fetch_feed caching broken in WP 6.7

[kaygee79]

This is a follow-up to #55604.

Feed caching appears to be broken after WP6.7 was updated to SimplePie 1.8.0. I believe the issue is with SimplePie as there is a fix merged (but not yet released): ​https://github.com/simplepie/simplepie/pull/883/files

[oglekler]

Hi @kaygee79 thank you for the report.

Can you, please, describe the symptoms of the broken caching and how to test that is now working anymore?

We need to reproduce the issue to work on the solution to fix it.

Thank you!

[kaygee79]

If I run the following code in WP 6.7.1

<?php
add_filter('wp_feed_cache_transient_lifetime', function() {
    return 600;
});

add_action('init', function () {
  $feed_url = 'https://news.un.org/feed/subscribe/en/news/all/rss.xml';
  $feed = fetch_feed($feed_url);
});

I see an HTTP API request in Query monitor on every load, as well as the transient being updated:

When I run the same code in WP 6.6.2 I see the initial request:

And as expected, I do not see any HTTP API requests on subsequent loads for 10 minutes:

[peterwilsoncc]

Reviewing the upstream ticket ​SimplePie#830, it doesn't appear that the fix is intended to be included in a 1.8 minor release, it's currently on the 1.9.0 milestone and ​tracking issue.

It might be worth backporting the upstream fix prior to the release of 1.9.0, although that's risky as it may be missed as we update SimplePie 1.8.x versions.