Cacheable HTML and JSON responses handled differently when HTTP 4xx occurs

mxr576 → changed the visibility of the branch 3451483-html-json-handling-diff to hidden.

mxr576 → changed the visibility of the branch 3451483-html-json-handling-diff to active.

@fabianx @wim.leers or others, what does "UNCACHEABLE" means exactly? Because the current fix in the blocked issue is changing the order of if (!isset($this->requestPolicyResults[$request])) {} and if (!$this->shouldCacheResponse($response)) {n. The other potential alternative is also adding X-Drupal-Dynamic-Cache: UNCACHABLE when if (!isset($this->requestPolicyResults[$request])) {} is true... but is not that rather "UNHANDLED"?

https://git.drupalcode.org/project/drupal/-/merge_requests/8198/diffs?co...

I see that I was not the only one who wanted to clarify how many "UNCACHEABLE" scenarios/reasons exists and explicit headers to early returns \Drupal\dynamic_page_cache\EventSubscriber\DynamicPageCacheSubscriber::onResponse()

📌 Improve X-Drupal-Cache and X-Drupal-Dynamic-Cache headers, even for responses that are not cacheable Needs work

Now that user view access is also going to vary per user, we also hit this bug there.

See 🐛 Insufficient cacheability information bubbled up by UserAccessControlHandler Active .