Child theme on Multisite does not work

[javiercasares]

Description

When activating a Child Theme in a Multisite it says:

The parent theme is missing. Please install the "abc" parent theme.

Also, the child theme goes to the "Broken" tab.

After doing the "step-by-step"

When you go to the canva part, it broke /wp-admin/site-editor.php?canvas=edit

Related: #58549

Step-by-step reproduction instructions

1. Install a new WP Multisite with 2 subsites (main + subsite)
2. Install the Create Block Theme plugin
3. On the main site, go to the Editor → Create Block Theme → go to the "new" canva editor (using the new options and not the old ones).
4. Go to the Create new theme from scratch.
5. Go to the Multisite options and activate the new theme.
6. Delete all the other themes.
7. Go, again, to the canva editor, and Create New theme → create a Child theme
8. Activate the Child Theme as Network (both parent and child may be activated)
9. Go to the subsite and activate the Child theme

Screenshots, screen recording, code snippet

No response

Environment info

• WordPress 6.5
• nginx
• PHP 8.2
• MariaDB 10.11
• No plugins

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[javiercasares]

One interesting that also happened is, if I install the TT24 theme, and leave it activated on all the sites / subsites and deactivate the parent theme, then, the Child Theme looks like it works because goes from the Broken Tab to the All tab.

[javiercasares]

I think I found it… it needs an "index.php". If there is no file there, it doesn't work.

[nicofyve]

Adding an empty index.php to TT24 on my multisite installation solved the problem for me, too. Thank you @javiercasares !

EDIT: By chance I found another way to work around this issue:

When I encountered the issue mentioned in the OP, I had the plugin Create Theme Block Network Activated.

The OP issue also disappears for me when the plugin Create Theme Block is NOT Network Activated (without the index.php file added to the TT24 theme). It seems fine to have the plugin activated for the individual site.

[luminuu]

Can confirm this is an issue with a missing index.php in a block theme that is used as a parent theme in a multisite environment.

[carolinan]

I am not able to reproduce this using the following steps:

• WordPress: 6.7-alpha-58576-src
• PHP: 7.4.30
• Server: nginx/1.23.1
• Database: mysqli (Server: 8.0.36 / Client: mysqlnd 7.4.30)
• Browser: Chrome 126.0.0.0
• OS: macOS
• Theme: (various themes tested)
• MU Plugins: None activated
• Plugins:
  • Create Block Theme 2.3.0
  • Health Check & Troubleshooting 1.7.0
  • Test Reports 1.1.0
  • With and without Gutenberg 18.7.0.

Enable multisite that uses the path, not the subdomain.
Network enable the parent theme (twenty twenty-four) and two child themes: one classic, one block.
✅ No issues with either theme on activation.

With the classic theme active, the Site Editor does not load the PHP template from my child theme. The preview looks like it is trying to load something, and there is no message saying that the current template is not editable. Is this what you mean with "When you go to the canva part, it broke /wp-admin/site-editor.php?canvas=edit" @javiercasares?

---

Using Create Block Theme Version 2.3.0 to create:

1. a new parent block theme directly on the subsite, or
2. a new child block theme directly on the subsite,

redirects me to /wp-admin/site-editor.php?canvas=edit which does not load.
It seems more like a plugin problem to me, where it should not be redirecting to canvas=edit ?

[carolinan]

I am testing the same steps on Windows 11:

• WordPress: 6.7-alpha-58576-src
• PHP: 8.2.12
• Server: nginx/1.25.3
• Database: mysqli (Server: 8.0.37 / Client: mysqlnd 8.2.12)
• Browser: Chrome 126.0.0.0
• OS: Windows 10/11
• Theme: (various themes tested)
• MU Plugins: None activated
• Plugins:
  • Create Block Theme 2.3.0
  • Test Reports 1.1.0
  • With and without Gutenberg 18.7.1.

Manually created child themes:

Both the classic child theme and the block child theme activate without problems or error messages.

Create Block Theme:

• When I am on the subsite and I use Create Block Theme to create a new parent theme, the parent theme is not immediately activated, nor network enabled.
• When I am on the subsite and I use Create Block Theme to create a new child theme of Twenty Twenty-Four, the child theme is not immediately activated, nor network enabled.

After creating the theme and pressing OK to reload the browser, it looks like the theme is active, but its not since it is not network enabled. Refreshing the theme screen in the admin shows that the new theme is not active.
Once network enabled, the child theme can be activated without error messages.

[carolinan]

I was able to test sub domains using "Local", WordPress 6.5.5 and 6.6 RC2 on macOS and Windows11, both installations using PHP 8.1.29, and I can not reproduce the issue where the parent theme is missing.

[luminuu]

Have you also checked you had the index.php removed from the parent block theme?

[carolinan]

Yes, neither Twenty Twenty-Four or the parent theme created with create block theme has an index.php.

[carolinan]

My classic child theme that I manually created, did not include theme.json.

[luminuu]

I have been trying to reproduce this but can't do it either.