Warn on ignored annotations...

[kevmoo]

Depending on JsonSerializable createToJson and createFactory - some annotations may be just ignored.

Might be nice to warn about them

Fields that only apply if generating toJson

• JsonSerializable
  • includeIfNull
• JsonKey
  • toJson
  • includeIfNull

Fields that only apply if generating fromJson

• JsonSerializable
  • disallowUnrecognizedKeys
• JsonKey
  • fromJson
  • defaultValue
  • disallowNullvalue
  • required