invalid_sealed_annotation

The annotation '@sealed' can only be applied to classes.

The analyzer produces this diagnostic when a declaration other than a class declaration has the @sealed annotation on it.

The following code produces this diagnostic because the @sealed annotation is on a method declaration:

import 'package:meta/meta.dart';

class A {
  @sealed
  void m() {}
}

Remove the annotation:

class A {
  void m() {}
}