super_in_extension_type

The 'super' keyword can't be used in an extension type because an extension type doesn't have a superclass.

The analyzer produces this diagnostic when super is used in an instance member of an extension type. Extension types don't have superclasses, so there's no inherited member that could be invoked.

The following code produces this diagnostic because :

extension type E(String s) {
  void m() {
    super.m();
  }
}

Replace or remove the super invocation:

extension type E(String s) {
  void m() {
    s.toLowerCase();
  }
}