annotate_overrides 
            
            Annotate overridden members.
This rule is available as of Dart 2.0.0.
Rule sets: recommended, flutter
This rule has a quick fix available.
Details
DO annotate overridden methods and fields.
This practice improves code readability and helps protect against unintentionally overriding superclass members.
BAD:
class Cat {
  int get lives => 9;
}
class Lucky extends Cat {
  final int lives = 14;
}
GOOD:
abstract class Dog {
  String get breed;
  void bark() {}
}
class Husky extends Dog {
  @override
  final String breed = 'Husky';
  @override
  void bark() {}
}
Usage
To enable the annotate_overrides rule,
add annotate_overrides under linter > rules in your
analysis_options.yaml
file:
linter:
  rules:
    - annotate_overrides