implicit_reopen

Don't implicitly reopen classes.

Using an interface, base, final, or sealed modifier on a class, or a base modifier on a mixin, authors can control whether classes and mixins allow being implemented, extended, and/or mixed in from outside of the library where they're defined. In some cases, it's possible for an author to inadvertently relax these controls and implicitly "reopen" a class. (A similar reopening cannot occur with a mixin.)

This lint guards against unintentionally reopening a class by requiring such cases to be made explicit with the @reopen annotation in package:meta.

BAD:

interface class I {}

class C extends I {} // LINT

GOOD:

interface class I {}

final class C extends I {}

import 'package:meta/meta.dart';

interface class I {}

@reopen
class C extends I {}

To enable the implicit_reopen rule, add implicit_reopen under linter > rules in your analysis_options.yaml file:

linter:
  rules:
    - implicit_reopen

If you're instead using the YAML map syntax to configure linter rules, add implicit_reopen: true under linter > rules:

linter:
  rules:
    implicit_reopen: true