[wp-trac] [WordPress Trac] #59732: Theme live preview is broken

[WordPress Trac]

#59732: Theme live preview is broken
--------------------------+------------------------------
 Reporter:  karl94        |       Owner:  (none)
     Type:  defect (bug)  |      Status:  new
 Priority:  normal        |   Milestone:  Awaiting Review
Component:  Themes        |     Version:  trunk
 Severity:  normal        |  Resolution:
 Keywords:                |     Focuses:
--------------------------+------------------------------

Comment (by karl94):

 @flixos90 can you give a look at this?

 It appears that WP is invoking `get_stylesheet_directory()` before that
 `WP_Customize_Manager` attaches its filters for previewing the theme.

 `WP_Customize_Manager` [https://github.com/WordPress/wordpress-
 develop/blob/9352b2a/src/wp-includes/class-wp-customize-
 manager.php#L683-L693 adds its preview filters] in
 `WP_Customize_Manager::start_previewing_theme()`, which is called from
 `WP_Customize_Manager::setup_theme()`, which [https://github.com/WordPress
 /wordpress-develop/blob/9352b2a/src/wp-includes/class-wp-customize-
 manager.php#L369 is run on action] `setup_theme` at default priority (10).

 The first invocation of `get_stylesheet_directory()` appears to be from
 `wp_theme_has_theme_json()` (https://github.com/WordPress/wordpress-
 develop/blob/9352b2a/src/wp-includes/global-styles-and-settings.php#L399)
 which is called by `wp_enable_block_templates()`
 (https://github.com/WordPress/wordpress-develop/blob/9352b2a/src/wp-
 includes/theme-templates.php#L227) yet again during the hook `setup_theme`
 at priority 10 (https://github.com/WordPress/wordpress-
 develop/blob/9352b2a/src/wp-includes/default-filters.php#L721).

 So, both `wp_enable_block_templates()` and
 `WP_Customize_Manager::setup_theme()` are attached to the same hook at the
 same priority, therefore they get invoked in the same order they were
 attached to the hook.

 `default-filters.php` is executed before, then the callback order is:
 first `wp_enable_block_templates()`, then
 `WP_Customize_Manager::setup_theme()`.

 Because `get_stylesheet_directory()` is used inside
 `wp_enable_block_templates()`, the global variable `$wp_stylesheet_path`
 is set, caching `$stylesheet_dir`. Any following
 `get_stylesheet_directory()` call will always return the same value.

 The [https://github.com/WordPress/wordpress-develop/blob/9352b2a/src/wp-
 includes/theme.php#L215-L216 cache-bypass logic] doesn't help in this case
 since when `get_stylesheet_directory()` is first invoked (via
 `wp_enable_block_templates()`) the customizer hasn't added its filter yet.

 `get_template_directory()` has the same issue.

 Maybe a `doing_it_wrong()` should be added to both
 `get_stylesheet_directory()` and `get_template_directory()` to warn of
 every usage before or during the hook `setup_theme`? And bypass their
 cache until that hook completes?

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/59732#comment:1>
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