Change record status: 
Project: 
Introduced in branch: 
8.x
Introduced in version: 
8.0.0
Description: 

Field settings, field storage settings as well as field formatter and widget settings used to be able to store arbitrary keys of data. That makes it impossible to control what is in settings. Following #2224761: Add a generic way to add third party configuration on configuration entities and implement for field configuration and its integration with field settings and entity view / form displays, it is now possible to store arbitrary third party settings on fields and entity displays with clear ownership.

It was a logical next step to make the field/widget/formatter controlled settings limit storage to only those keys that are defined for the field (storage) settings and formatter/widget respectively. If a key is not defined in the corresponding default settings method, then that setting will not be persisted anymore. See defaultStorageSettings() and defaultFieldSettings() in your field item classes and defaultSettings() in your widget and formatter classes.

Impacts: 
Module developers
Updates Done (doc team, etc.)
Online documentation: 
Not done
Theming guide: 
Not done
Module developer documentation: 
Not done
Examples project: 
Not done
Coder Review: 
Not done
Coder Upgrade: 
Not done
Other: 
Other updates done