[wp-trac] [WordPress Trac] #53479: Unable to add widgets after Opting out of the Widgets Block Editor in WordPress 5.8-Beta2

[WordPress Trac]

#53479: Unable to add widgets after Opting out of the Widgets Block Editor in
WordPress 5.8-Beta2
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 Reporter:  jamesros161   |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Customize     |    Version:  trunk
 Severity:  blocker       |   Keywords:  needs-patch has-screenshots
  Focuses:                |
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 So, in the process of testing our theme Crio to ensure compatibility with
 WordPress 5.8 once it is released, I seem to have stumbled upon a rather
 breaking bug in the Customizer > Widgets panel when opting out of the new
 Widgets Block Editor.

 Long story short, some of our custom controls don't play nicely with the
 new widget editor, so we are choosing to opt-out of the new widget editor
 at the time of the 5.8 release, to give us time to overhaul the controls
 to be more Gutenberg friendly. In the following ticket,
 [https://core.trac.wordpress.org/ticket/53424], it has been made clear
 that the instructions for opting out are not correct in the documentation,
 so instead of hooking the `remove_theme_support` to `after_setup_theme`
 hook as instructed in the article, I am hooking to `widgets_init` as
 suggested by @Mamaduka in the ticket thread. This seems to work fine to
 force the traditional widget editor to be used, however; anytime I try to
 add a widget, I receive an 'invalid data' error, and the added widget does
 not save. I tested this in our theme, Crio, and then I also tested it on
 Twenty Fifteen ( I chose an older default theme, because I wanted to test
 this on a theme that also did not have block support built in to it, but
 afterwards I tested in Twenty Twenty One as well, and had the same results
 ). and was able to replicate in both, which is why I believe it is a core
 bug.
 So.... Steps to replicate.
 1. Install any theme, however i've only tested this with Crio, Twenty
 Fifteen, and Twenty Twenty One.
 2. Create a function in the functions.php ( or wherever is most fitting
 for your theme ), in that function place `remove_theme_support( 'widgets-
 block-editor' );` and then add that function as an action on the
 `widgets_init` hook.
 3. Open the customizer, and as expected, you should see the old familiar
 widgets interface.
 4. Attempt to add a widget. Any widget will do.
 5. After adding the widget, the 'Invalid value' error will display within
 that widget's box in the customizer panel, and the widget will fail to
 appear in the preview pane.
 NOTE: While there are no console or PHP errors logged at this point, there
 is a customizer_changeset XHR response, indicating that for the widget
 added, there is an invalid_value object with the message being 'invalid
 value' and the data being 'null'
 My particular response was as follows:

 {{{
 {"success":true,"data":{"contents":{"widget[media_gallery-3]":[""]},"errors":[],"setting_validities":{"sidebars_widgets[sidebar-1]":true,"widget_media_gallery[3]":{"invalid_value":{"message":"Invalid
 value.","data":null}}},"nav_menu_instance_args":[]}}
 }}}

 7. Upon trying to then publish, the 'Unable to save due to 1 invalid
 setting' error is displayed. Once again, no console log errors or php
 errors logged at this point, but this time an admin_ajax.php XHR response
 indicated the same error as before. My particular response was this:

 {{{
 {"success":false,"data":{"message":"Unable to save due to 1 invalid
 setting.","code":"transaction_fail","setting_validities":{"sidebars_widgets[sidebar-1]":true,"widget_media_gallery[3]":{"invalid_value":{"message":"Invalid
 value.","data":null}}}}}
 }}}

 I am also attached some screenshots, and a gif demonstrating this.

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Ticket URL: <https://core.trac.wordpress.org/ticket/53479>
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