[wp-trac] [WordPress Trac] #23290: When using switch_to_blog() with a persistent object cache that lacks wp_cache_switch_to_blog() support, non-persistent groups are not maintained

[WordPress Trac]

#23290: When using switch_to_blog() with a persistent object cache that lacks
wp_cache_switch_to_blog() support, non-persistent groups are not maintained
-------------------------------------+------------------------------
 Reporter:  markjaquith              |       Owner:  johnjamesjacoby
     Type:  defect (bug)             |      Status:  assigned
 Priority:  low                      |   Milestone:  7.0
Component:  Cache API                |     Version:  3.0
 Severity:  normal                   |  Resolution:
 Keywords:  has-patch needs-testing  |     Focuses:  multisite
-------------------------------------+------------------------------

Comment (by johnjamesjacoby):

 23290-3.patch is a shower-thought approach:

 * Add a fallback `wp_cache_switch_to_blog()` function in `cache-
 compat.php`
 * Move the fallback code out of `switch_to_blog()` and
 `restore_current_blog()` and stop using `function_exists()`

 This works because `cache.php` is included before `cache-compat.php`, so
 WordPress can easily identify internally that `wp_cache_switch_to_blog()`
 is missing when it should not be and then include its own fallback for it.

 I really like this approach, because it also ensures that
 `wp_cache_switch_to_blog()` is always callable by plugins.

 The only compromise with this patch iteration is: I could not see how to
 retroactively introduce a new `switch_to_blog` feature inside of
 `wp_cache_supports()` - it's a catch-22 because existing drop-in plugins
 would not have needed to announce/register their supporting this, its
 default return value is `false`, and it's already confusing enough without
 added logic inside of the compat `wp_cache_supports()` function.

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/23290#comment:20>
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