[wp-trac] [WordPress Trac] #57630: Site Editor: Template part customization is not saved for certain child themes

[WordPress Trac]

#57630: Site Editor: Template part customization is not saved for certain child
themes
--------------------------+-----------------------------
 Reporter:  mreishus      |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Themes        |    Version:  trunk
 Severity:  normal        |   Keywords:
  Focuses:                |
--------------------------+-----------------------------
 == Issue Summary

 For some FSE child themes, when using the site editor to make the first
 customization of a template part, the edit appears to save but does not
 display on the front-end of the site.

 The bug applies to editing template parts that do not exist in the child
 theme.

 == Steps to reproduce

 * Clone https://github.com/WordPress/wordpress-develop (Tested using
 bd4d4af7849, 2023-02-03, 6.2-alpha-54642-src).
 * {{{npm install}}}
 * {{{npm run build:dev}}}
 * {{{npm run env:start}}}
 * {{{npm run env:install}}}
 * Download these two themes onto your computer: https://public-
 api.wordpress.com/rest/v1/themes/download/twentytwentytwo-wpcom.zip and
 https://public-api.wordpress.com/rest/v1/themes/download/twentytwentytwo-
 red.zip
 * Visit http://localhost:8889/wp-admin/themes.php
 * Click add new, then upload theme, then browse. Choose twentytwentytwo-
 wpcom-1.2.zip then install. Repeat the process for twentytwentytwo-red-
 wpcom-1.0.zip.
 * Activate the theme: Twenty Twenty-Two (Red) - WordPress.com.
 * Visit http://localhost:8889/wp-admin/site-editor.php
 * Click on “WordPress Develop” in the header, then click the block
 inserter button (the plus icon).
 * Choose blocks -> paragraph to insert a new paragraph block, which should
 be to the right of “WordPress Develop”. Select the new block and type
 “Hello” in it.
 * In the top bar, click save. The sidebar will expand, asking “Are you
 ready to save?” and “header” will be checked. Click save again.
 * Visit http://localhost:8889/ in a new tab. Expect to see: The new
 “hello” paragraph in the header. Actually see: No changes were applied.

 == Testing Notes - Certain types of child themes trigger the bug

 The bug is related to child themes, but only certain types. Both Twenty
 Twenty-Two (Red) - WordPress.com and Geologist are child themes, but only
 the former is affected by the bug.

 Child themes that have a template part present in both the child theme and
 the parent theme (example parts/header.html) has shown to allow template
 editing. However, child themes that don’t have a specific template in, but
 the parent theme does, will not allow template editing.

 == Testing Notes - Bug only occurs when making the first customization to
 a non-customized template part

 If the header has already been customized, the bug cannot happen: You will
 always be able to edit an already customized header.

 For example: When following the above directions with a fresh site, I will
 not be able to edit the header. After applying the patch below, I will be
 able to edit the header.
 After one edit is saved, even if I rollback the patch and remove the fix,
 I’m still able to apply more edits. The bug will only reappear if I use
 the “Clear customizations” for that template part in the site editor.
 (Site editor -> Middle Top Bar -> “Browse all templates” -> Template Parts
 -> Header -> Three dots menu -> Clear customization).

 == Related change

 Reverting the change introduced in
 https://core.trac.wordpress.org/ticket/55437 fixes the issue:

 {{{
 diff --git a/src/wp-includes/block-template-utils.php b/src/wp-includes
 /block-template-utils.php
 index acbb7724c5..55ad6e15d0 100644
 --- a/src/wp-includes/block-template-utils.php
 +++ b/src/wp-includes/block-template-utils.php
 @@ -503,7 +503,8 @@ function _build_block_template_result_from_file(
 $template_file, $template_type

        $template                 = new WP_Block_Template();
        $template->id             = $theme . '//' . $template_file['slug'];
 -       $template->theme          = ! empty( $template_file['theme'] ) ?
 $template_file['theme'] : $theme;
 +       //$template->theme          = ! empty( $template_file['theme'] ) ?
 $template_file['theme'] : $theme;
 +       $template->theme          = $theme;
        $template->content        =
 _inject_theme_attribute_in_block_template_content( $template_content );
        $template->slug           = $template_file['slug'];
        $template->source         = 'theme';
 }}}


 However, I cannot determine the exact mechanism why; or how to resolve the
 issue in #55437 while also resolving this issue.

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Ticket URL: <https://core.trac.wordpress.org/ticket/57630>
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