[wp-trac] [WordPress Trac] #54762: Site breaking if "full-site-editing" tag in use and Gutenberg plugin disabled

[WordPress Trac]

#54762: Site breaking if "full-site-editing" tag in use and Gutenberg plugin
disabled
--------------------------+-----------------------------
 Reporter:  ajcreate      |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Customize     |    Version:  5.8.2
 Severity:  normal        |   Keywords:
  Focuses:                |
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 This happened while editing a custom theme that did not have FSE fully
 implemented.

 I added the tag "full-site-editing" to the tag list in my custom theme's
 style.css file.

 I had the Gutenburg plugin installed, and my theme and site worked fine.

 On deactivation of the Gutenberg plugin, the "Publish" button in the
 Customize area was greyed out and read "Cannot Activate". I was no longer
 able to publish with Gutenburg deactivated.

 There were no other errors and nothing was picked up on any Debugging
 tools that I used.

 Removing the tag "full-site-editing" from my style.css fixed the issue.

 I can see there might be something in WP theme.php that might be in place
 to display an error, although nothing showed up to point me in the right
 direction.

 I tried to replicate this situation by adding the "full-site-editing" tag
 to WP twentytwentyone theme and I experienced the same issue.

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Ticket URL: <https://core.trac.wordpress.org/ticket/54762>
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