Form to edit a group content entity has help text that says 'add'

That field should be disabled or even hidden during edits. Valid bug report.

This patch uses the same approach used by the group membership plugin to solve this issue.

Note that it likely has the same issue noted here: https://www.drupal.org/node/2693215 but I'd like to get some opinions on how that should be solved rather than including a fix for that with this.

That will disable the field on add forms as well, which is not the point :)

Haha, well that was slightly embarrassing. I'll blame it on not being able to read late at night. :P

This should prevent it from showing up on the add forms.

Looks great!

Perhaps in a later phase we can make it configurable on the plugin so it can choose whether a relationship can change its subject. For now, I don't see any use cases and it would severely cause issues for any access controlling extensions such as Group Node. So your patch seems excellent for the time being.

Will commit after running some tests, but setting to RTBC so it's on my radar :)

Does this need a re-roll?

Lost track of this, thanks for the reminder zerolab. It did need a reroll but it was so ridiculously easy I went ahead and did it. Credit goes to jludwig.

Bad testbot! :)