I can confirm the comment in #4, this resolves the fatal error mentioned there in a case where I used the inline entity form complex formatter with an entity browser.
The Entity Browser module needs the parent entities bundle, in order to retrieve the third party settings with information about which Entity Browser to load.
This can be done easily for config fields, since the $widget_state added to the FormState by IEF holds information about the field instance. However when the field is a base field, there is no bundle information available, neither can it be easily accessed with the variables available.
See https://www.drupal.org/project/entity_browser/issues/2897622#comment-143... 🐛 IEF integration is broken for bundleless entities, base fields and unsaved form displays Needs work
My proposal is to add the 'parent' entity to the widget state, so we can easily access it to fetch the bundle.
Needs work
1.0
Code
The change is currently missing an automated test that fails when run with the original code, and succeeds when the bug has been fixed.
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I can confirm the comment in #4, this resolves the fatal error mentioned there in a case where I used the inline entity form complex formatter with an entity browser.