean false causing get_feed_link() return incorrect non-feed url.

ref: ​https://github.com/WordPress/wordpress-develop/blob/4f28c68eb61c656ba6ee3305ee066ff76d7e7403/src/wp-includes/link-template.php#L628

Patch file to fix is attached.

[peterwilsoncc]

Thanks for the report, I've verified the issue. It was introduced in [47808] during the 5.5 release.

I'll move this to the 5.7 milestone. It would be good to include some tests for get_feed_link() when the permalink structure is undefined so I've added the needs-unit-tests keyword too.

[peterwilsoncc]

In 51839.diff​ I've moved the change to get_feed_link() rather than changing the return value and type of $wp_rewrite->get_feed_permastruct().

This is to avoid backward compatibility breaking for theme or plugin developers using the condition if ( $wp_rewrite->get_feed_permastruct() === false ) {}.

[peterwilsoncc]

In 51839.2.diff​ :

• Same change to get_feed_link() as earlier, using a truthy check rather than strict check
• Unit tests x3 sets
  • plain permalinks
  • pretty links without a plain text prefix
  • pretty links with a plain text prefix

All looks to be passing but another set of eyes would be ideal.

[SergeyBiryukov]

Thanks @hauvong for catching the issue and @peterwilsoncc for the tests!

51839.2.diff​ looks good to me.

[johnbillion]

Agreed and the tests fail as expected if the strict check is reintroduced.

[johnbillion]

In 50354:

Feeds: Fix the URL returned by get_feed_link() when pretty permalinks are not in use.

Props hauvong, peterwilsoncc, SergeyBiryukov

Fixes #51839