[wp-trac] [WordPress Trac] #63062: Parent theme incorrectly not getting resolved in WordPress 6.8-beta1

[WordPress Trac]

#63062: Parent theme incorrectly not getting resolved in WordPress 6.8-beta1
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 Reporter:  fabiankaegy                          |       Owner:  joemcgill
     Type:  defect (bug)                         |      Status:  closed
 Priority:  high                                 |   Milestone:  6.8
Component:  Themes                               |     Version:  trunk
 Severity:  normal                               |  Resolution:  fixed
 Keywords:  has-patch needs-unit-tests needs-    |     Focuses:
  testing has-testing-info has-screenshots       |
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Comment (by gigitux):

 Thanks, @wildworks, for the initial exploration. As mentioned in [63086],
 this change causes regressions in plugins relying on
 `wp_is_block_theme()`, such as WooCommerce.

 Based on the discussion, this change seems necessary because
 `wp_is_block_theme()` may return an incorrect value due to inaccurate
 parent theme resolution before `after_setup_theme`. A potential solution
 could be addressing the parent theme resolution issue.

 After some investigation (cc @nerrad), we found:

  * `wp_is_block_theme()` calls `wp_get_theme()` to retrieve the theme and
 invokes the `is_block_theme()` method.
  * `wp_get_theme()` instantiates `WP_Theme`, which sets a cache on the
 first run. If executed before `after_setup_theme`,
 [https://github.com/WordPress/wordpress-
 develop/blob/7475126055ddf7b9fd6c303d2468676926b762f0/src/wp-
 settings.php#L689-L705 the theme's functions.php] will not have been
 processed, resulting in an incorrect cache.

 A possible solution could be to only set the cache on `WP_Theme` if
 instantiated after `after_setup_theme`; otherwise, avoid caching.

 It is essential to take careful consideration of performance implications.

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Ticket URL: <https://core.trac.wordpress.org/ticket/63062#comment:29>
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