Change default value of enableCustomFields to undefined

[mreishus]

Problem

When using a plugin to disable Custom Fields in the post editor, WordPress attempts to change $editor_settings to tell Gutenberg not to render the Custom Fields settings toggle in a preferences modal. However, Gutenberg is listening for a value that is impossible to send in PHP, and the settings toggle remains visible even when the feature itself is disabled.

This change makes it so when PHP uses unset() to not send a value, then undefined is the value, allowing the field to be hidden.

Steps to reproduce and more context

Please see #33912. This is tackling the same problem but in a different way.

[mreishus]

@getsource How can I help move this one forward?

[getsource]

@mreishus My apologies for the wait on a reply -- I was out for a few days and got back today.

Just left a comment here since I wasn't totally clear on the feedback.

[noisysocks]

I haven't tested it but this looks right to me 👍

Could you please add a comment explaining the difference between true, false and undefined?

[mreishus]

Could you please add a comment explaining the difference between true, false and undefined?

Sure, added in 40d8269 - was a bit unsure about location.

[noisysocks]

This works great! Thanks for the PR.

I tested by installing Advanced Custom Fields which disables custom fields in favour of its own meta boxes.

One (existing) issue I noticed is that we still show the "Additional" section in Preferences when custom fields are disabled and there are no meta boxes. I pushed up a fix for that.

[getsource]

Ah, sorry, we were testing at the same time!

I tested as well, with the most recent changes, using the plugin provided in #33912 by @mreishus and it looks to work as expected.

Thank you both!

[mreishus]

• Tweaked comments (0659d1c)
• Tested new changes
  
  ^ BEFORE: When undefined, the toggle was hidden, but the section header was appearing

^ AFTER: When undefined, the toggle and the section is hidden

^ AFTER: When displayed, the toggle and section appear as before

👍

I do not have the capability to merge, so I'll need you help when it's time for that @noisysocks. :)

[noisysocks]

Thanks @mreishus!